second edition Greg Rickard Isabella Brown Nici Burger Warrick Clarke Janette Ellis Faye Jeffery Caroline Jeffries Karin Johnstone Dale Loveday Geoff Phillips Peter Roberson Kerry Whalley
Sydney, Melbourne, Brisbane, Perth, Adelaide and associated companies around the world
Contents Acknowledgements
v
Series features
vi
How to use this book
CHAPTER
1
CHAPTER
2
CHAPTER
3
Syllabus correlation
x
Verbs
xi
Forensics
1
Unit 1.1 Forensics and identification
2
Unit 1.2 Is it real?
12
Unit 1.3 Evidence
20
Science focus: Investigating the death of Azaria Chamberlain
31
Chapter review
33
The periodic table
34
Unit 2.1 Atoms and elements
35
Unit 2.2 Structure of the periodic table
41
Unit 2.3 Using the periodic table
47
Unit 2.4 Families of elements
56
Science focus: Development of the periodic table
62
Chapter review
64
Chemical change
66
Unit 3.1 Chemical reactions
67
Unit 3.2 Combination, combustion and decomposition
74
Unit 3.3 Precipitation reactions
80
Unit 3.4 Acids and bases
88
Chapter review
CHAPTER
4
viii
Sense and control
100
102
Unit 4.1 Sight
103
Unit 4.2 Hearing
112
Unit 4.3 Smell, taste and touch
117
Unit 4.4 Responding
124
Unit 4.5 Nervous control
129
Science focus: Understanding memory
139
Unit 4.6 Chemical control
142
Chapter review
149
iii
CHAPTER
5
CHAPTER
6
CHAPTER
7
CHAPTER
8
CHAPTER
9
Reproduction Unit 5.1 Types of reproduction
153
Unit 5.2 Human reproductive systems
161
Unit 5.3 Human reproduction
168
Unit 5.4 Reproductive health
174
Chapter review
183
Ecosystems
185
Unit 6.1 Energy for life
186
Unit 6.2 Recycling in nature
192
Unit 6.3 Human impact on ecosystems
200
Science focus: The right balance—a human problem
210
Chapter review
215
Light
216
Unit 7.1 Bending light
217
Unit 7.2 Focusing devices: Lenses and curved mirrors
226
Unit 7.3 Colour
239
Chapter review
248
The universe
250
Unit 8.1 The expanding universe
251
Unit 8.2 The Big Bang
256
Unit 8.3 The life of a star
261
Unit 8.4 Are we alone?
266
Unit 8.5 Using space
270
Science focus: Long-distance space travel
276
Chapter review
279
Earth’s fragile crust
280
Unit 9.1 Plate tectonics
281
Unit 9.2 At the edges
289
Unit 9.3 Earthquakes
297
Unit 9.4 Volcanoes
308
Unit 9.5 Landscaping the crust
314
Unit 9.6 Geological time
322
Chapter review
330
Sci Q Busters Index
iv
152
332 336
Acknowledgements The publishers wish to thank the following for their contributions and who kindly gave permission to reproduce copyright material in this book: Alamy Limited: pp. 74, 119, 123, 187 (kookaburra), 201b, 202, 280, 317. ANT Photo Library Pty Ltd: p. 201tl. Australian Associated Press Pty Ltd: pp. 3br, 12l, 15, 133l, 145, 205l, 206, 210br. Australian Associated Press Pty Ltd: pp. 213 (logger, traffic), 299, 308r. Corbis Australia Pty Ltd: pp. iv (volcano), 6r, 27, 62l, 75t, 76b, 81b, 117t, 187 (snake), 205r, 210l, 210tr, 211tl, 213br, 213tr, 239t, 258bl, 262br, 263r, 268t, 290r, 311, 316l, 323c, 324l. Dorling Kindersley: pp. 103, 318, 323b. Getty Images Australia Pty Ltd: pp. 23c, 24, 133br, 151, 152, 155l, 157tl, 161br, 163b, 169br, 180t, 186, 239b, 310, 316r. iStockphoto: pp. iii (soft drink), 47, 68t, 76l, 105bl, 106l, 106r, 107, 114, 161t, 171, 179, 180b, 185, 187 (moth), 190, 192tl, 213 (farm), 326r, 330. John Fairfax Publications: pp. 32, 203. Jupiter Images: pp. 22l, 57c, 57t, 256. Lennart Nilsson / Albert Bonniers Forlag: p. 163t. Lochman Transparencies: p. 192b. NASA: pp. 251t, 258br, 258t, 261t, 262bl, 262t, 267br, 267t, 272, 273; ESA: pp. iv (galaxy), 259t; JPL: p. 271; Marshall Space Flight Center: p. 258c. National Library of Australia: pp. 3tl, 211l. Nationwide News Pty Ltd: pp. 26, 31, 274t. NOAA: p. 291. Paramount Television / The Kobal Collection: p. 278b. Pearson Australia/Penelope Naidoo: p. 168t; Gordon Aird: p. 217b; Natalie Book: p. 217t. Photodisc: pp. 68c, 69tr, 124tr, 139t, 140l, 200, 201tr, 226. Photolibrary Pty Ltd: pp. iii (fingerprint scan, periodic table, rods and cones), iv (butterfly wing, tulip), 1, 2, 3tr, 4, 5tl, 5tr, 6l, 7b, 7t, 13, 14b, 19, 20b, 20t, 21, 22r, 23b, 23t, 34, 35, 37, 41, 49, 56r, 57b, 58, 59, 62r, 63, 66, 67t, 69b, 69tl, 70, 75b, 80, 81t, 88, 89, 90, 91, 93r, 102, 105tl, 108, 109, 117b, 118, 120, 124b, 125, 129, 130, 131t, 132, 133tr, 139b, 142, 143b, 143t, 144, 146, 153, 154br, 154cl, 154cr, 155r, 157bl, 157r, 160, 161bl, 162, 168b, 169bc, 169bl, 169t, 176, 178, 187 (frog), 193, 216, 219r, 220, 231, 233, 241l, 242, 250, 252, 257, 259b, 261b, 263l, 266b, 267bl, 268b, 270b, 270t, 276, 277, 278t, 281l, 281r, 290l, 292, 297, 303, 303, 308l, 315, 322, 324r. Picture Media Pty Ltd: p. 195. Public Library of Science, Journal of Biology / William M. Gray: p. 148; Charles Fisher: p. 188. Reserve Bank of Australia: pp. 14t, 18. Royal Victorian Eye & Ear Hospital: p. 95. Shutterstock: pp. iii (butterfly), iv (optical fibres), 12r, 56l, 67b, 68b, 84, 92, 93l, 105br, 105c, 112, 124tl, 131b, 134, 140r, 154bl, 154tl, 174, 187 (lantana), 192tr, 196, 204, 213 (city, fox), 219l, 229, 241r, 289, 309, 313, 314, 326l, 332, 333, 334, 335. The Picture Desk/The Kobal Collection: p. 266t. Tourism Queensland: p. 323t. US Navy/Ensign John Gay: p. 251b. US National Archives and Records Administration: p. 302. Cover: Getty Images Australia Pty Ltd, NASA, Shutterstock. Every effort has been made to trace and acknowledge copyright. The publisher would welcome any information from people who believe they own copyright to material in this book.
v
Series features
Science Focus Second Edition
The Science Focus Second Edition series has been designed for the revised NSW Science Syllabus, Stages 4 and 5. This fresh and engaging series is based on the essential and additional content.
Student books with student CD
NENTW ENT O
C The student book consists of chapters with the following features: • A science context at the beginning of each chapter encourages students to make meaning of science in terms of their everyday experiences. • Science Clip boxes contain quirky and fascinating science facts and provide opportunity for further exploration by students. • Unit and chapter review questions are structured around Bloom’s Taxonomy of Cognitive Processes. Questions incorporate the key verbs, so that students can begin to practise answering questions as required in later years. • Investigating sections incorporate ICT and research skills. These tasks are designed to push students to apply the knowledge and skills they have developed within the chapter. • Practical activities are placed at the end of each unit to allow teachers to choose when and how to incorporate the practical work. • Science Focus spreads use a contextual approach to focus on the outcomes of the prescribed focus area. Student activities on these pages allow for further investigation into the material covered. Each student book includes an interactive student CD containing: • an electronic version of the student book • a link to Pearson Places for extensive online content.
Homework books
NENTW ENT
CO The homework book has a fresh new design and layout and provides the following features: • A syllabus correlation grid links each worksheet to the NSW Science Syllabus. • Updated worksheets cover consolidation, extension and revision activities with explicit use of syllabus verbs so that students can begin to practise answering questions as required in later years. • Questions are clearly graded within each worksheet, allowing students to move from lower-order questions to higher-order questions. • A crossword for every chapter spans across a double-page spread so students can easily read the clues and instructions. • Sci-words are listed for each chapter in an easy-to-follow tabulated layout.
vi
Teacher editions (including teacher edition CD and student CD)
NEW
The innovative teacher edition contains a wealth of support material and allows a teacher to approach the teaching and learning of science with confidence. Teacher editions are available for each student book in the series. Teacher editions include the following features: • pages from the student book with wrap-around teacher notes covering the learning focus, outcomes and a pre-quiz for every chapter opening • approximately 10 different learning strategies per unit in addition to the activities provided in each unit of the student book • assessment ideas • answers to student book questions • practical activity support including a safety spot, common mistakes, possible results and suggested answers to practical activity questions • Teacher Resource boxes highlighting additional resources available, such as worksheets, online activities and practical activities. Each Science Focus Second Edition Teacher Edition CD includes: • student book answers • homework book answers NEW Pearson Places • chapter tests and answers • curriculum grids www.pearsonplaces.com.au • teaching program for each chapter Pearson Places is the online • student risk assessments destination that is constantly evolving ng • lab technician risk assessments to give you the most up-to-date educational • safety notes content on the web. Visit Pearson Places to • lab technician checklist and recipes. access educational content, download lesson material, use rich media and connect with NEW LiveText™ DVD students, educators and professionals around Australia. • Pearson Reader The LiveText™ DVD is designed More than an eBook, Pearson Reader for use with an interactive provides unique online student books whiteboard or data projector. that allow teachers and students to It consists of an electronic harness the collective intelligence of version of the student book all who participate. Search for a unit of with component links, some of work and contribute by adding links and which are unique to LiveText™. sharing resources. The features include one-touch • Student Lounge zoom and annotation tools that One location for student support allow teachers to customise ise material—interactives, animations, lessons for students. revision questions and more! • Teacher Lounge One location for teacher support material—curriculum grids, chapter tests and more!
For more information on the Science Focus Second Edition series, visit the Bookstore at www.pearsonplaces.com.au
vii
How to use this book
Science Focus 3 Second Edition
Science is a fascinating, informative and enjoyable subject. Science encourages us to ask questions and helps us understand why things happen in our daily lives, on planet Earth and beyond. Scientific knowledge is constantly evolving and challenges us to think about the world in which we live. Science shows us what we knew, what we now know and helps us make informed decisions for our future. Science Focus 3 Second Edition has been designed for the revised NSW Science Syllabus. It includes material that addresses the learning outcomes in the domains of knowledge, understanding and skills. Each chapter addresses at least one prescribed focus area in detail. The content is presented through many varied contexts to engage students in seeing the relationship between science and their everyday lives. The student book consists of nine chapters with the following features: Unit
4
Sense and control
Prescribed focus area
The key prescribed focus area addressed within the chapter is clearly emphasised.
The nature and practice of science
key outcomes
Additional
Essentials
5.2, 5.8.4
s s
(UMANS HAVE FIVE SENSES 4HE DEVELOPMENT OF NEW TECHNOLOGIES HAS ALLOWED HUMANS TO CORRECT DIFFICULTIES IN HEARING AND SEEING
s
9OUR SENSES ARE COORDINATED BY THE NERVOUS SYSTEM
s
9OUR SENSES ARE TRIGGERED BY SPECIALISED CELLS
s
4HIS STIMULUS WILL OFTEN TRIGGER A RESPONSE
s
(ORMONES CAN ALSO BE RELEASED AS A RESULT OF A REACTION TO A STIMULUS
s
.ERVOUS IMPULSES ARE MUCH QUICKER THAN HORMONES
s
$IFFERENT HORMONES TRIGGER DIFFERENT RESPONSES
s
$IFFERENT HORMONES ARE RELEASED BY DIFFERENT ENDOCRINE GLANDS
The learning outcomes relevant to the chapter are clearly listed. A clear distinction between essential and additional outcomes is presented in student-friendly language.
Units
Unit
context
Context The context section appears at the beginning of each unit to encourage students to make meaning of science in terms of their everyday experiences.
4.1
The eye
Unit
4.1
context
3 State which of the groups in Question 2 has the most detailed description of the organisms in it.
14 A mnemonic is a silly sentence that helps remind you of something. You could, for example, remember the order in organism are classified (kingdom—phylum—class— which organisms order—family— order—family—genus—species) by, instead, remembering ‘Kind people can often find green shoes!’ Create your own mnemonic to re represent the order of classification from kingdom to spec species.
4 Organisms are grouped into five kingdoms. List them.
15 The complete classification cl of a human is:
2 List these groups from the one that contains the greatest ms to the group that contains the least: number of organisms m, genus, order, class. family, species, phylum, kingdom,
5 State the structural feature that splits animals into twoo phyla.
Kingdom: Anima Animal
6 State the two major groups into which plants are classified. ed.
4.3
Phylum: Chorda Chordata (vertebrate)
QUESTIONS Understanding
Class: Mammali Mammalia (mammal) Order: Primata ((primates)
7 Explain how you know a terrier and a poodle belong to the same species.
Family: Hominid Hominidae (hominids)
8 Explain how you know that a horse and a donkey are different species.
Genus and spec species: Homo sapiens Use this and inf information from the text to construct a table s that shows the similarities between a human with a dog and the differences bbetween them.
9 Describe how the unique scientific name for every living thing is created.
Remembering 10 A subphylum represents a group smaller than a phylum but
166 You have just discovered di a new species! You must now report your findings to the AS4NT (The Australian Society for Things) Naming Things).
bigger than a class. Use this information to explain what you
1 State the meanings of terms taxonomy and taxonomist. thinkthe a subclass represents.
a Outline the ccharacteristics of your new organism. Be creative!
2 List these groupsApplying from the one that contains the greatest 11 The scientific name of the Tasmanian devil is Sarcophilus number of organismsharrisii. to Identify the group that contains the least: its:
b Construct a diagram d or model of your new species. c Classify your organism by placing it in a kingdom.
a genus
family, species, phylum, kingdom, genus, order, class. b species. Identify important characteristics shared by all animals in the 3 State which of the12groups 2 has the most detail genus Felis in (the Question cat family). description of theAnalysing organisms in it.
d Further class classify your organism by giving it a name using the binomial naming system.
13 Four native plants found in the Blue Mountains are Banksia anksia
4 Organisms are grouped into fivepunctata, kingdoms. Listandthem. d Banksia ericifolia, Eucalytpus Acacia floribunda marginata. Analyse this information to:
5 State the structural feature that ofsplits animals a State the number species this represents. ents.into two phyla b Name the plants that are in the same ame genus.
6 State the two major cgroups into which plants are classified. Predict if botanists couldd ever cross any of these plants to
Understanding
edlings. make new seedlings.
113
Investigating
TRANSMITTED FOCUSED COLOUR IMAGES OF SEVERAL OBJECTS LOCATED DIFFERENT DISTANCES AWAY TO YOUR BRAIN AND WITH VIRTUALLY NO EFFORT
p lip Cllilip Clip C
S
4HE EYES PROVIDE WHAT M AS THE MOST IMPORTANT OF SIGHT 4AKE A LOOK AROUND EYES ARE WORKING NORMALL
Creating
1 State the meanings of the terms taxonomy and taxonomist.t
2002 and beyond
e ce nce enc ie cie Science Sci Sc
The structure of the eye allows it Fishy focusin focusing to limit or maximise the amount of -OST ANIMALS FOCUS BY -OST ANIMALS FO light entering it, focus the light to USING THE CILIARY USING THE CILIAR form an image and then transmit MUSCLES TO CHANGE THE MUSCLES TO CHA the image to the brain. SHAPE OF THE LENS SHAPE OF THE LEN &ISH HOWEVER FOCUS &ISH HOWEVER These primary functions are IMAGES BY MOVING IMAGES BY MOV carried out by: EACH LENS BACKWARDS EACH LENS BACKW s THE iris and pupil: these close AND FORWARDS JUST LIKE AND FORWARDS J down to limit light when it is AA CAMERA CAMERA bright and dilate (open up) to maximise the light entering the eye in the dark s THE cornea and lens: these bendd the rays of light ht focuses on the rretina entering the eye so that the light mage should form. s THE retina: this is where the image na then transmit the Specialised cells in the retina image to the brain.
QUESTIONS
Remembering
Voyager 1 & 2
The solar system
Sight
4HE EYES PROVIDE WHAT MANY WOULD REGARD 4HE EYES PROVIDE WHAT MANY AS THE MOST IMPORTANT OF ALL OUR SENSES AS THE MOST IMPORTANT OF ALL SIGHT 4AKE A LOOK AROUND YOU NOW )F YOUR SIGHT 4AKE A LOOK AROUND YO EYES ARE WORKING NORMALLY THEY JUST EYES ARE WORKING NORMALLY
4.3
4.3
Chapter opener
creating questions. Questions incorporate a variety of verbs, including the syllabus verbs. All verbs have been bolded so students can begin to practise answering questions as required in examinations in later years.
Fig 4.1.1 4HE AMOUNT OF LIGHT ENTERING THE EYE IS CONTROLLED BY THE COLOURED IRIS WHICH OPENS AND CLOSES THE PUPIL
The rest of the eye is there basically to keep it in shape (vitreous humour, aqueous humour and sclerotic layer), to stop stray light from entering or reflecting around the eye (the choroid) and to change the shape of the lens to allow it to focus (suspensory ligaments and ciliary muscles).
Prac 1 p. 110
Prac 2 p. 111
The investigating activities can be set for further exploration and assignment work. These activities may also include a variety of structured tasks that fall under the headings of reviewing and e - xploring.
19 Much of the information we know about the outer uter planets came from the Voyager 1 and 2 missions. Use the information in the table to construct a scaled timeline for each mission. N Date
Mission
20 August 1977
Voyagerr 2
5 September 1977
Voyagerr 1
5 March 1979
Voyagerr 1
9 July 1979
Voyagerr 2
12 November 1980
Voyagerr 1
25 August 1981
Voyagerr 2
24 January 1986
Voyagerr 2
25 August 1989
Voyagerr 2
1998
Voyagerr 1
2002 and beyond
8.4 8 4
What happened? Launches
8.4 8 4 Launches
Flies by Jupiter
INVESTIGATING INVESTIG INVE STIGATIN STIG ATING ATIN G
Flies by Jupiter Flies by Saturn
Flies by Saturn Flies by Uranus
Investigate your available resources (e.g. textbook, Flies by Neptune Most distant human-made encyclopaedias, Internetobject etc.) to: Exploring past Pluto 1 Find out what or who each planet was named after.
Voyagerr 1 & 2
Construct a booklet that summarises this information, including pictures of each planet and the person or object the planet was named after. L
INVESTIGATING INVESTIGAT INVESTI GAT ATING ATIN NG N G
2 Find out what the given statement means. Money spent on space exploration would be better spent on e -xploring
Investigate your available resources (e.g. textbook, encyclopaedias, Internet etc.) to: 1 Find out what or who each planet was named after.
things like medical research and aid programs.
mation, Construct a booklet that summarises this information, including pictures of each planet and the personn or object the planet was named after. L 2 Find out what the given statement means.
To find ou out more about the solar system, a list of web destinations can be found oon Science Focus 1 second edition Student Lounge. There, you will also find a link to a website that allows you to construct a model of a spac space probe, such as the Cassini spacecraft that was sent to explore Saturn.
Organise a class debate on this issue. L
etter spent on Money spent on space exploration would be better things like medical research and aid programs. Organise a class debate on this issue. L
272
iris retina
lens optic nerve
diaphragm
Practical activities
film shutter
convex lens
Fig 4.1.2 4HE EYE FOCUSES IMAGES IN THE RETINA !LTHOUGH THE IMAGE IS UPSIDE DOWN THE BRAIN PROCESSES IT SO THAT WE PERCEIVE IT THE CORRECT WAY UP 4HE OPERATION OF THE EYE ACTS VERY MUCH LIKE AN OLD FASHIONED FILM LOADED CAMERA
103
Unit content
g
y
y
Making a pasta key
Aim
To construct a key to classify pasta.
4.1
PRACTICAL ACTIVITIES VIT VI TIE T IE IES ES
1
Aim
Unit
The unit includes illustrations, photos and content to keep students engaged and challenged as they learn about science. A homework book icon appears within the unit indicating a related worksheet from the Worksheet supporting homework book.
Practical activities are placed at the end of each unit, allowing teachers to choose when and how to best incorporate practical work into the teaching and learning. A practical activity icon will appear throughout the unit to signal suggested times for practical work. Within some practical activities a safety box 4.1 appears that lists very importantt 2 Constructing keys ur safety information. Some practical activities are design ! your own (DYO) tasks and others may be conducted using ed to a data logger. Icons are inserted indicate these options.
4 When en you get to the poin point where you are at a particular type, draw the pasta or paste a sample of it in that place on your key.
5 Gather all the pasta togeth together again and decide on a new set of To construct different types of keys to classify collect Equipment eristics by which tto reclassify your pasta. Once again, characteristics A sample of at least five different kinds of uncooked pasta (e.g. spiral pasta, tubes, shells, bows, spaghetti etc.) in a beaker or cup.
Safety Method
uct a dichotomous key. construct
Questions ns
1 Identify fy the main feature of a dichotomous key.
1 Pour the contents of the beaker onto your bench.
2 Look at the keys designed by other groups. State whether
2 As aplants group, decide(e.g. on the characteristics (e.g. shape, size etc.)rhus)they Some oleander and are used the same chara characteristics that you did. you will use to classify your sample of pasta. 3 Evaluate uate the different key keys you constructed. Which do you 3 In your workbook, construct a dichotomousin key tosome classify nk was better? Why? think cause allergic reactions people. your pasta. pasta
Equipment
A collection of at least ten of one of the following: Fig 4.1.15 s LEAVES COLLECTED FROM DIFFERENT TREES AND SHRUBS school Start off your key like this.
Unit questions
viii
A set of questions related to the unit are structured around Bloom’s Taxonomy of Cognitive Processes. The questions move from straightforward, lower-order remembering, understanding and applying questions, through to more complex, higher-order evaluating, analysing and
2
C Constructing Constructi t ting g keys k
Aim
Method
To construct different types of keys to classify collected objects.
!
Safety
Some plants (e.g. oleander and rhus) are known to cause allergic reactions in some people.
Equipment
A collection of at least ten of one of the following: s LEAVES COLLECTED FROM DIFFERENT TREES AND SHRUBS AROUND THE school s PIECES OF COMMON LABORATORY GLASSWARE AND EQUIPMENT s OBJECTS FROM A PENCIL CASE
?
1 As a group, decide on the characteristics you will use to classify your ten objects.
2 Group the objects according to the characteristics you chose. 3 Construct a dichotomous key and a tabular key that would allow others to classify your ten objects in exactly the same way as you did.
Questions
1 Outline some practical advantages of classifying different EQUIPMENT USED IN THE LABORATORY 2 Compare the dichotomous keys you constructed with your tabular keys. Which was easiest to construct? Suggest why.
101
DYO
1 List three examples of each of the following: a organisms b vertebrates
c Identify a feature of birds that resembles re a feature of those long-extinct dinosaurs.
c invertebrates d endotherms
8 Identify whether the following ques questions are dichotomous:
e ectotherms
a Does the animal have a backbone?
f angiosperms
CHAPTER REVIEW g conifers h fungi
i protists.
1 List three examples each of the following: b the three main of orders of mammals c the four main classes of invertebrates
a organisms d the five main orders of arthropods
e the five main classes of vascular plants. b vertebrates
Understanding invertebrates Explain why.
e ectotherms 5 Clarify the meanings of the following terms: a respiration f angiosperms b excretion
g conifersc h fungi
stimulus
d response species
g vertebrate
a the person b the lion. 10 Identify whether the he following pairs of animals belong to the same species: a a Lebanese mann and a Chinese w woman c a greyhound and nd a poodle d a lizard and a crocodile e a donkey and a horse. 11 You are standing ng by a campfire, list listening to the rustle of the he bushes, the crackle of the fire and the laughter possums in the of your friends. all of the things mentioned in nds. Identify whether al this sentence nce are alive. Do any of the non-living things show any of the Explain. he characteristics of life? Ex
a Identify some of the other ways in which they classify the music.
h exoskeleton
heterotroph. a the five imain classes of vertebrates
b the
d What type of animal is that?
12 Electronic ronic music storage systems ssuch as iTunes classify the music usic they contain in a number of different ways (e.g. by artist).
e taxonomy
i protists.f
c Did you feed the dog?
b a tiger and a gorilla rilla
3 Explain why scientists classify things.
d endotherms 4 Cells were unknown before the invention of the microscope.
2 State:
b What colour is your T-shirt?
9 You watch somebody run across a field being chased by a hungry lion. Identify characteristics of life are shown dentify which character by:
2 State: Remembering a the five main classes of vertebrates
c
b Recent research has indicated th that many (if not all) dinosaurs were warm blooded aand that birds may have evolved from them. Use this info information to classify dinosaurs, placing them in the ccorrect animal kingdom.
6 Plants and animals both use cellular respiration for energy. threeExplain main orders ofundergo mammals Explai o photosynthesis. why only plants can
Applying Ap plying ying th f Appl i l
fi
t b t
7 Until recently, it was thought that dinosaurs were reptiles. a If this was correct, list the kind of features you would expect dinosaurs to have.
b Explain the advantages of using ddifferent keys to classify the same music.
Analysing Ana 13 Classify the following as angiosper angiosperm, conifer, fern or bryophyte: a pine b tree fern c apple tree d liverwort.
135
Fact File Mars
Fig 8.4.7 Mars showing red earth and polar caps.
Mass
0.107 times that of Earth
Moons
Two (Phobos—diameter 23 km, Deimos—diameter 10 km)
Diameter
6794 km ( = 0.53 × Earth’s diameter)
Surface
Soft red soil containing iron oxide (rust), its red ( ), giving g g the planet p appearance. Cratered regions, large volcanoes, a large canyon and possible possibl dried-up water channels. Polar caps of frozen carbon dioxide and water.
Atmosphere Atmo
Very thin, mainly carbon dioxide
Gravity Gr
0.376 times that on Earth
Surface temperature
–120 °C to 25 °C
25.2°
1.52 AU (228 million km)
Time to orbit Sun (year)
687 Earth days
Scale model (Sun = 300 mm) Diameter
1.4 mm
Distance from Sun
49.1 m
Mars
Fig 8.4.8 The Mars Phoenix mission. The landing system syste stem on Phoenix allows the spacecraft to touch down within 10 kilometres etres res of its targeted landing area.
The asteroid belt The asteroid belt is made up of thousands ds of small ound the Sun rocky metallic bodies and dust in orbit around Sun. ameter of about The largest asteroid is Ceres, having a diameter 1000 kilometres. Researchers have found several nearEarth asteroids, but none are predicted to crash into Earth in the near or distant future.
Two (Phobos— Deimos—diam
Diameter
6794 km ( = 0 diameter)
Fig 8.4.9 Thousands of asteroids lie in a belt between Mars and Jupiter. One is Ida, an asteroid big enough too have a gravitational field that has trapped its own orbiting moon,, Dactyl.
266
Worms
Polyps Polyps are cnidarians that att attach themselves to something like a rock. Corals and anemones are examples of polyps.
There are three different phyla of worms—roundworms, flatworms, and segmented worms. Roundworms Roundworms have long cylindrical bodies that are in one piece without segments. They have a digestive tube with a mouth and anus. Some roundworms are parasitic, living off (and weakening) other living animals. Others live ‘free’ in water or damp soil. Examples of roundworms are threadworms, hookworms and the parasitic roundworms found in the intestines of humans, dogs, pigs and horses.
Science
Science Clip features contain quirky information related to the topic that students will find interesting.
Clip
What do I do?
Flatworms Flatworms are similar to roundworms in that they also can be parasitic or ‘free’. They differ in that they have flat bodies instead of round ones. If they have a digestive system, it has only one opening, which acts as both mouth and anus. Flukes and tapeworms are examples of flatworms.
Fig 4.4.18 Coral polyps olyps are living ng things th called cnidarians.
opening acts as both mouth and anus
Medusas Medusas are cnidarians nidarians that can swim about freely. Jellyfish are medusas. Many ar are harmless, whereas some, ellyfish, can kill. kill The stinging cells of like the box jellyfish, others, such as bluebottles, in inject a mix of chemicals that leave painful, raised red w welts wherever they touch the skin.
It is currently recommended that bluebottle stings are soaked for about 20 minutes in hot water (say under a hot shower or
4.4
0.107 times th
Moons
hooks anchor the worm to the internal wall of the gut
Fig 9.3.14 One of the jobs of a palaeontologist is to inspect fossils and ancient skeletons, such as this fossilised dinosaur skull.
Career Profile
Career Profile
Palaeontologists can be involved in: s LOCATING LOCATING SITES WHERE FOSSILS MAY BE FOUND SITES DIG s CAREFULLY CAREFULLY DIGGING FOSSILS OUT OF THE ROCKS IN WHICH they are fou found s PREPARING PREPARING FOSSILS FOR DISPLAY OR STORAGE FO s DATING DATING FOSSILS TO WORK OUT THEIR AGE IN s USING USING INFORMATION ABOUT FOSSILS TO STUDY OTHER THINGS SUCH A SUCH AS OIL EXPLORATION OR THE HISTORY OF LIFE ON THE Earth. A goo good palaeontologist will: AB s BE BE ABLE TO WORK SAFELY AS A TEAM MEMBER OR ALONE AB s BE BE ABLE TO WORK VERY CAREFULLY AND PATIENTLY AS IT CAN take yyears to remove fossils from rocks A s HAVE HAVE A GOOD EYE FOR DETAIL FO s LOVE LOVE FOSSILS
Ask Fig 4.4.19 Jellyfish are
The big Moon Worksheet 4.3 Classifying
Fig 4.4.21 The segments are clear on the body of this leech. Prac 2 p. x
Hot versus cold
Chalk talk
The big Moon
115
Hot versus cold
Hi Q Busters, I was at school yesterday when there was a loud squeal coming from the chalk as the teacher wrote on the blackboard. What causes this? Can you suggest anything I can pass on to our teacher so she doesn’t do it again? It’s driving the whole class mad! Best wishes, Isabella REPLY
Hi Isabella, If a piece of chalk is held incorrectly, it first sticks to the blackboard and then suddenly crumbles. The chalk then slips and vibrates, causing the loud squeal. As the vibrations die down and the chalk dust falls out of the way, friction between the chalk and the board increases until the chalk sticks once again and the cycle is repeated. The frequencies of the squealing chalk depend on the following things:
Career Profile boxes appear throughout the book, covering information about specific careers in science.
That’s one theory anyway. There is another, which is based on impurities in the chalk stick. These small hard bits of grit scratch against the blackboard much like your fingernails would. And what about the solution? Well, you can ask your teacher to try these: s 3NAP THE CHALK IN TWO 4HIS SHOULD DOUBLE THE frequency of the sound and therefore should not be heard.
s AT WHAT ANGLE IT IS HELD
s 0USH DOWN HEAVIER ONTO THE BLACKBOARD This should rub the grit off quickly and the lesson should be squeak free.
s HOW TIGHTLY THE PIECE OF CHALK IS HELD
s 5SE THE WHITEBOARD
s THE LENGTH OF THE PIECE OF CHALK
Or maybe you could experiment yourself, and then pass on the results to your teacher.
s WHERE THE CHALK IS HELD BY THE FINGERS
For example, if the chalk is held just above the blackboard contact point and at right angles to it, the frequencies are higher than if the chalk is held at a 45° angle. In the first case, vibrations are generated along the length of the chalk. In the second case, the chalk vibrates by bending.
Pic of full moon?
Another way to prove it is to look at the low Moon though a rolled-up piece of paper. This will block out the surroundings and the illusion should vanish. Happy moon gazing! The Q Busters Team
Hot versus cold Dear Q Busters Someone at school said she heard on the TV that hot water freezes faster that cold water. This can’t be true, can it? Please help as I am now confused about freezing water. Regards, Alexandra REPLY
This would seem to be completely wrong by what you have been taught so far in Science. This phenomenon, where hot water appears to freeze faster than cold water, actually has a special name. It’s called the Mpemba effect. It is named after the Tanzanian high school student, Erasto Mpemba, who, in 1963, discovered it when experimenting at school.
The Q Busters Team
Dear Q Busters, The other night when we had a full moon it looked enormous just as it rose, but then got smaller later in the night. How can this be? I thought the Moon was the same distance away from the Earth all of the time! From Rachel REPLY
Hi Rachel,
326
One theory suggests that the mind judges the size of an object based on its surroundings. With a low Moon the trees and houses near you appear smaller against the moon which, in turn, makes it appear bigger than it really is.
Hi Alexandra,
Happy chalking!
The big Moon
Many, theories have been put forward, and many, experiments have been conducted. The findings suggest thats it’s only an optical illusion.
until the Moon is higher in the sky. Measure it again, compare your measurements, and you’ll find it’s more or less the same size no matter where it happens to be in the sky.
To prove this for yourself, hold a ruler at arm’s length and measure the Moon as it rises. Make a note of this measurement, and then wait a while
There is still great debate out there over whether this is fact or fiction, but here are the two main theories at present.
the surface. Well, this is removing most of the dissolved gases in the water. The gases actually reduce water’s ability to conduct heat. Therefore, with less dissolved gas in the water, it can cool faster. But we still don’t know for certain. Happy freezing! The Q Busters Team
1. Evaporation. As you know, when hot water is placed in an open container it begins to cool with steam coming off. This will reduce the amount of water in the container. With less water to freeze, the process can take less time. 2. Dissolved gases. When you are boiling water, Alexandra, you know that it’s boiling because you can see the bubbles rising and popping on
Insert pic?
327
ACCURATE RECORDS AND PREPARE s KEEP KEEP ACCURATE RECORDS AND PREPARE REPORTS SAFELY IN A NUMBER OF DIFFERENT ENV s WORK WORK SAFELY IN A NUMBER OF DIFFERENT ENVIRONMENTS
299
Case study boxes cover an in depth exploration of a single case or topic.
Case study
1.2
Case study
Fig 9.3.15 Geologists studying sedimentary rock layers in the field.
Unit
Geologists study the composition and structure of the Earth. This allows them to locate materials and minerals. Geologists work in laboratories and in the field, usually as part of a team. Fieldwork can involve spending time in remote deserts, or in tropical or Antarctic areas. Geologists can be involved in: s ADVISING ON SUITABLE LOCATIONS FOR TUNNELS AND BRIDGES s EXAMINING ROCK SAMPLES USING ELECTRON MICROSCOPES s STUDYING THE NATURE AND EFFECTS OF NATURAL EVENTS LIKE weathering, erosion, earthquakes and volcanoes s TAKING ROCK SAMPLES FOR ANALYSIS s FINDING THE AGE OF ROCKS AND FOSSILS A good geologist will be able to: s WORK AS A TEAM MEMBER OR ALONE
ladies, mare’s fart, hound’s piss, open arse, bum-towel and pissabed. Using his binomial system, they became Taraxacum officinale.
Chalk talk
123
Stormy weather
! PALAEONTOLOGIST EXAMINES CLASSIFIES AND animal and plant fossils found in sedimen This helps us understand the history of lif
Geologist
Sci cii Q B Busters Bu us team
Chalk talk
medusas, a type of cnidarian.
Cereal sounds
Palae
Fig 4.3.9 Until Linnaeus, common dandelions were known as naked
Sci Sc Sci ci Q Bus Buster B Bu uste us ters tter ers er
What do I do?
9.3
! PALAEONTOLOGIST EXAMINES CLASSIFIES AND DESCRIBES animal and plant fossils found in sedimentary rocks. This helps us understand the history of life on Earth.
Linnaeus and Cuvier proposed their kingdoms and classes based on the information they had available at the time. The development of the microscope, however, revealed characteristics of organisms that had never been seen before, particularly in plants and microorganisms such as bacteria. With this new information, new kingdoms were needed and others could be re-organised.
Sci Q Busters appears after Chapter 9 and provides answers to student questions. Students are able to email questions that come up during class time to the Q Busters team at
[email protected]
Segmented worms Also known as annelids, segmented worms can be found both on land and in water. They have welldeveloped body systems and bodies with multiple segments. Examples are leeches and earthworms.
Unit U
Palaeontologist
north of Finland in 1732, Linnaeus nearly fell into an icy crevasse. He saved himself from near-death and went on to discover 100 new plant species on this expedition.
microscope (SEM) of the head of a dog’s parasitic tapeworm.
p Clilip Clip
Some leeches are used in medicine to suck out blood from clots and to encourage blood flow into newly attached limbs after microsurgery.
Career Profile
Arguments in science
Fig 4.3.7 While on a scientific expedition to the far
Fig 4.4.20 An image obtained by a scanning electron
nce enc cience cie cien SScience Sc
It is currently recommended that bluebottle stings are soaked for about 20 minutes in hot water (say under a hot shower or in a bath). The traditional vinegar solution does little since the bluebottle injects a chemical irritant that is neither acid nor base.
Linnaeus originally left room in his kingdoms for mythical animals such mermaids, satyrs, unicorns and ‘monstrous humans’. Room was left for
Unit
Mass
for unicorns (white horses with single long, spiralled horns growing from their foreheads), unicorn-like horns are found on narwhals (rare arctic mammals that resemble dolphins) and some seahorses.
Homo ferus (humans Many students of Linnaeus who walked on all fours went on to explore the world like dogs) and Homo for new plants and animals. caudatus (humans who One, Daniel Solander, had a tail)! accompanied Captain James Cook on his first journey (on which he discovered the east coast of Australia in 1770). He and Joseph Banks brought back to Europe the first ever collection of Australian plants. Botany Bay (originally called Stingray Bay, then Botanist Bay) in Sydney was also named by them. Although some changes were made by the French zoologist Georges Cuvier in the early 1800s, the basic system as developed by Linnaeus is still used today.
Indigenous Australian classification Aborigines traditionally classify animals according to their usefulness, where they live or how they were used. Penguins and emus, for example, are placed in the same category as kangaroos—both are ground-dwelling sources of meat and so they are grouped together. Other birds are placed in the ‘flying food source’ category. In some instances, an animal has no Aboriginal name because it was not used for anything. Some Aboriginal tribes in northern Australia name plants according to their uses or their locations, such as a swamp. In these tribes, fish (guya) are also classified according to where they live. This gives five categories: garrwarpuy living near the surface ngopuy living near the bottom mayangbuy living in rivers raypinbuy living in freshwater gundapuy living among rocks and reefs.
Clip
Monstrous humans! Fig 4.3.8 Although there is no evidence
Pearson Places icons direct students to the Science Focus 3 Second Edition Student Lounge on Pearson Places. The Student Lounge contains animations, video clips, web destinations, drag-and-drop interactives and revision questions.
1.03 Earth days
Distance from Sun
The Laps are the indigenous people of Scandinavia. Reindeer are important to them and so they have more than 107 different categories for them! Their native Saami language classifies them according to their age, condition, body shape and the shape of their antlers!
Science
Aboriginal flag icons denote material that is included to cover Indigenous perspectives in science.
Fact File
Tilt of axis
Clip
107 Reindeers!
Clip
Carl Linnaeus In 1735, the Swedish naturalist Carolus (Carl) Linnaeus (1707–1778) proposed a systematic way of grouping and naming living things. He classified all living things as either animal or plant. He then further divided all animals into six classes: Mammalia (mammals), Aves (birds), Amphibia (amphibians and reptiles), Pisces (fish), Insecta (insects) and Vermes (all the other invertebrates). In recognition of his pioneering work, Linnaeus was made a noble in 1761. From then on, he was known as Carl von Linne.
Scientists still argue over how many kingdoms there should be. Some claim that the protists should not have their own kingdom and that, instead, they should be split amongst the animal, plant and fungi kingdoms. Recent research suggests that the monera kingdom could also be split to form Science two new kingdoms. Although the argument continues, most accept that there are five basic kingdoms Penis worms! (animal, plant, fungi, protists and Science Focus 1 presents monera). nine main classes of animals, Scientists also argue about how but there are other obscure many phyla and classes there are. animals with their own specialised classes. Sponges, There is no hard-and-fast definition for example, have their own for a phylum and so scientists also class (ponifera), whereas argue about its definition, too, starfish belong to another sometimes merging the idea of class class called echinoderms. and phyla together. For these Another small class is called reasons, there may be up to 89 priapulida, otherwise known as penis worms! different classes.
Go to icons direct students to a unit within the same stage of the NSW curriculum. This unit reference allows students to revisit or extend knowledge. Go to
Science Period of rotation (day)
Science
Likewise, shellfish and crustaceans (maypal) have at least ten categories. These are determined by how they attach to rocks, how they move about and whether they live amongst rocks or on a reef. Four distinct subgroups are: gundapuy attached to reefs or rocks warranggulpuy move over the outer surface of rocks lirrapuy move around the edges of rocks djinawapuy attached beneath rocks or inside coral.
Literacy and numeracy icons appear throughout to indicate an emphasis on literacy or numeracy. N L
Science Fact File boxes contain essential science facts relevant to the topic.
Science
On each continent, indigenous peoples established their own keys to classify the living things around them. Many early keys were based on whether the animals or plants were useful as a food source, a source of fur or natural fibres that could be woven or whether they were part of their spirituality. Animals, for example, were sometimes classified as wild or domesticated. Other classification keys were based on whether the animal lived on the land or in the sea. The term ‘fish’, for example, used to refer to anything swimming or anything that lived in the sea. Even today, creatures such as jellyfish, shellfish, crayfish and starfish include ‘fish’ in their names, despite them now being classified as creatures other than fish.
114
Other features or icons The solar system
Grouping living things
Prescribed Focus Area: The history of science
4.3
Remembering
Unit
Chapter review questions follow the last unit of each chapter. These questions are structured around Bloom’s Taxonomy of Cognitive Processes and cover the chapter learning outcomes in a variety of question styles to allow students the opportunity to consolidate new knowledge and skills.
CHAPTER REVIEW
Science Focus
and current research and development. The features allow students to explore science in further detail through a range of student activities.
Chapter review
The medicine man
British GP, Dr Harold Shipman killed an estimated 236 23 of his patients between 1974 and 1998. His visits to sick, elderly people were often followed by a worsening off their ailment and then what seemed to be an ious death. Dr Shipman would return and wri unsuspicious write out the death certificate and alter the records to say th that the person was so sick that they were close to death. at the doctor was actually giving Very few suspected that ction. his patients a lethal injection. However, in 1986 he killed a healthy elderly lady and st will and testament that fabricated a poorly worded last made him the sole beneficiary. The police investigated the forged will and then exhumedd (dug up) her body. They also exhumed the bodies of Shipman’s other und in each of patients. Traces of morphine were found aths. Shipman’s them—the probable cause of their deaths.
computer system became vital evidence as the date of every file he modified was recorded. The files for many of the deaths showed that they were modified on the day the patients died, uncovering many more likely murders. Shipman was convicted and given 15 life sentences, but he committed suicide in custody, leaving many questions unanswered. The motives for his crimes remain a mystery.
Fig 1.2.8 Dr Harold Shipman killed at least 236 patients. A poorly forged will led to his capture.
The m Clip
Science
Plastic money Australia was the first to use the plastic banknote— banknote—a $10 commemorative note introduced in January 1988 tto coincide with the Australian Bicentenary. Plasticc banknotes are m more durable than paper ones, lasting four to five times imes longer. A paper pap $5 note had an average life of about six months, lasts more than nths, a plastic one la three years. Note Printing Australia ralia (NPA) is owned by the Reserve
British GP, Dr Harold Shipman killed an est of his patients between 1974 andQUESTIONS 1998. His ON NS S sick, elderly people were 1.2 often followed by a of their ailment and thenRemembering what seemed to be 1 List five documents that a criminal might try to falsify. 2 State what indicated that hat the Hitlerretur diaries were fake. unsuspicious death. Dr Shipman would 3 State what can be used to determine which typewriter was ansom note. used for a ransom out the death certificate and alter the record 4 List the advantage(s) of Australian banknotes being printed plastic. the person was so sick thatonthey were close t 5 List the features that usually give away fake banknotes. V f d h h d
The Science Focus 3 Second Edition package
Bank of Australia and prints all Australian banknotes. It has also produced plastic banknotes for Thailand, Indonesia, Papua New Guinea, Kuwait, Western Samoa, Singapore, Brunei, Sri Lanka and New Zealand. NPA also sells plastic blank notes to government printers in other countries so that they can print their own money. Old and ‘worn-out’ Australian plastic money is recycled into plastic objects such as plumbing fittings and compost bins.
Understanding 6 Investigators generally ignore the slant and spacing of letters in a handwritten document. Explain why. 7 Describe how a computer printer can be identified from a fake letter.
Don’t forget the other Science Focus 3 Second Edition components that will help engage and excite students in science: Science Focus 3 Second Edition Homework Book
8 Explain how inks can be identified using: a fluorescence b chromatography 9 Describe the following: a intaglio printing b microprinting c a water mark
>> 15
Science Focus spreads appear throughout the book. These are special features on various aspects of science including history, the impact of science on society and the environment
Science Focus 3 Second Edition Teacher Edition, with CD Science Focus 3 Second Edition Pearson Reader Science Focus 3 Second Edition LiveText™
ix
Stage 5
Syllabus Correlation chapter
1 2 3 4 5
The Forensics periodic table
Outcomes
Science Focus 3
•
5.1 5.2 5.3 5.4 5.5
Chemical change
Sense and control
▲
▲
•
▲
•
Note:
•
•
▲
•
•
• • • • • • • • • •
• • •
• •
• • •
• •
▲
• •
•
•
•
• • • • • • • • • •
• • • • • • • • • •
• • • • • • • • • •
• • •
• •
• • •
• • • • • • • • • • • •
Earth’s fragile crust
▲
▲
• • • • • • • • • • • • • • •
• • • • • • • • • • • • • • •
▲ indicates the key Prescribed Focus Area covered in each chapter. Chapters may also include information on other Prescribed Focus Areas.
x
•
Light
The universe
▲
•
• • • • • • • • •
Ecosystems
▲
▲
5.6 5.7 5.8 5.9 5.10 5.11 5.12 5.13 5.14 5.15 5.16 5.17 5.18 5.19 5.20 5.21 5.22 5.23 5.24 5.25 5.26 5.27
Reproduction
6 7 8 9
• • • • • • • • • • • • • • •
Verbs Science Focus Second Edition uses the following verbs in the chapter questions under the headings of Bloom’s Taxonomy of Cognitive Processes. The verbs in black are the key verbs that have been developed to help provide a common language and consistent meaning in the Higher School Certificate documents. All other verbs listed below feature throughout the book and are provided here for additional support to teachers and students.
Remembering
Analysing
List Name Present Recall Record Specify State
Analyse
write down phrases only without further explanation present remembered ideas, facts or experiences provide information for consideration present remembered ideas, facts or experiences store information and observations for later state in detail provide information without further explanation
Understanding Account Calculate
Clarify Define Describe Discuss Explain Extract Gather Modify Outline Predict Produce Propose Recount Summarise
account for: state reasons for, report on. Give an account of: narrate a series of events or transactions ascertain/determine from given facts, figures or information (simply repeating calculations that are set out in the text) make clear or plain state meaning and identify essential qualities provide characteristics and features identify issues and provide points for and/or against relate cause and effect; make the relationships between things evident; provide why and/or how choose relevant and/or appropriate details collect items from different sources change in form or amount in some way sketch in general terms; indicate the main features of suggest what may happen based on available information provide put forward for consideration or action retell a series of events express, concisely, the relevant details
Applying Apply Calculate
use, utilise, employ in a particular situation ascertain/determine from given facts, figures or information Demonstrate show by example Examine inquire into Identify recognise and name Use employ for some purpose
identify components and the relationship between them; draw out and relate implications Calculate ascertain/determine from given facts, figures or information (requiring more manipulation than simply applying the maths) Classify arrange or include in classes/categories Compare show how things are similar or different Contrast show how things are different or opposite Critically (analyse/evaluate) add a degree or level of accuracy/depth, knowledge and understanding, logic, questioning, reflection and quality to (analyse/evaluate) Discuss identify issues and provide points for and/or against Distinguish recognise or note/indicate as being distinct or different from; to note differences between Interpret draw meaning from Research investigate through literature or practical investigation
Evaluating Appreciate Assess
make a judgement about the value of make a judgement of value, quality, outcomes, results or size Critically (analyse/evaluate) add a degree or level of accuracy/depth, knowledge and understanding, logic, questioning, reflection and quality to (analyse/evaluate) Deduce draw conclusions Draw draw conclusions, deduce Evaluate make a judgement based on criteria; determine the value of Extrapolate infer from what is known Investigate plan, inquire into and draw conclusions Justify support an argument or conclusion Propose put forward (for example a point of view, idea, argument, suggestion) for consideration or action Recommend provide reasons in favour Select choose one or more items, features, objects
Creating Construct Design Investigate Synthesise
make; build; put together items or arguments provide steps for an experiment or procedure plan, inquire into and draw conclusions about put together various elements to make a whole
xi
Forensics
1
Prescribed focus area Applications and uses of science
Key outcomes 5.3, 5.12, 5.15, 5.16, 5.17
•
Evidence can be used to support different viewpoints.
•
Observations and measurements must be accurately made and recorded.
•
A range of data collection strategies can be used.
•
Information from a number of sources needs to be collated.
•
Information must be distinguished as relevant or irrelevant.
•
Technological developments have extended the ability of scientists to monitor and collect information about events in the world.
Additional
Developments in science impact on society and how it works.
Essentials
•
Unit
1.1
context
Forensics and identification
Society has a framework of laws based on the rights, responsibilities and the safety of its citizens. Theft, assault, murder and forgery (the faking of documents or money) are all crimes that carry penalties—from monetary fines
and community service orders to prison terms and, in some countries, execution. Forensic scientists collect and analyse evidence that can be used to find the person who committed a crime and later bring them to justice. Forensic evidence can also be used to prove their innocence.
Pathologists are medical doctors who have specialised in the study of disease and injury and the damage these do to organs and tissues. Forensic pathologists perform autopsies. In an autopsy, a dead body is dissected to find signs of damage that may point to the likely time and cause of death. Forensics also uses the expertise of specialists in many fields such as information technology, medicine, dentistry and psychology (the study of how people behave and why).
Forensic methods of identification Fig 1.1.1 Who is it and how and when did they die? Forensics attempts to find out all this information and more.
Forensic science Forensic science is scientific knowledge that can be used by the legal system. A crime scene will contain multiple pieces of evidence and forensic science is used to analyse it. Forensic science helps to answer questions such as when a death occurred and why, how fast a car was travelling on impact, what the blood alcohol concentration of the driver was at the time and the type of white powder found in a suitcase by Customs.
2
Forensic scientists Forensic scientists help investigators to collect scientific evidence. Crime scene units are made up of police who are specially trained to collect, bag and label all types of evidence at a serious crime such as a homicide (murder or manslaughter). Regular police members also collect and bag evidence in less serious crimes.
Forensic methods of identification assist in identifying dead bodies and people who are living but are avoiding justice. Most of the time these methods are not needed. People usually carry some form of photo-identification in their pocket, wallet or purse. This identification is readily available to police if they die, commit a crime or are a witness to a crime. Family, neighbours, co-workers, schoolmates and personal web pages such as Facebook provide another way of identifying someone. Identity is usually easy to establish. Sometimes, however, none of this information is available. Dead people are often difficult to identify, especially if they are just bones. The identity of a living person can also be hard to determine: criminals often change their name to establish a new identity and to hide past crimes. Before the invention of photographs, they could simply move to a new location, change their name and start a new life. The chance of being recognised was slim. If caught for a new crime, then the probability of being charged for others was very low. This was especially so in large and populous cities. Forensic methods of identification can be used in such cases.
Unit
1.1
Identikit and composite drawings Throughout history, drawings of wanted criminals have been used as a tool of identification on ‘wanted posters’ for suspected criminals like bushrangers in Australia and outlaws in what was known as the ‘wild west’ of the USA. Initially, artists produced these images. Another system called Identikit became popular after 1959 when it was used to successfully identify an assassin, Guy Trebert, in Paris. Identikit uses re-drawn facial features that can be slotted together without the need of an artist. Today, computerised methods involving thousands of images are used to generate a composite drawing in minutes. Some produce three-dimensional images. Identikit and computer composites have limited effectiveness, however, as it is difficult for a witness to get all the features correct. Only about two per cent of these images result in a Prac 1 positive identification. p. 9
Fig 1.1.2 Wanted posters and newspapers were once the only ways of spreading information to the public about criminals. This 1879 poster is calling for information about the assassin Ned Kelly.
Science
Facial recognition The face is one of the best indicators of someone’s identity. This is why photographs appear on drivers’ licences and passports.
Clip
Identification Mexico-style In 2004, the Minister for Police, the Justice Minister and other important law makers in Mexico had microchips surgically implanted. These chips identified them and allowed only them to gain computer access to sensitive information on criminal activity. Dogs and cats commonly have microchips inserted under their neck skin allowing them to be identified if lost.
Photographic identification Photography was invented in 1854. From the 1870s it was used in conjunction with anthropometry (the proportions of the body) to identify suspects. In the early 1900s, photography began to be used as a reliable way of recording, identifying and proving identity. Photographs are difficult to classify and police may need to sift through hundreds of photographs to determine the identity of someone in custody. A witness to a crime will also find it difficult to identify a suspect. Looking at so many photographs can also alter their memory. New information interferes with old memories, making a positive identification improbable. This is called retroactive interference.
Fig 1.1.3 The computerised Identikit system was developed to speed up the production of composite images.
Fig 1.1.4 This computerised Identikit photo of an Italian mafia boss helped police catch him in 2005. It shows a remarkable similarity with the real man.
3
Forensics and identification The Bertillon system Alphonse Bertillon was a French anthropologist and chief of criminal identification for the Paris police. About 1870 he devised the first scientific method of criminal identification. His identification system was called anthropometry or the Bertillon system. It involved measuring and recording the dimensions of a series of bony body parts and was based on the assumption that no two people would ever look exactly alike or have exactly the same measurements. It was widely used from about 1882 to 1905, however, there were cases of mistaken identity including one when a man was sent to jail for a crime committed by his twin brother. It was eventually superseded by fingerprinting. Fig 1.1.5 Biometric cameras scan a face and computer software measures the position of certain points on the face. These can then be compared with profiles on the computer database.
Biometric facial recognition Specialised computer systems and software can recognise a face by matching it to one stored in a database. The position of points formed by the eyes, chin, nose, ears and other facial features are measured and compared with thousands of profiles. The process takes only a few milliseconds and so facial recognition can be used to screen people for access to secure areas. It is likely that this technology will be used in the near future at airports and major train stations to help recognise known terrorists. However, the rate of false positives (the computer detecting a match when there is none) and false negatives (missing a match) is still quite high. Slight changes in the angle and in the quality of the image make it difficult to get consistent results. There is also a privacy issue: do people want government and corporations to be able to track their movements through biometric facial recognition every time they enter a building?
Identification using the body Each person has features that identify their body. Different methods have been developed to measure these features and use them as a method of identification.
4
Science Fingerprints Fingerprints are found on the palms of the hands and soles of the Australia’s first feet of all primates (apes, monkeys In 1903, all prisoners and humans). They help us grip in NSW were things, acting in a similar way to fingerprinted for the first time. Their 6000 the tread patterns on shoes and car prints started tyres. Each fingerprint consists of Australia’s first ridges and valleys that form a fingerprint collection. distinct pattern. The ridges form beneath the outer layers of skin and will grow back in exactly the same pattern if removed. It wasn’t until 1892 that scientists and police started to agree that they could serve another purpose—to positively identify people. After collecting and analysing thousands of fingerprints, English scientist and statistician Sir Francis Galton and the head of London police Sir Edward Richard Henry concluded that no two fingerprints were exactly alike. Henry then invented a system of collecting and classifying fingerprints using ink on cards with letter codes for each fingerprint type. These could be indexed and searched. This enabled police to: • collect the fingerprints of existing criminals in jail and index them • match a person with their collection, even if they had changed their name and appearance • match a fingerprint collected at a crime scene with one in their collection
Clip
Unit
1.1 Fig 1.1.7 An Automatic Fingerprint Identification Fig 1.1.6 Fingerprints are regularly taken from suspects to compare with those collected from a crime scene.
• use the fingerprint from a corpse to help identify it. Fingerprints also allowed people who could not write to ‘sign’ their name with a thumbprint instead. Prac 2 p. 10 Fingerprint scans Over time, so many fingerprints were collected that it became very slow to search through them manually. Each law enforcement agency had its own fingerprint collection which also made it difficult to compare a print with those in the collections stored in other cities, states or countries. Computers now provide a faster system of storing, searching, matching and identifying prints. At first, existing fingerprint cards were scanned. Today, wholehand prints and fingerprints are scanned directly into a
Loops have ridges that enter and leave from the same side like a loop of string. Loops can begin and end on the left or the right side of the finger. Worksheet 1.1 Fingerprints
Arches look like an arched bridge.
System (AFIS) uses infra-red (IR) light to scan a person’s fingerprint. In Scotland, banks are trialling ATMs which use fingerprints for identification instead of a PIN.
computer allowing instantaneous comparison of millions of fingerprint records. Although computers can find probable fingerprint matches, the final analysis and match must be made by trained fingerprint specialists. Even so, errors can be made. As well as their forensic use, fingerprint scans are now widely used as a ‘password’ that restricts access to computers and buildings and to sign in and out of work. As a result of the terrorist attacks on 11 September 2001, visitors entering or leaving the USA via its international airports must have their fingerprints scanned. Types of fingerprints Fingerprints come in four types: loops, whorls, arches and composites.
Whorls contain circular/oval or yin-yang patterns.
Composites are rare and are a mixture of the other three types.
Fig 1.1.8 The four basic fingerprint types: loops, whorls, arches and composites
5
Forensics and identification Iris and retina identification Although initially a device of science fiction or spy films, a person’s identity can be determined by scanning their eyes. Computerised devices scan either the iris pattern or the pattern of blood vessels in the retina. The chances of incorrect identification are very low because: • two scans are taken, one of each eye • a glass eye cannot be forged. A glass eye never moves, whereas a real iris moves constantly • an iris is far more detailed than a fingerprint, with 266 identifiable features • the iris never changes, even with age, and is therefore a good long-term identifier. Retina scans are more difficult to obtain than iris scans but they are more accurate. Retina scans are currently used to gain access to high-security facilities containing nuclear weapons. Although potentially useful in criminal investigations, iris and retina scans are very difficult to obtain from uncooperative suspects.
any microscopic sample left by them. This sample might be a few cells of skin, hair, sperm or even dandruff. Evidence obtained through DNA profiling can be used in a court of law to prove identity. Use of DNA samples DNA samples can be useful to an investigation, even if they do not match any samples in the police database. DNA can be used to determine whether the sample came from a male or a female and will be kept in the database until a match is found. In the future, it may be possible to tell more about a person from their DNA, such as their probable height, weight or even what they may look like. While DNA is not always recovered from a crime scene, in some cases a definite sample can be collected. A rapist, for example, can leave behind a sample of semen. A negative match can prove the innocence of a suspect; a positive match can be used to prove guilt. The development of DNA profiling has forced a review of many cases where people have been imprisoned. Thousands of falsely Science imprisoned people have been proven innocent through new DNA evidence and have been released. In Leftovers the USA for example, the Wherever you go you ‘Innocence Project’, largely leave a little of managed by volunteer law students, yourself behind. DNA has used DNA profiling and other matching has different success rates evidence to support the release of depending on the those jailed for crimes it appears sample. For example, they did not commit. This has the success rates for called into question much of the blood are 90 per cent, legal system, including the accuracy saliva on a cigarette butt 67 per cent, fallen of eyewitness testimony.
Clip
Fig 1.1.9 Computer scans convert markings in the iris into a coded series of black and white patches. These special contact lenses show irises as the computer program sees them. Go to
Science Focus 4 Unit 4.1
hair 25 per cent, and sweat on a weapon handle 17 per cent.
Genetic identification DNA (deoxyribonucleic acid) is a chemical that is present in every cell of your body. The structure of DNA provides the cell with a set of coded instructions on how the cell can build all the materials that make a human. Almost every person has their own unique DNA. The only exceptions are children from identical multiple births, such as identical twins who have identical DNA.
6
DNA profiling DNA profiling is a set of tests that measure the DNA code. DNA profiling is an extremely sensitive and powerful technique because it can identify a person from
Fig 1.1.10 The blood on this knife will contain the DNA of the victim. Sweat and oils on its handle will contain the DNA of the attacker. There are also fingerprints in the blood which will provide further evidence.
Science Focus 4 Unit 3.3
1.1
Go to
of the person. Sex and age can be determined by careful examination of the pelvis, skull and other key bones. This data can then be entered into a missing persons database which will hopefully result in a match, or a set of matches. Dental and hospital records, photographs and other materials can then be collected to help positively identify the person. Additional information can come from the remains of clothing, buttons, buckles or other objects which might still be around the skeleton. These provide an invaluable aid to determining both the identity of the person and the year or decade in Prac 4 p. 11 which they died.
Unit
When DNA gets it wrong Errors in judgment and contamination of equipment and DNA samples occasionally do occur. In 2000, a toddler named Jaydyn Leskie disappeared in Moe, Victoria. His body was found in a dam later that year. DNA was analysed but it came from a person that police knew had nothing to do with the investigation. Despite all precautions, the ‘innocent’ DNA had ended up in the forensic testing laboratory and had somehow found its way into the sample. It may have come from a visitor to the laboratory.
Identifying a body Corpses are often degraded to the point where they are difficult to identify. Degradation occurs very quickly in fires and explosions which can happen in a plane crash or bomb blast. Sometimes it occurs more slowly. This could be because a body has been hidden before being discovered, when someone gets lost and dies in the bush or after a natural disaster such as a tsunami. Sometimes there is nothing left of the body except a skeleton or perhaps a few bones. Fingerprints are no longer present and DNA may have deteriorated to the extent that it is no longer reliable as a method of identification. This is when the forensic odontology (dental measurements) and anthropometry (body measurements) are used. Worksheet 1.2 Time of death
Fig 1.1.11 Fillings and dental work can be compared with existing
‘Known’ bodies Sometimes police are reasonably sure of the identity of a body. A body recovered from a house fire, for example, probably belongs to someone who lived there. X-rays of the body will show previous bone injuries and any pins which have been used to stabilise and strengthen serious breaks. Comparison can then be made with the hospital records of who they think it is. Usually X-rays of the teeth are also taken and compared with dental records. These X-rays can be used to confirm identity and make sure that the remains are returned to the family for burial or cremation. Prac 3
dental records, helping to determine a person’s identity. This 18-yearold has fillings (seen in this X-ray as bright areas) and impacted wisdom teeth.
p. 11
Mystery bodies Sometimes the identity of a corpse or skeleton is a complete mystery. Much information, however, can be gathered through careful examination by a forensic anthropologist. Measurement of key bones such as the femur (the main bone of the leg) can be used to find out the height
Fig 1.1.12 Measuring the skull can help to determine a victim’s age, sex and other characteristics.
7
Forensics and identification
Case study
The ‘Pyjama Girl Murder Case’
In 1934, a burnt and mutilated female body dressed in pyjamas was found in a ditch beside the road near Albury NSW. Everything matched missing woman, Linda Agostini. Her husband did not recognise the body, however, and there were subtle differences between her dental records and the body’s teeth.
1.1
QUESTIONS
Remembering 1 State the job of:
9 List the types of animals that have fingerprints and explain what they help these animals do.
a a forensic scientist
10 Explain what DNA is and where in the body it is found.
b a crime scene unit
11 Explain how a negative DNA match is sometimes very useful.
c a forensic pathologist
12 Teeth impressions left on a victim often cannot be used to positively identify the culprit. Explain why.
2 List the identification you normally carry around with you. 3 List the advantages and disadvantages of the following methods of identification: a photographs b Identikit c biometric facial recognition 4 List the advantages and disadvantages of: a the Bertillon system b fingerprints c iris and retina scans 5 List what checks are made when a body is found whose likely identity is already known. 6 List the measurements and details that need to be taken of a body whose identity is a mystery.
Understanding 7 Summarise the different methods of identification presented in this unit by constructing a table. For your columns use these headings: method, how it is used, effectiveness of method and comments about the method. 8 Explain why it was much easier in the past than it is today for a criminal to simply ‘disappear’.
8
The body was stored in a formalin bath and after 10 years a previously undetected porcelain tooth filling fell out. Another detailed dental examination proved it was Linda. Her husband, Antonio, then confessed to murder. He was convicted of manslaughter because of confusing presentation of evidence by the prosecutors and served less than four years.
Applying 13 A person is shown dusting for fingerprints in the photo on page 1. a Identify whether the person is likely to be a forensic scientist, a member of a crime scene unit, a pathologist or a forensic pathologist. b Propose a likely reason why the person is wearing rubber gloves.
Evaluating 14 At the start of the ‘Pyjama Girl Murder Case’, victim Linda Agostini was not identified because of ‘subtle differences’ between the teeth of the body and her dental records. a Describe how your teeth can be different to the records kept at your dentist. b Describe other changes that might happen to your teeth over time. c Propose a reason why X-rays were not used to analyse the skull and teeth of the body. The case occurred in 1934. 15 Assess whether this delay in identification could happen today. Explain your answer. 16 Propose at least five likely reasons why identification of the bodies of the 2004 Boxing Day tsunami was so difficult.
Unit
1.1
17 Propose a likely reason why teeth are sometimes the only things that remain of a skeleton after a long time. 18 Propose a reason why the final identification of fingerprints is always done by a person and not a computer.
a TV shows like this one have characters carrying out multiple tasks b it is better for a criminal investigation if different people carry out different tasks
19 TV shows like ‘CSI’ have their characters collecting evidence, testing it back at the laboratory, carrying out autopsies and interviewing witnesses and suspects. In reality, different people carry out each role. Propose reasons why:
20 A blind experiment is one where the samples are all encrypted so that the scientist does not know which is which. Propose a reason why this might be especially important in forensic science.
1.1
INVESTIGATING
Peter Falconio
a what happened the night Peter Falconio disappeared
While driving in the Northern Territory in 2001, British tourists Peter Falconio and Joanne Lees were stopped by a man. Peter Falconio got out of the car. Lees heard what she thought was a shot and never saw Falconio again. She was kidnapped, then escaped, hid and later flagged down a passing truck. Although Falconio’s body was never found, Bradley John Murdoch was found guilty in 2005 of his murder. Investigate your available resources (for example, textbooks, encyclopaedias, internet) to find out the following:
b the key forensic evidence presented in the court case
1.1
c other evidence presented in the case d why some doubted Joanne Lees’ story of murder and kidnap. Present your work in one of the following ways by creating: L • a labelled timeline showing relevant events • an oral, written or videotaped interview with Joanne Lees • an interview with one of the jurors at Murdoch’s trial • a videotaped segment or script for a TV show like ‘CSI’ • a series of articles for the front pages of a newspaper.
PRACTICAL ACTIVITIES
1 Make your own Identikit
Method
Aim
1 Set up the camera (preferably on a tripod) in a bright spot, about one to two metres away from a plain background.
To construct a basic Identikit and use it to create images of different people
2 Get someone to stand facing the camera and zoom in so that their face takes up most of the picture.
Equipment
3 Take a test photo and adjust the lighting or camera settings until you are obtaining consistently good quality photos.
• • • • • •
digital camera computer printer and optional camera tripod A4 paper scissors or Stanley knife sticky tape or glue
4 Use sticky tape to mark the position on the ground of their feet. 5 Take individual photos of everyone in the class, making sure that they are standing in exactly the same position marked by the sticky tape. 6 Print out all the photos in black and white and at A4 size.
>> 9
Forensics and identification 7 Photocopy all the photos so that every four to six students have a complete set. 8 Cut each photo into sections as shown in Figure 1.1.13. 9 Use features from different people to construct different and imaginary faces. 10 When you have a face that ‘works’, stick it onto a fresh sheet of A4 paper.
Questions 1 Assess how realistic the constructed faces are. 2 Assess whether you had enough different features to make a wide range of faces. 3 Identify parts of the Identikit faces that do not join up. 4 Propose how a computer could be used to fix this problem.
Fig 1.1.13
2 Fingerprints Aim
Name
Thumbprint
Forefinger print
Me
To take the fingerprints of classmates and identify if they are loops, whorls or arches
Equipment • blank paper • inkpad
Jasmine
Method 1 In your workbook, construct a table similar to the one shown here. You will enter fingerprints in this table, so leave plenty of room for them. 2 Practise making ‘rolled prints’ with the inkpad and blank piece of paper. This involves rolling your thumb and forefinger from one side to the other on the paper to make the print. Do not use too much or too little ink, and only roll once. Rolling back and forward will smudge the print. 3 Collect a clear thumbprint and a clear forefinger print of the right hand of as many members of the class as you can. If smudged, collect another one.
10
Fig 1.1.14
Questions 1 State how many loops, arches and whorls you collected. 2 Identify the most common type of fingerprint in the class.
4 Paste the page into your workbook for later reference.
3 Identify which is the least common.
5 Identify what type of prints they have and write it next to each print. Use the code LL (left loop) RL (right loop) W (whorl) A (arch).
4 State whether there are any people whose fingerprints are hard to distinguish. 5 Discuss how you could tell them apart.
Unit 3 Count how many teeth are displayed in the impression.
Aim
4 Use a string and ruler to measure the curving length of the impression.
To make teeth impressions and analyse them for features that may be used for identification
5 Note and mark any irregularities in the impression, such as large gaps or missing teeth.
Equipment
6 Use a mirror to compare any irregularities in the impression with those in the mouth.
• • • • • •
‘jelly’ lollies such as jelly frogs or snakes (one per student) grey-lead pencil string ruler access to a mirror tracing paper (optional)
Method 1 Carefully bite into the jelly lolly or snake. If possible, bite right through it. In doing so: • bite the lolly so that the fullest set of teeth impressions are formed. If using a snake, you may need to bend the snake and push it into the teeth instead of biting through it • take only one bite • do not ‘tear’ the lolly.
7 Compare your tracing with those of your neighbours. Tracing paper will help.
Questions 1 State whether you have the same number of teeth markings as in the impression. 2 Propose reasons why the number may be different. 3 State whether the curved lengths of each student’s impressions were the same. 4 Explain how they might be different. 5 Teeth impressions can be found on bodies in murders and sexual assaults. Identify what a forensic investigator might look for in the impression.
2 Remove the lolly and trace the teeth impressions made in it into your workbook.
6 Identify the types of fluids that an investigator might take from such a teeth impression. Why would they take them?
4 Forensic anthropometry
2 Pair up with a partner and measure the length (in centimetres) of each person’s femur, either using the string and ruler or the tape measure.
The length of many bones can be used to determine the height of a skeleton
Aim To measure the length of the femur and determine if it can be accurately used for identification
Equipment • • • • •
string metre ruler or tape measure pencil and calculator tape measure or metre ruler access to a model human skeleton
Method 1 Check the location of the femur on the skeleton, taking particular notice where the bone begins and ends.
1.1
3 Collecting teeth impressions
3 Use the following formula to calculate your estimated height and that of your partner, based on these bone lengths: • male: height (in cm) 쏁 69.089 쎵 2.238 쎹 femur length • female: height (in cm) 쏁 61.412 쎵 2.317 쎹 femur length 4 Measure your actual height using the metre ruler or tape measure. 5 Repeat the measurement and calculation, but this time use the skeleton.
Questions 1 State whether your calculated heights were close to the actual heights of the people you tested. 2 Propose reasons for any differences.
11
Unit
1.2
context
Is it real? of money. Forensic examiners analyse the handwriting, typesetting, paper and inks used in a document to establish its origin and whether it is authentic.
Forged documents such as licences, passports, bank documents, cash and bonds are commonly used to commit fraud and to embezzle large amounts
start direction of line
Fig 1.2.2 These are some of the many ways of writing the letter ‘E’.
This gives them a set of differences that occur naturally in the person’s writing. The slant of letters, their spacing and style are easy to disguise, and so they pay more attention to the formation of certain letters such as ‘E’.
Fig 1.2.1 In 2007, a man tried to open a bank
Science
Clip
The Hitler diaries The Hitler diaries were sold for $8.2 million in 1983 ($15.5 million if sold today). Although the handwriting matched a previous sample of Hitler’s, the paper on which it was written was of later, post-war origin. The material had been clearly copied from Hitler’s speeches and other historians’ documents and included well-known errors the historians had made.
account with this fake $1 million US banknote. Unfortunately for him, there has never been a US banknote for this amount.
Analysis of writing and print
Handwriting analysis Handwriting analysis tries to identify who wrote or signed a particular document. The investigation might involve someone forging the signature on a cheque or perhaps trying to disguise their own handwriting when scribbling out a ransom note. Like most skills, a person’s handwriting is learnt and practised and takes years to develop. It alters little over time. The capital letter E, for example, can be written in many different ways depending on where the pen starts and finishes, and where it is lifted off the paper. Document examiners typically spend many hours analysing other documents known to be written by a person before they examine the questioned document.
12
Prac 1 p. 17
Typewriter matching Handwriting is easily traced and so criminals often used a typewriter to produce ransom notes, fake documents, extortion demands and death threats. Typewriters, however, could still be traced. The shape or font of the letters formed by a typewriter could easily be tracked to particular typewriter brands and models. This was enough to remove any suspects who had different typewriters. When the typewriter brand matched, microscopic examination of an individual typewriter could reveal
Raised letters and numbers: these can have characteristic pits and cracks in them allowing the machine to be identified.
Type-bar acts as a hammer
Keyboard
Fig 1.2.3 An old-fashioned typewriter. Imperfections in the typewriter’s metal letters showed up in any document typed on that machine.
Unit
Printer matching Modern computer printers are harder to match than typewriters because they produce their letters in a different way. The paper, however, often shows marks from the transport mechanism that moves the paper through the machine. This can be seen and photographed when lit at a very low angle (oblique lighting). Ink analysis The ink used to handwrite or print a suspect document can be analysed using different forensic methods. Documents are often examined and compared by reflecting different coloured lights (e.g. ultraviolet light) off them or by passing light through them. Many inks look different or will fluoresce (glow) under these lights. This is particularly useful for detecting forgeries of paper money and official documents which have used the wrong inks. Inks can also be examined using a technique called chromatography. This involves cutting out a sample and
1.2
that it was used to write the suspect document. Each key on a typewriter links to a metal ‘type-bar’ or ‘hammer’ that has the raised shape of a letter on it. These metal letters are all slightly different when examined closely, despite coming from the same make and model. Tiny pits and cracks could be compared under the microscope and a positive match proved.
Fig 1.2.5 A forensic scientist inspects the pigments used in different black industrial dyes. Chromatography can produce rings like this or straight streaks of different pigments.
drawing a solvent up through the paper. This will dissolve the different pigments in the ink, causing them to move up with the solvent and streak out like a rainbow. Black inks may all look the same, but chromatography causes them to produce different patterns and show their different component colours. Different solvents such as water or methylated Prac 2 spirits also produce different patterns. p. 17
Forgery Governments and banks use a range of technologies to make it difficult to counterfeit money, cheques and official documents. Since realistic forgery is beyond the ability of most amateurs, the circulation of counterfeit notes usually indicates the involvement of organised crime. Science Counterfeit bills: • often have identical serial numbers. Fake Aussies Real notes all have different serial The first $100 notes in numbers Australia were made • will usually be of poorer standard from paper and had than the real note, particularly when little colour in them, comparing the finer details being largely black, white and shades of • will often be made from material that grey. Amateur has a different feel to the real thing. counterfeiters simply Successful prosecution of photocopied the notes counterfeiters requires locating the and some were able to equipment used to make the bills and a pass them off as real. positive match with the printed bills.
Clip
Fig 1.2.4 Some of the inks used to print banknotes and important documents will fluoresce under UV light. The stars and stripes in this European banknote glow red or blue.
13
Is it real? Paper banknotes are printed on specialty paper with its own characteristic feel.
Intaglio printing is a raised form of printing that can be felt with your fingers.
Optically active devices are images that are holographic (producing multi-colour effects) or clear.
Australian banknotes are printed on polymer film (plastic). They last longer than paper notes and are harder to counterfeit.
Australian banknotes notes have their mination number and portraits, denomination alia in intaglio printing. the word Australia
Most Australian banknotes have an image of a seven-pointed star that is only complete when held up to the light. The $10 has a windmill.
Fluorescing inks glow under UV light. On the back of the $5 note, the wattle flowers, horizontal bars and sunburst fluoresce, so does the number 5.
Australian banknotes use a second optical device: the denomination of the note appears when held up to the light.
Fig 1.2.6 An Australian Aust $5 note with some off iits counterfeit protecti protection features identified
The Australian $5 note has an early version of Advance Australia Fair on its back. The $10 note has the poem The Man from Snowy River on its front.
Microprinting produces very small printed details such as sentences, initials etc. that can not be reproduced by a colour printer or photocopier. A magnifying glass is needed to read it.
Not shown Serial numbers: prominent letters and/or numbers on each one or both sides of the bill. Each number is different. Counterfeit notes often all have the same serial number. Watermarks: hidden images in paper notes that are only seen when the note is held up to the light. Australian banknotes have something similar. The $50 note has the Australian coat of arms. Metal bands: paper notes often have a metal band inside the layer of the paper. This can be felt and seen under backlighting.
Science
Clip
DNA can stop counterfeiting Money is not the only thing criminals try to forge. Merchandise for the last few Olympic Games has included tags and stickers impregnated with DNA to ensure their authenticity. Purchasers have been asked to send tags and stickers with their name, address, purchase date, store and product description for verification and to assist in tracking fake merchandise. Likewise, modern art—especially paintings—now often includes some of the artist’s DNA in the paint.
Fig 1.2.7 The Dutch passport is probably the hardest in the world to fake. The image on the right is made up of tiny holes that can only be seen when the page is placed over a light.
14
Prac 3 p. 18
Prac 4 p. 19
Unit
1.2
Case study
The medicine man
British GP Dr Harold Shipman killed an estimated 236 of his patients between 1974 and 1998. His visits to sick, elderly people were often followed by a worsening of their ailment and then what seemed to be an unsuspicious death. Dr Shipman would return and write out the death certificate and alter the records to say that the person was so sick that they were close to death. Very few suspected that the doctor was actually giving his patients a lethal injection. However, in 1986, he killed a healthy elderly lady and fabricated a poorly worded last will and testament that made him the sole beneficiary. The police investigated
the forged will and then exhumed (dug up) her body. They also exhumed the bodies of Shipman’s other patients. Traces of morphine were found in each of them— the probable cause of their deaths. Shipman’s computer system became vital evidence as the date of every file he modified was recorded. The files for many of the deaths showed that they were modified on the day the patients died, uncovering many more likely murders. Shipman was convicted and given 15 life sentences, but he committed suicide in custody, leaving many questions unanswered. The motives for his crimes remain a mystery.
Fig 1.2.8 Dr Harold Shipman killed at least 236 patients. A poorly forged will led to his capture.
Science
Clip
Plastic money Australia was the first country to use the plastic banknote—a $10 commemorative note introduced in January 1988 to coincide with the Australian Bicentenary. Plastic banknotes are more durable than paper ones, lasting four to five times longer.
1.2
A paper $5 note had an average life of about six months—a plastic one lasts more than three years. Note Printing Australia (NPA) is owned by the Reserve Bank of Australia and prints all Australian banknotes. It has also produced plastic banknotes for Thailand, Indonesia, Papua New Guinea, Kuwait,
Western Samoa, Singapore, Brunei, Sri Lanka and New Zealand. NPA also sells blank plastic notes to government printers in other countries so that they can print their own money. Old and ‘worn-out’ Australian plastic money is recycled into plastic objects such as plumbing fittings and compost bins.
QUESTIONS
Remembering 1 List five documents that a criminal might try to falsify.
Understanding
2 State what indicated that the Hitler diaries were fake.
6 Investigators generally ignore the slant and spacing of letters in a handwritten document. Explain why.
3 State what can be used to determine which typewriter was used for a ransom note.
7 Describe how a computer printer can be identified from a fake letter.
4 List the advantage(s) of Australian banknotes being printed on plastic.
8 Explain how inks can be identified using: a fluorescence b chromatography
5 List the features that usually give away fake banknotes.
9 Describe the following: a intaglio printing b microprinting c a watermark
>> 15
Is it real? 10 Explain why early $100 bills were easy to counterfeit when first introduced. 11 Explain why chromatography produces different coloured bands from black ink. 12 Predict what would happen to society if everyone could print their own money.
Applying 13 Write your signature on a piece of paper. Swap signatures with another classmate and then apply what you know about writing slant and letter formation to reproduce their signature.
Analysing 14 List the evidence that helped convict Dr Harold Shipman. Classify each piece of evidence that suggests he committed the murders as direct or circumstantial evidence.
1.2
Evaluating 16 Assess whether a person’s personality can be deduced from their handwriting. 17 ‘Identity theft’ is a common form of false identification. Propose what this might be. 18 Imagine a new paper $200 note has just been released and you have been given one as payment for a job. Assess whether you are going to accept it or whether you are going to check it out. If so, identify the tests that you will carry out.
INVESTIGATING
Reviewing Catch Me If You Can The movie Catch Me If You Can (rated M) shows the early life of Frank Abignale Junior, a young forger and fraud who pretended to be an airline pilot, doctor and lawyer. Watch the movie and prepare a film review about it. In your review you must investigate: • details about its length, leading actors, director, producer, studio and year of production • the era or timeframe in which the film is set • the forms of forgery and fraud Abignale used • how he bluffed his way into the various positions • if and how he was exposed as a fraud • what happened in the end • what Abignale does today for a job • whether Abignale could get away with his forgery and fraud today. Present your review in one of the following ways: • an interview with the director or who plays the leading actor Frank Abignale • a segment for a TV program such as ‘ET’, ‘At the Movies’ or ‘The Movie Show’. L
16
15 Write the letter E in your workbook and analyse how you did it. Add arrows to indicate the direction of each stroke and numbers to indicate the order in which they were made.
e -xploring To assist with the following activity, a list of web destinations can be found on Science Focus 3 Second Edition Student Lounge. a How are coins minted? (This is the term used when coins are made.) Construct a simple diagram or flowchart explaining the process. Find out what the term ‘legal tender’ means, what the highest legal tender is and why the mint produces coins other than legal tender. b How are plastic Australian banknotes made? Construct a simple diagram or flow chart explaining the process. Find the advantages of using plastic banknotes and the reason for using each of the security devices included in them.
Unit
1
PRACTICAL ACTIVITIES
1.2
1.2
Testing handwriting
Aim To detect writing imprints left in paper
Equipment • • • •
2 pieces of paper hard-tipped pen (not felt pen) grey-lead pencil lamp or torch
Method 1 Place one sheet of paper on top of the other and use the pen to write a message on the top one. Swap the bottom sheet with a classmate. 2 Use the lamp or torch (or even sunlight through a window) to shine light obliquely onto the paper.
Fig 1.2.9
Questions 1 Compare the final message with the original message. 2 Propose how this technique could be used in forensic science.
3 You should be able to see an impression of what was written. Use a grey-lead pencil to write over the impression. Compare with the original.
2 Chromatography catches a criminal A note, written in black ink, is found at the Taste Better Biscuits factory. The note threatens that poison will be put into one of the batches of biscuits unless money is transferred to an offshore bank account. The manager thinks that it is an inside job. Pens are collected and labelled from the desks of those who have had past disagreements with the boss.
Aim To use chromatography to determine the black pen most likely to have been used in writing a ransom note.
Equipment • a ‘ransom’ note written with an unknown brand of black felt pen • several different black felt pens including the one that wrote the note, the name of each suspect attached • gas jars • scissors • paper • ethanol or methylated spirits
Method 1 Cut out a single letter (e.g. F) from the extortion note so that you have a long strip of paper, with the letter at the bottom. At its top, label it as evidence. 2 On another piece of paper, write the same letter with each of the pens you have. 3 Cut out these letters and write the name of each suspect at the top. 4 Collect a gas jar for each strip that you have and place a small amount of methylated spirits at the bottom of each jar. 5 Place each strip in a jar, with the letter at the bottom. 6 The methylated spirits will move through the paper carrying the different pigments with it. Remove the strip when the ethanol or methylated spirits has nearly reached the top. 7 Match up the ransom note to the suspect using the ink patterns.
>> 17
Is it real? Questions
3 Identify which pen wrote the extortion note.
1 State whether there were any pens that did not show any chromatography patterns. Propose reasons why.
4 Explain why there are different coloured pigments in the black pens.
2 Describe how the patterns differed for each pen.
5 Predict what you would see if you repeated the experiment with water. If possible, try it and explain your observations.
3 Examining money Aim To identify the features used to make forgery of banknotes difficult
Equipment • access to a banknote (doesn’t need to be Australian) • magnifying glass or stereo microscope • access to UV light (optional)
Method 1 Perform the following tests on the banknote. • Record whether the note is paper or a polymer film (plastic). How do you know? • Feel the note. Feel its texture and feel for intaglio printing. • Look at the note from different angles and hold it up to the light to see if there are any optically active devices, watermarks or metal bands. For example, if the note is Australian then it should display a seven-pointed star when held up to the light. Note: the $10 note does not have a star. • Inspect the note under a magnifying glass or stereo microscope, looking for micro-printing and other hidden marks. • Smell the note. Can you smell real money?
Questions 1 Propose reasons why Australian banknotes do not have metal bands or watermarks. 2 The Reserve Bank of Australia website can be used to identify the portraits on each of the Australian banknotes. It also explains what the other diagrams mean. On your photocopies, identify the portraits and explain why they are important in Australia’s history. 3 The micro-printing found on the note will be an important Australian poem, speech or text. Use the Reserve Bank website to find what this poem, text or speech is. Surf the net to find a copy of it. Print it out and paste it next to its microprinted version. 4 Design a new banknote for Australia. Your design must include: • a portrait on both sides • diagrams showing why that person is important • relevant text to appear as micro-printing • a design of an optically active device.
2 Photocopy both sides of the note. Photocopying is only illegal if you intend to use the photocopy as a counterfeit note. 3 Cut out and paste the photocopied note into your workbook. Mark and label on it the different features that make it difficult to counterfeit that note.
Fig 1.2.10
18
Unit
1.2
4 Forging a photograph Aim To create a forged digital photograph of yourself at a place you have never been
Equipment • • • •
a computer digital camera a classmate image manipulation software (e.g. Adobe® Photoshop®, Microsoft® Photodraw)
Method 1 Use the internet to find an outdoor photograph of a famous location (e.g. Disneyland, Eiffel Tower, Big Ben). Save in an appropriate file of images. 2 Take note of the direction of the sunlight, and any people who are in the scene (you might want to make a photograph of yourself with your arm around the shoulder of someone in the picture). 3 Go outdoors and place yourself so that the Sun falls in a similar way to that in the photo. 4 A classmate now must take a digital photo of you in a suitable pose. 5 Transfer your image into the computer. 6 Open both images at the same time in your image manipulation software.
Fig 1.2.11 This photo is a fake but was presented as evidence of UFOs.
Questions
7 Use the Lasso tool to trace around your image. Feather the cut edge if your program allows it.
1 State whether the fake photo was easy to produce or not.
8 Change to the Move tool and drag the cut-out image over to your location photo. Alternatively, copy and paste if this is how your program works.
3 Assess whether this photo would fool the average person. Explain why/why not.
9 Resize the image, add shadows, alter the colours etc. so that it really looks as if you are at this location. 10 Save your ‘forged’ photograph. Print it out in colour if you can. Assess how realistic it is.
2 State whether it fooled the person you showed it to.
4 Examine your printed photograph closely with a magnifying glass or stereo microscope. What evidence is there of your tampering? 5 Discuss the phrase ‘the camera never lies’.
11 If needed, alter the contrast and brightness and/or change the image to a greyscale image and see if there is evidence that it is a fake. 12 Invent a story to go with your photo. Show it to an unsuspecting classmate or teacher and assess their reaction.
19
Unit
1.3
context
Evidence
Everyone leaves a little of themselves behind wherever they go. It doesn’t matter how careful or clean a person is, they constantly shed tiny flakes of skin, hair and dandruff and tiny droplets and smears of
sweat and body oils. Footprints and fingerprints might also be left behind. Video surveillance, mobile phone data and website and chatroom data are also being collected. All this is evidence and proves that a person was at some time at the scene of a crime, making a threatening phone call or was checking out particular internet sites.
What is evidence? Evidence is information that has legal value in a court of law. Evidence can come from: • eyewitnesses—people give verbal or written testimony of what they have seen or heard • physical evidence—evidence that can be touched, observed, smelt, recorded or collected at a location. The saliva on a cigarette butt is an example of physical evidence. It can be analysed for DNA and used to identify a suspect. Forensic scientists are mainly concerned with physical evidence. Information such as rumour and gossip has no value in a court and is not evidence.
Collecting fingerprints Fig 1.3.1 The collection of evidence takes time and must be carried out so that contamination cannot occur.
Science
Clip
Deadly serious! In an average lifetime, a human will flake off and shed a massive 18 kg of dead skin.
Fig 1.3.2 Fine powders will attach to fingerprints if gently dusted onto them. Black powder is used on glass.
Latent fingerprints are commonly found at crime scenes. These are the sweaty hard-to-see prints left behind on objects that are touched. Most fingerprints remain on non-porous (nonabsorbent) materials like glass, plastic and mirrors, and polished or painted wood. Police dust for them by brushing a powder onto door handles, stair railings, rear-vision mirrors, steering wheels, windows and so on. Light-coloured surfaces require black carbon powder while dark surfaces require white aluminium powder. Highly coloured or decorative surfaces require fluorescent powders that glow under UV light. Other techniques are used to collect prints from porous (absorbent) materials such as stone and raw or unpolished wood. One technique uses high powered ‘poly lights’ that cause fingerprints to fluoresce. Prac 1 p. 28
20
Unit
1.3
Collecting body products and fibres People in close contact can transfer materials between them. In assaults or sexual crimes, hair and fluff from clothing will often be transferred between victim and offender. In many cases, blood, skin, saliva and vaginal and seminal fluid can also be collected. Evidence from the inside and outside of a condom can be collected, conclusively linking victim and offender. Biological evidence such as this can then be DNA profiled to positively identify them both. Fibre analysis Fibres such as hair, fluff, torn cloth or animal fur/feathers can be compared using a comparison microscope. This allows a fibre from the crime scene to be directly compared with another sample collected by the police. Fibres can be: • animal in origin (e.g. fur, wool, hair or feathers) • vegetable in origin (e.g. hessian, cotton and string) • mineral in origin (e.g. industrial fibres such as glass wool and rock wool from insulating roof batts) • synthetic (e.g. polyester, rayon, viscose, elastane, lycra and nylon). Finding a match is not conclusive but is strong circumstantial evidence. The fibre or hair may have come from someone else with similar clothing and the same hair colour. Hair is particularly useful as it can
Fig 1.3.4 A forensic scientist uses a comparison microscope to compare two bullet casings. One was found at a crime scene, the other taken from the gun of the suspect.
indicate the hair colour of a person, and may also show what ethnic group they belong to. Prac 2 p. 29
Collecting impressions Criminals usually carry with them their ‘tools of trade’—items that they can use to commit an offence if they see the opportunity. These tools could be a pistol, a knife, a jemmy bar, wire-cutters or a screwdriver. Although some of these objects are innocent enough, most ordinary citizens do not normally carry them around or conceal them.
Wool fibres: animal fibres, hair and fur have characteristic growth patterns that look a little like scales. Thickness varies.
Synthetic fibres: these fibres are smooth with no surface pattern or breaks. Their thickness is the same all along the fibre.
Cotton fibres: plant fibres often twist and change in thickness. The surface is rough.
Fig 1.3.3 Each type of fibre has its own characteristic surface texture. This allows comparisons to be made between the suspect, the victim and the crime scene and victim. These images are from a scanning electron microscope (SEM). Go to
Science Focus 4 Unit 2.4
21
Evidence
Science
Clip
DNA proves all but one innocent In 1999, a 91-year-old woman was raped in the small NSW town of Wee Waa. Most of the 600 local men volunteered to have their DNA tested and, as expected, none proved to be the rapist. The rapist turned himself in soon after, probably realising that the police now only had a few men to investigate.
Fig 1.3.6 A suspect’s shoe is being printed and measured Fig 1.3.5 Tool marks found at a crime scene will be photographed and compared with tools collected from the suspect or their residence.
Tool marks Any object used to pry open a door or cut wire will leave a tell-tale impression or tool mark in the material that it damages. These marks are typically lines (called striations) that are caused by imperfections in the surface of the tool when it cuts a surface. Tool marks can even be left in bone when it is cut or chopped using a saw or axe. Soft tissue such as skin and muscle usually do not show detailed tool marks. Soft tissue injuries can still, however, indicate the shape, size and length of the weapon used, and how it was used (for example, in a downward stabbing movement).
Impressions left in soft materials like mud, clay or snow can be collected by pouring plaster into the imprint to produce a hard mould. Prints are photographed at the scene next to a ruler to indicate their actual size.
Track impressions Impressions from feet, shoes and tyres can be left behind: • in mud, clay or snow • by someone stepping or driving in blood or grease that has spilt over a hard surface • by someone with dirty shoes or tyres who has stepped or driven onto a clean surface. Even though millions of shoes and tyres are manufactured each year, individual treads can often be identified and linked to a crime scene. This is because all tyres and shoes wear differently and have imperfections, cuts or embedded objects such as tacks or stones that can make them traceable to the owner.
Water organisms Small single-celled aquatic organisms are called diatoms. Diatoms are partly made of silica, a very hard material that forms amazing shapes that last well after the diatom dies. Each pond has its own unique colonies of different shaped diatoms. Their shape can often be used to pinpoint the location of a drowning.
Prac 3 p. 29
22
so that it can be compared with a cast taken at a crime scene. A database called SICAR holds all old and new shoe tread patterns. SICAR quickly identifies the make, model and size of the shoe that made the cast or print.
Collecting biological evidence Biological evidence, other than fibres, is often collected from a crime scene. This evidence can be swabbed with wet cotton wool or lifted using sticky tape. Seeds, blood, DNA from body secretions, and microscopic pollens will be collected and then identified to aid an investigation.
Insects Insects can also be very helpful in identifying the time and location of death. Insects change forms at different times in their life cycle and any insect infestation of a body can be used to reliably estimate how long the person has been dead.
Fig 1.3.7 Different colonies of microscopic diatoms will exist in different bodies of water. They will saturate the lungs of a drowned person and can be used to pinpoint where it happened.
You’re being watched Although video footage from security cameras or CCTV (closed-circuit TV) is useful, the images are often not clear enough to give a clear identification of the culprit. Video footage consists of many individual images called frames that are played back one after the other, very quickly, to produce the illusion of a ‘moving picture’. Technology allows the footage from several frames of video to be added together to make a still image that is much clearer than each individual frame. Footage can also be watched in slow motion, and the brightness and contrast enhanced to get further important details. Fig 1.3.9 CCTV images are being collected everywhere. This CCTV image shows suicide bombers entering a London station in July 2005. Soon after, they detonated their bombs on three underground trains and one bus, killing 52 and injuring at least 700.
Different insects inhabit different ecosystems at different seasons, and this knowledge can also assist investigators. Insects in the wood of boxes or in the plant material of packaged cannabis can be identified and DNA tested to determine their origin. In cases such as these, a specialist biologist is consulted, as the investigator would not normally have the detailed knowledge needed to examine, test and interpret the clues, or give evidence in court. A blowfly detects the aroma of decomposition from a dead body and lays eggs on it. This SEM image shows a blowfly laying eggs.
If eggs are present then the time since death is only a few hours.
1.3
Electronic evidence can consist of photographs, video footage, audio recordings, computer, internet and mobile phone records.
Unit
Collecting electronic evidence
Maggots hatch from the eggs within 24 hours. They feed on the body for two to three weeks. This SEM image shows a maggot feeding.
Maggots undergo metamorphosis inside a pupa. This process can take weeks. This SEM image shows an adult blowfly emerging from its pupa.
If maggots are present then the time since death is between one day and three weeks. Bigger maggots suggest the body has been dead longer than if smaller maggots are present.
If pupae are present then the time since death is over three weeks.
Fig 1.3.8 Blowflies can be found on a dead body. The stage in their lifecycle will indicate how long the person has been dead.
23
Evidence You’re being tracked When a mobile phone is switched on it can be used to pinpoint its exact location to within a radius of about 100 metres. Criminals may, however, plant their phone in another spot as an alibi, or plant someone else’s phone to implicate them in a crime. You’re being recorded Everything that is done, stored or retrieved on a computer is stored on its hard-drive—a spinning disk about 9 cm in diameter. The disk is covered in iron oxide (rust) and information is magnetically recorded on its surface in binary code, using the numbers 0 and 1. If information is erased on a computer then all that is erased is its normal access route: the original 0 and 1 series storing the actual information is still there, awaiting any investigators with special retrieval software. After prolonged and extensive use, however, this coding may be overwritten, deleting it forever.
What does a bloody mess tell us? There are usually copious amounts of blood in violent crimes. To a trained investigator, the pattern of blood sprays, pools and drips can tell a vivid story. • Drips on the ground, initially of the same volume, will vary in size depending on the height from which they dropped.
Science
Clip
Information set in concrete Although software is available to overwrite computer information, an Atomic Force Microscope has the ability to find traces of any information you are trying to hide. This means that even top-secret government and military information can still be read. To stop this happening, some disks are ground into a powder that is then mixed into concrete that is about to be poured as foundations of a new building.
Fig 1.3.10 Blood marks, bruises and smears give important clues to what happened.
Case study
Eaten twice by shark!
Visitors to Coogee Aquarium in Sydney on Anzac Day 1935 were surprised when a recently caught shark they were watching vomited up an almost complete human arm decorated with a tattoo of two boxers. The arm belonged to Jimmy Smith, a local boxer and petty criminal. Smith was identified when fingerprints taken from the arm matched those on his criminal file. Analysis also showed that the arm had been cut from Smith and had not been chewed off by the shark. A much smaller shark had eaten the arm and had just been hooked by someone fishing when it was eaten by
24
another larger shark. It was this 4.3 m long monster shark that was on display. Smith had apparently blackmailed a wealthy local, Reginald Holmes, who then hired Patrick Brady to kill him. After Brady had killed Smith, he cut the arm off as proof of having done the job and later threw it into the sea. Holmes soon admitted everything to police and so Brady was caught. On the day of the trial, Holmes shot himself. Brady was acquitted on the argument that Smith could still be alive, but without one arm!
Prac 5 p. 30
What do gunshot injuries tell us?
What do wounds tell us? Many serious stab wounds are not fatal. However, a relatively ‘minor’ wound can kill if it cuts a major artery or damages vital organs. The wounds on a body also tell much about the attack. • Blunt objects often leave bruising, split the surface of the skin and fracture bone tissue.
1 External examination Examining body marks or injuries provides information that may determine the order of the autopsy procedure. Some injuries are clear, while other less obvious clues may give hints to unnatural deaths.
Many people each year die from accidental and intentional gunshot wounds. Gunshot wounds are particularly lethal because of the speed of the projectiles and the energy they carry. This energy is often transferred into the victim’s organs when they are struck, causing a pressure wave that ‘explodes’ the organ. At other times bullets can drill right through a victim and become lodged elsewhere.
2 Simple incision If the death appears natural the pathologist cuts up the torso and removes internal organs for examination. The pathologist attempts to chart the progress of a disease and identify the cause of death. 4 Major organs Removing the chest plate by cutting the ribs allows upper and lower internal organs to be removed for examination. Body fluids are collected for testing.
1.3
Prac 4 p. 30
• Sharp objects often slice neatly through flesh. Once the skin is punctured, the implement meets little resistance from other body tissues until bone is struck. Therefore it will cut to its full depth. • Wounds primarily on the right side of a victim generally indicate that the offender was left-handed and vice versa. • A piece of the weapon may break off (e.g. the point of a knife) and can be matched to the offending weapon if found. Doctors in a emergency department or a forensic pathologist will probe the width, depth and angle of the wound as part of their examination. This can indicate what size, shape and length weapon was used.
Unit
• Drips elongate in the direction of movement to produce elliptical shaped drips. These can show which direction a person was going or the movements of a bloody weapon. • Very fine sprays usually indicate a gunshot wound. • Splattering on the ceiling shows that someone was repeatedly striking from above. Drips hit the ceiling after flying off the weapon when it is brought back for the next strike. • Blood stains dry and fade over time. These give an indication of when the act occurred. • Blood groups and DNA matching can be done on a drip to find out whose blood it is.
3 Suspicious death If the death appears unnatural the pathologist will cut a Y or T shape to get better access to the body.
5 The head The brain is removed for examination. Microscopic examination of brain slices can show various types of damage and help identify the cause of death.
Fig 1.3.11 An autopsy can reveal whether the cause of death is natural or unnatural.
25
Evidence The height and direction that bullets have come from can be determined by drawing a line from where they are lodged through the point where they pierced the person, towards where the perpetrator was thought to be standing. In an autopsy, the pathologist will probe the bullet hole, particularly its entry, exit and the angle of its path. Usually the entry wound is quite small, while the exit wound is much larger.
Science
Clip
Licensed to kill Police are trained to use firearms as a last resort and only to protect themselves or other people from serious threat. When they do shoot, police are trained to aim for the body to maximise their chances of hitting the attacker, and minimise the possibility of hitting a bystander. If police aimed at legs or arms the chances of missing would be high and they would then be under even more threat. In most cases, non-lethal weapons such as capsicum spray or Tasers (a stun gun) will be used.
Fig 1.3.12 Capsicum spray is a non-lethal but highly irritant weapon now used by Australian police officers in threatening situations.
1.3
QUESTIONS
Remembering 1 a State what is and is not evidence.
8 Explain why fibres are considered circumstantial evidence. 9 Explain how insects can be used to:
b State two broad categories of evidence.
a date a death
c List three examples of physical evidence.
b determine where a drug crop came from
2 List five substances that might transfer in an assault between an offender and a victim.
10 Explain whether deleting a file from your computer erases it completely.
3 List three ways in which track foot impressions can be left.
11 Explain how bullets kill.
4 State how accurately you can be located when using your mobile phone.
12 A bullet passes right through a body. Explain how investigators can tell which direction it came from.
5 List what information blood drips can provide for investigators.
Applying
6 List two things that a wound can tell investigators.
Understanding 7 Explain how latent fingerprints are obtained from: a non-porous substances like glass b porous substances like stone
13 Identify the tool marks likely to be found: a at a house break-and-enter b in a case where important papers have been cut up c at a stabbing murder d in a rail derailment in which the tracks seem to have been tampered with e in a suspect car accident where it is thought the brakes lines may have been cut
26
Unit
a a particular brand b a particular person 15 A body has been dumped. It is thought that the person was murdered by drowning them in a nearby lake or pond. Identify the evidence that could be used to pinpoint the lake. 16 Identify ways you are:
Creating 20 Construct a flow chart to track the order of events in the case study. 22 Circumstantial evidence is not conclusive by itself, but adds together with other pieces of evidence to prove a case. Construct a murder case where no body has been found but in which multiple pieces of circumstantial evidence add together to make a strong case against the accused.
1.3
14 Identify the features of tracks that would indicate that a pair of shoes belong to:
22 The following phases of a blowfly can be used to date the death of a body on which they are found. Order the following phases and construct a scaled timeline that can be used to determine the time since death:
a watched b tracked c recorded 17 Identify what the case study suggests about fingerprints obtained from dead bodies.
• small blowfly
Analysing
• large blowfly
18 Discuss whether shoe prints can definitely prove that a person was at a particular location.
• pupa
19 Audio and video footage does not always accurately represent what happened at a crime scene. Discuss how and why.
• small maggots N
• large maggots
• eggs
Worksheet 1.3 Careers
1.3
INVESTIGATING
The assassination of John F. Kennedy American President John F. Kennedy (known to most as JFK) was assassinated on 22 November 1963. Lee Harvey Oswald was arrested for the assassination and was gunned down by mobster Jack Ruby in a police bungle before any trial could take place. Many believe this was a set-up to get rid of him without a trial. Many others dispute that Oswald could have been the assassin. Some believe that other people were involved as well as Oswald. Before being shot dead, Oswald proclaimed his innocence, stating that he was a ‘patsy’, meaning that he was framed. It was even claimed that some of the photographs incriminating him were faked. Oswald had an interesting history. Although at one time he worked for the US Marines, he also defected to the Cold War enemy, the USSR.
Fig 1.3.13 Lee Harvey Oswald always said that he did not kill JFK. Oswald was shot soon after and so never went to trial.
>>
27
Evidence 1 Investigate your available resources (for example, textbooks, encyclopaedias, internet) to find forensic evidence relevant to the assassination. 2 Summarise all the evidence you find and place it in a table similar to that shown below. If a piece of evidence implicates Oswald, then tick the Oswald column. If it implicates other unknown persons, tick the ‘Others’ column. If it implicates both, tick both. Evidence
Oswald
Others
3 Assess all the evidence in the table and decide whether you think that: a Oswald was not involved at all b Oswald was involved but was not the killer c Oswald was one of several gunmen d Oswald acted alone.
1.3
5 Assess whether there is enough strong evidence to convict Oswald beyond reasonable doubt in a court of law.
Reviewing ‘CSI’ ‘CSI’ is just one of many TV shows which demonstrate the methods used by forensic scientists. Watch an episode of one such show and prepare a review about it. In your review you must investigate: • details about its length, leading actors, director, producer, studio and year of production • the crime being investigated • what forensic evidence was collected • what other evidence was collected • what happened in the end • whether the forensic science in the episode was realistic • improvements to the film to make it more accurate. Present your review as a single page spread for an entertainment magazine or for a TV guide such as ‘TV Week’. L
PRACTICAL ACTIVITIES
1 Comparing fingerprints
6 If the print is not clear, clean the slide and try again until you perfect your technique.
In this Prac you will dust for prints and compare with fingerprints collected earlier.
7 When you have a good print, get your teacher to write an evidence number on it.
Equipment
8 Your teacher will then mix up all the fingerprint evidence collected around the class.
• • • • •
clean microscope slides small soft bristle brushes or puff-brushes graphite powder sticky tape paper
Method 1 Hold the microscope slide firmly between your thumb and forefinger for about 30 seconds. 2 Let go, being careful not to smudge the fingerprints. 3 Gently brush on a small amount of graphite powder using a swirling motion.
28
4 What motive (if any) did Oswald have for assassinating JFK?
9 Take one of the collected prints. Identify what type it is then try to match it to the correct class member using the reference prints that you collected in Unit 1.1 Prac 2. 10 See how many you can identify in the time given. 11 At the end, your teacher will read out who all the evidence codes correspond to. Tally up how many you got correct.
Questions 1 State whether the dusting and collecting of fingerprints was difficult or not. 2 List any mistakes you made in procedure.
4 Blow off the excess powder. You should see a clear print.
3 List any skills that you need to improve.
5 Place a clear piece of sticky tape over the print then remove it and stick onto a sheet of paper.
4 State the number of fingerprints you correctly matched. 5 Assess whether you got better at identifying prints as time passed. Explain why.
Unit
Aim To observe the different surface structures of different fibres
!
• • • • • • •
Part B: Monocular microscope 4 Brush your hair over a piece of paper. The hair that is not growing should fall onto the paper. 5 Place a hair on a microscope slide and stick it down. Place the slide on the microscope stage.
Safety
6 Focus on the hair, starting on the lowest magnification.
1 Some fibres (e.g. animal fur) may cause allergic reactions. 2 Do not use glass fibres (used to make fibreglass) as they easily pierce the skin. 3 Do not use asbestos fibres since they are a known cause of the lung disease asbestosis.
7 Move up to the highest magnification that is still clear and sharp.
Equipment sticky tape hairbrush white paper access to monocular and stereo microscopes 2 microscope slides pencil samples of a selection of fibres (natural, animal, vegetable, synthetic)
Method Part A: Stereo microscope 1 Adjust the focus and magnification of the stereo microscope to obtain the most detail. 2 Place each sample of fibre under the stereo microscope and carefully draw what you see. 3 Record the magnification that you are using.
1.3
2 Fibre analysis
8 Draw what you see. (Note: you should be able to see the inside and the surface of the hair depending on where you are focused and how your lighting is set up.) 9 Draw your observations—noting the magnification. 10 Mount and observe other fibre types and draw them carefully.
Questions Part A 1 Name any materials that looked the same under the microscope. 2 List any materials that needed greater magnification than what was available through the stereo microscope. 3 Assess whether your drawings are good enough for the identification of the material in future. 4 List observations that you could use to differentiate animal, mineral and vegetable fibres. Part B 5 Identify the magnification that gave the right balance of detail and brightness for your observations. 6 State whether you were able to observe the outside and inside of the hair samples. 7 Construct an illustrated chart that could be used by an investigator to identify a variety of different fibre types.
3 Collecting foot impressions Aim To make plaster impressions of the soles of different shoes
Equipment • • • • • •
plaster of Paris a 5 cm wide cardboard strip water paddle-pop sticks salt plastic disposable cups
• stapler • shoes (old shoes from home or opportunity shops are good)
Method 1 Make clear foot impressions in damp soil with different but similar-sized shoes. 2 Staple the ends of the cardboard strip together to make a circle. 3 Place the circles down into the soil around the footprint. 4 Mix up some plaster of Paris in a cup with warm water and a pinch of salt. Make it at least ½ water and ½ plaster.
>> 29
Evidence 5 Tap the bottom of the cup against the ground until all the bubbles are removed. 6 Carefully pour the plaster into the foot impression.
Questions 1 Compare each plaster mould with the shoes they came from. State how many matches you got.
7 Wait until the plaster sets. This will depend on the temperature, the amount of salt added and the thickness of your mixture.
2 Explain the purpose of the paper-strip circle.
8 Remove the plaster mould and carefully wipe or wash off any dirt.
4 Propose ways in which the quality of the moulds could be improved.
4 Investigating stride length The height of a person can be determined from the length of bones in their legs. The length of their stride is also related to this.
Method 1 Devise and test a method for determining a person’s height based on the distance between their footprints when walking. 2 Plot a line graph of your results, placing stride length on the horizontal axis and the predicted height on the vertical axis. Draw a line of best fit or curve of best fit through the data.
5 Blood drips Aim To make fake blood and to determine if there is a relationship between the height a drop falls from, and the diameter of the drip it produces when it strikes the ground
Equipment • • • • • • • •
100 mL of hot water starch red ink (e.g. for a stamp pad) brown food colouring butcher’s paper metre ruler electronic balance 250 mL beaker
3 Did you get a clear mould from the impression? If not, propose reasons why.
Questions 1 Identify why it would be inappropriate to join all the dots in your graph dot-to-dot. (Hint: do people of the same size all walk the same way?) 2 Describe the shape of the graph you plotted i.e. is it linear (a straight line), parabolic, random etc. 3 If it is a straight line, evaluate what its mathematical equation would be (Note: the equation for a straight line that takes the form of y 쏁 mx 쎵 c, where m 쏁 gradient or slope, c 쏁 vertical intercept).
• • • •
dropper bottle spatula small funnel heating apparatus
Method Part A: Making blood 1 Place the empty beaker on the balance and tare it so that it reads zero. 2 Add 100 mL of hot water to the beaker and heat until nearly boiling. 3 Measure out 2 to 3 grams of starch on the electronic balance and add to the water, stirring constantly. 4 Mix until all the starch has dissolved. Allow to cool. 5 Add small amounts of red ink and brown food colouring until it looks like blood. 6 Pour into a dropper bottle using the funnel and cool.
30
Unit
Questions
7 Drip the blood from 10 cm, 30 cm, 50 cm, 1 m and 1.5 m heights onto butcher’s paper.
1 Assess whether your graph could be used to predict blood drips at a crime scene. Explain your answer.
8 Write the dropping height next to each drip mark.
2 Identify whether there is a point where going any higher does not increase the spatter width. If so, state the height at which it occurred.
9 When they are dry, cut out the drips and paste them in your workbook. 10 Measure the maximum diameter of each drip and enter the details in a table.
1.3
Part B: Dripping blood
3 Predict what would happen to the drip shape and size if the person was running or walking instead of standing.
11 Plot a graph of drip diameter versus height of drop (place height on the horizontal axis).
Science Focus
Investigating the death of Azaria Chamberlain
Prescribed focus area Applications and uses of science In 1980, a holiday at Uluru turned into a nightmare for Michael and Lindy Chamberlain. Their youngest daughter, 10-week-old Azaria, was taken by a dingo from her tent and was never seen alive again. Initially Lindy Chamberlain’s story of the dingo was widely believed and many were sympathetic to her ordeal. Some members of the Northern Territory Police, however, believed that Lindy and her husband were responsible for the death. She was later charged with murdering her daughter. The court case attracted enormous global interest and much community debate. Many forensic experts were employed to give evidence and put forward a convincing case for the prosecution. Lindy Chamberlain was found guilty by the jury, and sentenced to prison. Several years later, evidence confirming her dingo story was accidentally discovered near Uluru. Her murder conviction was overturned and the whole affair is considered by many to be Australia’s greatest miscarriage of justice. After this, much of the forensic evidence so critical to her initial conviction was examined again. It was determined that much of this evidence had been given far more importance that it should have been given. Some was considered little more than ‘educated guesses’ because this field of science was still in its infancy and was on the fringe of
the accepted scientific knowledge and practice. Attempts to re-examine critical evidence were often unsuccessful since much of it had been ‘lost’ or destroyed. This was very unprofessional, especially given the circumstances of the case. It also meant that the validity of the previous forensic tests, and any associated professional opinions, could not be substantiated.
Fig 1.3.14 The Chamberlain car and tent the day after Azaria went missing.
31
Evidence
STUDENT ACTIVITIES Investigating the Chamberlain case
Reviewing Evil Angels
Investigate your available resources (textbooks, encyclopaedias, internet) to find details about the death of Azaria Chamberlain and the subsequent inquests, trials, sentencing and final outcome. In particular, find: • details of the night on which Azaria disappeared • the evidence that was used initially to support the idea that a dingo took the baby • the result of the initial inquest • why the Northern Territory police doubted the dingo story • when Lindy was accused of murder • the ‘forensic evidence’ that was used to convict her • what evidence or testimony was overlooked at the trials • the evidence that made Lindy look guilty to the jury • what the Australian people thought of how Azaria was killed • if there were any external factors that influenced the jury. While you are collecting this information, assess: • how you think Lindy felt when the dingo took her child • how she felt when charged and then convicted of murder • what you think of the ‘forensic evidence’ presented in court. Present your work in one of the following ways: a a labelled timeline showing relevant events
Evil Angels (sometimes called A Cry in the Dark) is a film about the disappearance of Azaria Chamberlain. Watch this movie and prepare a film review about it. In your review you must: • give details about its length, leading actors, director, producer, studio and year of production • record all key dates • describe what allegedly happened the night Azaria disappeared • record the order in which major events happened • list the ‘forensic evidence’ on which Lindy was convicted • assess the quality of this ‘forensic evidence’ • assess how Lindy coped with the disappearance, inquests and trials • portray the opinion of the Australian public. Present your review in one of the following ways: • an oral, written or videotaped interview with Lindy or Michael Chamberlain • a segment for a TV program such as ‘ET’, ‘At the Movies’ or ‘The Movie Show.’ L
b a PowerPoint presentation.
Fig 1.3.15
32
CHAPTER REVIEW Remembering 1 Name four different uses for fingerprints.
• get the security camera footage
2 State the type of information gathered by forensic pathologists.
• get everyone to sit down
3 List the factors that affect the rate at which a body decays. 4 List three types of electronic evidence and what each can show investigators.
Understanding 5 Explain what pattern matching is. 6 Explain why bite-mark comparisons are only sometimes helpful. 7 The fire brigade is called to a fire in a ‘granny flat’ at the back of 54 Smokers Lane, Ashwood. After quenching the fire, firefighters enter the building. Among the smouldering remains sits a charred corpse, on a very charred chair. You are the forensic investigator who is called to investigate the following. a Find out the identity of the person who is supposedly the grandfather of the residents in the main dwelling. List what you could do to confirm his identity. b You suspect that the person may have been dead before the fire was lit. Outline further evidence you might collect to confirm your suspicion. c You ask the fire brigade to determine where and how the fire started. Outline what they might look for to answer these questions. 8 A hiker’s body is found in the bush. The body is relatively fresh, having died in the last day or two. There are what appear to be animal bite marks around the neck. There are also cuts and bruises on the body. As chief forensic examiner, you must determine the cause of death. Explain what you would do in this case.
Analysing 9
• carefully enter the building checking for danger
A police officer is the first to arrive at the scene of a bank robbery. The following are a series of steps that the police officer should follow. The steps are out of order. Analyse the steps and re-order them to outline what should happen at the crime scene:
• ask everyone to write down everything that they saw and heard • allow people to leave the building. 10 You are working at the local newsagency and a man with dark glasses and a bushy beard and moustache steals a bunch of magazines from the shelf. List all the observations that you might make in such as situation. Classify your observations as either extremely helpful to the investigation or not very helpful. 11 A woman puts expensive jewellery in her handbag and walks out of a shop. The owner calls out and runs after her but she quickly jumps into a waiting car which drives off. Police track her down and find the jewellery hidden under a mattress in a spare room. The woman claims that the jewellery is hers and says that she does not know what they are talking about. Analyse the evidence and outline what suggests that she is guilty.
Evaluating 12 A person arrives at hospital with long dark bruises and swelling on the right-hand side of their face and their forearms and hands. They refuse to explain what happened. a Propose a likely set of events that might explain these observations. b Outline the evidence doctors at the hospital should collect to help solve the mystery. 13 You are presented with two photographs, one from a security camera and one from the police records. The photographs were taken with different lenses and so they are distorted and cannot be directly compared by anthropometry. Propose how you are to solve the mystery. 14 At Customs, a man is caught smuggling eggs out of the country, but crushes most of them when he is taken into custody. You suspect that they are galah eggs, an illegal export but with a value of $500 each on the black market. The man claims that they are pigeon eggs.
• call for back-up
a Analyse this evidence and state what makes him appear guilty.
• get the names and addresses of all people present
b Propose what should be done to prove his guilt.
• make sure no robbers are still present at the crime scene • clear bystanders away from the building
Worksheet 1.4 Crossword
Worksheet 1.5 Sci-words
33
2
The periodic table
Prescribed focus area The history of science
Key outcomes
Additional
Essentials
5.1, 5.7.1, 5.7.2
•
An atom is the smallest unit of an element.
•
An atom is made up of a nucleus surrounded by a cloud of electrons. The nucleus is made up of protons and neutrons.
•
Different elements can be defined by the numbers of protons, neutrons and electrons in the atom.
•
Molecules are made up of two or more atoms.
•
Elements in the same group in the periodic table display similar properties.
•
Our understanding of the structure of atoms has progressed throughout history.
•
The electrons surround the nucleus of an atom in shells.
•
The subatomic structure of atoms can be used to explain the physical properties of the elements they make up.
•
An atom can combine with other atoms by gaining, losing or sharing electrons.
•
You can refer to elements using an internationally recognised set of symbols.
Unit
2.1
context
Atoms and elements
Atoms are the building blocks of all matter and determine a material’s physical and chemical properties. Everything you see around you is made up of atoms. Even things you can’t see,
like air, are made up of atoms. Therefore to understand the world around you it is important you understand exactly what an atom is and how it behaves.
Atoms Atoms are invisible particles that make up all matter. It was once thought that atoms were indivisible, but scientists now know that atoms are made up from even smaller particles called protons (often shown as p), neutrons (n) and electrons (e). Protons and neutrons are roughly 1800 times heavier than electrons and are located at the centre of the atom, in the nucleus. Electrons spin fast around the nucleus in a region of empty space. Neutrons are neutral, and have no electrical charge. Protons have a positive charge and electrons have a negative charge. Opposite charges attract each other and this keeps the electrons from e– spinning out from the atom.
Fig 2.1.2 Molecules are made up of atoms bonded together.
p+ n nucleus n p+
e–
Fig 2.1.1 A simple model of a helium atom
Science
Clip
Now that’s small! Although atoms are too small to see with the naked eye, scientists can use a scanning tunnelling microscope (STM) to create images of atoms. An STM scans a very sharp needle over the surface of a crystal to sense the atoms—much like when a person uses their finger to read Braille. In this way, the microscope is able to construct an image of the atoms on the surface of the crystal.
Fig 2.1.3 A scanning tunnelling microscope (STM) image of the surface of a silicon crystal
35
Atoms and elements
Atomic and mass numbers
Compounds
Atoms are electrically neutral and must have the same number of electrons as protons. The number of protons in an atom is called its atomic number. atomic number of number of number protons electrons The total number of particles in the atom’s nucleus (protons neutrons together) is called its mass number. Neutrons have no charge and while the number of neutrons in an atom of a particular element can vary, the number of protons and electrons is always the same. mass number of number of number protons electrons These numbers can be shown as:
Compounds are also considered to be pure substances. However, their building blocks are made up of two or more different types of atom. These atoms are chemically bonded to each other by chemical reactions in which they gain, lose or share electrons. Usually a compound will have very different properties to the elements that make them up. For example, sugar is made up of carbon atoms, hydrogen atoms and oxygen atoms.
Mass number 씮 19 Symbol of the element 씮 Atomic number 씮 9 This indicates that the atom is fluorine and has: • 9 protons and 9 electrons • 10 neutrons (19 9 10)
F
Science
Clip
Common compounds
Chemical formula
Water
H2O
2 hydrogen atoms, 1 oxygen atom
Water
Methane
CH4
1 carbon atom, 4 hydrogen atoms
Marsh gas
Nitrous oxide
N2O
2 nitrogen atoms, 1 oxygen atom
Laughing gas
Sucrose
C12H22O11
12 carbon atoms, 22 hydrogen atoms, 11 oxygen atoms
Sugar
Elements
Elements are pure substances made up of only one type of atom: gold contains only Pure fluorine is an extremely dangerous gold atoms, and oxygen contains only gas that will react oxygen atoms. Atoms belonging to the violently with just same element all have the same number of about anything. It was protons and the same atomic number. For not successfully example, all gold atoms have 79 protons prepared until 1886 and only after several and all oxygen atoms have eight protons. scientists died trying. Today, scientists know of 118 different types of atoms. Only 92 of these occur naturally, the others are made solely in the laboratory by nuclear reactions. All of these synthetic elements break down quickly into other more stable elements. Some change so quickly that few experiments have been able to be performed on them, or with them. Each element is given its own symbol. Those known in ancient times often have symbols based on their Latin or Greek names. For example, silver has the atomic symbol Ag from its Latin name argentium. Other symbols come from the element’s common name such as O for oxygen or C for carbon. It is important to note that there is a correct way of writing symbols for elements. The first letter is always a capital and if there is a second letter, it is always in lower case. For example, Prac 1 p. 39 calcium is always written Ca, never CA or ca. Warning, warning!
36 Worksheet 2.1 Elements
Common name
Composition
H O H
H
H
H
H
H H
H
O H
O
H
H O
O
H O
O H
H H O O H
H
H
O
H O
H H
H O
H
Fig 2.1.4 A compound is made up of many identical molecules or units.
Unit
Science
Atoms do not normally exist by themselves but exist in molecules or crystal lattices. A molecule is a small group of atoms bonded or joined together. In a crystal lattice, atoms keep bonding together to form much larger structures. Molecules and lattices have a chemical formula that tells what type of atoms they contain and the proportion of atoms in them. The chemical formula for carbon dioxide (CO2) tells us that each molecule contains one carbon (C) and two oxygen (O) atoms. The chemical formula for table salt (NaCl) tells us that for every one sodium ion (Na) in the lattice there is also one chloride ion (Cl).
What a difference an ‘O’ makes Different compounds made from the same elements can have very different properties. When you combine two hydrogen atoms with an oxygen atom we make water (H2O). However, if we just add an extra oxygen atom to a water molecule, we make common household bleach—hydrogen peroxide (H2O2), which is poisonous, flammable and even explosive!
2.1
Molecules and lattices
Fact File
O H
H2O
H
Prac 2 p. 40
Mixtures
O H H O
H2O2
Fig 2.1.5 Molecules of water and the bleach hydrogen peroxide are both made from hydrogen and oxygen atoms.
A mixture is made of different elements or compounds simply thrown together. This means that no chemical reaction occurs. As a result, mixtures can be separated by simple physical techniques such as filtration or evaporation. No formula can be written for a mixture since each mixture can be different even when they contain the same materials. Mud for example, is dirt and water. It can be stiff mud or sloppy mud, depending on the quantities of each. Examples of mixtures include salt water, a can of cola, soil, air and blood. Prac 3 p. 40
water sugars
colourings and flavourings
carbon dioxide
Fig 2.1.6 This is the Atomium, a 103 m high building in Brussels,
Fig 2.1.7 Soft drinks are mixtures of many compounds.
Belgium, that was built for the 1958 World Fair. The building represents a small part of the lattice formed by iron atoms when they form crystals, magnified 165 billion times!
37
Atoms and elements
2.1
QUESTIONS
Remembering 1 State the smallest unit of an element. 2 For each of the molecules listed below, state the elements and how many atoms there are of each: a CO2 (carbon dioxide) b H2S (hydrogen sulfide) c C12H22O11 (sucrose) d H2SO4 (sulfuric acid) e CH3COOH (acetic acid) N
13 Use Figure 2.1.8 to identify and label each diagram a to e as: atom, molecule, compound, lattice or mixture. b
a
c
d
e
Understanding 3 Use Figure 2.1.2 to help you describe the structure of an atom using the terms ‘protons’, ‘neutrons’ and ‘electrons’. 4 Explain the relationship between the number of protons and the number of electrons in an atom. 5 Clarify the following expressions: a atomic number b mass number c nucleus
Analysing
6 Describe how compounds are formed.
14 What information would you use to distinguish between atoms of different elements?
7 Use an example to outline how a mixture can be identified.
15 Use examples to distinguish between atoms and molecules.
8 Explain why a chemical formula could never be written for a glass of cordial.
16 Distinguish between: a an element and a compound b the element iron and an atom of iron c the compound water and a molecule of water d a compound and a mixture e an atom and a molecule
Applying 9 Identify which of the three subatomic particles (protons, neutrons or electrons): a is the smallest b is the heaviest c is positive d is negative e is neutral f spins around the nucleus g are in the nucleus 10 Calculate the number of protons, neutrons and electrons that would be found in each of these atoms. N 56 Fe, 59 Ni, 64 Cu, 197 Au 26 28 29 79
11 a State three examples of compounds. b Identify where these compounds may commonly be found. 12 Identify each of the following as an element, compound or mixture. Explain your choice for each. a lead, Pb b nitric acid, HNO3 c sea water d ammonia, NH3 e peanut butter
38
Fig 2.1.8
17 Atoms can be compared by examining their atomic structure. Copy and complete the table on page 39. N
Evaluating 18 Deduce which of the following statements are false and evaluate how they can be rewritten to make the statements true. a The mass number is usually bigger than the atomic number of an atom. b The chemical symbol for iron is FE. c Salt is the compound NaCl. d Most of the atom is empty space. e A molecule is the same as a lattice.
Creating 19 Construct a diagram to represent: a an atom of carbon, C b a molecule of water, H2O c a molecule of oxygen, O2 d the lattice of sodium chloride, NaCl
Unit
Carbon
Atomic number
Mass number
6
12 C 6
12 8
9
8
19 127
74 atomic world of atom 40 K. Construct a story of your journey 19 to the centre of the atom, describing what you see, particle size, distances travelled and the problems you encounter. L
INVESTIGATING
1 Check the nutrition information on the labels of: • a canned food • a milk drink • a breakfast cereal • a soft drink List the ingredients under the headings: element, compound, mixture. 2 Find what foodstuffs are rich in these elements: Na, Ca, Fe, Mg, Zn, I.
3 Investigate your available resources (textbooks, encyclopaedias, internet) to find out what an isotope is. Illustrate this concept using examples and diagrams.
e -xploring To explore some comic strips, a list of web destinations can be found on Science Focus 3 Second Edition Student Lounge.
PRACTICAL ACTIVITIES
1 Making elements Aim To form oxygen and hydrogen gas from electrolysis of water
Equipment • • • • • •
6 16
20 You board your spacecraft-like machine and ready yourself for subatomic miniaturisation. Your mission: to explore the
2.1
Symbol of the atom
11
Iodine
2.1
Number of electrons
32
Oxygen Fluorine
Number of neutrons
6
Sulfur Sodium
Number of protons
2.1
Atom
large beaker 9–12 V power supply or battery alligator clips 2 metal electrodes 0.1 M sulfuric acid safety glasses
Method 1 Half-fill the beaker with the dilute sulfuric acid. 2 Place both electrodes into the beaker so that they do not touch each other. 3 Connect the electrodes to the 9–12 V power supply and switch on. 4 Record what you observe at both electrodes.
Questions 1 Explain how this experiment shows that water is a compound and not an element. 2 Identify if one electrode produced more bubbles than the other.
>> 39
Atoms and elements
2 Making a compound rubber hose
Aim
glass tubing
To prepare the compound carbon dioxide
rubber stopper
Equipment • • • •
2 test tubes test-tube rack drinking straw 1-hole rubber stopper with glass tubing
• limewater • marble chips • 2 M hydrochloric acid
Part A
test-tube rack
Fig 2.1.9
1 Place 5 mL of the limewater in a test tube. Place a fresh straw in the test tube and gently blow bubbles through the limewater. Record your observations as you finish blowing in the test tube, then again, when the tube has been left standing in a rack for 5 minutes. Part B 1 Add a couple of marble chips to another test tube. Cover with 2 cm of hydrochloric acid. 2 Stopper immediately and pass the rubber tubing into a test tube filled with limewater (see Figure 2.1.9).
3 Compounds in soft drinks Aim To compare the amount of carbon dioxide in soft drinks
Equipment • access to an electronic balance with a full scale reading above 400 g and an accuracy of 0.1 g • 500 mL measuring cylinder • large beaker (over 400 mL), stirring rod • a selection of 375 mL cans of soft drinks including ‘lite’ drinks (Note: if the scale cannot read to 400 g, then choose smaller ‘mixer’ cans of tonic and dry ginger.)
Method 1 Create a table like the one below. 2 Record the mass of a full, unopened can.
40
limewater
marble chips
Method
Drink
2M hydrochloric acid
Ingredients
Mass of full can (g)
Mass of empty can (g)
3 Record what you see happening in both test tubes.
Questions 1 Identify the gas in the air we breathe out that causes a change in the limewater. 2 Evaluate evidence to determine whether the gases made in Parts A and B are the same. 3 Is carbon dioxide an element, compound or mixture? Explain.
3 Find the mass of the empty beaker. 4 Pour the entire can into a measuring cylinder. Record the actual volume. 5 Empty the drink into the beaker and stir until it is ‘flat’. 6 Find the mass of the beaker and flat drink. 7 Repeat for other drinks or share your results with other groups.
Questions 1 Assess if all the cans contain their advertised volume. 2 Calculate the mass of CO2 in each drink. 3 Predict which drink you would expect to go ‘flat’ first. Which drink would you expect to stay ‘fizzy’ for longest? 4 Lite soft drinks are lighter than normal drinks. Assess the validity of this statement. 5 Define the term ‘lite’. Mass of empty beaker (g)
Volume of drink (mL)
Mass of beaker and flat drink (g)
Mass of CO2 (g)
Unit
2.2
context
Structure of the periodic table
The periodic table is one of the most important tools for chemists because it helps them to understand and predict the properties of the elements. In particular, the periodic table shows which elements belong to certain ‘families’ giving them similar chemical properties.
The periodic table The periodic table arranges the elements according to their atomic numbers. Horizontal rows in this table are called periods and are numbered 1 to 7. Vertical columns are called groups and are given the Roman numerals I to VIII. In general, elements in the same group tend to have the same chemical properties. For example, all the elements in Group I are highly reactive metals while all the elements in Group VIII are very stable and unreactive gases.
Features of the periodic table If you take a close look at the properties of elements in the periodic table, you will find many trends. These trends help scientists to predict both the chemical and physical properties of each of the elements. About 80 per cent of the elements in the periodic table are metals. Fig 2.2.1 Once you know how the periodic table is structured, The elements on the left-hand side of the periodic table you can use it to predict how atoms will bond with each other, how violently they will react and what their chemical formula are all metallic. The most reactive metals are at the will be … very useful! bottom left of the table (for example, francium, Fr). Elements on the right-hand side of the periodic table tend to be non-metals. In general, the most reactive Science non-metals are in the upper right (fluorine, F) although all the elements in Group VIII are chemically inert. Different-sized atoms Separating the metals and non-metals is a set of elements The element uranium, number 92 that act a little like both—the semi-metals (sometimes on the periodic table, is the largest called the metalloids). Silicon, germanium and arsenic and heaviest naturally occurring are examples of some common semi-metals. element. Hydrogen, number 1 on The periodic table also has three special blocks the periodic table, is the smallest, lightest atom. The nucleus of a without normal group numbers: transition elements, hydrogen atom is just a single the lanthanides and the actinides. Every one of proton; all other elements have Prac 1 Prac 2 these elements is a metal. Many of the lanthanides p. 45 p. 46 neutrons in the nucleus as well. and actinides are radioactive.
Fact File
41
Period 1
Group II
Group III
Group IV
Group V
Group VI Group VII Group VIII
H
He
hydrogen
helium
1
2
Li
Be
B
C
N
O
F
Ne
Period 2
lithium
beryllium
boron
carbon
nitrogen
oxygen
fluorine
neon
3
4
5
6
7
8
9
10
Na
Mg
Al
Si
P
S
Cl
Ar
Period 3
sodium
magnesium
aluminium
silicon
phosphorus
sulfur
chlorine
argon
11
12
13
14
15
16
17
18
K
Ca
Sc
Ti
V
Period 4
potassium
calcium
scandium
titanium
vanadium
19
20
21
22
23
Rb
Sr
Y
Zr
Nb
Mo
Tc
Ru
Rh
Pd
Ag
Period 5
rubidium
strontium
yttrium
zirconium
niobium
molybdenum
technetium
ruthenium
rhodium
palladium
silver
37
38
39
40
41
42
43
44
45
46
47
48
Cs
Ba
La*
Hf
Ta
W
Re
Os
Ir
Pt
Au
Hg
Tl
Pb
Bi
Po
At
Rn
Period 6
cesium
barium
lanthanum
hafnium
tantalum
tungsten
rhenium
osmium
iridium
platinum
gold
mercury
thallium
lead
bismuth
polonium
astatine
radon
55
56
57
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
Fr
Ra
Ac**
Rf
Ha
Sg
Ns
Mt
Ds
Rg
Uub
Uut
Uua
Uup
Uuh
Uus
Uuo
Period 7
francium
radium
actinium
rutherfordium
hahnium
87
88
89
104
105
106
107
112
113
114
115
116
117
118
Nd
Pm
Sm
Lanthanides
Actinides
Ce
Pr
cerium
praseodymium
58
59
Cr
Mn
chromium manganese
24
25
60
61
Co
Ni
Cu
Zn
Ga
Ge
As
Se
Br
Kr
cobalt
nickel
copper
zinc
gallium
germanium
arsenic
selenium
bromine
krypton
26
27
28
29
30
31
32
33
34
35
36
Cd
In
Sn
Sb
Te
I
Xe
cadmium
indium
tin
antimony
tellurium
iodine
xenon
49
50
51
52
53
54
Hs haffium
seaborgium nielsbohrium
neodymium promethium samarium
Fe iron
108
meitnerium darmstadtium roentgenium
109
Eu
Gd
Tb
Dy
Ho
Er
Tm
Yb
Lu
gadolinium
terbium
dysprosium
holmium
ersium
thulium
ytterbium
lutetium
63
64
65
66
67
68
69
70
71
Cf
Es
62
Th
Pa
U
Np
Pu
Am
Cm
Bk
protactinium
uranium
neptunium
plutonium
americium
curium
berkelium
90
91
92
93
94
95
96
97
metals liquid at room temperature metalloids gas at room temperature
111
europium
thorium
Legend
non-metals noble gases (non-metals)
Fig 2.2.2 The periodic table
110
H hydrogen
1
californium einsteinium
98
99
Fm
Md
No
Lr
fermium
mendelevium
nobelium
lawrencium
100
101
102
103
symbol name atomic number transition elements Ce Th
lanthanides actinides
Lu Lr
Fig 2.2.3 Special blocks in the periodic table Worksheet 2.2 Who am I?
Structure of the periodic table
42 Group I
Unit
e–
The role of electrons e–
Second shell
Third shell
Fourth shell
Maximum of 2 e
Maximum of 8 e
Maximum of 18 e but stable if it holds only 8
Maximum of 32 e but stable if it holds only 8
e–
2 e–
1 Hve
e– e– e–
Electron shells Electrons do not orbit just anywhere around the atom, but in shells or energy levels, which are numbered 1, 2, 3 and 4. It is easy to picture these shells if you imagine a pea as the nucleus of the atom. The pea sits in the middle of a table tennis ball (our first shell). All this sits inside a tennis ball (second shell), which sits inside a basketball (third shell), which sits inside a beach ball (fourth shell). Electrons repel each other because of their negative charges and so need to have a certain amount of space. Only two electrons fit on the small inner shell (otherwise they would be too close) but more electrons can fit onto the next three shells because those shells are bigger. The number of electrons that can actually fit in each shell is shown below. First shell
3
e–
e–
2.2
4
It is the electrons in an atom that determine all the chemical reactions that an atom takes part in. Chemical reactions may occur when atoms bump into each other. The protons and neutrons are relatively unaffected by the bump, being at the centre of the atom in the nucleus. The outermost electrons, however, are greatly affected and are often ‘grabbed’ or shared by other atoms.
Fig 2.2.4 The structure of an atom showing its energy levels. The negative electrons repel each other because they have the same charge.
four go into the outer shell: its electron configuration is written as 2,8,4. The electron configurations of the first 20 elements are shown in the table below.
Periods, groups and electrons An element’s position in the periodic table is strongly determined by its electron configuration. Notice that: • the period number of an element is determined by how many electron shells contain electrons • the group number of an element is equal to the number of outer shell electrons (helium, He, is an exception). For example, F has the configuration 2,7. It has two shells, so it is placed in Period 2. It has seven electrons in its outer shell and so is placed in Group VII. The chemical properties of an element are determined by how many electrons are in its outer-most shell. If two atoms are in the same group, they have the same number of outer shell electrons and will have similar chemical properties. However, as you move down a group, more shells are filled and the atoms get bigger so slight differences in properties can be expected.
Electron configuration The arrangement of electrons in the shells is called the atom’s electron configuration. Silicon (Si) has 14 electrons. Two electrons go into the first shell, eight into the second and the remaining Group
Group
Group
Group
Group
Group
Group
Group
I
II
III
IV
V
VI
VII
VIII
Period 1
H
He
1
2
Period 2
Li
Be
B
C
N
O
F
Ne
2,1
2,2
2,3
2,4
2,5
2,6
2,7
2,8
Na
Mg
Al
Si
P
S
Cl
Ar
2,8,1
2,8,2
2,8,3
2,8,4
2,8,5
2,8,6
2,8,7
2,8,8
K
Ca
2,8,8,1
2,8,8,2
Period 3 Period 4
43
Structure of the periodic table
2.2
QUESTIONS
Remembering 1 List the names of the semi-metals.
13 At normal room temperature, identify how many non-metals exist as:
2 List the symbols of the non-metals.
a solids
3 List five common transition elements.
b liquids
4 List four elements in Group I.
c gases
5 List four elements in Period 2. 6 Recall how many electrons need to be in each shell in order for it to be stable.
Understanding 7 Copy the following and modify any incorrect statements so they become true. a Horizontal rows in the periodic table are transition metals. b Vertical columns are called ‘periods’. c The most reactive metallic atom would be lithium, Li. d The most reactive non-metallic atom would be fluorine, F. e The transition elements are all metals. 8 Define the term ‘energy levels’. 9 Describe what the following have in common: a atoms in the same group b atoms in the same period 10 Use the periodic table to predict the mass number of: a a hydrogen atom with 3 neutrons N b a chlorine atom with 20 neutrons c a nickel atom that has 30 neutrons
Applying 1 Identify the Roman numeral for each of the following numbers. a 5
14 Identify three non-metallic elements that: a are gases at room temperatures b are liquids at room temperatures c are in Group V d are in Period 2 e would be related to chlorine f would have larger atoms than those of oxygen 15 Identify in which groups most metals and non-metals are found. 16 Identify five physical properties that can be used to describe elements. 17 Identify three elements that: a are in Group VI b are in Period 3 c would be in the same ‘family’ but not in Group VI d would show similar chemical properties but are not in a, b or c above e are noble gases
Analysing 18 Identify the following elements and classify them as either metal, non-metal or semi-metal: Cl, Na, Ar, Si, Cu, Ge 19 a Copy the following table into your workbook with space for eight more rows. N
b 4 c 7 d 2 12 Identify the metal(s) that: a is the only metal that is a liquid at 25°C b are in Period 3 c are in Group IV
44
Atomic number
Element (name and symbol)
Number of protons
Number of electrons
7
Nitrogen (N)
7
7
Unit
Evaluating 20 The symbols of some elements come from their Greek or Latin names. Use the periodic table to determine the names of these elements:
i an atom with 8 protons
a cuprum
ii an atom with 18 protons
b aurum
iii an atom with an atomic number of 3
c plumbum
iv an atom with an atomic number of 19
d wolfram
v an atom in Period 2, Group VII
e bromos
vi an atom in Period 3, Group II vii an atom of phosphorus viii an atom of aluminium
2.2
b Here is information about eight different atoms. Distinguish between them by finding their atomic number, name and symbol, number of protons and number of electrons and place all this information in the table.
21 Plumbing pipes were once made of lead. Deduce where the words ‘plumber’ and ‘plumbing’ came from. L
Creating 22 Construct a timeline to represent the historical development of the periodic table. Include dates, scientists’ names and their main contribution.
2.2
INVESTIGATING
These scientists—Curie, Mendeleev, Einstein, Nobel, Lawrence, Fermi—had elements named after them. Investigate your available resources (for example, textbooks, encyclopaedias, internet) to find out about their lives and the important work done by each. Write a short biography to summarise your information. L
2.2 1
e -xploring To find out more about the elements, a list of web destinations can be found on Science Focus 3 Second Edition Student Lounge.
PRACTICAL ACTIVITIES
Investigating a physical property
Aim To compare the density of some elements and compounds
Equipment • cubes or cylinders of aluminium, brass, lead, wood, ice • a collection of small items such as pebbles, candles, chunks of concrete or cement, copper wire • access to an electronic balance, rulers, beakers and measuring cylinders
Method 1 Measure the mass of each sample of material in grams. 2 You must also find the volume. Use a mathematical formula for samples with a regular shape such as a cube. You need to develop a way of measuring volume accurately for strange shapes. Volume must be measured in ‘centimetres cubed’ or cm3. You can measure in mL, but you will need to convert your measurement into cm3 (1 mL = 1 cm3). N 3 Draw a series of sketches showing how you intend to measure the volume of the irregular shapes. 4 Collect all the necessary measurements for each sample you have.
>> 45
Structure of the periodic table 5 Test whether each sample floats on water.
Questions
6 Density measures the mass of material that fits into a certain volume. Use the following equation to calculate the density of each sample. N mass (g)
1 Using your results, propose a rule about the density of objects and floating on water. 2 Identify how to convert between mL and cm3.
7 Place your results in a table like one shown below.
3 The density of water is 1.0 g/cm3. How does your answer compare to this? Identify the errors that may have caused your answer to be different.
8 Take measurements to find the density of a sample of water. N
4 What is heavier, a tonne of lead or a tonne of feathers? Account for your answer.
density =
3
volume (cm )
Sample
Mass (g)
Dimensions (cm)
Volume (mL)
2 Comparing elements
Volume (cm3)
Density (g/cm3)
Float/sink
5 Place some of the sample in water: does it float? Watch for any reaction.
Aim
6 Test whether the sample conducts electricity.
To examine the physical and chemical properties of common elements
Questions 1 Identify the properties that are similar in each of the metals.
Equipment
2 Identify the properties that are similar in each of the non-metals.
ammeter
DC
AC
VOLTS 0.2
0.4
0
–
power pack
Method
5A V
0.6
1.0
AMPS
0.8
• samples of sulfur, aluminium, carbon, silicon, tin, zinc, lead, magnesium, calcium, iron • steel wool • 3 to 4 test tubes and rack • power pack about 2 V or battery • wires with alligator clips • light globe • safety glasses
1A
1 Construct a table in your workbook like the one below. 2 Describe the appearance of each sample. 3 ‘Shine’ the sample with the steel wool. Record its appearance now.
material to be tested
4 Try and bend the sample. Does it bend or crumble? switch
Fig 2.2.5 Does it conduct?
Element
46
Metal or non-metal
Appearance
Shiny or dull
Floats or sinks
alligator clip
Action with water
Electrical conductivity
Unit
2.3
context
Using the periodic table
Although all atoms are made up of protons, neutrons and electrons, they can have vastly different properties. The chemical properties of an atom are almost entirely determined by its electron configuration or how the electrons are arranged around
the nucleus. This determines if an atom is reactive or inert, what sort of chemical reactions it can take part in, and even if the element is a metal or non-metal.
Atoms that react and atoms that don’t Group VIII (sometimes called Group 0) contains elements that are stable and rarely react. Group VIII elements are called the noble gases. Helium (He) was the first to be discovered—by the British scientists Lord Rayleigh and Sir William Ramsay in 1894. Ramsay later discovered all the other noble gases and added them to Group VIII. The noble gases are stable because He and Ne atoms have their outer shells filled and Ar, Kr, Xe and Rn have eight electrons in their outer shell. All other atoms react so that they can become as stable as the noble gases: they also want a filled outer shell, or eight electrons. To do this, atoms gain electrons, lose electrons or sometimes share electrons. Knowing this allows us to start to predict what atoms will do in a chemical reaction.
Ions If the number of electrons changes in an atom, it becomes electrically charged and is called an ion (a Greek word for ‘the ones that move’). • If an atom loses electrons, it becomes a positive ion. • If an atom gains electrons, it becomes a negative ion. To see an example of how ions form, let’s look at how common table salt, sodium chloride, is formed. If a sodium atom meets a chlorine atom they will rearrange their electrons so that both can become more stable. The sodium has only one electron in its outer shell so the easiest way for it to become stable is to lose this electron to form the positive sodium ion Na. On the other hand, chlorine has 7 electrons in its outer shell so the easiest way for it to become stable is to gain an extra electron and make the negative ion Cl. It also has a new
Fig 2.3.1 Elements of Group VIII are known as the noble gases. They have a stable electron configuration and don’t need to lose or gain electrons. This makes them very unreactive. Many signs are filled with the noble gas, neon.
name: chloride. Both ions are stable and happily exist as NaCl … sodium chloride (common salt). The attraction between the positive and negative ions holds the salt crystal together as shown in Figure 2.3.2. Ionic charges for several common elements are Prac 1 Prac 2 p. 51 p. 52 shown in the table on page 48. I
H
I H
I
H H
I I
H
H I
H H I
H
I
H
I
I
H
I
H I
H
I
H
Fig 2.3.2 The sodium chloride lattice: positive and negative attract
47
Using the periodic table Ionic charges for several common elements Element
Atomic number
Number of electrons
Electron configuration
The atom could lose
The atom could gain
Most likely scenario
Most likely ion formed
H
1
1
1
1e
1e
Uncertain
H or H
He
2
2
2
Li
3
3
2,1
1e
7e
Lose 1 e
Li
Be
4
4
2,2
2e
6e
Lose 2 e
Be2
B
5
5
2,3
3e
5e
Lose 3 e
B3
C
6
6
2,4
4e
4e
No ion formed
Uncertain
N
7
7
2,5
5e
3e
Gain 3 e
N3
O
8
8
2,6
6e
2e
Gain 2 e
O2
F
9
9
2,7
7e
1e
Gain 1 e
F
Ne
10
10
2,8
Sodium After
11
11
e
11
Charge
Neutral
Science
Clip
Helios, the Sun Helium (He) was discovered on the Sun before it was discovered on Earth. This is because every element emits specific colours of light when it is heated—a unique set of colours called a spectrum that is like a fingerprint for an element. When scientists looked at the light coming from the Sun, they noticed a ‘fingerprint’ they’d never seen before— this was the spectrum for helium. As a result, helium was named after the Greek name for the Sun, helios.
Unreactive
Chlorine
Before p
48
Unreactive
Before
After
p
17
17
17
No ion formed
Metals, non-metals and semi-metals
As mentioned, the elements in the periodic table can be classified as either metallic, non-metallic or 1 Charge Neutral 1 semi-metallic depending on their physical and chemical properties. These properties are mainly determined by the Hydrogen has only one electron so it can electron configuration of the atom, although Prac 3 either lose it to become the hydrogen the atomic weight also plays a role. p. 53 ion, H, or it can gain another one to What is a metal? become the hydride ion, H. It can In the periodic table, metallic elements outnumber nontherefore act like a Group I or Group VII metallic elements four to one. element, depending on what it comes • Metals allow heat and electricity to pass easily into contact with. through them. They are excellent conductors of Helium’s two electrons fill its outer heat and electricity. shell and therefore it acts like to the • Metals shine when polished or freshly cut. Metals are noble gases of Group VIII. It could be described as lustrous. placed in Group II but is • Metals can be hammered into new shapes. Scientists usually placed in Group VIII call this malleable. because of family • Metals are ductile. This means that they can be resemblances. stretched and drawn into long thin wires. 10
e
18
The odd couple: H and He
Those electrons again!
Metals have little control over their outer electrons, while non-metals have tight control over theirs and are greedy for more. In a chemical reaction, nonmetals try to ‘rob’ metals of their outershell electrons. The metal forms a positive ion and the non-metal forms a negative ion. The name of the non-metal often changes too, as shown in the table opposite.
Nonmetallic atom
Name of atom
Ion formed
Name of ion
F
Fluorine
F
Fluoride
Chlorine
Chloride
Bromide
2
Cl Br
Bromine
Cl
Br
O
Oxygen
O
Oxide
N
Nitrogen
N3
Nitride
Unit
Prac 4 p. 54
2.3
• Metals are solid at normal room temperature. (Mercury, however, is a liquid.) • Metals have high densities. Most metals sink in water. • Metals have atoms that form lattices. Prac 5 p. 54
About non-metals Non-metals share the following properties. • All (except carbon) are either poor conductors of electricity or do not conduct at all (insulators). • They have relatively low melting and boiling points and are usually liquids or gases at normal room temperature. • They are brittle and tend to crumble into powders. • They are dull, having little or no shine. • Group VIII elements can exist as single atoms. • Most other non-metallic atoms form molecules containing two atoms. Some have more atoms than this, and a few form lattices. Prac 6
Fig 2.3.3 Metals (from left to right): copper, liquid mercury and magnesium
p. 55
Semi-metals The semi-metals or metalloids act like non-metals in most ways. They do, however, have some properties that are metallic: most importantly, they can conduct electricity. Worksheet 2.4 Periodic table properties
Worksheet 2.5 The periodic table
Fig 2.3.4 Non-metals (clockwise from top left): sulfur, bromine (liquid only), phosphorus, iodine and carbon
2.3
QUESTIONS
Remembering 1 State the electron configuration of silicon, Si. 2 State whether metal atoms in a sample of a metal are present as molecules or lattices.
Understanding 8 Explain what information the electron configuration of an atom provides. 9 Describe the electron configuration of magnesium.
3 Recall four non-metallic elements and their ions.
10 Describe what happens when a sodium ion forms.
4 State which type of element tends to attract electrons: a metal or a non-metal.
11 Explain the difference between the formation of a positive ion and a negative ion. Use a diagram to clarify your answer.
5 a State another name for the semi-metals. b List the properties of semi-metals.
12 Explain why sodium chloride contains ions but has no overall charge.
c Name two examples of semi-metals.
13 Explain why H could be placed:
6 Recall three positive and three negative ions by name and symbol.
a in Group I
7 State the number of electrons each shell normally holds.
c by itself
b in Group VII
>> 49
Using the periodic table 14 Helium could be placed in Group II but is normally placed in Group VIII. Explain. 15 Define the following words.
21 Identify the ions that these atoms would probably form. a Na b S
a lustrous
c I
b malleable
Analysing
c ductile d brittle
22 Distinguish between atoms that are reactive and those that are not reactive.
e semi-metal L
23 Compare a chlorine atom with a chloride ion.
16 Outline the likely charges of the ions that belong in Groups I, II, III, V, VI, VII and VIII.
24 Copy the table below and complete it. N
Evaluating
Applying 17 Identify which group in the periodic table contains elements that rarely react. 18 Identify the period and group these atoms belong to: a an atom with configuration 2,4
25 We don’t worry about the number of neutrons when calculating the charge of an ion. Justify this statement. 26 Propose why you think metals might be malleable and ductile while non-metallic solids are usually brittle.
Creating
b an atom with configuration 2,8,6
27 Construct a mobile of an atom. You could use different coloured plasticine to represent protons, neutrons and electrons. Wire could represent each electron shell. Shells increase in diameter as you move from the first shell outwards. Use string to assemble the atom.
c an atom with seven electrons d an atom with 15 electrons 19 Write the electronic configuration of these atoms. a an atom in Period 2, Group VI
28 Construct a table to classify the following properties into those that belong to metals and those that belong to non-metals: ductile, normally gas or liquid, dense, malleable, brittle, lustrous, excellent conductors, dull, poor conductors, normally solid.
b an atom in Period 3, Group VIII c an atom in Period 1, Group VIII d an atom of Mg (be careful) e an atom of S (be careful) 20 Copy out the table on ionic charges (on page 48). Extend and complete it to include all the elements up to calcium, Ca. Number of protons
50
Number of neutrons
Number of electrons
Overall charge
8
6
8
10
10
10
11
10
10
17
16
18
15
15
18
19
18
1
20
19
2
8
7
10
2
Is it an atom or an ion?
Symbol
K
Unit
INVESTIGATING
Investigate your available resources (textbooks, encyclopaedias, internet) to research the following. 1 Find out about fireworks:
c How do they affect us? d Create a warning leaflet that could be placed in particular areas to alert people of the potential dangers of exposure to lead and mercury. L
a when fireworks were first used and by whom b what determines the different colours that you see.
3 Find out about the Iron Age and how it represented a massive advance in the technology of food collection and warfare. Find when it occurred and explain how iron (and its alloy, steel) changed the lives of people at that time.
2 Find information about the metals lead and mercury. a Find out why they are cumulative poisons and what this means. 4
b Find out the main sources of these metals.
2.3
2.3
2.3
Investigate the meaning of the term electronegativity and the role this property plays in determining how reactive an atom is.
PRACTICAL ACTIVITIES 2 Briefly place the stick soaked in water in a blue Bunsen flame, then remove it. Record any colour that it gave the flame.
1 Firework colours
3 Briefly place each of the other sticks in the flame and record the colour you see.
Aim To identify elements by the coloured flames they produce
Equipment • • • •
Bunsen burner, bench mat and matches tongs safety glasses wooden icy-pole sticks soaked overnight in distilled water and solutions of barium chloride, copper chloride, potassium chloride, sodium chloride and strontium chloride • spectroscope (optional)
4 Optional: point a spectroscope towards a bright portion of the sky (not the Sun). Draw the spectrum you see. Observe each of the coloured flames through the spectroscope, recording what you see.
spectroscope
look for colour
Method
tongs
1 Copy the following table into your workbook. List all the solutions used.
blue flame icy-pole stick
Solution
Compound formula
Distilled water
H2O
Barium chloride
BaCl2
Colour of flame
Metallic element in solution
Nonmetallic element in solution
Bunsen burner
bench mat
Ba
Cl
Fig 2.3.5 What colour is produced?
>> 51
Using the periodic table grains of starch covered with explosive black powder
Questions 1 Clarify the purpose of the stick soaked in water only. 2 Explain why the water needs to be distilled and not from the tap.
propellant charge
3 Identify which of the solutions you tested would be best to colour a firework: a red b green c blue/green
grain of 2 salts fuse
4 The grains that spray out and give colour are made of starch soaked in the appropriate salt. Construct a diagram of a grain that would burn and give the colours: a blue/green, then purple b red, then green 5 Propose where the electrons got the energy to jump shells.
Fig 2.3.6 A firework ‘grain’
2 Ions get together!
Questions 1 Identify whether the overall charge of each compound is positive, negative or neutral.
Aim To construct models of ionic compounds using an ion jigsaw
2 Propose a rule that allows you to predict the formula of a compound. N
Equipment • photocopy of worksheet 2.3
and 3 K
3K
Worksheet 2.3 Ions
NaH
Method 1 Cut around the jigsaw pieces on the sheet provided by your teacher.
Mg2H
2K
O2I Al3H
N3 I
FI
2 Copy the table below into your workbook with space for nine rows. 3 Use the jigsaw pieces to ‘create’ the following compounds: sodium fluoride, sodium oxide, sodium nitride, magnesium fluoride, magnesium oxide, magnesium nitride, aluminium fluoride, aluminium oxide, aluminium nitride Put all the relevant information about each compound in the table. 5 Re-label some of the pieces to create: • lithium chloride • calcium bromide • barium sulfide
Compound
52
Positive ion used
Negative ion used
To make a compound: magnesium fluoride
FI Mg2H
MgF2 F
I
Fig 2.3.7 You need these jigsaw pieces.
Compound formula
Total positive charge
Total negative charge
Overall charge of compound
Unit
Aim To examine the crystal shapes formed by silver as it displaces out of solution
Equipment • sterilised Petri dish • 250 mL beaker • Bunsen burner • tripod • gauze mat • bench mat • 1 cm 쎹 4 cm strip clean zinc sheet • one 0.3 g sample of silver nitrate • 0.5 g agar powder • 40 mL distilled water • stirring rod • stereo microscope (optional) • safety glasses • gloves (Note: 0.3 g of lead nitrate, copper sulfate or tin chloride can be used instead of silver nitrate, although the crystals are not nearly as well formed or as large.)
!
Safety Silver nitrate badly stains the skin. Lead nitrate is very poisonous and reactive. Wear safety glasses and gloves at all times when dealing with these.
1 Place 40 mL of deionised water in the beaker and sprinkle 0.5 g of agar into it. Warm gently over the Bunsen burner, stirring until dissolved.
2.3
Method
3 Metal crystals
2 Remove the beaker and add the 0.3 g sample of silver nitrate to it. Stir until dissolved. 3 Pour the agar solution into a Petri dish and gently place the zinc strip in the centre. 4 Allow the agar to cool and set into a jelly. 5 Place the lid on top. 6 Inspect the metal crystals that form over the next few days. If available, use a stereo microscope for a better view. 7 Draw the shape of the crystals you see in each group’s Petri dish. Describe any colour changes.
Questions 1 Explain why the crystals were grown in agar and not in a liquid. 2 Would these crystals be molecules or a lattice? Explain. 3 Describe what happened to the colour of the agar with dissolved silver nitrate. This is also what happens if silver nitrate comes into contact with your skin. 4 Petri dishes and agar are often used in pathology. Investigate how and why they are used.
Part A 0.3 g sample
folded paper
stirring rod Part B 0.5 g agar in 40 mL water agar solution with dissolved sample
zinc sheet
Petri dish
Fig 2.3.8 Making an agar plate
53
Using the periodic table
4 More crystals
? DYO
cork stopper
Aim Design your own experiment to make silver metal crystals
!
Safety Silver nitrate badly stains the skin. Lead nitrate is very poisonous and reactive. Wear safety glasses and gloves at all times when dealing with these.
copper wire copper foil silver nitrate solution
Equipment • • • •
100 mL conical flask, cork or rubber stopper silver nitrate solution 10 to 15 cm length of copper wire and/or strip of copper foil safety glasses and gloves
Method
Fig 2.3.9
1 Use Figure 2.3.9 to design your own method for another way to prepare silver crystals. 2 Have your teacher check your method and, if it is approved, set up your experiment.
Question 1 Copper ions give solutions a blue colouring. Describe two observations to support this inference.
3 Place the flask in a safe, dark place for a few days.
5
Changing the properties of metals
Aim
Method 1 Copy the table below into your workbook. Treatment
To observe the effect of heating and cooling on crystal size
Equipment • • • • • • • • •
four steel hairpins (steel is about 98% iron) steel wool Bunsen burner bench mat matches 250 mL beaker filled with water wooden peg safety glasses pliers (optional)
Number of bends needed to break pin
Effect of treatment
None Normalising Quenching Tempering
2 Repeatedly bend a hairpin until it breaks. Count how many bends it took. 3 Normalising: take another hairpin and heat the middle in a blue Bunsen burner flame until it is red hot. Avoid touching the red hot pin or leaving it unattended until it is cool. 4 Quenching: heat another hairpin in the same way, then drop it into a beaker of water.
54
Unit 5 Tempering: heat and quench the remaining hairpin, then polish it with steel wool. Re-heat the shiny part of the pin. Remove the pin occasionally to check whether it has gone blue. Once it has, remove the pin from the flame and allow it to cool on the mat.
peg
blue flame top of blue cone
2.3
hairpin
6 Bend each of the pins until they break. Record your counts.
Questions 1 Describe what the terms ‘normalising’, ‘quenching’ and ‘tempering’ mean. 2 Identify the treatment that caused the steel to become: a more brittle b more malleable
cold water quenching
Fig 2.3.10
3 Fast cooling produces small crystals; slow cooling makes bigger ones. Identify which of the samples produced the biggest crystals. 4 Propose a reason why bigger crystals make steel tougher. 5 Distinguish between iron and steel.
6
Using metals to make non-metals
burning match
Aim To make a non-metal compound from a metal
Equipment • • • • •
samples of magnesium, iron and copper 2 M hydrochloric acid in a dropping bottle test tubes and rack matches safety glasses
Fig 2.3.11 Making and testing a gas
Method 1 Place the samples of metal in separate test tubes. 2 Use the dropping bottle to add sufficient hydrochloric acid to cover the metal in each. 3 If bubbles form, test the type of gas produced by placing a lit match near the mouth of the tube. You may need to place a stopper in the mouth to gather sufficient gas to test. 4 Record your observations.
Questions 1 Identify the gas present if a lit match: a causes a ‘popping’ sound b flares up brightly c is extinguished 2 Classify the gases in Question 1 as elements or compounds. 3 Draw a conclusion about the reaction of metals with acids.
55
Unit
2.4
Families of elements
context
Elements in the same group of the periodic table share many chemical properties due to the fact that they all have the same number of electrons in their outermost shell. As a result, we group these elements together into ‘families’.
Fig 2.4.2 Sodium burning in water. Reactions become more violent as you move down Group I.
They all react violently with water, producing an alkaline (basic) solution and hydrogen gas, which often ignites due to the heat produced.
2Na sodium metal
Fig 2.4.1 Elements belong in families: they are different
2H2O
씮
water
2NaOH sodium hydroxide
H2 hydrogen gas
but have many similarities.
Properties of Group I elements (the alkali metals)
Group I: the alkali metals The alkali metals: • form +1 ions • are far too reactive to be found free in nature, but are found in mineral salts • have typical metallic properties • are very chemically reactive. Lithium, sodium and potassium are light enough to float on water and are so soft that they can be cut with a knife. They all burn in chlorine gas (and in the other Group VII gases) and produce similar white salts. Lithium, for example reacts via: 2Li lithium metal
56
Cl2
씮
2LiCl
chlorine gas lithium chloride
Group I
Melting point (°C)
Boiling point (°C)
Uses of Group I compounds
Li
181
1342
Alloys, carbon dioxide filters, water absorbent
Na
98
883
Vapour lamps, fertilisers, sedatives, in the manufacture of paper, soap, textiles and other chemicals
K
63
760
Alloys, coolant in nuclear reactors
Rb
39
686
Radioactive tracer used to detect brain tumours
Unit
These metals all act in a similar but slightly less reactive way to Group I.
2.4
Group II: the alkaline earths Prac 1 p. 61
Properties of Group II elements (the alkaline earths) Group II
Melting point (°C)
Boiling point (°C)
Uses of Group II compounds
Be
1278
2970
Watch springs, sparkfree tools
Mg
649
1107
Alloys, rust protection, antacid, laxatives
Ca
839
1484
Alloys, quicklime in mortar, plaster, cement
Sr
769
1384
Fallout from nuclear explosions
Ba
725
1640
Used in medical diagnosis, rat bait
Amorphous carbon is the black powder on the top of burnt toast, burnt marshmallows, charcoal and coal.
Graphite is a soft, slippery solid that conducts electricity. It is a wonderful lubricant and forms the electrodes in many batteries and the brushes in electric motors.
Group IV Group IV begins with atoms that are non-metals (carbon and silicon), moves through the semi-metal germanium, then the metallic atoms of tin and lead, to finish with the synthetic element ununquadium. Carbon exists in molecules in every living thing on Earth such as trees and tigers. It also exists in anything that was once living. Wood and paper come from trees and so contain carbon, as does leather since it came from an animal. Pure carbon exists in three different forms or allotropes: amorphous carbon, diamond and graphite. All three allotropes have very different properties despite all being made up of the same type of atoms. Diamond is an allotrope or form of carbon and is the hardest known natural substance. Diamond needs to be heated to about 800°C to be converted to graphite. To turn graphite into diamond a pressure of between 50 000 and 120 000 of normal air pressure is needed. Silicon is found as silicon dioxide and metal silicates, which together make up 75 per cent of the Earth’s crust—sand, clay, asbestos, quartz and many gemstones contain silicon. It is the major component of glass. Germanium was predicted to exist 15 years before its discovery and was even given a name: eka-silicon. Germanium is used as the catalyst in fluorescent lights and its oxides are used in the production of lenses for optical instruments such as microscopes. Both silicon and germanium are semiconductors and are widely used in electronic components. Tin and lead are typical metals. Prac 2 p. 61
The ‘lead’ in pencils is a graphite–clay mix.
Diamonds are the hardest known natural substance. Only 20 per cent of diamonds are gem-grade. The rest are used to cut glass, metal and masonry or are crushed to make abrasives.
carbon atoms
Dental drills often have diamond tips. This SEM image shows one drilling into a tooth.
Fig 2.4.3 Carbon is found naturally as amorphous carbon (charcoal), graphite (the lead in pencils) and diamonds (used for jewellery and dental drills).
57
Families of elements Science
Group VII: the halogens
Clip
The halogens: • form ions with a charge of 1. • are never found in their pure form in nature but are in various types of salts, including sea salt • have coloured and poisonous vapours • all form molecules, each being made up of two atoms.
Dead bumblebees! The Swedish chemist Carl Scheele separated chlorine gas in 1774 and wrote that he was glad that he ‘did not take more than a tiny whiff’ as ‘a large bumblebee died instantly when put into the vapour’. Scheele often tasted his discoveries and this is probably what killed him at the age of 43.
Properties of Group VII elements (the halogens) Group VII
State at room temperature
Melting point (°C)
Boiling point (°C)
Uses of halogen compounds Prevention of tooth decay, etching of glass, insecticides, Teflon and the anaesthetic Fluothane
F
Greenish yellow gas
220
188
Cl
Green gas
101
35
Br
Red liquid with red vapour
7
59
Photographic film, sedatives
Black solid with purple vapour
114
184
Disinfectant, control of goitre
I
Disinfectant, sterilising agent, bleach, food seasoning, PVC, neoprene rubber, insecticides
Fig 2.4.4 Moving down Group VII, the halogens become larger and less reactive. This is demonstrated clearly in their reactions with iron. Although each reaction produces brown vapour and a brown solid, the iron glows less intensely when the reactant changes from Cl2 to Br2 to I2.
Science
Clip
Have you seen my ring? Sir Humphry Davy (1778–1829) demonstrated that diamond was a form of carbon by burning a diamond that belonged to his wealthy wife! All that was left was carbon dioxide.
Cl2
Br2
atoms get larger and less reactive
gas out chlorine gas in
iron wool
heat
58
I2
Hot steel wool glows brightly when chlorine passes over it. Brown smoke and brown solid form.
iron wool bromine liquid
iron wool crystals of iodine heat
heat The iron glows less brightly when bromine is used. Brown smoke and brown solid form.
The iron glows even less brightly with iodine. Brown smoke and brown solid form.
The transition metals
Clip
Squeaky voices Our voices go high and squeaky when we breathe in helium from a party balloon. Because helium is lighter than air, our vocal cords vibrate more quickly, making the pitch go higher. Don’t try this, though! Some people have actually died from performing this trick.
helium
neon
argon
krypton
xenon
rises quickly
rises slowly
falls slowly
falls quickly
falls very quickly
The transition metals include many of our most useful, colourful and valuable metals such as iron, copper, zinc, gold and silver. The transition metals have very similar properties: for example, the Period 4 metals—iron, cobalt and nickel—are all magnetic. All transition metals tend to be relatively hard and most have similar, high melting points.
2.4
The noble gases are colourless gases that occur naturally in the atmosphere. All can be separated by distillation of liquid air. They are very stable and react only in rare and extreme circumstances. Helium is safe and light enough to be used for balloons and airships. Balloons of the other noble gases get progressively heavier: although the atoms get bigger, they also get heavier and more dense.
Science
Unit
Group VIII: the noble gases
Worksheet 2.4 Periodic table properties Worksheet 2.5 The periodic table
density of gas increases 4
20
2
10
He
Ne
40
Ar
18
84
Kr
36
131
Xe
054
mass of atom increases
Fig 2.4.5 The atoms of noble gases get bigger and heavier as we go down the group.
2.4
Fig 2.4.6 The salts of transition elements are very colourful.
QUESTIONS
Remembering 1 Name three alkali metals.
6 Describe what happens to the melting points and boiling points of the halogens as you move down the group.
2 Name three noble gases.
7 Describe some typical reactions of the alkali metals.
3 State the element(s) in group four that are considered semi-metals.
8 Describe the main uses for:
Understanding 4 Describe the advantages of using helium and not hydrogen in airships. 5 Describe what happens to the mass and density of the noble gases as you move down the group.
a diamond b graphite c silicon d germanium 9 Explain how carbon could be classified as a semi-metal, not a non-metal.
>> 59
Families of elements Applying
c are used for jewellery
10 Identify which of the halogens is used as:
d are ‘silver’ grey in colour
a a disinfectant b a sedative c a way of controlling goitre
14 Identify which halogens would be solid, liquid or gas at these temperatures:
d a bleach
a 20°C
e an anaesthetic
b 100°C
11 Identify which of the alkali metals: a has a melting point of 98°C
c 199°C d 150°C
b is in caustic soda
Evaluating
c is used as an air filter
15 Evaluate if these statements about Group IV are true or false.
d would be the most reactive
a The group contains both metals and non-metals.
e would have the smallest atoms
b All the elements in this group contain four electrons in their outer shell.
12 Identify which of the alkaline earths: a would be closely related to potassium
c Diamond and graphite are forms of silicon.
b is used to kill pests
d Carbon is in all living things, but not in things that are dead.
c is found in plaster d is used to protect iron from rusting e would be the least reactive 13 Identify three transition elements that: a are in Period 5 b are magnetic or can be made magnetic
2.4
INVESTIGATING
Investigate your available resources (for example, textbooks, encyclopaedias, internet) to find out the following. 1 What is goitre and how it is treated? Write a set of guidelines for a person with goitre that could help them manage the condition. 2 What are the different noble gases used for? Make a summary of this information including pictures showing each gas in use. 3 Find out what lead and tin are used for and why. 4 Carbon forms a compound called methane with the chemical formula CH4. Silicon form silane, SiH4 when combined with hydrogen. Research and compare the properties of these two compounds. How are they similar and how are they different? Where are they used?
60
e have symbols from old Greek or Latin names
16 Carbon has been known for over 2000 years. Propose why it was found much earlier than most other non-metals.
Creating 17 Construct tables of the melting points, boiling points and uses of the elements in Groups III, V and VI like the tables shown in this section. N
Unit
PRACTICAL ACTIVITIES
1 The alkaline earths Aim To examine the reactivity of the alkaline earth elements
Equipment • • • • • •
crucible lid and clay triangle 2 test tubes and rack Bunsen burner tripod and bench mat phenolphthalein
• • • • • •
matches safety glasses distilled water a 5 cm strip of magnesium steel wool or emery paper small sample of calcium
2.4
2.4
4 Add one drop of phenolphthalein. 5 Record your observations.
Questions 1 Identify which alkaline earth is more reactive, Mg or Ca. 2 Describe what happens to reactivity as we move down Group II. 3 Assess whether Group II metals are more or less reactive than Group I.
Part A
Part B
Method tongs
Part A 1 Clean the magnesium strip with steel wool and then spiral it loosely around a pen. 2 Place the coil in a test tube and cover it with distilled water.
lit match
distilled water coil of Mg
3 Watch very carefully over the next five minutes. Look for bubbles.
distilled water Ca
4 If nothing happens, heat gently over a yellow flame. 5 When finished add 1 drop of phenolphthalein to the solution. Record the colour. Part B
Bunsen burner Phenolphthalein
1 Put about 5 cm of distilled water into a test tube. 2 Add a piece of calcium. 3 Test the gas given off with a lit match. Fig 2.4.7
2 Group IV Aim To examine family similarities in Group IV elements
Equipment • • • • • • •
samples of charcoal graphite silicon lead power pack or battery leads with alligator clips light
Method 1 Describe carefully the appearance of each sample. 2 Test whether each conducts electricity using the apparatus used in Prac 2 of Unit 2.2 (page 46).
Questions 1 Classify the Group IV elements as metals, non-metals or semi-metals. 2 Describe what happens to the properties of Group IV as we move down the group.
61
Science Focus
Development of the periodic table
Prescribed focus area The history of science The ancient Greek philosopher Aristotle suggested that all matter was made from four ‘elements’—earth, air, fire and water—and the theory lasted for nearly 2200 years. It successfully pushed the ideas of another ancient Greek, Democritus, into the background. His idea was that all matter was made of particles that he called atoms. In the twelfth century, alchemists attempted to change base metals such as copper and iron into gold. In doing so, they learned a lot about the chemicals and elements they worked with. This new knowledge made the ancient Greek ideas of the four elements seem less than satisfactory. Over the next 600 years, scientists continued to improve their understanding of the properties of matter. In 1808 the English scientist John Dalton proposed a new ‘atomic theory’ that stated the following. • All matter was composed of tiny particles called atoms. • Atoms could not be broken into smaller particles. • Atoms of the same element are alike. • Atoms join together in different ratios. Dalton also produced a table showing symbols and atomic masses of the elements, but Dalton was not 100 per cent correct. Later scientists discovered that it is possible to break down atoms into protons, neutrons and electrons. Dalton went on to produce a table of the known elements and their atomic weight.
62
The development of the periodic table Tables of elements became more complex as more elements were discovered. In 1829, the German chemist Johann Dobereiner built on the earlier work of Dalton and others to show that groups of elements acted remarkably similar to each other, as if they belonged to the same ‘family’. This meant their physical properties (colour, melting and boiling points, density, hardness) and Science chemical properties (the way they reacted with other chemicals) were alike. Being able to group similar Musical elements elements together was the Newlands recognised beginning of the periodic table. that every eighth In 1864, the English chemist element was similar, John Newlands arranged the 60 or like the notes used in music. His Law of so known elements in columns of Octaves was not increasing atomic mass. When each accepted at the time column contained seven elements, and occasionally his the elements along each horizontal fellow scientists row tended to be similar. laughingly asked him if his elements could Unfortunately, the rows of his table play a tune! also contained some dissimilar elements, but at least it was a start.
Clip
The modern periodic table In 1869, Russian chemist Dmitri Ivanovich Mendeleev arranged the known elements into horizontal rows of increasing atomic mass and put the known ‘families’ into vertical columns.
Fig 2.4.8 John
Fig 2.4.9
Dalton’s table of elements
Dmitri Ivanovich Mendeleev
Science
Clip
The perfect vodka! It is thought that Mendeleev structured his periodic table in rows and columns because that was the way the card game of patience or solitaire was played. Before developing his table, Mendeleev was best known for his long hair and beard (which was only trimmed once a year) and for the fact that he and his mother hiked 6000 km across Russia in 1848 to get to his first day of university in St Petersburg. He also spent time perfecting the formulation for the perfect vodka!
Fig 2.4.10 Dmitri Mendeleev’s 1869 version of the periodic table
To do this he needed to leave gaps in the table, predicting that these were elements not yet discovered. Using ‘family likeness’, Mendeleev predicted what chemical properties these unknown elements could have. When eventually these elements were discovered, their properties closely matched his predictions. At the same time, German chemist Julius Lother Meyer constructed a similar table to that of Mendeleev by comparing the physical properties of elements with atomic mass. He did not leave gaps for undiscovered elements and went into print in 1870, one year after Mendeleev. Despite losing the race to be first, Meyer is acknowledged as a joint ‘father’ of the periodic table. The present periodic table (see Figure 2.2.2) is very much like the later table designed by Meyer. The final ‘modern’ periodic table was the result of work by a young English physicist, Henry Moseley, in 1913. He suggested that the physical and chemical properties were related to the atomic number, rather than mass. He refined the previous periodic tables to come up with a more accurate one with fewer errors and fewer missing elements. The final steps: artificial elements Even today, the periodic table continues to grow. As a greater understanding of the structure of atoms developed, scientists can now use nuclear reactions to artificially create (synthesise) missing elements, such as
promethium (61) and technetium (43). The use of nuclear reactors and the explosion of nuclear weapons have added to the known elements. A number of new artificial (synthetic) elements have been created that have an atomic number greater than atomic number 92, uranium. In general, these elements rapidly decay into more stable elements. However, the periodic table allows us to predict what their properties are likely to be without even seeing them.
Science
Fact File
Not a bad guess! Mendeleev left spaces in his table for undiscovered elements and predicted their properties. The table shows his predictions for the element that is below silicon on the periodic table, and that he named Eka-silicon. The element was discovered in 1886 and is now called germanium (symbol Ge).
Property Atomic mass Colour 3
Density (g/cm ) Boiling point (ºC)
Mendeleev’s prediction
Germanium
72
72.6
Dirty grey
Grey/white
5.5
5.35
Below 100
84
63
Chapter review
STUDENT ACTIVITIES 1 a John Dalton proposed his atomic theory in 1808. Outline his theory. b Explain which part of Dalton’s atomic theory was later found to be incorrect. 2 Dalton developed a way to measure the relative atomic mass of the different elements. Using examples, research and describe the meaning of the term ‘relative atomic mass’.
3 Choose one of the scientists mentioned in this chapter and research their background. Find out: a when they lived and died (or are they still alive?) b what contribution they made to the knowledge of the periodic table, elements and science c whether they worked with other scientists, and if so, with whom. Present your research to the class as a short presentation (2 to 3 minutes long). L
CHAPTER REVIEW Remembering 1 State if the following are true or false. a The mass number of an atom is the number of protons it has.
5 Hydrogen and helium can be placed in a number of places in the periodic table. Explain.
b Mercury is a solid at room temperature.
6 Describe what happens to the size and weight of elements as we move down any group.
c There are millions of different types of atoms. e Period 4 atoms all have four shells in use.
7 Look back at the main scientists and their contributions to the understanding and development of the structure of the atom and the periodic table. Summarise this information in a table.
f An atom with an electron configuration of 2,8,5 would be in Period 5, Group III.
8 Explain what happens if a potassium atom meets a fluorine atom in a chemical reaction.
g Carbon dioxide is an element.
9 Carbon also forms a molecule CCl4. Predict the compounds that would form out of chlorine and the other Group IV elements.
d Group V atoms all have five electrons in their outer shell.
h Air is a compound. i The element carbon is found in all living things. j In an atom, the number of electrons equals the number of protons. k Ions are always charged.
Applying 10 Draw a simple outline of the periodic table, then use different colours to demonstrate the location of:
l Ions are formed when atoms lose or gain protons.
a the noble gases
m If an atom loses electrons it becomes a negative ion.
b the transition metals
n An atom that has gained three electrons would now be an ion of charge –3.
c the semi-metals
Understanding
64
4 Explain why elements of the same ‘family’ are always found in the same group.
d the non-metals 11 Identify which groups these families are in:
2 Describe the position of electrons in an atom and how many electrons each shell can hold.
a halogens
3 Define what the period number and the group number represent.
c alkaline earths
b inert gases
Creating
12 Identify the most likely charge of ions formed from an atom of:
20 Construct models of:
a 5 electrons b 17 electrons
a the molecules H2O, H2O2 and other molecules found in this unit
c oxygen
b the lattices of diamond and sodium chloride
d neon
c a mixture that could represent a soft drink
e Group II f Group V 13 Copy and complete the table. N Atom
Atomic number
Sulfur Hydrogen
Number of protons
Number of neutrons
32 1
Beryllium
Atomic symbol
0
127 28
Number of electrons
16
9
Iodine Nickel
Mass number
59
4 74 59 Ni 28
Analysing 14 Distinguish five ways metals are different to non-metals. 15 Distinguish between a chlorine atom and a chloride ion. 16 Calculate how many p, n and e these atoms have. N a
35 Cl 17
b
3 H 1
c
197 Au 79
17 The outer electrons control what the atom does in a chemical reaction. Analyse reasons why this is the case.
Evaluating
21 a Research an element of your choice and gather the following details. i name of element, symbol, atomic number and whether it is a metal, non-metal or semi-metal ii appearance: include a colour photograph and state (solid, liquid or gas) at room temperature iii at least two uses of the element iv a brief history of its discovery b Present your information as a poster. Worksheet 2.6 Crossword
18 Propose why francium, Fr is more reactive than sodium, Na. 19 Propose why fluorine, F is more reactive than iodine, I.
Worksheet 2.7 Sci-words
65
3
Chemical change
Prescribed focus area The nature and practice of science
Key outcomes
Additional
Essentials
5.2, 5.7.3
•
New compounds are formed when atoms rearrange themselves into different combinations.
•
Chemical reactions can be described by word equations and chemical equations that use the formulae for each chemical.
•
Combustion reactions burn a substance in oxygen.
•
Decomposition reactions break apart a substance.
•
Precipitation reactions form a solid precipitate.
•
Neutralisation happens when acids and bases are mixed.
•
Reactions between an acid and a carbonate produce carbon dioxide.
•
Reactions between an acid and a metal produce hydrogen gas.
•
Indicators determine the pH of an acid or base.
•
Acids, bases and salts can be distinguished by certain characteristics.
Unit
3.1
context
Chemical reactions
Chemical reactions are occurring constantly inside us, around us, in the soil, in the sea, in the air and throughout the universe—absolutely everywhere! A chemical reaction is taking place
whenever fireworks explode, iron rusts or you digest food. However, not all chemical reactions are obvious. Scientists must look for certain signs to tell them when a reaction is taking place.
Physical change There are many cases where a substance changes the way it looks, feels or behaves, even when no chemical change has taken place. If no new substance is formed during the change, then the process is classified as a physical change. When you break a plate, you have changed the way the plate looks but you have not created any new substance. This then is a physical change. It is important to be able to identify physical changes to distinguish them from chemical changes. Physical changes are happening whenever: • materials or objects are broken or crushed into smaller pieces • changes of state happen. A physical change is happening, for example, when a solid melts to form a liquid, or when a liquid boils to form a gas • a mixture is created by mixing different materials together without them reacting Fig 3.1.1 Explosions are chemical reactions that happen incredibly • something is dissolved in a liquid. For quickly, releasing large quantities of heat and light energy. example, the characteristics of sugar change when it is dissolved in water. The characteristics of the water change too. No new substance has been formed, however, and you can still taste the sugar and can easily get it back by evaporating off the water. Dissolving one material in another creates a mixture known as a solution • mixtures are separated, such as when sand is filtered from water or fresh water is distilled from seawater.
Chemical change The key difference between a physical change and a chemical change is that new substances are formed in a chemical change. When a chemical change occurs, scientists say that a chemical reaction has taken place.
Fig 3.1.2 Melting is a physical change. When ice cubes melt, the solid water forms liquid water. Although both solid and liquid water behave differently, no new substance has formed.
67
Chemical reactions Chemical changes happen regularly in everyday life. For example, it’s difficult to eat a lump of raw dough. Cook it, however, and the dough changes into a new substance called bread. By heating the dough in the oven, you have caused a chemical reaction to occur. Anywhere you see a new substance being produced, you can be sure that there has been a chemical change— whether it is cooking meat, letting an apple turn brown in the sun or leaving iron to rust in the rain. Chemical reactions are happening whenever: • food is cooked • fruit and vegetables ripen • something that was living rots and decays • something is burnt • something explodes • a metal corrodes. Prac 1 p. 72
Science
Chemists write chemical equations to show and explain what is happening in a chemical reaction. Chemical equations are useful because they provide a quick and easy way to represent complex reactions. Word equations The simplest form of chemical equation is a word equation. Word equations represent chemical reactions by using the full names of all the chemicals involved. Word equations take this general form: substance A substance B substance C substance D
In this word equation, substance A reacts with substance B to produce substances C and D. Substances A and B are known as the reactants and substances C and D are known as the products. This can be expressed even more generally using another word equation: reactants products
Clip
Consider, for example, the reaction between magnesium and copper oxide. This reaction produces copper and magnesium oxide and so can be written as the word equation:
Chemical reactions are all around you! When you strike a match, you are setting off several chemical reactions that you can detect with your senses. As the match is burning you can see energy being emitted as light, feel the heat energy being emitted and smell new gases being produced. Once the match has burnt, you are left with a black piece of charcoal, which is very different from what you started with. All of these are signs that a chemical reaction is taking place.
magnesium copper oxide copper magnesium oxide reactants products
Using formulae A chemical equation tells you even more information if it includes the element symbols and chemical formulae of all the substances involved. In the above reaction, for example, the reactants are magnesium (symbol Mg) and copper oxide (formula CuO). The products are copper (Cu) and magnesium oxide (MgO). The reaction can therefore be written as:
Cooking involves chemical reactions to make the substances more palatable and softer and making them easier to digest.
Mg CuO Cu MgO
Rusting happens because of a slow chemical reaction in which iron reacts with water and the oxygen in the air to form a completely new substance called rust. Rust contains iron but is very different from it. Iron is hard and grey while rust is orange and flaky.
Fig 3.1.3 Chemical changes happen regularly in everyday life.
68
Chemical equations
Solid, liquid, gas or aqueous? A chemical equation is even more useful to chemists if they know whether the reactants and products are solids, liquids, gases or aqueous, meaning that the chemical has been dissolved in water to make an aqueous solution. To make this clear in the chemical equation, chemists use the labels (s) for solid, (l) for liquid, (g) for gas and (aq) for aqueous, usually presented as subscripts written just below the chemical they are referring to. In the above equation, for example, all the substances are solid. The chemical equation then is best written as: Mg(s) CuO(s) Cu(s) MgO(s)
Unit
3.1
Fig 3.1.4 The reaction of magnesium and copper oxide is spectacular.
Fig 3.1.5 A colour change is a sign that a chemical reaction is taking place. Indicators are weak acids or bases that change colour because of the strength of another acid or base.
Science
As another example, consider what happens when a solution of sulfuric acid reacts with solid sodium carbonate. Liquid water, carbon dioxide gas and a solution of sodium sulfate are produced. This can be written simply using the word equation:
Clip
Carbon monoxide poisoning
sulfuric sodium carbon sodium acid carbonate water dioxide sulfate (aq) (s) (l) (g) (aq)
The whole equation can be written to give even more information by using chemical formulae instead of the full name of each chemical. Using chemical formulae, the equation becomes: H2SO4 (aq) Na2CO3(s) H2O(l) CO2(g) Na2SO4(aq) Go to
Science Focus 4 Unit 1.1
Signs of chemical change
Fig 3.1.6 Bubbles in a liquid or solution
There are several signs that indicate whether a chemical reaction has occurred. A chemical reaction has definitely occurred if one or more of the following is observed.
are an indication that a chemical reaction is happening. Here hydrogen gas is bubbling out of a reaction between magnesium metal and hydrochloric acid.
Permanent colour change A permanent change in colour is an indication that a chemical reaction has taken place. For example, if you bleach your hair with peroxide, toast bread to make it brown (or black!) or fry an egg to make it white. A gas is given off If a reaction is taking place in a liquid, it is very easy to see a gas being produced because bubbling will be observed. With other reactions it can be more difficult to see the gas because most gases, like oxygen, hydrogen, nitrogen and carbon dioxide, are colourless and odourless.
Carbon monoxide (chemical formula CO) is a deadly gas emitted by cars. It is produced when carbon-based fuels like petrol burn in a limited supply of oxygen. Haemoglobin is the molecule in red blood cells that transports oxygen around your body. Carbon monoxide, which is odourless and colourless, is extremely toxic because it binds to haemoglobin 200 times more strongly than oxygen does. This leaves no space for the oxygen, so your cells quickly become starved of oxygen and die … and so do you!
A precipitate forms A solution is made up of a solute (the substance that dissolves) and a solvent (the liquid that the solute dissolves in). A salt solution, for example, is made when solid sodium chloride (table salt NaCl) is dissolved in water (H2O). Solutions are always clear, although they can be coloured. Sometimes a precipitate forms when two solutions are mixed. A precipitate is an insoluble substance. It does not dissolve in water and first appears as cloudiness in the solution. If the solid precipitate particles are
69
Chemical reactions Fig 3.1.7 Lead iodide precipitate is a distinctive yellow colour.
Fig 3.1.8 This baby mouse has been genetically modified to glow. A gene from a naturally bioluminescent jellyfish was inserted into the egg from which the mouse developed. The release of energy is an indication that a chemical reaction is happening.
heavy enough then they will sink to the bottom of the solution. The appearance of a precipitate is an indication that a chemical reaction has occurred. Go to
Science Focus 3 Unit 3.3
Prac 2 p. 72
Energy is produced or absorbed Many chemical reactions produce or absorb energy in the form of heat, light or sound. Reactions that absorb energy are called endothermic. The general equation for an endothermic reaction can be written as: reactants energy products
If an endothermic reaction occurs in a test tube, you will feel the test tube getting colder because the reaction is absorbing the heat energy from its surroundings. Chemical cold packs, for example, work by absorbing heat from injuries and therefore work using an endothermic process. Photosynthesis is one endothermic chemical reaction that is vital to life on Earth. Plants contain a green dye called chlorophyll that absorbs energy from the Sun. Without this energy, the reaction of photosynthesis doesn’t happen. The overall chemical equation for the photosynthesis reaction can be written as a word equation: carbon dioxide water energy glucose oxygen
or an unbalanced chemical equation: CO2 H2O energy C6H12O6 O2
Reactions that produce energy such as heat or light are known as exothermic. The general word equation for an exothermic reaction is:
70
reactants products energy
Heat is generated when fossil fuels such as petrol, oil and coal are burnt. These are examples of exothermic reactions. The heat produced can be converted into other forms of energy and then used to do things like make cars move, produce electricity in power stations and heat your home. The burning of magnesium ribbon is an exothermic reaction that releases both heat and light energy. The word equation for this reaction is: magnesium oxygen magnesium oxide energy
It can also be written as an unbalanced chemical equation: Mg O2 MgO energy
Prac 3 p. 73
Why do chemical reactions occur? Most chemical reactions need some energy before they can occur. For example, a sparkler lit for a birthday party needs a flame to get it going. It then keeps burning until all of the chemicals have reacted. For some reactions, the energy needed to get them started is very small and so they occur on their own, simply by taking the heat energy from the environment. Rusting of iron is an example of a chemical reaction that occurs (slowly) without the need for any extra energy. Chemical reactions that can proceed by themselves, like rusting, are known as spontaneous reactions. The sparkler reaction is also classified as spontaneous because the reaction keeps going once it has been started. It needs no more energy to keep it going. Other reactions need a continual energy input to keep them going. The electrolysis of water splits water into hydrogen and oxygen gases. This reaction needs a continuous electric current for it to continue. Stop the current and the reaction stops too. These reactions are known as non-spontaneous reactions.
Unit
QUESTIONS
Remembering 1 List four examples of a physical change.
d Two colourless solutions at room temperature are mixed. After a minute, the temperature of the mixture is 60°C.
2 State the fundamental difference between a physical and a chemical change.
e Ice is taken from the freezer and left on the bench. The temperature rises from 0°C to 20°C and the ice melts.
3 List four signs of chemical change.
f Yellow sulfur powder and iron filings are heated in a crucible. After heating, only a black solid remains.
4 List the signs of chemical change you would observe when you strike a match. 5 Specify what happens in: a an exothermic reaction b an endothermic reaction c a spontaneous reaction d a non-spontaneous reaction 6 State an example of each of the reactions in question 5.
Understanding 7 Define the term solution. L 8 Explain what is meant by a solution is clear, but not always colourless. 9 Describe what happens when a precipitate forms. 10 Burning methane (natural gas) is a spontaneous reaction but you need to light a match to make it burn. Explain why.
Applying 12 Identify two common examples of a chemical change and two of a physical change. 13 For each of the following reactions, identify: a the reactants b the products c whether the reaction is exothermic or endothermic d whether the reactants or products contain more energy Reactions: i water energy hydrogen oxygen ii methane oxygen carbon dioxide water energy 14 For each of the following, identify whether a chemical change has occurred and give a reason for each choice. a A student mixes two unknown solutions together and notices a cloudiness forming. b Solid purple iodine crystals are heated slightly and a purple cloud of iodine gas is observed.
3.1
3.1
Analysing 15 Classify the following as examples of chemical change or physical change. a b c d e f g
cutting up cheese making toast burning gas melting chocolate freezing cordial water evaporating putting a soluble aspirin tablet in water
Evaluating 16 Justify why lighting a sparkler is considered a spontaneous reaction and propose other spontaneous reactions you might find in your everyday life.
Creating 17 Construct word equations for the following reactions. a When copper is added to nitric acid, copper nitrate, nitrogen monoxide and water are formed. b If sulfuric acid is poured onto solid sodium carbonate, bubbles of carbon dioxide are produced, as well as water and sodium sulfate. c Magnesium burns easily in oxygen, producing magnesium oxide. d During photosynthesis, the Sun’s energy, carbon dioxide and water are used by green plants to produce glucose and oxygen. e An iron nail exposed to air and water will rust, forming hydrated iron oxide. f When solutions of lead nitrate and sodium iodide are mixed, a precipitate of yellow lead iodide is formed, as well as sodium nitrate in solution. 18 Design an experiment to demonstrate how a cold pack works and perform your experiment for the class.
c When nitric acid is poured onto limestone, bubbling is seen.
71
Chemical reactions
3.1
INVESTIGATING
1 Use your available resources (for example, textbooks, encyclopedias, internet) to investigate the following tasks. a Research how a cold pack works, including whether it is a chemical or a physical change. b Design a box that could be used to sell a cold pack. On the back should be instructions for the user, and information that explains how the pack works. L c Predict whether a heat pack would be endothermic or exothermic.
e -xploring Acid rain is causing significant damage to forests, monuments and historical buildings in certain parts of the world. To find out more about acid rain, a list of web destinations can be found on Science Focus 3 Second Edition Student Lounge. a Research the chemical reactions that cause acid rain to form. b Research the chemical reactions that happen when acid rain reacts with buildings.
2 Find out how light sticks work. Explain why a light stick cannot go forever.
c Assess the damage that acid rain has caused to the natural and built environment. d Write a letter to the government explaining the problems associated with acid rain. In your letter, recommend action that should be taken to reduce the possible damage caused by acid rain. L
3.1
PRACTICAL ACTIVITIES
1 Chemistry in the kitchen
Method
?
1 Follow the recipe for baking your favourite biscuits or muffins.
DYO
Aim To identify the physical and chemical changes that occur during baking
Equipment • ingredients and kitchen utensils to make your favourite biscuit or muffin recipe or pre-made cake-mix • access to an oven
2 Before putting them in the oven, list all the physical changes that the ingredients have gone through (for example, did you melt butter?). 3 Place the biscuits or muffins in the oven and watch as the ingredients undergo a chemical reaction.
Questions 1 Identify the changes that occurred during the baking and explain why you think these are chemical or physical changes. 2 Compare the characteristics of the mixture before and after baking.
2 Signs of chemical change Aim To observe changes during chemical reactions
Equipment • splint • matches
72
• Bunsen burner • test-tube holder
• test-tube rack • thermometer • 5 test tubes (1 with stopper) • dropper or Pasteur pipette • solid copper carbonate • magnesium • solid zinc
• • • • • • •
dilute nitric acid dilute sodium hydroxide dilute sodium sulfate dilute copper sulfate dilute barium nitrate lab coat safety glasses
Unit
Method 1 Copy the following results table into your workbook. Reactant(s)
Observation
Conclusion
Copper carbonate
3 Add a small piece of magnesium to 2 cm of nitric acid in a test tube. Stopper the tube to collect some gas. Have your lab partner light a splint and place it near the mouth of the test tube. 4 Put about 2 cm of the dilute barium nitrate solution in a test tube. Add the dilute sodium sulfate solution to the barium nitrate solution using a dropper or Pasteur pipette.
Nitric acid and magnesium
5 Record the temperature of 2 cm of the nitric acid solution. Add 2 cm of sodium hydroxide solution and record the new temperature.
Dilute barium nitrate and sodium sulfate
6 Place a small piece of zinc into 2 cm of dilute copper sulfate solution. Record your observations.
Dilute barium nitrate and sodium sulfate Dilute nitric acid and sodium hydroxide Zinc and dilute copper sulfate 2 Carefully heat a small amount of copper carbonate in a test tube. Ensure that the test tube is pointed away from people. Stop as soon as you see a colour change. Record your observations.
3 Light sticks: chemiluminescence
3.1
(Note: 1.0 M is an appropriate concentration for these solutions, but anything between 1.0 M and 2.0 M would be suitable.)
Questions 4 Identify the gas formed in the reaction in step 2. 5 Describe what happened when you placed the lit splint near the mouth of the test tube in step 3. What does this test tell you about the gas in the test tube? 6 Propose where the white precipitate in step 4 might have come from. 7 State whether the reaction in step 5 is endothermic or exothermic. 8 Predict what you think would happen if the zinc in the reaction in step 6 was replaced with silver.
Questions 1 Compare the brightness of the light sticks.
Aim
2 Predict what would happen to an activated light stick if you put it into the freezer.
To investigate the effect of adding energy to a reaction
3 Discuss some uses for light sticks.
Equipment • • • •
two 250 mL beakers ice hot tap water 2 light sticks (from scuba-diving store)
light stick
light stick
ice water
hot water
Method 1 Set up two beakers: one with a mixture of ice and water, the other with hot water. Your beakers should be filled to the 200 mL mark. 2 Activate your light sticks by bending them. This snaps the capsule inside and allows the chemicals to mix. 3 Place one light stick in ice and the other in hot water. 4 After a few minutes, take them out and compare the intensity of the light.
Fig 3.1.9
73
Unit
3.2
context
Combination, combustion and decomposition
Although each substance is unique, similar substances behave in a similar way in chemical reactions. This allows chemists to classify reactions into several
general categories. Combination, combustion and decomposition reactions are three general classes of chemical reactions that occur when chemicals combine or break apart to form new substances.
O C
+
O
C
O
O C
+
O2
CO2
Fig 3.2.2 One atom of carbon combines with one molecule of oxygen to form one molecule of carbon dioxide.
Combustion reactions
Fig 3.2.1 A bushfire is a combustion reaction in which timber, leaves and grass burn in oxygen. The most obvious product is the black carbon and charcoal that the fire leaves in its path. The reaction is highly exothermic, releasing heat and light energy.
Combination reactions In combination reactions, different substances combine to form just one new substance. These reactions have the general equation: x y xy
For example, carbon and oxygen combine to form carbon dioxide. This is shown as a word equation:
Ever since the first cave dwellers learnt to use fire, people have been using combustion reactions to keep warm, to cook food, to give light, to scare off wild animals and to forge metals into tools and weapons. A combustion reaction is simply burning a substance in oxygen. This means that oxygen gas (O2) is always a reactant. The products will vary, depending on the substance that is burnt. Compare two gases, methane (CH4) and ethane (C2H6). Both burn in oxygen in a very similar way, giving out lots of heat in an exothermic combustion reaction. Word equations: methane (g) oxygen (g) carbon dioxide (g) water (g) ethane (g) oxygen (g) carbon dioxide (g) water (g)
Unbalanced chemical equations: CH4(g) O2(g) CO2(g) H2O(g) C2H6(g) O2(g) CO2(g) H2O(g)
carbon oxygen carbon dioxide
A chemical equation:
74
Balanced chemical equations:
C O2 CO2
CH4(g) 2O2(g) CO2(g) 2H2O(g)
O2 is used instead of just O because the oxygen in the air around us exists as pairs of atoms known as diatomic molecules. Diatomic means that two oxygen atoms bond together to form a stable molecule.
2C2H6(g) 7O2(g) 4CO2(g) 6H2O(g) Go to
Science Focus 4 Unit 1.1
How a bullet works A combustion reaction occurs when a bullet is fired. The combustion of the chemical propellant in the bullet case produces a gas which expands and forces the bullet out of the barrel at great speed.
Reactions can sometimes fall into more than one general category. Combustion reactions, for example, can also be combination reactions. Magnesium oxide is produced when you burn magnesium metal in oxygen. Its equation can be written as follows. A word equation:
3.2
Clip
Unit
Science
magnesium oxygen magnesium oxide
An unbalanced chemical equation: Mg(s) O2(g) MgO(s)
A balanced chemical equation: 2Mg(s) O2(g) 2MgO(s)
Prac 1 p. 78
Prac 2 p. 78
Decomposition reactions
Fig 3.2.3 The combustion of a chemical propellant forces a bullet from a barrel.
The term decomposition is often used to describe the rotting of animal or plant matter caused by bacteria and exposure to air. Chemists, however, use the word decomposition to describe a specific set of chemical reactions. Decomposition reactions are the opposite of combination reactions. One substance breaks down to form two or more new substances. The general equation for decomposition reactions can be written: xy x y
For example, household bleach or hydrogen peroxide (H2O2) spontaneously decomposes to form oxygen gas and water. The equation for this reaction is written as follows. A word equation: hydrogen peroxide (l) oxygen (g) water (l)
An unbalanced chemical equation: H2O2(aq) O2(g) H2O(l)
A balanced chemical equation: 2H2O2(aq) O2(g) 2H2O(l)
Science
Clip
Phlogiston
Fig 3.2.4 Magnesium burns in oxygen and releases intense light that is dangerous to look at. This reaction is both a combustion reaction (involving oxygen) and a combination reaction (combining Mg and O2).
Before scientists learnt about the chemistry of combustion, many thought that substances only burned because they contained an imaginary element called phlogiston. They believed that when a substance was burned, its phlogiston was released into the atmosphere. Only the ashes would be left behind. When magnesium ribbon is burnt, its ash is heavier than the metal ribbon it started as. This indicates that the magnesium metal must be gaining something from the air rather than losing phlogiston. These observations suggest that the phlogiston theory was incorrect!
75
Combination, combustion and decomposition Science
Clip
Airbags It’s hard to believe that a decomposition reaction saves lives every day! Inside the airbag in a car is a chemical, sodium azide, which decomposes explosively when triggered into sodium and nitrogen. Amazingly, 100 grams of sodium azide forms about 56 litres of nitrogen in 0.03 seconds which then inflates the airbag. The chemical equation for the reaction is as follows. Word equation:
sodium azide (s) sodium (s) nitrogen (g) Unbalanced chemical equation:
NaN3(s) Na(s) N2(g) Balanced chemical equation:
2NaN3(s) 2Na(s) 3N2(g)
Fig 3.2.5 Carbonic acid (H2CO3) decomposes
spontaneously over time to form carbon dioxide and water. This reaction is what puts the fizz in soft drinks: H2CO3(aq) H2O(l) CO2(g).
Thermal decomposition Decomposition reactions are usually endothermic and as such can be enhanced by adding heat to them. Thermolysis reactions are a special type of decomposition reaction. In these reactions, heat causes a reactant to break up into two or more products. The decomposition temperature of a substance is the temperature at which the substance decomposes into two or more components. Calcium carbonate, for example, decomposes at temperatures above 825°C into calcium oxide and carbon dioxide. The reaction for this is written as:
Fig 3.2.6 The deployment of an airbag during a crash is caused by a decomposition reaction.
calcium calcium carbon carbonate (s) heat oxide (s) dioxide (g) CaCO3(s)
heat
CaO(s)
Science
Clip
CO2(s)
In hot water
Prac 3 p. 79
76
Even water decomposes into its components hydrogen and oxygen when heated to well over 2000ºC.
Unit
QUESTIONS
Remembering 1 List two examples each of combination, combustion and decomposition reactions. 2 State the general formulae for combination and decomposition reactions. 3 Name the gas given off when calcium carbonate is heated. 4 Write the chemical equation of a reaction that can be classified as two different reaction types.
Understanding 5 Oxygen is written as O2 in chemical reactions rather than just O. Explain why. 6 Explain why combination and decomposition reactions could be considered the reverse of each other.
Applying 7 Identify the following reactions as either combination, combustion or decomposition reactions. a 2KClO3 씮 2KCl 쎵 3O2
a 2Mg 쎵 O2 씮 2MgO b 2H2O 씮 2H2 쎵 O2 c CaO 쎵 H2O 씮 Ca(OH)2
Analysing 10 Discuss how combustion is important in our everyday lives. 11 Compare how humans have used combustion reactions over the course of history.
Evaluating 12 Propose what you think would happen to a candle left to burn in a very small confined space. Explain your reasoning. 13 Hydrogen peroxide is often stored in a fridge. Propose why this is done. 14 Councils will often burn large areas of land in cool weather to prevent bushfires in summer. a Identify the type of reaction involved in this activity. b Identify the gas being used in this reaction.
b CH4 쎵 2O2 씮 CO2 쎵 2H2O
c Identify whether the reaction is spontaneous or nonspontaneous. Justify you answer.
c O2 쎵 2H2O 씮 2H2O2
d Use energy to explain why:
8 Use chemical formulae to rewrite the following word equations as unbalanced chemical equations. a carbon 쎵 oxygen 씮 carbon dioxide b copper carbonate 씮 copper oxide 쎵 carbon dioxide c propane 쎵 oxygen 씮 carbon dioxide 쎵 water 9 Use the names of the substances to rewrite the following chemical equations as word equations.
3.2
3.2
3.2
i bushfires are more likely to happen in summer than winter ii burnoffs are done in winter. e Propose reasons why burnoffs are useful.
Creating 15 Design an experiment to determine which soft drinks contain the most carbonic acid (H2CO3)
INVESTIGATING
1 Use your available resources (for example, textbooks, encyclopaedias, internet) to investigate why the decomposition of mercury oxide (HgO) was a very important reaction for the eighteenth century chemists Carl Wilhelm Scheele, Joseph Priestley and Antoine-Laurent Lavoisier.
2 a Research and explain the combustion reaction that drives a space shuttle. Use chemical equations in your answer. b Draw a diagram to illustrate how the shuttle engines work.
77
Combination, combustion and decomposition
3.2
PRACTICAL ACTIVITIES
1 Burning magnesium ribbon (teacher demonstration) Aim To demonstrate a combination reaction
Equipment • • • • • •
tongs lighter 15–20 cm of magnesium ribbon safety glasses gloves lab coat
Method 1 Wearing safety glasses, gloves and a lab coat, use the tongs to hold the magnesium ribbon a suitable distance away from yourself and others. 2 Use a lighter to ignite the ribbon while keeping it at arm’s length.
Questions 1 Construct the word equation for the reaction that occurs when magnesium ribbon is burned in air. 2 Explain why this reaction can be classified as both a combination reaction and a combustion reaction. 3 Propose whether you think that the reaction is endothermic or exothermic and explain your reasoning. 4 Propose whether you think that the reaction is spontaneous or non-spontaneous and explain your reasoning.
2 Stopping combustion
the test tube. (Note: carbon dioxide is heavier than air so it should displace the air in the test tube and remain there.)
Aim
6 Light the splint again and blow it out so that it is glowing.
To observe what happens to a combustion reaction when oxygen is removed
7 Remove the stopper from the test tube and quickly insert the glowing splint. Record your observations.
Equipment • • • • • • •
250 mL conical flask rubber stopper with a flexible plastic tube passing through it large test tube with rubber stopper wooden splint matches sodium bicarbonate 0.1 M hydrochloric acid
Method 1 Use the matches to light the wooden splint and blow it out. Record your observation then extinguish the splint. 2 Place a small amount of sodium bicarbonate in the flask. 3 Half-fill the beaker with limewater. 4 Add about 20 mL of 0.1M hydrochloric acid to the conical flask and immediately place the stopper in the flask. 5 Place the other end of the plastic tube in the large test tube to fill it with carbon dioxide gas then place the stopper in
78
sodium bicarbonate
0.1M HCl conical flask
test tube
Fig 3.2.7
Questions 1 Describe what evidence you have that a combustion reaction is taking place at the end of the glowing splint. 2 State whether this reaction is spontaneous or nonspontaneous. Explain your answer. 3 Propose why you think the glowing splint stopped glowing when you put it into the test tube filled with carbon dioxide.
Unit
clamp stand
Aim To perform a decomposition of a metal carbonate
Equipment • • • • • •
two large test tubes stopper for the test tube with a delivery tube retort stand and clamp Bunsen burner limewater copper carbonate
Method 1 Put a large measure of copper carbonate into a test tube. 2 Fit a stopper with delivery tube and then clamp the test tube. 3 Place the delivery tube so that it dips into a second test tube containing limewater. 4 Use the Bunsen burner to heat the solid gently at first, then more strongly. 5 Lift the delivery tube from the limewater as soon as the heating is stopped to avoid ‘suck-back’. 6 Write down all your observations.
3.2
3 Decomposition of a metal carbonate test tube
clamp
delivery tube
metal carbonate Bunsen burner
test tube
limewater
Fig 3.2.8
Questions 1 Assess if a chemical reaction has taken place. 2 Construct the word equation for the decomposition of copper carbonate. 3 Propose whether the mass of the substance left in the test tube after heating would be greater or less than the mass of copper carbonate put in the test tube originally. 4 Investigate how limewater acts as an indicator for carbon dioxide and construct a word equation for the reaction that takes place in the limewater when carbon dioxide is bubbled through.
79
Unit
3.3
context
Precipitation reactions
Another important class of reaction is precipitation, which occurs when two soluble substance come together to form an insoluble substance. Precipitation
reactions play a key role in the extraction of new compounds and in the purification of our water supply.
Fig 3.3.1 Precipitates are insoluble solids that appear when two clear solutions are mixed and ions from both solutions combine. Eventually, most precipitates settle out, falling to the bottom. Different precipitates come in different colours.
Precipitation reactions In a precipitation reaction, two clear solutions mix to form an insoluble solid known as a precipitate. These reactions can be written as: soluble salt soluble salt insoluble salt soluble salt A B C D (the precipitate)
Here the word salt doesn’t mean common table salt (sodium chloride). Chemists use the word salt to describe any substance that is made up of a lattice of positive and negative ions. Sodium chloride (NaCl) is
80
an example of a salt because it contains positive sodium ions (Na) and negative chloride ions (Cl). However, magnesium fluoride (MgF2) is also a salt made up of the ions magnesium (Mg2) and fluoride (F). So too is calcium oxide (CaO), which is made up of calcium ions (Ca2) and oxide ions (O2). A precipitation reaction occurs when we mix silver nitrate (AgNO3) with sodium chloride (NaCl). silver nitrate
sodium chloride
silver chloride
AgNO3(aq)
NaCl(aq)
AgCl(s)
sodium nitrate
NaNO3(aq)
sodium nitrate solution and solid silver chloride NaNO3(aq) + AgCl(s)
3.3
sodium chloride solution NaCl(aq)
Unit
silver nitrate solution AgNO3(aq)
H nitrate ion (NO3–)
chloride ion (Cl–)
silver ion (Ag+)
sodium ion (Na+)
Science
Clip
nitrate ion (NO3–)
Molten salts and ionic liquids
sodium ion (Na+)
Fig 3.3.2 Silver nitrate and sodium chloride are both soluble in water. Silver nitrate dissolves, releasing its positive silver ions (Ag) and negative nitrate ions (NO3) while sodium chloride releases positive sodium ions (Na) and negative chloride ions (Cl). However, silver chloride (AgCl) is not soluble in water and so it precipitates or falls out of solution. A solution of sodium nitrate (NaNO3) is left behind.
Silver chloride precipitates out as a white solid forming a white cloud at the centre of the test tube as shown in the photograph.
All naturally occurring salts have quite high melting points, above 800ºC. However, chemists discovered how to synthesise salts that have much lower melting points and which may even be liquid at room temperature. These new compounds, known as ionic liquids, contain no water molecules, just positive and negative ions that move around freely. As a result, they have many special properties—including the ability to conduct electricity.
Science
Clip
Hard water
Ions and salts
Water is said to be ‘hard’ when it contains high levels of calcium and magnesium salts. The calcium and magnesium ions combine with the molecules in soap to form an insoluble precipitate called soap scum. Hard water also forms hard calcium carbonate deposits (commonly called scale) which can completely block pipes.
Most salts are made up of a crystal lattice of positive metal ions combined with negative non-metal ions. This occurs because metal atoms need to lose electrons to become stable while non-metals prefer to gain electrons to become stable. Go to
Fig 3.3.3 Water pipes blocked by scale precipitated out of hard water.
Science Focus 3 Unit 2.2
As a result, when a metal atom meets a nonmetal atom, the metal atom gives up its electrons to the non-metal and they form a crystal lattice of positive and negative ions. For example, if a potassium (K) atom bumped into a chlorine atom (Cl), the chlorine would quickly steal an electron to form a chloride ion (Cl) leaving the potassium with a positive charge—making it a potassium ion (K). Because the two ions have opposite charges they will attract each other and stick together. An important exception to this rule is ammonium (NH4). Ammonium is a positive ion but is non-metallic. Nonetheless, it still combines with negative non-metal ions to form salts. For example, ammonium fluoride (NH4F) contains no metal atoms but is still considered a salt.
81
Precipitation reactions Simple ions Simple ions contain only one atom that has lost or gained electrons. Whether or not an atom gains or loses electrons depends on its electron configuration—that is, how the electrons are distributed around the nucleus of the atom. Electrons in an atom exist in shells. The first shell can hold two electrons while the second, third and fourth shells hold eight. The number of electrons that an atom has in its outer shell determines which group in the periodic table it belongs to. Atoms in Group I have one electron in the outer shell, atoms in Group II will have two electrons and so on. As a general rule, atoms will gain or lose electrons until they have a full outer shell of electrons. For atoms with four or less electrons in their outer shell, it is easier for them to lose these electrons to obtain a full outer shell. As a result they become positive ions. For atoms with five or more electrons in their outer shell, it is easier for them to gain electrons until their outer shell is full. They then become negative ions. Elements in Group VIII already have a full outer shell and so do not form ions. The table below can be used to predict the charges of simple ions.
loses 2 electrons
The magnesium atom has 2 electrons in the first shell, 8 in the second shell and 2 in the third shell.
magnesium ion
chloride ion Cl–
chlorine atom Cl
gains one electrons
The chlorine atom has 2 electrons in the first shell, 8 in the second shell and 7 in the third shell.
The chloride ion has gained an electron so that its outermost shell is full. It has 2 electrons in the first shell, 8 in the second shell and 8 in the third shell.
Fig 3.3.5 Electron configuration for a chlorine atom and a chloride ion
Group
I
II
III
IV
V
VI
VII
Most likely charge formed
1
2
3
Some form 4
3
2
1
Examples
82
The magnesium ion has lost the outer 2 electrons so that its outermost shell is full. It has 2 electrons in the first shell, 8 in the second shell.
Fig 3.3.4 Electron configuration for a magnesium atom and a
Polyatomic ions Some ions are made up of more than one type of atom and are called polyatomic ions. These ions have special names. The table below shows some of the more common ones. Naming salts When ions form salts, they combine in a ratio that ensures a total charge of zero. This means that there must be enough negative charges to balance the positive charges and vice versa. For example, sodium and chloride ions combine in a 1:1 ratio because sodium ions have a 1 charge and chloride ions have a 1 charge. Add these charges together: 1 (1) 0.
magnesium ion Mg2+
magnesium atom Mg
Na (sodium ion)
Mg2 Al3 (magnesium (aluminium ion) ion)
Pb4 (lead ion)
N3 O2 (nitride ion) (oxide ion)
Cl (chloride ion)
VIII (Group 0) No ions formed
Unit
Ion name
Formula OH
Sulfate
SO2 4
Nitrate
NO3
Hydrogen carbonate
HCO3
Ammonium
NH4
Carbonate
CO2 3
O
H
2 O C O
sodium (2, 8, 1)
Na
chlorine (2, 8, 7)
sodium ion (2, 8)
Cl
chloride ion (2, 8, 8)
Na+
Cl–
–
+ An electron is transferred from sodium to chlorine. These positive and negative ions are attracted to each other and form a crystal where the ions are stacked to maximise attraction.
– + – +
+ –
– +
Na ++
– + –
–
+ –
3.3
Hydroxide
+ – + –
+
+
–
Positive ion
O
Negative ion
Formula
Name
Mg2
Cl
MgCl2
Magnesium chloride
Na
O2
Na2O
Sodium oxide
Al3
S2
Al2S3
Aluminium sulfide
Ca2
N3
Ca3N2
Calcium nitride
Ba2
O2
BaO
Barium oxide
+
–
+
Fig 3.3.6
Therefore, two ions, one of each type, join to give a compound with a total charge of zero (0). The formula is NaCl, and the name of this compound is sodium chloride. To name salts, simply follow these rules. • The positive ion is named first and the negative ion second. • The name of a positive ion is the same as the name of the element that it comes from. For example, Na is also called sodium. • A negative ion is named by taking the first part of the parent element’s name and adding the suffix-ide. For example, Br (originally bromine) is called bromide, O2 (originally oxygen) is called oxide and N3 (originally nitrogen) is called nitride. In the chemical formula of the compound, the small number at the base of a symbol indicates how many of each ion is in the formula. If no number is given, it indicates that there is only one of that type of ion.
O2–
Ba2+
O2–
Ba2+
O2–
Ba2+
O2–
Ba2+
O2–
Fig 3.3.7
When more than one polyatomic ion is required in a formula, brackets are used. For example, in sodium sulfate, Na2SO4, only one sulfate ion is needed to balance the charge so no brackets are needed. For aluminium sulfate, Al2(SO4)3, three sulfate ions are required so brackets are used. Worksheet 3.1 Ionic compounds
83
Precipitation reactions The sodium ion takes its name directly from the sodium atom from which it was formed.
Na+
This was originally a chlorine atom but is now an ion and is given the new name chloride.
Cl–
Sodium chloride The total charge is zero. The chemical formula is NaCl.
Fig 3.3.8 Naming sodium chloride
The magnesium ion comes from a magnesium atom that has lost 2 electrons.
Cl– H
Mg2
Cl–
Predicting precipitation reactions Not all salts are soluble in water and it is difficult to tell whether or not a salt will be soluble without actually trying it. However, chemists have already tested the solubility of all common salts and have developed a set of solubility rules. Solubility rules help us to work out which substance in the mixture is precipitating. For example, in the reaction on page 80, it can’t possibly be sodium nitrate because all sodium Prac 1 Prac 2 salts are soluble and all nitrate salts are soluble. p. 86 p. 87
There are two chloride ions with a total charge of –2 to balance the charge of the 2H magnesium ion.
Magnesium chloride The chemical formula is MgCl2. It contains two chloride ions for every one magnesium ion.
Fig 3.3.10 The bright pigments in paints are often precipitates of ions from the
Fig 3.3.9 Naming magnesium chloride
transition metals. They include precipitates of cobalt, iron, titanium and chromium.
Solubility of common inorganic compounds in water Negative ions (anions) Acetate CH3COO
All
All
Alkali ions, Li, Na, K, Rb, Cs, Fr
All
Ammonium ion NH4
All
Hydrogen ion H
Chloride Cl
Ag, Pb2, Hg2
Bromide Br
Cu, Ti
Iodide I
All others
Hydroxide OH
Alkali ions, H, NH4, Sr2, Ba2, Ra2, Ti All others
Nitrate NO3
All
Phosphate PO43
Alkali ions, H, NH4
Carbonate CO32
All others
Sulfate SO42
Sulfide S2–
84
Positive ions (cations)
Ca2, Sr2, Ba2, Pb2, Ra2
Compounds with solubility
All others Alkali ions, H, NH4, Be2, Mg2, Ca2, Sr2, Ba2, Ra2 All others
Soluble Soluble Soluble Soluble Low solubility Low solubility Soluble Soluble Low solubility Soluble Soluble low solubility Low solubility Soluble
Soluble Low solubility
Unit
QUESTIONS
Remembering 1 State the meaning of the subscripts (s), (l), (g) and (aq) and specify which one would be used for a precipitate.
Evaluating 13 Refer to the table of solubility rules on page 84. Assess which of the following substances would be soluble in water.
2 Name a positive ion that is non-metallic.
a BaSO4
3 List the names and symbols of five polyatomic ions.
b LiNO3
4 State if nitrates are normally soluble or insoluble.
c CaCO3
Understanding 5 To non-chemists, salt is sodium chloride, NaCl. Define what chemists mean by the term salt. 6 Describe what observations suggest that a precipitation reaction has occurred.
Applying 7 Identify two types of salts that are almost always soluble and list any exceptions. 8 Use the table of solubility rules to predict the precipitate formed when these solutions are mixed:
d MgCl2 14 Using the periodic table from Chapter 2, deduce the chemical formulae for the compounds: a sodium bromide b magnesium sulfide c calcium fluoride d lithium nitride e aluminium carbide 15 Deduce the names of the following salts. a RbBr
a silver nitrate and sodium chloride
b K2S
b mercury(l) nitrate and potassium iodide
c BeO
c calcium nitrate and lithium carbonate
d Na3N
d barium nitrate and sodium sulfate
e NH4Cl
9 Use word equations and chemical formulae to write equations for the reactions in Question 8.
Analysing 10 Discuss why it is useful to classify reactions into different types. 11 Calculate the total charge of: a four sodium ions b eight manganese(IV) ions c three nitride ions N 12 Calculate the number of each type of atom in the following formulae.
3.3
3.3
f LiOH g Ag2CO3 h ZnSO4
Creating 16 Design an experiment to test whether the solubility of ionic compounds increases or decreases as the solutions get hotter. Investigate and explain your results. 17 Construct a board game that tests knowledge of how compounds are named. You may use die or cards. The game must involve answering questions about formulae or the rules for writing them. Design a list of rules, bonuses and challenges for the game. L
a (NH4)2SO4 b K2Cr2O7 c Ca(OH)2 N
85
Precipitation reactions
3.3
INVESTIGATING
Use your available resources (for example, textbooks, encyclopaedias, internet) to investigate the following. 1 Find out how precipitation reactions are used in the purification of water. 2 Find out how hard water can be softened.
e -xploring To test your understanding of chemical reactions and balancing equations, a list of web destinations can be found on Science Focus 3 Second Edition Student Lounge.
3 Research some of the properties and uses of ionic liquids. 4 Find all metal ions that are insoluble when combined with iodide (I). Find the colour of each.
3.3
PRACTICAL ACTIVITIES
1 Precipitation reactions
3 Use the Pasteur pipette to add Solution A to Solution B and record your observations.
Aim To observe common precipitation reactions
4 Repeat steps 2 and 3 for each pair of solutions.
Equipment • 0.1 M solutions of silver nitrate, sodium chloride, sodium hydroxide, barium nitrate and copper sulfate • Pasteur pipettes • lab coat • safety glasses • gloves
Method 1 Draw up a suitable table, similar to the one below, to record your results. Solution A
86
Solution B
Silver nitrate
Sodium chloride
Silver nitrate
Sodium hydroxide
Barium nitrate
Copper sulfate
Observations before mixing
2 Place small amounts of Solution A and Solution B in separate test tubes and record your observations.
Observations after mixing
Questions 1 Analyse the table of solubility rules to work out what salt has precipitated from solution. 2 Construct word equations to describe what is happening in each reaction.
Unit
step 1
step 2
step 3
Aim
3.3
2 Precipitation of unknowns To identify an unknown solution using the solubility table
Equipment • The table of solubility rules on page 84 • unknown 0.1 M solutions labelled A, B, C, D, E—these are (not in order): sodium iodide, sodium chloride, sodium sulfate, sodium carbonate and sodium nitrate • 0.1 M solutions of silver, lead, calcium and barium nitrates • 20 semi-micro test tubes • Pasteur pipettes • lab coat • safety glasses • gloves
Method
-
10 drops of unknown solution
Add 10 drops test solution and mix
Check for cloudiness—hold it up to the light if not sure
Fig 3.3.11
2
(Hint: Cu ions are blue in aqueous solution. Lead iodide is bright yellow.) 1 Draw up a suitable table, similar to the one below, to record your results. 2 Put about 10 drops of unknown A into each of four semimicro test tubes. Unknown
Silver nitrate
Lead nitrate
Calcium nitrate
Barium nitrate
3 Add 10 drops of silver nitrate solution to the first tube, 10 drops of lead nitrate to the second, 10 drops of barium nitrate to the third, and 10 drops of magnesium nitrate to the fourth. Record your results. 4 Repeat steps 2 and 3 for each unknown solution. 5 Use the table of solubility rules to work out which solution is which.
Questions
A
1 Were any of your results inconclusive? If so, propose a reason.
B
2 If you wanted to test a clear solution for the presence of lead, identify what you could add.
C D E
87
Unit
3.4
context
Acids and bases
Every day you come in contact with acids and bases. You drink an acid when you drink orange juice and there is a base in the toothpaste you use to brush your teeth. Other acids and bases can cause serious burns, especially when striking
sensitive parts of the body such as your eyes. Though dangerous, these acids and bases play an important role in many different chemical reactions used in industries such as mining and manufacturing and sciences such as medicine.
Strong and weak acids Acids can be classified as being strong or weak. Strong acids are corrosive which means they can destroy living tissue and ‘eat through’ some surfaces. Nitric acid (HNO3), sulfuric acid (H2SO4) and hydrochloric acid (HCl) are all strong acids. In strong acids the hydrogen breaks away very easily. Hydrochloric acid is so strong that almost 100 per cent of its molecules will break apart when it is added to water to make up a solution. When it breaks, it form hydrogen ions (H) and chloride ions (Cl).
Fig 3.4.1 Acids are corrosive and bases are caustic. Both burn and damage tissues. This eye damage was caused by exposure to ammonia, a strong base.
Acids Acids contain the element hydrogen in combination with other non-metal elements. For example, hydrochloric acid (HCl) contains hydrogen in combination with chlorine. Likewise, sulfuric acid (H2SO4) contains hydrogen and sulfate ions, each sulfate ion being made up of one sulfur and four oxygen atoms. When an acid is placed in water, the hydrogen breaks away from the other elements. Acids have some common properties. Acids: • have a sour taste. Although some acids are safe to taste (e.g. lemon, vinegar), most acids are far too dangerous to taste or even smell • have a gritty feel to the touch • can be corrosive • turn blue litmus red. Litmus is one of many indicators and chemicals that change their colour in the presence of an acid or base • neutralise bases.
88
Science
Clip
Fig 3.4.2 Hydrochloric acid (HCl) is the acid in the stomach that helps you digest food. HCl is a very strong acid yet the stomach is not irritated by it. This is due to a special lining that keeps it away from the muscle walls. The stomach ulcer shown here will allow the acid to attack the walls, causing pain.
Weak acids tend to hold on to their hydrogen and very little hydrogen breaks away. Examples of weak acids include vinegar (acetic
A strong stomach The hydrochloric acid that helps digestion of food in our stomachs is a highly concentrated strong acid with a pH of 1 to 2. Although this would normally destroy living tissue, it doesn’t eat through the stomach lining because the lining secretes protective mucus.
Unit
Science
Clip
weak acid—CH3COOH acetic acid
3.4
strong acid—HCl hydrochloric acid
Weak but deadly Hydrofluoric acid (HF) is considered a very weak acid but can cause serious burns and even death. However, it is the fluoride ion (F) not the hydrogen ion (H) that causes all the damage. The fluoride ion is so small that it can easily penetrate your skin. It then binds with the calcium in your bones which could result in amputation or death.
CH3COOH H+
Cl–
Cl–
H+
H+ Cl– H+
Cl– Cl–
H+
H+
Cl–
Strong acids such as hydrochloric acid (HCl) completely separate out into their ions. Many H ions are released.
CH3COOH H+
CH3COOH
CH3COOH CH3COO– CH3COOH
Science
Clip
Things that sting Worker bees can give you a very nasty sting. The painful sting is produced by the methanoic (formic) acid they inject. This is the same acid that puts the sting into bull ants and greenheads. Other stinging creatures, like wasps and some jellyfish, inject a base into the skin of their victims. This can be neutralised by washing the wound with a weak acid such as vinegar.
Only a few acid molecules split up and release H ions in a weak acid such as ethanoic (acetic) acid. The majority of the acid is still in its molecular form.
Fig 3.4.3 Strong acids break apart completely in water, while weak acids tend to stay together.
acid (CH3COOH) and citric acid. In a solution of vinegar, most of the molecules will remain as CH3COOH, while only a small fraction will break apart to form the hydrogen ion (H) and acetate ion (CH3COO). Likewise, hydrofluoric acid is a weak acid in which very few molecules split. The uses of acids You eat and drink weak acids such as the citric acid found in orange juice, lactic acid in yoghurt and acetic acid in vinegar. Strong acids tend to be more useful in industry for extracting metals from ores, in fertilisers, in the manufacture of automotive parts and even in the production of microchips. For these reasons, more sulfuric acid (H2SO4) is manufactured each year than any other chemical. The table below shows some acids and the common uses of each. Acid
Fig 3.4.4 This scanning electron microscope (SEM) image shows the sting of a bee. The acid is ejected from the red glands at the bottom of the image.
Common name
Common use
Cetylsalicylic acid
Aspirin
Pain reliever
Benzoic acid
Sorbic acid
Preservatives in foods
Ascorbic acid
Vitamin C
Vitamin supplement, antioxidant
Sulfuric acid
Battery acid
Car batteries, manufacturing fertilisers
4-chloro-2-methyl phenoxyacetic acid
MCPA
Herbicide
Hydrochloric acid
Spirit of salts
Brick cleaners, cleaning metals
Ethanoic (acetic) acid
Vinegar
Flavour and preserving food
89
Acids and bases
Bases Bases are commonly thought of as the opposite of acids. This is because when an acid and bases are mixed together, the resulting solution is often neutral. This means that the solution is neither acidic or basic. Bases in solution produce hydroxide (OH) or (O2) ions. Both of these ions combine with the hydrogen ion (H) produced by the acid to create water (H2O). This process is called neutralisation. Bases share certain properties. They: • taste bitter. (Although some bases are safe to taste, like toothpaste, most are not) • have a soapy feel (as with taste, most bases are not safe to touch) • can be caustic • turn red litmus blue • neutralise acids. Strong and weak bases Like acids, bases can be classified as either strong or weak. While strong acids break apart easily to release their hydrogen ion (H), strong bases break apart easily to release a negative hydroxide (OH) or oxide ion (O2). Lithium hydroxide is an example of a strong base. In solution, almost 100 per cent of the lithium hydroxide will break apart to form lithium ions (Li) and hydroxide ion (OH). Other examples of strong bases are sodium hydroxide (NaOH) which is commonly known as caustic soda. Strong bases can cause serious burns. They are said to be caustic. Quite often, weak bases will not contain a hydroxide ion but will steal a hydrogen ion from a water molecule to produce the hydroxide ions. For example, ammonia (NH3) in solution will steal a hydrogen from a water molecule (H2O) to produce a positive ammonium ion (NH4) and a negative hydroxide ion (OH). The equation for this looks like: ammonia water ammonium hydroxide NH3
H2O
NH4
OH
The carbonate ion (CO32) is another weak base that behaves in this way. Base
90
Fig 3.4.5 This train is transporting bulk caustic soda (sodium hydroxide), an important chemical in the mining industry. Caustic soda is so caustic and damaging that it is often used as a paint stripper.
The uses of bases Many household cleaners contain bases because they are excellent at dissolving oil and grease. Oven cleaners usually contain sodium hydroxide (NaOH), a strong base, because it reacts with oils to form soap, which then washes away easily. Bases include ionic compounds such as hydroxides, oxides, carbonates and hydrogen carbonates. The table below shows some bases and their uses.
Common name
Common use
Sodium hydroxide
Caustic soda
Making soaps, cleaning ovens
Calcium hydroxide
Slaked lime
Reducing acidity in soil
Ammonium hydroxide
‘Cleaning’ ammonia
Cleaning products
Sodium hydrogen carbonate
Baking soda, bicarbonate of soda
Cooking
Sodium carbonate
Washing soda, soda ash
Washing powders
The pH scale The pH scale is used to describe how strong an acidic or basic substance is. At 25°C, the pH scale goes from 0 to 14. • Acidic substances have a pH less than 7, with strongly acidic substances being closer to pH 0. • Basic substances have a pH greater than 7, with strongly basic substances being closer to pH 14. • A neutral substance is neither acidic nor basic and has a pH of 7. The pH is a measure of how much free hydrogen is present in a solution. If there is a lot, then the pH is very low. If there is hardly any, then the pH is higher. Every time you take a step along the pH scale (say from pH 3 to pH 4) the hydrogen present decreases by a factor of 10. If you have 10 mL of a solution with a pH of 1 and add 90 mL of water, the new volume will be 100 mL and you will have diluted the solution by a factor of 10. The pH of the new solution will be 2.
4
5
6
7 pH
8
Prac 2 p. 96
Prac 3 p. 97
Prac 4 p. 98
Fig 3.4.7 Red cabbage contains a natural indicator that changes colour at pH 1, 4, 7, 10 and 13. Many other plants (e.g. beetroot, hydrangeas, hibiscus and rose) also produce dyes that can be used as indicators. Hydrangeas, for example, have blue flowers in acidic soil and pink flowers in alkaline soil.
9
10
11
12
13
14
dishwashing powder
3
Prac 1 p. 96
strong bases
detergents
2
vinegar orange juice wine coffee tap water
stomach acid
0 1
neutral
pure water blood sea water baking soda
strong acids
Worksheet 3.3 pH levels
3.4
Solutions of acids and bases can be either concentrated or dilute. In concentrated acid or base solutions, there is a high proportion of acid or base particles compared to water particles. In contrast, dilute solutions have only a few acid or base particles. Concentrated and strong are not the same thing. Neither are weak and dilute. Indeed, it is possible to have a dilute solution of strong acid or a concentrated solution of a weak acid. For example, if you add a single drop of sulfuric acid to an entire bucket of water, then you would have a very dilute solution of a strong acid.
Indicators Indicators are chemicals that are used to show the pH of a solution. Some indicators are not very precise and only tell us whether a solution is acidic or basic. Litmus is an indicator that is made from plants called lichens. Litmus is red in acidic solutions and blue in alkaline solutions and only gives you a broad range of possible pH values. Other indicators are far more precise. Universal indicator, for example, can undergo many colour changes and gives you a good estimation of the pH of a solution. You may have seen universal indicator used to check the pH of a swimming pool or spa.
Unit
Concentration
Fig 3.4.6 The pH scale (pH is short for ‘power of hydrogen’)
Fig 3.4.8 Citric acid has a pH less than 7. It turns blue litmus paper red.
91
Acids and bases Science
Clip
Antacids Heartburn and indigestion are caused when there is more acid in your stomach than the amount normally present for digestion. Antacids work by neutralising this excess acid. They contain a non-toxic base such as magnesium hydroxide. This reacts with the excess hydrochloric acid in your stomach to form salt and water … and relief!
pH 1
2
3
deep red
red
red
4
5
6
7
8
9
red orange yellow green green green orange blue
10
11
blue
blue violet
12
13
14
violet
Fig 3.4.9 The colours of universal indicator at each pH value
Neutralisation A neutralisation reaction is when an acid reacts with a base. Water is always a product in neutralisation reactions, as is a salt: acid base salt water
Neutralisation reactions are very common. Every time we brush our teeth, the toothpaste, which contains a base, neutralises the damaging acids left on our teeth by bacteria. Farmers can reverse the effects of acid rain on soil by adding the base calcium hydroxide. Indigestion caused by too much acid in the stomach can be relieved with antacids, which are just bases in solid or liquid form. Acids and hydroxides The general reaction equation for an acid combining with a hydroxide is:
92
HCl(aq)
nitric acid
HNO3(aq)
water
NaCl(aq)
H2O(l)
lithium hydroxide
lithium nitrate
water
LiNO3(aq)
H2O(l)
NaOH(aq)
LiOH(aq)
Acids and oxides The general reaction of an acid with an oxide is: Examples of acids reacting with solid oxides are: hydrochloric acid
Some examples of acids reacting with hydroxide solutions are: sodium chloride
that neutralises acids and cuts oil and lifts dirt, allowing it to be washed away.
acid oxide salt water
acid hydroxide salt water
hydrochloric sodium acid hydroxide
Fig 3.4.10 Most soaps, detergents and toothpastes contain a base
calcium calcium oxide chloride
water
2HCl(aq)
CaO(s)
CaCl2(aq)
H2O(l)
sulfuric acid
lithium lithium oxide sulfate
water
H2SO4(aq)
Li2O(s)
H2O(l)
Li2SO4(aq)
Acids and carbonates Like the last two neutralisation reactions that we’ve looked at, the reaction of an acid with a carbonate produces a salt and water. It also produces a third Prac 5 p. 98
Unit
3.4
Fig 3.4.11 Self-raising flour contains baking powder which releases carbon dioxide as it is baked. This causes scones, cakes, bread and muffins to rise.
product, carbon dioxide. The reaction of an acid with a hydrogen carbonate produces the same three things: acid carbonate salt water carbon dioxide acid hydrogen carbonate salt water carbon dioxide
Examples are: nitric acid
2HNO3(aq)
sodium sodium water carbon carbonate nitrate dioxide Na2CO3(s) 2NaNO3(aq) H2O(l) CO2(g)
hydrochloric ammonium ammonium water carbon acid carbonate chloride dioxide 2HCl(aq)
(NH4)2CO3(s) 2NH4Cl(aq) H2O(l) CO2(g)
sulfuric acid
sodium sodium carbon hydrogen sulfate water dioxide carbonate
H2SO4(aq) 2NaHCO3(s) Na2SO4(aq) 2H2O(l) 2CO2(g)
You can test for carbon dioxide by bubbling the gas through limewater. The limewater goes from clear to milky if carbon dioxide is present because of the formation of a calcium carbonate precipitate. Another test is that carbon dioxide will extinguish a lit match. Worksheet 3.2 Neutralisation
Fig 3.4.12 Hydrochloric acid reacting with
Science
magnesium to form a salt and hydrogen
Clip
Acids and metals
Water fit for a king Although gold is extremely unreactive, it can be dissolved by a mixture of concentrated nitric and hydrochloric acids. This mixture is called aqua regia, which is Latin for royal water because of its ability to dissolve gold.
When an acid reacts with a metal, hydrogen gas and a salt are produced. A salt is an ionic compound containing the ions left over after reaction. The general reaction can be written as: acid metal salt hydrogen
Technically, this type of reaction is not call a neutralisation reaction as metals are not bases and no water is formed. An example of an acid-metal reaction is:
hydrochloric magnesium magnesium hydrogen acid chloride 2HCl(aq)
Mg(s)
MgCl2(aq)
H2(g)
Most metals will react with acids. Some, like the Group I metals, react violently, while other metals, like lead, need hotter or more concentrated acid solutions to make them react. The table below shows the reactions between some acids and metals. You can test for the hydrogen gas given off by using the ‘pop’ test. A spark in the presence of H2 causes a popping sound as the gas combines with the O2 in air to form water. Prac 7 p. 99
Prac 6 p. 99
Acid
Metal
Reaction equation
Salt produced
Nitric acid
Calcium
2HNO3(aq) Ca(s) H2(g) Ca(NO3)2(aq)
Calcium nitrate
Sulfuric acid
Magnesium
H2SO4(aq) Mg(s) H2(g) MgSO4(aq)
Magnesium sulfate
Hydrochloric acid
Iron
2HCl(aq) Fe(s) FeCl2(aq) H2(g)
Iron(II) chloride
93
Acids and bases
3.4
QUESTIONS
Remembering 1 Define the terms acid and base. 2 List three properties each of acids and bases.
a aluminium
3 List two examples of:
b zinc
b strong acids
c iron
c weak acids
d lithium
d strong bases
12 Use word equations to describe the following reactions.
e weak bases
a hydrochloric acid iron(II) hydrogen carbonate b nitric acid silver hydroxide
4 State the likely pH of: a a strong acid
c sulfuric acid barium oxide
b a weak acid
d Use the formulas given throughout this chapter to write the reactions as chemical equations.
c pure water d a weak base
Applying
e a strong base
13 Identify the acid present in vinegar.
5 Name the colour of the following indicators at pH 8:
14 Identify an important use for an indicator.
a universal indicator
15 Identify three fruits containing citric acid.
b red litmus
16 Identify the salt produced by each of the following neutralisation reactions.
c blue litmus 6 Name the products when an acid reacts with a carbonate and when an acid reacts with a metal
a nitric acid strontium hydroxide b sulfuric acid copper carbonate c hydrochloric acid silver oxide
Understanding 7 Describe some everyday examples of neutralisation. 8 Describe how you could test for: a hydrogen gas
d nitric acid magnesium hydrogen carbonate 17 Identify which acid and base you could combine to make: a barium chloride b calcium nitrate
b carbon dioxide gas 9 a Name some examples of stinging creatures.
c iron(III) sulfate
b Explain what can be done to neutralise the sting.
Analysing
c Explain why vinegar would not relieve bee stings.
18 Distinguish between a dilute solution of nitric acid and a concentrated solution of nitric acid.
10 The normal pH in the mouth is about 6.5. The pH in the stomach is around 1 to 2. Explain why you get a burning sensation in the oesophagus, throat and mouth when you vomit. Reaction type acid hydroxide acid oxide acid carbonate acid metal
94
11 Use word equations to describe the reactions of the following metals with nitric acid:
Example (word equation and chemical formulae)
19 Discuss the importance of acids and bases in our daily lives. 20 Distinguish the reactants and products of the following reaction types to complete the table. Reactant(s)
Product(s)
Unit
Evaluating 22 Azaleas grow only in soil with pH less than 7.
3.4
a Propose which substance should be added to basic soil to lower its pH. Choose either water, an acid or a base. b Explain your answer. 23 A certain food is found to be slightly acidic. It contains either hydrochloric acid or acetic acid. Evaluate which acid it is more likely to contain.
3.4
21 You are given 10 mL each of two solutions. Solution A has a pH of 2. Solution B has a pH of 4. Calculate how much water you would have to add to solution A to make its pH the same as that of solution B. This is a hard one! N
INVESTIGATING
Use your available resources (for example, textbooks, encyclopaedias, internet) to investigate the following. 1 Find other acids that are used either in cooking or in medicine. These could include salicylic acid or tartaric acid. 2 Research shampoos and skin lotions that mention their pH and find the best pH for your skin and the best for your hair. Find if the age of a person and their type of skin or hair changes the pH that should be used. 3 Describe how pH levels of swimming pools are tested, why they change and how the pH is kept at 7.2 (the ‘best’ pH to control bacteria).
!
Safety Always use safety glasses in science classes when handling or heating chemicals that could spit or spill from their containers. If a foreign substance does get into your eye, flush it immediately with water while trying to keep your eye open to allow water to contact the affected area. An eyewash bottle should be available for this purpose. In other subjects such as technology, always use the protective eyewear provided to keep splinters and metal or plastic filings from entering your eye.
4 Find what anaphylactic shock is, how it is often related to bee or ant stings, what an Epi-pen is and how it is used. Present your information as an instruction leaflet on how, why and when to use the Epi-pen. L 5 a Sulfuric acid is one of the most important chemicals in the world. The sulfuric acid production of a country is said to be a good indicator of the state of its economy. Investigate what sulfuric acid is used for and analyse the reasons why sulfuric acid is a measure of the economy. b Create a flow chart showing how sulfuric acid goes from the factory and into products that we use in our everyday lives.
Fig 3.4.13 An eyewash bottle can be used to rinse foreign matter from the eye— make sure you know where it is in your science rooms.
95
Acids and bases
3.4
PRACTICAL ACTIVITIES
1 Common indicators Acid-base indicators are used to show the approximate pH of a solution.
Aim
2 Using the beakers, pour 2 cm of acid into one test tube, 2 cm of sodium hydroxide (base) into another test tube, and 2 cm of distilled water into the third test tube. 3 Add 3 drops of red litmus to each tube. Record your results. 4 Repeat steps 2 and 3 for the other indicators.
To determine the colour changes of common indicators
Equipment • • • • • • • •
0.1 M solutions of sodium hydroxide and hydrochloric acid distilled water three test tubes test tube rack three 100 mL beakers liquid red and blue litmus universal indicator methyl orange, methyl red, bromothymol blue, phenolphthalein • lab coat • safety glasses
Questions 1 Propose a reason why distilled water was used for this experiment, rather than tap water. 2 Compare your results with those shown in Figure 3.4.14. pH
indicator
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 bromothymol blue litmus
yellow
change
blue
red
change
blue
methyl orange red-orange change
yellow
colourless
change
phenolphthalein
Method
universal deep red indicator
1 Copy the results table below into your workbook. Fig 3.4.14
Colour in strong acid (hydrochloric acid)
pink
red orange yellow green blue violet
deep violet
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14
Colour in strong base (sodium hydroxide)
Colour in neutral solution (water)
Red litmus Blue litmus Universal indicator Methyl orange Methyl red Phenolphthalein
2 Universal indicator Aim To investigate the colour changes of universal indicator with increasing pH
Equipment • 0.1 M hydrochloric acid • 1.0 M sodium hydroxide
96
• distilled water • Pasteur pipette
• 10 mL measuring cylinder • waterproof felt-tip pen • 14 large test tubes
• universal indicator • lab coat • safety glasses
Method 1 Label your test tubes 1 to 14. 2 Place 10 mL of 0.1 M hydrochloric acid in test tube number 1. 3 Using a pipette, transfer 1 mL of this solution to the measuring cylinder. Add 9 mL of distilled water and pour the mixture into test tube number 2.
Unit
5 Add 10 mL of distilled water to tube number 7. 6 Add 10 mL of 1.0 M sodium hydroxide to tube number 14. 7 Using a pipette, remove 1 mL of this solution, add 9 mL of water and pour the mixture into tube 13. Continue this method down to tube number 8.
3 Natural indicators Aim To prepare and use natural indicators
Equipment • • • • • • • • • • • • • • • • • •
0.1 M hydrochloric acid 0.1 M sodium hydroxide distilled water pink or red flower petals beetroot juice tea bag three 100 mL beakers filter paper cut into strips Bunsen burner heat mat tripod gauze matches 3 test tubes test-tube rack Pasteur pipettes lab coat safety glasses
8 Add 3 drops of indicator to each tube and sketch the result. The number of the tube is approximately the same as the pH.
Questions 1 On your sketch, indicate which tubes contain strong acids, weak acids, strong bases and weak bases.
3.4
4 Using a pipette, transfer 1 mL of the solution in tube 2 to the measuring cylinder. Add 9 mL of water and pour the mixture into test tube number 4. Continue this method up to tube number 6.
2 Calculate the dilution factor between: a tubes 2 and 4 b tubes 10 and 11
6 Add about 10 drops of flower-petal water to each and record the colour of each solution. 7 Clean the test tubes and repeat steps 5 and 6, first using beetroot juice, then tea. 8 Carefully dry the freshly made indicator paper over a Bunsen burner flame, being careful not to burn it. 9 When dry, put a drop of acid on one end of each piece of paper, and a drop of base on the other end. Allow them to dry, then stick them in your book.
Questions 1 Propose a suitable conclusion for this experiment. 2 Identify which of the three indicators was best. Explain your choice. red flower petals
beaker 50 mL water
pipette
indicator Bunsen burner
test-tube rack
tripod
Method 1 Gently boil 50 mL of water in a beaker combined with the flower petals until the water becomes strongly coloured, then remove from heat.
heat-proof mat making flower petal indicator
hydrochloric sodium distilled acid chloride water
2 Place 20 mL of beetroot juice in another beaker. 3 Boil 50 mL of water in another beaker and add a tea bag. 4 Using tongs, dip a strip of filter paper into each solution and lay all the strips on paper towel to dry. 5 Place 2 cm of hydrochloric acid in a test tube, 2 cm of sodium hydroxide in a second test tube and 2 cm of distilled water in a third test tube.
Fig 3.4.15
3 How did the colours produced with the paper compare to the colours produced when using the liquid indicators? 4 Can you think of any other substances that might be natural indicators? If so, explain why you think they would work.
97
Acids and bases
4 Testing household solutions
test-tube rack
test tubes
Aim
Pasteur pipette
To test the pH of various household solutions
!
Safety 1 The chemicals in this Prac are toxic—avoid contact with eyes, skin and mouth. 2 Clean up spills immediately to prevent slip and trip hazards.
Equipment • • • • • • • • • •
test tubes test-tube rack Pasteur pipettes 2 watch-glasses blue and red litmus paper liquid universal indicator distilled water safety glasses lab coat a variety of household solutions including orange juice, soft drink, fresh and sour milk, vinegar. Solids may be used if dissolved in water first.
Method 1 Place 2 cm of solution into a test tube using a Pasteur pipette. 2 If the colour of the solution is quite strong, add distilled water until it is faint.
5 Acids and hydroxides
blue
red test solution
watch-glass
test solution universal indicator
test solution red litmus paper
test solution blue litmus paper
Fig 3.4.16
3 Pipette a small amount of the solution onto each of two watch-glasses. Add red litmus paper to one and blue litmus paper to the other. Record your results. 4 Add 3 drops of universal indicator to the test tube and record the pH of the solution. 5 Clean the equipment—repeat procedure for other solutions.
Questions 1 Arrange your solutions in a list from most acidic to least acidic. 2 A brick cleaner is marked as highly corrosive. Identify where you think it would go on your list. 3 Explain why there is a difference in pH between fresh and sour milk.
Method 1 Pour 25 ml of 0.1 M hydrochloric acid into the beaker.
Aim
2 Measure the pH using a digital pH meter or universal indicator.
To investigate the neutralisation of an acid using a hydroxide
3 Add 5 mL of 0.1 M sodium hydroxide.
Equipment
4 Re-measure the pH of the solution in the beaker.
• • • • • • • •
98
250 mL beaker 50 mL measuring cylinder 0.1 M hydrochloric acid (HCl) 0.1 M sodium hydroxide (NaOH) digital pH meter or universal indicator Pasteur pipette lab coat safety glasses
5 Repeat steps 3 and 4 until you have added 35 mL of the sodium hydroxide solution.
Questions 1 Identify at what point the solution was neutral. Explain why. 2 Construct a word equation to describe the reaction.
Unit
3.4
6 Acids and carbonates
5 Add nitric acid to the other two tubes, but don’t stopper. Record your observations. 6 Repeat steps 2–5 using hydrochloric acid.
Aim To observe the reaction of an acid with metal carbonates
Equipment • • • • • • • • • • • •
test tubes test-tube rack and stopper 100 mL beaker matches limewater solid samples of sodium hydrogen carbonate lithium carbonate sodium carbonate and ammonium carbonate spatula 0.1 M solutions of nitric and hydrochloric acids lab coat safety glasses
stopper
Test 1 If carbon dioxide is present, a lit match goes out.
match
Test 2 If carbon dioxide is present, limewater goes from clear to milky.
Fig 3.4.17
Method 1 You will be combining each acid with each solid. Draw up a suitable results table, similar to that used in Prac 1. 2 Add a small amount of each solid (about the tip of a spatula full) to four different test tubes. 3 Add 2 cm of nitric acid to the first tube and quickly stopper. Light a match and, removing the stopper quickly, put the lit match in the mouth of the tube. Record your observations.
Questions 1 Construct word equations for all reactions. 2 Identify the salt in each equation by circling it. 3 Draw a diagram to explain how you could set up this experiment so that the gas produces bubbles through a separate beaker of limewater as it is produced.
4 Add 2 cm of nitric acid to the second tube and quickly stopper. Remove the stopper and add a small amount of limewater. Re-stopper the tube, but don’t let too much gas build up. Record your observations.
7 Acids and metals Aim To observe the reaction of an acid with a metal
!
Safety 1 The chemicals in this Prac are corrosive—avoid contact with eyes, skin and mouth. 2 Clean up spills immediately to prevent slip and trip hazards.
Equipment • • • • • • • • • • •
test tubes with stoppers test-tube rack matches 100 mL beaker small pieces of aluminium magnesium zinc iron and tin 0.1 M solutions of hydrochloric, sulfuric and acetic acids lab coat safety glasses
>> 99
Acids and bases Method 1
i
Copy the results table into your book. Hydrochloric acid
Sulfuric acid
Acetic acid
Aluminium
Hold stopper on tube for 15 seconds.
Magnesium Zinc Iron
ii
Tin 2 Pour 2 cm of hydrochloric acid into each test tube. 3 Add one of the metals to the first test tube. If there is an obvious reaction, hold the stopper on the tube for about 15 seconds. Light a match and, removing the stopper quickly, hold the lit match to the mouth of the tube. Record your observations. 4 Repeat step 3 for the other metals. You do not have to repeat the gas test for every reaction.
A second person lights a match and holds it to the mouth of the tube as the stopper is removed. ‘pop’
iii
5 Repeat steps 2–4 for the other acids.
Questions 1 Construct word equations for the reactions of the metals with one of the acids tested. 2 For the other two acids, identify the salts produced in each reaction. 3 From the speed of the reaction with each metal, list the metals tested in order from most active to least active.
A ‘pop’ indicates hydrogen is present.
Fig 3.4.18
CHAPTER REVIEW Remembering 1 State the difference between a chemical change and a physical change and give two examples of each.
6 Name the following ions:
2 List the four indications that a chemical reaction has occurred and give examples.
a HCO3
3 List four polyatomic ions.
c S2
4 State formulae for:
d NH4
b I
a lithium hydroxide
7 State the difference between an acid and a base.
b barium sulfate
8 List the products and reactants in an acid-metal reaction and give an example.
c aluminium bromide
100
5 List two types of salts that are almost always soluble and two that are almost always insoluble.
Understanding 9 Scientists use a number of tools to make understanding science easier. Using examples from this chapter, explain how scientists have used the following tools.
20 Classify the following substances as acids or bases: a NaOH b Li2CO3 c HCl
a classification
d MgO
b models
e HNO3
c rules 10 Define the terms exothermic and endothermic and give examples of each. 11 Explain why burning a match is considered a spontaneous reaction even though it needs energy to start it.
21 If you have 10 mL of HCl acid solution at pH 1, calculate how much water you need to add to increase the pH to 2.
Evaluating 22 Deduce what charge the ions of these metals have:
12 Describe the observations you might make if a chemical reaction occurs.
a sodium
13 Define the word salt.
c aluminium
14 Explain how solubility rules help us to predict precipitation reactions. 15 Explain how a weak base like ammonia or carbonate can form hydroxide ions in solution.
Applying 16 Identify the reaction type for each of the following equations: a lithium chlorine lithium chloride b sulfuric acid barium carbonate barium sulfate carbon dioxide water 17 Identify what specific chemical is found in antacids. 18 Identify what colour the following indicators would be at pH 4: a blue litmus
b strontium 23 Deduce the products of the following neutralisation reactions: a sodium carbonate hydrochloric acid b calcium hydroxide nitric acid 24 You are given three unlabelled colourless solutions. You are told that one is pure water, one is a solution of hydrochloric acid and one is a solution of sodium hydroxide. You are also given some universal indicator which you can add to only one. Propose how you could identify each solution.
Creating 25 Design an experiment to show how the pH of an acid changes as it is diluted. Predict what results you’d expect to see. 26 Design an acid spill kit taking into account all possible safety risks involved.
b red litmus c universal indicator
Worksheet 3.4 Crossword
d methyl orange
Analysing
Worksheet 3.5 Sci-words
19 Classify the following salts as either soluble or insoluble: a AgCl b NaCl c AgNO3 d PbI2 e CuSO4 f HgCl2 g PbSO4 h BaSO4
101
4
Sense and control
Prescribed focus area The nature and practice of science
Key outcomes
Additional
Essentials
5.2, 5.8.4
• •
Humans have five senses.
•
Your senses are coordinated by the nervous system.
•
Your senses are triggered by specialised cells.
•
This stimulus will often trigger a response.
•
Hormones can also be released as a result of a reaction to a stimulus.
•
Nervous impulses are much quicker than hormones.
•
Different hormones trigger different responses.
•
Different hormones are released by different endocrine glands.
The development of new technologies has allowed humans to correct difficulties in hearing and seeing.
Unit
4.1
context
The eye
Sight
The eyes provide what many would regard as the most important of all our senses— sight. Take a look around you now. If your eyes are working normally, they just
transmitted focused colour images of several objects located different distances away to your brain and with virtually no effort!
Science
Clip
The structure of the eye allows it Fishy focusing to limit or maximise the amount of Most animals focus by light entering it, focus the light to using the ciliary form an image and then transmit muscles to change the the image to the brain. shape of the lens. Fish, however, focus These primary functions are images by moving carried out by: each lens backwards • the iris and pupil: these close and forwards, just like down to limit light when it is a camera. bright and dilate (open up) to maximise the light entering the eye in the dark • the cornea and lens: these bend the rays of light entering the eye so that the light focuses on the retina • the retina: this is where the image should form. Specialised cells in the retina then transmit the image to the brain.
Fig 4.1.1 The amount of light entering the eye is controlled by the coloured iris which opens and closes the pupil.
The rest of the eye is there basically to keep it in shape (vitreous humour, aqueous humour and sclerotic layer), to stop stray light from entering or reflecting around the eye (the choroid) and to change the shape of the lens to allow it to focus (suspensory ligaments and ciliary muscles).
Prac 1 p. 110
Prac 2 p. 111
iris retina
lens optic nerve
diaphragm
film shutter
convex lens
Fig 4.1.2 The eye focuses images in the retina. Although the image is upside down, the brain processes it so that we perceive it the correct way up. The operation of the eye acts very much like an old-fashioned film-loaded camera.
103
Sight Sclerotic layer: a tough, white-coloured protective layer (coloured pink here) that surrounds the eye and helps maintain its shape.
Vitreous humour: a jelly that helps maintain the shape of the eye. Choroid: a black layer that forms part of the inside lining of the eye behind the lens. It prevents light from reflecting all around the eye and nourishes it with blood and oxygen.
Conjunctiva: a clear, thin layer covering the front of the eye. An infection of the eye called conjunctivitis can occur here.
Retina: a layer containing over 100 million light-sensitive cells which transmit messages to the brain.
Cornea: a clear 'window' in the sclerotic layer and under the conjunctiva that allows light to enter the eye.
Yellow spot (fovea): a section of the retina directly behind the pupil that contains a large number of colour-sensitive cells. This is why you should look directly at an object to see it most clearly.
Pupil: hole in the centre of the iris. In the dark, the pupil opens up to let more light in. It is then said to be dilated. When very bright, the pupil shuts down to a small hole.
Blind spot: where blood vessels and the optic nerve join the eyeball. There are no light-sensitive cells to detect image information.
pupil
dilated (dim light)
Optic nerve: joins the eye to the brain. Passes information about the image to the brain for processing so that the image is seen the right way up.
bright light
Aqueous humour: a watery liquid that fills the space between the cornea and the lens. Helps maintain the shape of the eye.
Lens: a clear jelly-like ‘window’ that helps focus an image on the back surface of the eye.
Iris: just in front of the lens. Changes size to control the size of pupil. It also gives eyes their colour.
Suspensory ligaments: hold the lens in place. Ciliary muscles: change the shape of the lens to bring images into focus.
Fig 4.1.3 The human eye Worksheet 4.1 The eye Prac 3 p. 111
Eye protection A number of features help protect your eyes: • eyebrows and eyelashes help keep dust out • tear ducts produce tears to flush out any foreign particles • eyes are set back in depressions in our skulls called orbits. This gives them some protection from being knocked. Why two eyes? Two eyes allow you to judge distances more accurately since each eye sees a slightly different view. The brain combines the two images to create a three-dimensional view that gives us more information about how far away an object is. This is known as binocular vision.
104
Colour vision The retina contains special cells called rods and cones. Rods are more sensitive than cones, but respond only to light and dark, helping us to detect shapes. Cones need more light to be activated and come in three types which detect the colours red, blue and green. Only the rods are activated at night or in the dark and so you see everything in shades of grey without much colour. If red light falls on the retina, ‘red’ cones are activated. With purple light, both red and blue cones are activated. Both rods and cones send messages to the brain to help you see. Some people lack some types of cone cells and cannot easily differentiate between some colours, most notably red and green. This condition is known as red/green colour blindness. It is an inherited disease and affects about 1 in 15 males and 1 in 1000 females.
Clip
Fig 4.1.4 A scanning electron microscope photograph of rods and cones
Fig 4.1.5 A colour blindness test. What do you see?
Lots of colours cannot be seen by humans. Infra-red (IR) and ultraviolet (UV) are two colours, for example, that are impossible for us to see. We feel IR, however, as heat and UV is known to damage our skin. Special cameras can detect IR and make it possible to detect sources of heat (such as people lost in the bush). Likewise, some dyes, fabrics and detergents can convert ‘invisible’ UV into a strange violet-white glow that can be seen.
4.1
What colours can’t you see?
Unit
Science
Animal eyes The eyes of different animals are adapted to increase their chances of survival by detecting predators or food more easily. A rabbit’s eyes, for example, are positioned on the sides of its head so that it can see most of its surroundings without moving its head and attracting attention. Other animals that are preyed on also have their eyes facing sideways: mice, rats, sheep and small birds all have good all-round vision to protect them from attack. Predators tend to have forward-facing eyes: this gives them excellent eyesight and helps them judge distances accurately when swooping on prey. The eagle, for example, has excellent eyesight and can detect a rabbit from three kilometres away! Fig 4.1.7 Many insects have multiple lenses to provide an all-round view.
Fig 4.1.6 The forward-facing eyes of the owl give it good binocular vision, allowing it to judge distance as it swoops on prey.
Fig 4.1.8 Spiders have four, six or eight eyes while scorpions have between six and twelve.
105
Sight Science
Clip
Wobbly chook heads
Science
Clip
The largest eyes in the world The giant squid can grow up to 14 metres long and has eyes as large as soccer balls!
Fig 4.1.9 A rabbit can see both sides at once.
Fig 4.1.10 A chicken must continually
This is because the rabbit’s eyes are positioned on the sides of its head so that it can see most of its surroundings without moving its head and attracting attention.
move its head to obtain a complete view of its surroundings.
Do animals see in colour? Many animals see in colour, but not the same as we do—it depends on the number and type of cones they have. Some animals, like bees, have extra types of cones in their eyes. This allows them to see colours that we can’t. Birds that are active in Science daytime are able to see colours, but those that are active at night cannot. Cats, dogs and Cats’ eyes rabbits are thought to have Cats’ eyes are unusual. They have a very poor colour vision, and see slit-shaped pupil which opens and closes much faster than a round virtually in black and white. one, allowing their eyes to adjust to Sheep and horses have good changes in light intensity more colour vision. Insects can see quickly. Cats’ eyes shine at night colours, but not red. Some because of a mirrored lining at the insects can see ultraviolet light, very back of the eye (called a tapetum). It reflects light through which is normally invisible to the rods and cones a second time, humans.
Clip
giving the cat more chance of seeing objects even in very dim conditions. It is because of this reflectivity that roads have ‘cats eyes’ installed to show lane markings at night.
Eye focused on a distant object
Eye defects The job of the lens is to bend light so that an image is formed on the retina. It does this by using the ciliary muscles to change its shape. When these muscles relax, they pull on the suspensory ligaments and stretch the lens, making it thinner so it bends light less. When the ciliary muscles contract, they pull less and allow the lens to fatten up. Fatter lenses bend light more, which is what’s required when looking at close objects. The ability of your eyes to change lens shape and focus at different distances is called accommodation. In some people, the lens becomes less elastic and is unable to become thin enough or fat enough to focus images at exactly the right position in the eye. This can result in one of three conditions:
circular fibres relaxed
image on retina
focuses on close and distant objects: the ciliary muscles in each eye stretch and relax the lens making it thinner and thicker. This changes the amount of bending of light that occurs as it passes through the lens.
106
Eye focused on a near object
circular fibres contracted
image on retina
meridional fibres relaxed
meridional fibres relaxed
Fig 4.1.11 This is how the eye
Chickens wobble their heads around frequently to obtain better vision. Their eyes are on opposite sides of their heads and to judge distance accurately they need to see an object with both eyes. The only way they can do this is to quickly move their heads to view the object with one eye, then the other!
light from close object
light from distant suspensory object ligaments taut
suspensory ligaments slack light bent little by thin lens
light bent more by fatter lens
concave lens distant object
4.1
distant object
the bottom for reading, and concave at the top for distance vision). As well as spectacles, contact lenses can be used to correct vision. Soft plastic lenses are available which are more comfortable than hard glass lenses, but they are not suitable for everyone. Wearers of contact lenses must ensure that their eyes still receive enough oxygen. Modern plastic contact lenses are gas permeable, allowing some oxygen to pass through to the cornea. The eye may react to a lack of oxygen by growing additional blood vessels to supply more oxygen via the bloodstream, but the extra vessels can cause irritation and other problems.
Unit
• short-sightedness—people can focus on objects a short distance away, but not on distant objects. This condition is known as myopia.
Prac 4 p. 111
Fig 4.1.12 Short-sightedness (myopia) can be corrected by wearing concave lenses that move the focus point of the image back onto the retina.
• long-sightedness—people can see long distances away, but cannot focus on close-up objects. Another name for long-sightedness is hyperopia.
close object
convex lens close object
Fig 4.1.14 Contact lenses can be used to correct impaired eyesight.
Science Science Fig 4.1.13 Long-sightedness or hyperopia, can be corrected by wearing convex lenses which bend light more so the focus point of the image is brought forward onto the retina.
• presbyopia—as people age, they often lose the ability to focus at short distances, particularly when reading. Some people have trouble focusing at both short and long distances, and may use bifocal lenses, which have two types of lens in one (e.g. convex at
Clip
Bifocal contacts The first bifocal contact lenses were invented by Queensland optical research scientist Stephen Newman in 1992.
Clip
Artificial eyes Medical researchers are working on an artificial eye that they hope may restore sight to blind people. The artificial eye implants directly into the optic nerve.
107
Sight Laser surgery A more recent development in eyesight correction is laser surgery. The two main methods are PRK (photoreactive keratotomy) and Lasik (laser in situ keratomileusis). • PRK involves removing a layer of cells from the surface of the cornea and remodelling the shape of the cornea using a laser. • Lasik treatment involves a thin flap of the cornea being lifted up, but not removed, and a laser is used to reshape the cornea before the flap is replaced over the laser-treated area. Patients undergoing Lasik feel less discomfort and healing time is reduced, while with PRK, there is more cornea to work with.
Science
Clip
Monovision Monovision does not mean having one eye! The term refers to vision correction in which a person who is unable to focus at both short and long distances wears a different strength contact lens in each eye. With time, the brain learns which lens to use depending on the distance of the object being viewed.
Fig 4.1.15 The Lasik procedure being used to correct myopia
QUESTIONS
4.1
7 Explain what causes colour blindness.
Remembering 1 Specify where in the eye: a most of the focusing of light occurs
9 Clarify the purpose of blinking.
b the amount of light is controlled
Applying
c the image should be formed 2 Specify whether cones or rods detect:
10 Identify examples of animals that have their eyes:
a light or dark
a facing forward
b colour
b facing to the sides
3 If you only had one eye, state what you would not be able to do as well. 4 List ways in which the eye is naturally protected. 5 State the common names for hyperopia and myopia.
Understanding 6 Copy and complete the table below to summarise each part of the eye described in Unit 4.1. The first entry has been done for you. Part Conjunctiva
108
8 There are no light-sensitive cells in the blind spot. Explain why.
Description/function Thin, clear layer covering front of eye
11 Robert can drive safely without glasses, but has trouble reading the street directory without them. Identify the condition Robert may have. 12 Aunt Agnes always had good sight. She’s now 50 and needs to get reading glasses. Identify what condition she has.
Analysing 13 Classify the animals in question as prey or predator. 14 Compare the eye and the camera, listing similarities and differences. 15 Distinguish between Lasik and PRK surgery.
Unit
Creating
16 Propose a reason why:
20 Use Word or PowerPoint to construct an eye chart. Use your chart (on screen or a printed version) to test the sight of different people.
a it is difficult to see when you walk from a very bright room into a dark one b you squint when suddenly exposed to a bright light c the choroid is black d flies are very hard to swat and kill 17 How good is an owl’s colour vision? Justify your answer. 18 Justify the need for humans to have two eyes. 19 Propose a reason why it is important for insects and animals that are active during daytime to see colours.
4.1
Evaluating
21 The approximate angle of vision for a person is shown in Figure 4.1.16. Construct similar diagrams showing the approximate angle of vision for: a an owl b a rabbit c a fly
angle of vision
Fig 4.1.16
4.1
INVESTIGATING
Investigate your available resources (for example, textbooks, encyclopaedias, internet) to answer the following questions. 1 a Find out about other eye defects such as glaucoma or cataracts, and their possible treatments. b Produce a brochure for a doctor’s waiting room that outlines the defect—its signs, symptoms, and treatments available. 2 Investigate the Braille system used by blind people to read.
e -xploring To assist with the following activities, a list of web destinations can be found on Science Focus 3 Second Edition Student Lounge. • Watch an online dissection of a cow’s eye. • Explore further information about the eye and perform an interactive labelling of the eye’s structure.
Fig 4.1.17 The feel of the bumps allows blind people to read.
109
Sight
PRACTICAL ACTIVITIES
4.1
1 Eye tests
-
Aim To construct a mini eye chart and to find your eye’s blind spot
Equipment
Fig 4.1.19
3 Gradually bring the textbook closer and note when the dot disappears. This happens when light from the dot falls on your right eye’s blind spot.
• eye charts
Method
4 Repeat with your left eye open and right eye closed.
Part A: Your yellow spot 1 Use the eye chart shown in Figure 4.1.18, or one which is provided.
Part C: Distance perception 1 Have a partner hold a pen upright at arm’s length as shown. 2 With one eye shut, try to vertically line up another pen to touch your partner’s pen. This may take several attempts.
R N F S K R
N
F
S
K
K
S
F
N
R
K S F N R
Fig 4.1.18
2 Hold the chart about 20 cm from your right eye while shutting your left eye. 3 Stare at the dot in the middle of the chart. 4 Note which letters you can make out clearly (do not memorise them). 5 Repeat, this time looking with your left eye while shutting your right. Part B: Your blind spot 1 Hold the textbook at arm’s length and look directly at Figure 4.1.19. 2 Shut your left eye, and stare at the cross with your right eye.
110
Fig 4.1.20
3 Repeat steps 1 and 2 with the other eye shut. 4 Try again with both eyes open.
Questions 1 a State the number of letters you could see in part A. b Calculate a class average. N 2 a At what distance from your eye did the dot disappear (when its light fell on your blind spot)? b Compare this with others in your class. 3 Evaluate your ability to judge distance with one eye only, as compared to two eyes.
Unit
2 Persistence of vision
1 Explain what is meant by persistence of vision as it applies to this activity.
Aim To investigate the persistence of images formed by the eye
3 Compare this activity to movies at the cinema (which some people refer to as ‘the flicks’).
Equipment • • • • •
2 Describe the difference caused by varying the speed of rotation.
4.1
Questions
wooden rod (e.g. bamboo skewer) stiff white cardboard pencils sticky tape scissors
side 1
side 2
rod
Method 1 Construct the apparatus shown in Figure 4.1.21. 2 Look at the card and spin it about the central rod. 3 Study the effect of various speeds of rotation. Fig 4.1.21
drawing of cage
drawing of bird
2 Sketch the eye, labelling any parts you can identify.
3 Eye dissection Aim To identify the main structures of the eye
Equipment • • • • •
a cow’s eye sharp fine scissors paper towel dissection board newspaper
Method 1 Place the eye on a dissection board on some newspaper and carefully trim any fat or muscle away from the outside of the eye.
4 Lens and retina Aim To replicate what is happening in the lens and retina
Equipment • convex lens • sheet of paper
Method 1 Hold the convex lens up to the window. 2 Hold a sheet of paper up so that the lens is between the window and the paper.
3 Carefully cut a hole in the back of the eye near the optic nerve. 4 Hold the eye so it ‘looks’ at a window, and look through the hole you cut at the back of the eye. What do you see? 5 Use scissors to remove the lens from the front of the eye. Describe the shape of the lens. Place it above a scrap of newspaper containing small text. Press down on the lens. How does this affect the view of the newspaper?
Questions 1 Describe the appearance and consistency of each part of the eye. 2 Determine which way up the image appeared when you looked through the rear of the eye. 3 Explain why the lens is flexible.
3 Move the sheet of paper slowly in and out until a focused image is formed on the paper. 4 If possible, repeat with lenses of different thicknesses.
Questions 1 State whether the image was the right-way-up or upside-down. 2 Identify what in this experiment was modelled by: a the lens b the retina 3 Describe what happened when lenses of different thicknesses were used.
111
Unit
4.2
Hearing
context
The ears work by detecting sound waves. They also sense the position of your head, helping you to keep balance. The ears are really two sense organs in one.
Ear problems
Fig 4.2.1 In sport, players don’t want to take their eyes off the ball and so often rely on sound to help them decide who to pass the ball to.
Sound Sound travels through air at as a wave of vibrating air particles at about 340 metres per second. When the sound wave reaches your ears the vibrations travel through the auditory canal and cause your eardrum to vibrate. The various parts of the ear then convert the sound energy into electrical impulses, which are sent via nerves to your brain for interpretation.
Damage to the cochlea Prolonged exposure to loud sounds flattens the hairs of the cochlea. Some hairs are flattened permanently and destroyed. Repeated loud noise will destroy more hairs, leading to more permanent deafness. Some flattened hairs do recover but this takes time. Partial deafness and ringing in the ears can result from such damage. As these hairs recover so does the hearing, but not completely. Any ringing in your ears after exposure to loud noise means that some permanent damage has been done to your hearing. Lots of people experience muffled hearing and ringing ears after leaving an area where there has been loud noise, like a rock concert or nightclub. This is evidence that they may have damaged their hearing. The damage will, however, get worse each time it happens. For this reason many old rock stars are near-deaf.
Coo-eee
The ear The ear consists of three main sections: the outer, middle and inner ear. The outer and middle ear are filled with air while the inner ear is filled with fluid. right ear detects sound first
Why two ears? Two ears help you determine the direction of a sound. If a sound reaches both ears at the same Prac 1 p. 116 time then your brain places the source of the sound directly in front of, behind or above you. If a sound reaches the left ear before the right ear then the brain places the source of the sound to your left.
112
Fig 4.2.2 Two ears help you locate the direction of a sound.
Unit
Oval window: this is what the stirrup vibrates against, causing vibrations to pass into the cochlea. The oval window marks the boundary between the middle and inner ear.
Semi-circular canals: contain three sections, each perpendicular to the others. These contain fluid which moves when you do. Nerves send messages to the brain, which in turn signals muscles to help us keep our balance. to brain
Pinna: the visible part of the ear. Helps to collect sounds and funnel them into the auditory canal.
Auditory canal (ear canal): connects the outer ear with the eardrum.
Auditory nerves: send messages to the brain, which are then interpreted as sounds.
Eardrum (tympanic membrane): made of a thin sheet of muscle and skin that vibrates in response to sounds. The eardrum is the start of the middle ear.
outer ear
middle ear
Cochlea: coiled, fluidfilled tube. This fluid passes vibrations to a layer of tiny hairs connected to auditory nerves.
4.2
Hammer, anvil and stirrup (the ossicles): a group of three tiny bones, known as the ossicles. By the time the sound reaches the stirrup, it has been amplified to about 30 times louder than at the eardrum.
Science
Clip
Ears in your armpit! A grasshopper’s ears are not on its head, but on each side of its body, below its wings.
Eustachian tube: connected to the throat. It helps maintain pressure between the middle and inner ear.
inner ear
!
Fig 4.2.3 The human ear Worksheet 4.2 The ear
Tinnitus is a condition in which a person hears a permanent ringing in their ears even when there is no sound. Tinnitus can be caused by exposure to loud sounds over a long period of time. Damage to the middle ear A blow to the head or a very loud sound such as an explosion will rip the eardrum. A small tear in the eardrum may heal itself, but usually leaves permanent scarring. This interferes with its vibration, so the hearing impairment is also permanent. Damage to the nerves cannot be repaired at all and results in permanent hearing loss. Wax is produced in the auditory canal to help prevent entry of dust and bacteria, but a build-up of wax can stop the eardrum from vibrating correctly. This causes temporary deafness but can be easily fixed by a doctor flushing out the excess wax with warm water. Deafness or partial deafness can also occur due to the ossicles being jammed together due to exposure to loud sounds or infection. This jamming stops vibrations from being passed on to the cochlea.
Safety The eardrum is delicate and can easily be broken. Sharp, loud noises such as explosions can rip it, as can things inserted into the auditory canal. Never put anything smaller than your little finger into the auditory canal. Even cotton buds are too small. They can easily reach the eardrum and rip it.
Science
Clip
Popping ears Sometimes when you climb to a higher altitude, you experience an uncomfortable ‘blocked ear’ sensation. This is caused by a pressure difference between the outer and middle ear. When climbing (e.g. in an aircraft), the outer ear responds quickly to the falling pressure, but the middle ear lags behind and is at a higher pressure. The resulting pressure difference causes the blocked feeling. Eventually the Eustachian tube opens and allows air to rush out of the middle ear so pressure on both sides of the eardrum is again equal. Some people experience a ‘popping’ sensation when this happens. When descending, air rushes into the middle ear to increase pressure to the same level as that in the outer ear. If the Eustachian tube gets blocked due to an infection such as a cold, pressure differences will once again give that ‘blocked ear’ sensation.
113
Hearing transmitter coil
mastoid bone
microphone receiver-stimulator cochlea behind-the-ear speech processor
body worn speech processor
auditory nerve
electrode array
Fig 4.2.4 A bionic ear takes over the function of the ear. The wearer needs to then learn the identity of each sound.
Fig 4.2.5 Ears should be protected when exposed to loud sounds.
Decibels (dB) 160 150
Harmful
140
Dangerous
Hearing aids Some people are born with ear defects that reduce the amount of vibration reaching the auditory nerves. Hearing aids work by amplifying sounds and transmitting them to the auditory canal. If the cochlea is damaged, however, hearing aids may not be as effective, since unclear signals to the brain are produced, even if they are amplified. An Australian invention known as the cochlear implant or bionic ear can restore a degree of hearing to some people. The bionic ear replaces a nonfunctioning inner ear. It consists of a microphone that sends information to a small speech processor worn behind the ear or attached to a belt.
jumbo jet on take-off
130 120
threshold of pain
110
loud thunderclap
100 90 80
train lawn mower
Loud
70 Worksheet 4.3 Hearing
60
blah blah blah
normal conversation
Normal
50
People who operate noisy machinery, mow the lawn or use power tools are exposed to loud noises for a prolonged time. Small earplugs or earmuffs protect the ears by reducing the noises to more manageable and safe levels.
Quiet
Ear protection
Prac 2 p. 116
114
whisper
20 10 0
quietest sound that can be heard
used to work out which sounds will harm your hearing.
Clip
White noise is constant background noise such as the hum of a machine. It reduces the apparent noise levels of all other sounds and so is often used to ‘deaden’ offensive sounds.
30
Fig 4.2.6 Sound levels are measured in decibels. This chart can be
Science
White noise
40
Prac 3 p. 116
Unit
QUESTIONS
Remembering 1 State two facts about how sound travels. 2 Name: a the part of the ear that is filled with fluid b the three small bones in the middle ear c the part of the ear that has hairs in it that vibrate with the sound
Analysing 13 In young children, the Eustachian tube is almost horizontal. In the adult ear shown in Figure 4.2.3, this tube is nearly vertical. Use these facts to analyse why young children are more prone to middle-ear infections.
Evaluating 14 Propose a reason why:
3 State where most sound amplification happens in the ear.
a an ear infection may upset your sense of balance
4 Name the unit used to measure the loudness of sound.
b there are three semicircular canals instead of just one
5 State the sound level in decibels at which sound becomes hazardous to your hearing.
c some airlines sometimes offer lollies to travellers during take-off and landing
Understanding 6 Explain why it is dangerous to clean out your ears with cotton buds. 7 Describe how ear wax may be: a useful b a hindrance 8 Describe two ways damage can be done to your hearing. 9 Explain what happens to your hearing after a loud concert.
d animals such as rabbits, deer and zebras have large ears 15 Sounds from directly in front arrive at both ears at the same time and so do sounds from directly behind. Propose how you know which direction the sound is coming from. 16 Caleb and Sarah both have hearing difficulties. Speaking louder to Caleb makes it easier for him to hear but it makes no difference to Sarah’s hearing. Propose a reason why. 17 Evaluate whether two ears are more valuable than one for survival.
Applying
Creating
10 A sound arrives at your right ear just before it reaches the left. Identify which direction the sound came from.
18 Construct a model ear to demonstrate how the ear works, labelling the important parts. Demonstrate the path of sound energy through the ear and the energy transformations that occur.
11 Identify three common situations in which some form of ear protection is advisable. 12 Use Figure 4.2.6 to identify some sounds that can be: a dangerous b harmful c quiet
4.2
4.2
4.2
19 a Design an experiment in which a sound level meter measures the sound levels produced by different MP3 players. Record your results in an appropriate table and column graph. b Evaluate your results to determine whether the levels at which you regularly listen are harmful to your hearing. N
INVESTIGATING
Investigate your available resources (for example, textbook, encyclopaedias, internet) to answer the following questions. 1 Describe how a stethoscope works. 2 Find out more about how the bionic ear works. Illustrate the important parts of the bionic ear to show how it functions. Who was the first recipient of a bionic ear?
e –xploring To find out more about the ear, a list of web destinations can be found on Science Focus 3 Second Edition Student Lounge.
115
Hearing
4.2
PRACTICAL ACTIVITIES
1 Hearing tests 1
?
Method DYO
Aim To examine the directional ability of our ears in detecting sounds
Equipment • blindfold • tape measure
Ask one of your group to sit down and blindfold them. Ensure they are facing straight ahead. Design your own experiment to test how well the person can detect a sound coming from various directions. Test what effect changing distance and blocking one ear have on your results.
Questions 1 Describe how the distance of the sound source affects results. 2 Describe what happens if the person covers one ear. 3 Evaluate the need for two ears.
2 Modelling hearing difficulties The ability to hear high-frequency sounds gets poorer as you age. Likewise, if you were born with a hearing difficulty, it is probably the high-frequency sounds that are the most difficult for you. In speech, the high-frequency sounds are the hissing sounds like s, sh, c, ch, t, f and ph.
Aim To model a hearing difficulty
Equipment • a grey-lead pencil • a book that you are allowed to write in with a pencil • eraser
3 Measuring decibels Aim To measure the sound level of various sounds around the school
Equipment • sound level meter
Method Each sound level meter operates slightly differently. Acquaint yourself with how to measure and read the sound level.
116
Method 1 Select any two paragraphs in a book. 2 Use the grey-lead pencil to cross out every s, sh, c, ch, t, f and ph in the paragraphs. 3 Read out aloud what is left in the paragraphs to a classmate.
Questions 1 Describe how easy it was to understand your classmate when they read their paragraphs. 2 People with hearing difficulties often speak a little differently too. Explain why. 3 Elderly people and people with hearing difficulties generally find men easier to understand than women. Propose a reason why.
1 Use the meter to measure at least five different sounds around the school. For example, you might measure the sound levels of two people chatting and then arguing, a noisy classroom, and traffic on the road outside the school. 2 For each measurement, estimate your distance from the subject.
Questions 1 Use a table to record your sound level measurements. 2 Use the table and Figure 4.2.6 to classify each of the sounds as harmful, dangerous, loud, normal or quiet.
Unit
4.3
context
Smell, taste and touch
It is said that we have five senses. The eyes give you your sense of sight, the ear gives you hearing, the nose your sense of smell, the tongue your taste and the skin gives you the ability to feel things. This is the sense of touch.
Smell You detect a smell because a few tiny chemical particles enter your nose and dissolve in its moist lining. Considering some of the nasty smells you detect each day—this may not be a pleasant thought! The dissolved substance triggers nearby nerve cells in the upper part of the nasal cavity, called olfactory cells. Electrical impulses in the olfactory nerve send messages to the brain so you can smell the substance. The typical human nose can detect around 2000 smells, and can be trained to detect up to 10 000. Fig 4.3.2 Smell and taste allow you to enjoy food while touch helps you avoid pain and getting burnt.
brain
tiny particles from pizza
moist lining
mmmmm!
nerve cell (olfactory cell) pizza
Fig 4.3.1 You smell a pizza because a few of its particles have been dissolved in your nose. You smell sewage for the same reason! Fig 4.3.3 Sneezing is a reflex action that removes irritating dust or other foreign particles from the nasal passages. A sneeze can travel at 160 kilometres per hour, allowing it to spread throughout a room.
117
Smell, taste and touch
Taste The surface of your tongue is covered with thousands of bumps, called papillae. More than 10 000 taste buds are embedded between the papillae. Humans can detect five primary taste sensations: sweet, sour, salty, bitter and umami (umami is the savoury taste of glutamate found in processed meats, cheeses and monosodium glutamate, commonly known as MSG). Each primary taste sensation has its own type of taste bud that detects it. Saliva in your mouth must first dissolve samples of food so that the taste buds can detect them and send
Fig 4.3.4 Scanning electron microscope image of taste buds (red) surrounded by papillae (pink)
messages to the brain. Your taste buds also provide information on the intensity and pleasantness or Prac 1 Prac 2 unpleasantness of taste. Although p. 122 p. 123 all areas of the tongue are able to detect all taste sensations, some areas are more sensitive to certain tastes. Flavour As you eat, your senses of smell and taste work together to detect flavour. As much as 80 per cent of what you perceive as flavour is actually smell. Flavour is largely the smell of gases emitted from food that has just passed out of your mouth. Your sense of smell is not as good as usual, for example, when you have a blocked nose. That’s why food seems less tasty when you have a cold. Likewise, pinching your nose will lessen the flavour of the food in your mouth, making it more tolerable. The tongue is most sensitive at temperatures between 20°C and 30°C. Sweet and sour tastes are increased at higher temperatures, and bitter and sour tastes increase at lower temperatures.
Science
Clip
sou
sweet
r
bitter
sour
118
Clip
Artificial flavouring Many processed foods have artificial flavours. Although made in laboratories, they are often identical to those found in nature. If the banana flavouring amyl acetate is distilled from bananas, it is classified as a natural flavouring. Amyl acetate is also made in the laboratory by mixing vinegar with amyl alcohol, using sulfuric acid as a catalyst. Although exactly the same flavouring, it is now classified as artificial flavouring.
Touch
Animal tongues The giant anteater’s tongue may reach lengths of over 60 cm. Dogs and cats do not sweat through their skin and only sweat from their footpads and nose. They lose water by panting rather than sweating. A dog can rapid pant at rates of up to 200 times per minute— this allows heat to be removed from the dog’s body as moisture evaporates from the tongue.
Science
sweet and salty
Fig 4.3.5 The entire surface of your tongue can detect all five primary taste sensations but some parts are more sensitive to particular tastes than others. This tongue map is what food and wine tasters use to identify the components in them.
The skin might not look like an organ such as a heart or kidney, but it comprises the largest organ in the body. It contains millions of nerve endings that send information about touch, pain, pressure and temperature to the brain. In humans, the touch receptors are more concentrated in the face, tongue, lips, fingertips and toes. Body hair also plays an important role in our ability to sense touch. A large number of receptors are found in the skin at the base of hair follicles. Below the top protective layer of dead skin cells is a ‘living’ layer of skin. It has different nerve receptors located at varying depths. Thermoreceptors respond to heat and cold, and there are about four times as many heat receptors as cold receptors. Pain receptors are located throughout the skin and can experience prickling pain (fast pain) or burning and aching pain (slow pain). The sebaceous glands produce oil that helps keep the skin soft and stops it cracking. The sweat glands produce
Clip
layer of dead skin
hair
Smelling without a nose
sebaceous gland light contact receptor
pore
The male fruit fly can detect smells emitted by a female fruit fly using chemically sensitive hairs on its front legs and its antennae.
epidermis
4.3
pain receptor
Unit
Science
Science
dermis
Clip
The biggest organ
sweat gland
The average human adult has a 290 g heart, 1090 g of lungs, 1330 g of brain and 1560 g of liver. At nearly 11 kg, however (10 886 g to be exact), the skin is by far the largest organ. Over an average lifetime, a human will shed roughly 18 kg of dead skin!
fattty layer pressure receptor
cold receptor
hair movement
heat receptor
Fig 4.3.6 A cross-section of human skin
sweat, which on reaching the surface, removes heat from the body when it evaporates. Worksheet 4.4 The skin
Prac 3 p. 123
Skin conditions Many conditions can affect the skin. One of the most common is acne, which causes pimples to appear, often on the face. Pimples tend to occur more frequently during puberty, when the skin secretes more oil than usual from the sebaceous gland into a hair follicle. Dead skin cells or dirt can block the follicle. If it becomes infected with bacteria, it can become swollen with pus. Contrary to popular opinion, diet has little to do with pimples. Apart from puberty, other possible causes include stress, medications and some cosmetics. Pimples may be treated with pharmaceutical creams and lotions, and by gently washing the affected area. Over-washing and harsh soaps should be avoided. Skin cancers The major cause of skin cancer is exposure to ultraviolet or UV radiation. Unfortunately, Australia leads the world in skin cancer rates. Sunbaking is the deliberate exposure of your skin to UV radiation and is very
Fig 4.3.7 Pimples happen when dirt or dead skin cells block a hair follicle, resulting in an infection and pus.
dangerous. A suntan is a sign that damage has been done to the skin. The skin’s reaction is to produce more melanin and go darker, giving you a tan. Getting sunburnt is even worse as the damage is more severe and more immediate. Today most of us cover up, using hats and protective clothing and swimwear, or stay in the shade and use sunscreens to reduce the damage caused by UV rays. UV levels from the Sun are most dangerous between 11 am and 2 pm during summer. Whatever the time of day, even on cloudy days, UV rays are always present and damaging. Go to
Science Focus 4 Unit 4.5
119
Smell, taste and touch
Fig 4.3.8 Dermatitis is a condition in which the skin becomes itchy and swollen and exhibits a red rash. It may be caused by exposure to certain chemicals. Eczema is a common type of dermatitis.
Fig 4.3.9 Warts are rough, raised lumps that grow on the surface of
Fig 4.3.10 Moles are raised, dark spots that are normally harmless,
Fig 4.3.11 Freckles are darker spots caused by a pigment called melanin in the skin cells. Darker-skinned people have more melanin in their skin than those who are lighter-skinned. Freckles are normally harmless, but any change in the size or shape of one should be referred to a doctor. If freckles change shape, then see a doctor.
but have the potential to develop into skin cancer. Again, any changes to a mole should be referred to a doctor. Moles have the potential to develop into skin cancer and so any change should be investigated by a doctor.
Basal cell carcinoma (BCC): the most common form of skin cancer and the least dangerous. Appears as a red, flaky or waxy bump on the skin. Provided it is treated as soon as possible, it rarely spreads to other parts of the body.
the skin. They are caused by a virus, and can spread if scratched open to other parts of the body. Doctors can freeze off warts with liquid nitrogen. Chemical treatments are also available.
Squamous cell carcinoma (SCC): is not as common but is more serious. Appears as red scaly sores, and can spread to other parts of the body.
Fig 4.3.12 The three most common types of skin cancer Worksheet 4.5 Codes
120
Melanoma: is the least common and most deadly form of skin cancer. New spots, or old spots that change colour or size, or itch or bleed, may be a sign of a melanoma, and should be checked immediately.
Unit
QUESTIONS
Remembering 1 a List the five different taste sensations. b Recall the different sense organs and what they do by copying and completing the following table. Sense
Sense organ
Sight
6 Explain how you could more easily eat a food or vegetable you don’t like.
4.3
4.3
7 Explain the purpose of the fatty layer of the skin. 8 Evaporation of sweat from the skin helps remove heat from the body. Describe how. 9 Outline what you can do to be ‘sunsmart’.
Applying The ear
Smell The tongue 2 State whether the following are true or false.
10 Phoebe picks up a hot Bunsen burner tripod and drops it immediately. Identify the sense that gave her the most messages. 11 Identify a food that would give each of the five basic types of taste.
a When you smell a substance, tiny parts of it have dissolved inside your nose.
12 Identify a profession or situation in which the senses of smell and taste are important.
b Olfactory cells are nerve cells in the nose. c You can only taste sweet things down the centre of your tongue.
13 Smells may be put in one of the following categories: burned, foul, fragrant, fruity, resinous (e.g. nail polish), spicy. Identify something that has each type of smell.
d The skin is not an organ.
14 Besides taste, identify what else the tongue is used for.
3 List:
15 Fred develops a rash whenever he washes the dishes. Identify the skin condition he probably has.
a the layers of the skin (list in order starting from the outer layer)
Analysing
b the five types of skin receptors
16 Are papillae the same as taste buds? Compare.
c the three most common types of skin cancers
Evaluating
Understanding 4 You get some bad smells from a toilet. Outline what is actually happening when you smell them. 5 A chemical is added to normally odourless liquefied petroleum gas (LPG) to make it smell unpleasant. Explain how this makes LPG safer.
17 Most people find kissing pleasurable and stubbing their toe not pleasurable. Propose scientific reasons why. 18 Propose reasons why Australia has such a high skin cancer rate compared to other countries.
Creating 19 Create a poster promoting ‘sunsmart’ behaviour.
121
Smell, taste and touch
4.3
INVESTIGATING
Investigate your available resources (for example, textbooks, encyclopaedias, internet) to answer the following questions. 1 Determine what pheromones are and how insect-eating plants use them. 2 Research the history of perfumes. Possible starting points include: Ma Griffe, Dior, Nina Ricci, Guerlain, Givenchy and Estée Lauder. Summarise your information in a timeline. 3 Research other skin conditions, and their causes and treatments. Possible conditions to research include tinea, boils, cold sores, thrush, ringworm, scabies, shingles and psoriasis.
b Use peer assessment to evaluate the effectiveness of the presentation. 4 a Research skin cancer statistics in Australia over the past decade or so. Is it increasing or decreasing? What reasons could you suggest? Comment on your findings. b Analyse whether increased awareness of the dangers (e.g. through the media or doctors) has had an impact on the occurrence of skin cancer. c Examine what it means if a sunscreen is ‘factor 30’ or ‘SPF 30’. Are other factors available?
a In small groups, present your information to the class using a presentation medium such as PowerPoint.
4.3
PRACTICAL ACTIVITIES
1 Taste regions B
Aim To determine whether some areas of the tongue are more receptive to certain tastes A
!
D
C
Safety Do not share cotton buds with others. Use a new end for each sample.
E
Equipment • clean cotton buds • samples of the following solutions in new plastic cups (do not use beakers or other lab glassware): sugar, salt, vinegar or lemon juice, coffee • blindfold
Method 1 Carefully blindfold your partner. 2 Then dip a cotton bud in one of the solutions and touch to each area of your partner’s tongue (shown as A, B, C, D and E in Figure 4.3.13). 3 Record which area is sensitive to the solution (e.g. sweet). 4 Repeat for the other three solutions.
122
Fig 4.3.13
Questions 1 Record your results on a copy of Figure 4.3.13. 2 Compare your results with those of your classmates. 3 Compare your own map with that shown in Figure 4.3.5. 4 Using your own and class results, evaluate the accuracy of the tongue map.
Unit
4.3
?
2 Taste trickery
DYO
Aim To determine if taste can be tricked
Equipment • blindfold • apple, potato, pear
Method Design your own experiment to test whether a blindfolded person who is pinching their nose can tell the difference between the taste of apple, potato and pear.
Fig 4.3.14
3 Skin receptors
2 Make sure your partner cannot see while you touch both toothpick points to a region of their skin. Ask your partner how many points they feel.
Aim
3 Move the toothpicks closer to each other and test again. Progressively move the toothpicks closer together until only one can be felt.
To investigate the sensitivity of your skin in various areas
Equipment • • • •
toothpicks tape ruler blindfold
4 Test other regions of the skin the same way. Some possible areas to try are the back of the hand, palm, inside forearm, back of forearm, leg, foot, back of neck. 5 Swap jobs and have your partner test you.
Method
Questions
1 Attach two toothpicks to a ruler as shown here.
1 Give each area of your skin a sensitivity rating. 2 Compare results with your partner.
toothpick
3 Propose reasons why some areas are more sensitive than others.
ruler 0
1
2
3
4
5
6
7
8
9 10 11 12 13 14 15 16 17 18
20 21 22 23 24 25 26
28 29 30
tape
Fig 4.3.15
123
Unit
4.4
context
Responding
Your senses are constantly providing you with information about your surroundings. This information might be the smell of a classmate’s tuna sandwich, the hot air near a Bunsen burner, or the noise of a passing bus. Each piece of information will probably trigger a
different response. You might hold your nose, move away from the flame or turn towards the bus. Your responses enable you to react to the changes that are happening around you and enhance your chances of survival in a world full of potential threats.
Fig 4.4.1 A dog responds to the smell of food, the sound of their
Fig 4.4.2 Humans respond to a hot day by wearing less clothing,
name or the sight of a cat.
grabbing a cold drink, moving into the shade or heading to the beach. Different organisms often display different responses to the same stimuli. Dogs, for example, don’t have sweat glands and so must cool down by panting and lying down on a cool surface.
Responding to stimuli One of the fundamental characteristics of living things (organisms) is that they respond to information received from their surroundings. This ability is needed to feed, escape, move, reproduce and keep warm or cool down. A stimulus is anything that triggers a change or response in the way an organism acts. Touch an animal or make a loud noise and a variety of responses are possible: it might bite, sting, snarl, run away or curl into a protective ball. Other stimuli are far less noticeable. Subtle changes in temperature or the levels of water or a specific chemical in the environment can trigger an equally subtle response. Humans, for example, involuntarily respond to a hot day by sweating and increased blood flow to the skin, making the face look red and ‘flushed’.
124
Fig 4.4.3 Homeostasis maintains the human body at a temperature of approximately 37°C and blood acidity (pH) at around 7.38, regardless of whether the human lives in a desert, a jungle or on the ice of the Arctic.
Step 1 Detecting the stimulus This happens when a sense receptor is stimulated. These are specialised areas or cells that are sensitive to a change in the environment such as a change in temperature, light, pressure, touch, sound, chemicals and water levels. Your body contains receptors to detect all these stimuli. Step 2 Effector The message is then sent to an effector—an organ, a gland or a muscle. Step 3 Response The effector then causes a response. A response could be anything from an increased heartbeat to a rush of adrenalin. It could be a surge of sexual attraction, tears, or the feeling of fear. Some stimuli, their receptors and the location of the receptors are shown in the following table. Stimulus
Receptor
4.4
Humans show an amazing ability to respond to changes in their surroundings. This maintenance of a constant internal environment despite changes in the surroundings is called homeostasis. Homeostasis allows cells to keep working efficiently, maintaining temperature, glucose and water levels within strict limits. Homoeostasis happens via a sequence of steps known as the stimulus–response model.
Consider what happens when you burn your finger. Step 1: Detecting the stimulus: heat and pain receptors in your finger detect that there is too much heat. Step 2: Effector: messages are sent via nerves to an arm muscle. Step 3: Response: the muscle contracts, pulling your hand away from the source of heat.
Unit
Keeping things constant
Feedback and coordination Often this sequence of events involves some kind of feedback of information. The response generally affects the original stimulus in some way, so the organism is able to adjust its response. Consider a big dog approaching a small dog. The small dog might respond by wagging its tail, barking, snarling or running away. This response is feedback to the big dog and is the stimulus for another action. Depending on the feedback it gets, the big dog might wag its tail too, bark back or chase the small dog. The total response of an organism is often complex, involving several parts of the body. For this to occur, some kind of coordination is required. All organisms are coordinated in some way. Even a single-celled amoeba responds to changes in temperature or pH by moving into a more favourable region. In larger organisms there are a number of structures to detect, transmit, coordinate and respond to stimuli.
Location of receptor
Heat or cold
Thermoreceptors
Skin
Water levels in blood
Osmoreceptors
Brain and large arteries
Pressure and touch
Mechanoreceptors
Skin
Sound
Cochlear cells in the inner ear
Inner ear
Light
Photoreceptors
Retina at the rear of the eye
Chemicals
Chemoreceptors on the tongue and in the nose
On the tongue and in the nose
Gravity
Semicircular canals
Ears Fig 4.4.4 Dogs, dingoes and wolves use feedback to determine what to do next: do I fight, bark or run away? Prac 1 p. 128
Prac 2 p. 128
125
Responding Science
Science
Clip
Clip
Holding your breath
Thermostat feedback
Hyperventilation is rapid deep breathing. Its effect is to remove more carbon dioxide than normal from the lungs. The responses are slower breathing (possibly even stopping it), a rapid drop in blood pressure, dizziness and possibly unconsciousness. To get breathing normally again, carbon dioxide must be re-introduced into the lungs. This can be done by breathing in and out of a paper bag or cupped hands. Before the invention of scuba equipment, Japanese pearl divers would deliberately hyperventilate. Their much slower breathing rates gave them a few extra moments before they had to surface for air.
A thermostat on a heater uses a stimulus–response model and feedback to keep the temperature stable. When the temperature of the room drops, the thermostat detects the change (stimulus) and turns the heater on (response). The increasing temperature is then detected (feedback). The thermostat responds by turning off the heater. This cycle of feedback continues, keeping the temperature almost constant.
Stimulus: during exercise, the amount of carbon dioxide (CO2 levels) in the blood rises
Feedback: CO2 levels in the blood drop. If the drop is insufficient, the cycle continues until the CO2 levels drop back to normal. Breathing rate returns to normal when they do. Response: breathing rate increases and heart pumps faster Effector: nerves relay the message to the diaphragm and chest muscles which control breathing
Receptor: receptor cells in the main arteries detect this rise
Coordinating centre: nerves relay the message to the brain
Fig 4.4.5 The control of carbon dioxide levels in your blood is an example of the stimulus–response model that includes both feedback and coordination. Worksheet 4.6 Responding
4.4
QUESTIONS
Remembering
Understanding
1 List the different responses that are coordinated when stepping barefoot onto hot sand at the beach. 2 State the most usual response to a stimulus for single-celled organisms. 3 State the approximate value of the:
a stimulus b response c homeostatis d feedback
a body temperature of a healthy human b pH level in the blood of a healthy human 4 Match each receptor with the stimulus to which it responds:
126
5 Define the following terms:
e coordination L 6 Alcohol slows the operation of the stimulus–response model. Explain how the risk of accident is increased if a driver has consumed alcohol.
Receptor a cells of the retina
Stimulus i gravity
b cells of the inner ear
ii chemicals
c taste buds
iii heat
a calmed a situation
d osmoreceptors in the brain
iv light
b made a situation worse
e semicircular canals in the ears
v sound
f thermoreceptors in the skin
vi water levels
7 Describe a situation where you have personally used feedback that has:
Unit
8 Identify three substances in the body whose levels are controlled by homeostasis. 9 Copy and complete the following table by identifying likely responses or the stimulus that might have caused them. Stimulus
viii (decrease in body temperature)
ii thermoreceptors in the skin
Response
A very cold wind Emily pinches her nose
4.4
i increase in body temperature
Applying
iii vii increase in sweating and blood flow to skin
A bus sounds its horn
iv hypothalamus in the brain vi blood vessels and sweat glands
Reuben takes off his shirt
v
Fig 4.4.6
The smell of sausages on the BBQ Patrick yawns A salty meal Lan screams 10 A dog barks at another dog. Identify: a possible responses of the second dog b the feedback these responses would give to the first dog c further responses of both dogs based on feedback 11 If the carbon dioxide level in your blood was to increase after exercise, identify: a where the receptors that detected this increase would be located b the coordinating centre that would receive messages c the structures that would act as effectors d the response you would notice 12 Use the terms in the list below to identify and label the parts of the diagram in Figure 4.4.6 (marked i to viii) showing control of body temperature: response, relay, feedback, stimulus, effectors, coordinating centre, receptor, relay
13 Soula shivers as she goes outside into the snow. She puts on a heavy coat and soon stops shivering, but after another minute starts to sweat. Identify: a the initial stimulus, initial responses and two other possible responses b the feedback after she put the coat on and the new response c further feedback and further response
Evaluating 14 A large dog runs up to a small child. Propose likely responses from the child, the feedback it might give the dog and likely further responses from the dog. 15 A science teacher has just caught a student doing something unsafe in an experiment and is angry with them. Propose: a what the stimulus might have been for the teacher b three possible responses from the teacher c three ways these responses might affect the student d possible feedback from the student that would calm the teacher e possible feedback that would anger the teacher even more
Creating 16 Construct a diagram to demonstrate the stimulus–response model that happens when you touch a hot stove.
127
Responding
4.4
INVESTIGATING
Investigate your available resources (for example, textbooks, encyclopaedias, internet) to complete these tasks. 1 Research hyperthermia (an abnormal rise in body temperature) or hypothermia (an abnormal fall in body temperature). Specifically: a list their symptoms and likely causes
4.4
b prepare a report explaining how to avoid these two conditions. L 2 Find out why body temperature rises when you have a fever. Research how this happens and whether the higher temperature is beneficial or damages body cells. 3 Find what might cause a change in blood pH and how the body responds.
PRACTICAL ACTIVITIES 5 Continue tasting each solution of the next higher concentration until you can taste the sugar. Try the next higher concentration to be sure of your results.
1 Sweet and salty Aim
6 Thoroughly rinse your mouth using the bottled water.
To identify the threshold of a stimulus
7 Repeat the procedure using the salt solutions, once again starting with the most dilute.
Equipment • 12 new small paper cups • 2–3 mL each of solutions of sugar of varying concentrations (0.001%, 0.005%, 0.01%, 0.05%, 0.1%, 0.5%) • 2–3 mL each of solutions of salt (0.001%, 0.005%, 0.01%, 0.05%, 0.1%, 0.5%) • waste jar for rinsings • bottled water for rinsing mouth
Method
Questions 1 The minimum intensity that causes a response is known as the threshold for the stimulus. State your taste threshold for sweetness. 2 State your taste threshold for saltiness. 3 Compare the class results. Is there a difference in the taste thresholds between males and females?
1 Draw up a results table as shown below.
4 Justify the value of receptors in the body having thresholds.
2 Sip the most dilute (0.001%) sugar solution. Can you taste the sugar? Record a ‘+’ in the table if you can, or a ‘0’ if you cannot.
5 a You knew what type of solution you were tasting. Evaluate whether this knowledge affected your judgement. b Describe how you could modify the activity to overcome any problems.
3 Spit the sample into the waste jar. 4 Repeat the test with 0.005% sugar solution. Concentration
0.001%
0.005%
0.01%
0.05%
0.1%
0.5%
Result for sugar Result for salt
? 2 Sound threshold
DYO
The loud tick of a mechanical clock or watch can be used to test hearing. The distance of the clock from the ear can be used as a
128
measure of the loudness of the sound. Design your own experiment to test the sound threshold for members of your class. Compare the thresholds for males and females.
Unit
4.5
context
Nervous control
Your nervous system controls and coordinates all parts of your body. It is the most complex and the least understood of all your body systems.
The nervous system The nervous system has two parts: • the central nervous system (CNS) • the peripheral nervous system (PNS). CNS The central nervous system is made up of the brain and spinal cord. The CNS acts as the control centre, receiving messages from all parts of the body. It examines the information received, and then sends out messages instructing different parts of the body about what they are to do. CNS: brian and spinal cord
Fig 4.5.1 The brain is the coordinating centre for the nervous system and the spinal cord is its main carrier of messages. While the skull protects the brain, bony vertebrae in the spine protect the spinal cord.
PNS: sensory receptors and nerves
Organs
Sight, hearing, taste, smell
Large arteries and other tissues
Heat, touch
Effectors
Fig 4.5.2 The nervous system
Muscles and glands
129
Nervous control PNS The peripheral nervous system is made up of sensory receptors and nerves. These continuously inform the CNS of changing conditions, and transmit the decisions made by the CNS back to effector organs.
Neurons and nerves Messages are passed through the system by nerve cells called neurons. These are specialised cells that transmit and receive messages in the form of electrical impulses. A neuron has the usual features of any cell found in an animal. It has a nucleus, cytoplasm and cell membrane, but it also has a number of other specialised parts. Around the cell body are small threads called dendrites which make contact with other cells and receive information from them. One long thread known as the axon carries information away from the cell. Axons are often encased in a white fatty substance called myelin. Myelin insulates the axon like the plastic coating on an electrical wire, enabling messages to pass more quickly along the axon. The information is carried by electrical impulses that travel at speeds between one and 100 metres per second. Neurons are grouped together in bundles called nerves, in much the same way as an electrical cable is made up of smaller wires bound together.
Types of neurons Different types of neurons have different functions within the nervous system. • Connecting neurons or interneurons transfer electrical messages within the CNS. • Motor neurons transfer messages from the CNS to effector organs such as muscles. • Sensory neurons have specialised endings sensitive only to stimuli such as heat and light. These form part of the body’s larger sense organs (eyes, ears etc.), which function by collecting different energy forms. The sensory neuron then converts this energy into an electrical impulse. For example, cells in the eye’s retina convert light energy into electrical energy. The synapse and neurotransmitters Between neurons are small gaps called synapses. Messages cross these synapses, but not as electrical impulses. Instead, the message is carried chemically by special compounds called neurotransmitters. When an impulse reaches a synapse, neurotransmitters are released and quickly move across the gap. They move to sites on the other side, restarting the electrical impulse. The neurotransmitter is then broken down so that new messages can be received.
Cell body cell membrane
nucleus
cytoplasm
Dendrites: small threads arranged around the body of the neuron cell. Dendrites make contact with other cells and receive information from them.
Axon: a long thin thread that carries information away from the cell. Myelin: a white fatty substance that encases the axon, allowing messages to pass along it and insulating it much like the plastic coating on an electrical wire.
Nerve endings
Fig 4.5.3 These are some of the specialised endings a typical neuron can have.
130
Muscle fibres: in motor neurons, the endings connect directly to muscle fibres.
Sensory receptor: in sensory neurons there are specialised endings that are sensitive to a particular stimuli such as heat, pressure or light.
Neurotransmitters cross the gap.
4.5
Synapse: a small gap between neurons. Slows the message and allows it to be redirected to different neurons and parts of the body.
Unit
Neurotransmitters: a message causes these special chemicals to form in the end of the axon of one neuron.
Dendrites: collect the neurotransmitters, passing on the message
Fig 4.5.4 A synapse is a small gap between the neurons that make up nerves. Chemicals called neurotransmitters carry messages across the gap.
Types of neurotransmitters Around 50 different neurotransmitters have been identified. The neurotransmitter noradrenalin is associated with alertness. Another is dopamine, associated with emotions. Drugs such as amphetamines, cocaine and ecstasy increase production of these neurotransmitters. This results in an increased state of alertness and
Science
Clip
Pain relief The pain-relieving processes of acupuncture and hypnosis appear to be related to neurotransmitters called encephalins. These are the body’s own pain-deadening neurotransmitters. Acupuncture is thought to stimulate the production of encephalins. Morphine, codeine and pethidine act in much the same way as these neurotransmitters.
heightened emotions, along with high blood pressure, irritability and, later, depression and insomnia. Many drugs and poisons affect neurotransmitters. Curare is a poison that was used by South American Indians on arrow tips. It blocks reception of the neurotransmitter acetylcholine, preventing messages from getting to muscles, stopping breathing and other movements. Some insecticides work by preventing the breakdown of acetylcholine, so messages are constantly received, resulting in continuous muscle spasms. Why synapses? If neurons touched each other it would be something like turning on one switch and having every light in the house come on at once. Synapses are similar to a switchboard, allowing messages to be directed to the correct places. It is also thought that synapses in the brain play an important part in learning and memory. Worksheet 4.7 The nervous system
The brain
Fig 4.5.5 Acupuncture is thought to stimulate pain-relieving neurotransmitters.
The brain is soft, wrinkly tissue with a mass of around 1.4 kg. Each of its 25 billion neurons is connected to as many as 1000 others and so there are as many as 100 million million synapses. This huge number of neurons does not exist as a tangled mess, but forms networks with neurons arranged in specific circuits. Not even the largest, most intricate computer comes close to the complexity of the human brain. It is hardly surprising then that scientists know little about what actually happens in processes such as thinking, feeling sadness, or when you try to remember what happened yesterday.
131
Nervous control
Damage to the nervous system Multiple sclerosis (MS) Multiple sclerosis is a disease that breaks down patches of myelin along neurons in the CNS. The affected areas cannot conduct impulses and so some of the messages from the brain to the muscles are lost. Common symptoms of MS are loss of coordination, tremors, vision difficulties and partial paralysis. The cause of MS is still a mystery, but evidence suggests a measles-like virus may be responsible in those who are genetically susceptible. The disease is incurable since neurons cannot rebuild or be replaced if damaged.
Fig 4.5.6 A front view of the human brain showing its left and right hemispheres and the wrinkly mass of the cerebrum.
vis ion
ati on
taste ring ci hea o as s
area
rea
touch smell
tor a
ea ar
mo
associa
Cerebrum: a mass of wrinkled tissue that makes up 90 per cent of the brain. It is responsible for complex thoughts, the senses, muscle control, memory and thinking.
tio n
Parts of the brain The brain has three main structural parts: the cerebrum, cerebellum and medulla. The most visible part of the brain is the cerebrum. Its surface is grey in colour (hence the expression ‘using your grey matter’) and it is folded to create a large surface area with billions of neurons. It is divided into two hemispheres. The right hemisphere is responsible for artistic and musical ability, intuition and perception while the left takes care of language, learning mathematics and logical thinking. The sensory areas are specialised regions that receive and interpret impulses from sense organs. The motor areas control muscles. The association areas are concerned with memory and thinking.
Spinal cord injuries (SCI) Spinal cord injury occurs if the spinal cord is broken, crushed or weakened in some way. If the cord is severed completely, then messages from the brain cannot get past the break to the organs and muscles below. This results in paralysis and a loss of function below the break. The extent of injury is therefore very dependent on where the break is. More function is lost the higher the break. If the injury is low then paraplegia is probable. Paraplegia is a loss of function of the lower body, often resulting in paralysis of the legs, incontinence (loss of urine and bowel function) and impotence (inability for males to get an erection). If the injury is high, such as in the neck (a so-called broken neck), then the loss is greater. Arms and legs are likely to be paralysed and many functions such as breathing can be difficult or impossible. This is termed quadriplegia or tetraplegia.
Cerebellum: the ‘base’ of the brain. It controls complex muscular movements like cycling, walking and running. Medulla: the ‘stem’ of the brain. It controls vital activities that do not require conscious thought, like breathing and heartbeat.
Fig 4.5.7 Parts of the brain
132
Spinal cord: a bundle of nerves running the length of the spine. They transmit messages between the brain and the PNS, and control some actions that do not require thinking.
Prac 1 p. 136
Prac 2 p. 137
Prac 3 p. 138
Go to
Science Focus 3 Unit 5.4
Brain damage Although the brain makes up only two per cent of the body’s weight, it receives 20 per cent of its blood and uses 20 per cent of its oxygen. Consciousness is lost rapidly and irreversible damage occurs within minutes if blood flow to the brain is interrupted. To avoid this, jet fighter pilots wear special pressure suits to maintain blood flow to the brain during rapid turns. The most common form of brain damage is stroke, where part of the brain is deprived of blood. This can happen if a blood vessel bursts in the brain (a haemorrhage) or more commonly when a blood clot blocks a vessel.
4.5
function. The occurrence of spina bifida is reduced if prospective mothers regularly take folic acid.
Unit
Some organ and muscle function, however, may exist past the injury if the spinal cord is partially crushed or if some of the nerves in the cord are still intact. Around 9000 Australians currently have some form of SCI, with another 400 developing an SCI each year. Nerves and the spinal cord cannot repair themselves and so, once damaged, the injury and loss of function is permanent. The most common causes of SCI are: • motor accidents that involve speed or a rollover—41 per cent • falls from ladders, playground equipment, balconies etc.—34 per cent • sport injuries—6 per cent • water injuries caused by surfing—5 per cent • water injuries caused by diving into shallow water— 5 per cent. Spina bifida Spina bifida is a genetic condition in which some of the vertebrae are not completely formed, exposing parts of the spinal cord. These parts of the spinal cord have limited protection and usually do not develop completely. If severe, the vertebrae can be repaired soon after birth or even while the baby is still in the uterus. Most people with spina bifida never experience any problem because of it. Others, however, experience some loss of nervous
Science
Clip
No-one is a Superman, not even Superman! American actor Christopher Reeve (1952–2004) played Clark Kent/Superman in four films between 1978 and 1987. In 1995, he was thrown from his horse. His arms got tangled in the reins and he landed head first, shattering two vertebrae in his neck and severing his spinal cord. From that day to his death, Reeve was paralysed from the neck down and needed respirators to breathe for him.
Fig 4.5.9 Parts of the brain will die if any of these arteries block or rupture, even for a moment.
Fig 4.5.10 Stroke happens most often in older people but it can affect people as young as 10. Although supremely fit and at the peak of his career, AFL footballer Angelo Lekkas experienced a stroke in 2005 at the age of 25. He retired from his team, Hawthorn, soon after.
Fig 4.5.8 Christopher Reeve as Superman
133
Nervous control Protecting the nervous system The spinal cord and brain are so important that the body protects them very carefully. The spinal cord is protected by the bony vertebrae of the spine (backbone) and the brain is protected by the skull. Both the spinal cord and brain have a jacket of fluid around them called cerebrospinal fluid (CSF) to cushion them against shock. The brain is also protected by layers of connective tissue called meninges.
Fig 4.5.12 Practise establishes pathways that make some actions seem automatic, such as music (like playing a trumpet), sport, touch-typing, riding a bike, driving a car and tying your shoelaces.
Using the nervous system Reflex action Reflex actions are fast, occurring automatically and without thinking. They use a pathway known as a reflex arc made up of only a few neurons. The brain is not directly involved. Examples of reflex actions are blinking, sweating, shivering, coughing and the kneejerk reaction. Another example is when someone cuts their finger on a knife (see Figure 4.5.11). Thinking about it More complex actions require messages to be sent to the brain, decisions made and responses sent back to various effectors. Some learned actions may become so automatic that they appear to be reflexes.
a message may be sent to the brain but only to keep it informed of what is happening. The brain might trigger tears or a cry of pain
spinal cord
Clip
For a toddler, eating is a task that requires conscious effort. As we get older, the pathways controlling this process become so well established that the action becomes automatic. This is particularly obvious in sport and music. Those who excel have practised until they can perform automatically. The rest of us stumble.
What a pain! An epidural is an anaesthetic that is injected into small spaces around the spinal cord. Messages from the sensory nerves are blocked and pain is not felt. Epidurals are commonly used during childbirth.
Stimulus: finger is cut by knife
message crosses synapses to a motor nerve in the spinal cord
vertebra
Science
Effector: muscles contract, withdrawing the hand from the knife
message from pain receptors travels along a sensory nerve to the spinal cord
Receptors: pain receptors in the skin detect the cut
Message relayed to arm muscle
message travels along motor nerve to muscle
muscle
pain receptors in skin
Fig 4.5.11 A reflex arc does not require conscious thought as it does not involve the brain directly.
134
Prac 4 p. 138
Unit
QUESTIONS
Remembering 1 a Name the two main parts of the nervous system. b State what each part consists of and the main function of each.
10 Identify the parts of the diagram shown in Figure 4.5.14, using the following words:
4.5
4.5
cerebellum, medulla, spinal cord, cerebrum
2 State three ways in which: a
a the brain is protected from injury b the brain can be damaged c the spinal cord can be damaged b
3 State one reflex action that occurs when:
c
a a bright light is shone in your eyes d
b food enters your windpipe c you are hungry and you smell food
Fig 4.5.14
d you spend a long time in the sun on a hot day 4 Name two conscious acts that are so automatic that they often appear to be reflex actions.
Understanding
11 Identify which part of the brain: a you use to think b controls breathing c helps you balance while cycling
5 Describe the function of neurotransmitters. 6 Explain why synapses are necessary. 7 Explain the advantage of the cerebrum of the brain being wrinkled and not flat. 8 Arrange the following list of events in the correct order to outline a reflex action. Write your answer as a flow chart. An impulse is sent along a sensory neuron to the brain. An impulse is sent along a motor neuron to iris muscles. A bright light is shone in the eye. Iris muscles contract, causing the pupil to narrow. Receptors detect a change in light intensity.
d gives you sensations of touch 12 Identify which of the following would be reflex actions: coughing, sneezing, reading, cycling, writing, blinking 13 Identify the side of the cerebrum that is most active in helping you answer these questions. 14 Receptors convert specific types of energy into electrical impulses that then travel down the nerves. Identify what form of energy is being converted in each of the receptors listed: a retina cells in the eye b cochlear cells in the ear c taste buds on the tongue
Applying 9 a Identify the type of neuron shown in Figure 4.5.13.
d thermoreceptors in the skin
Analysing
b Identify and label parts i to v.
15 Compare the neuron with other cells in the body. iii
i
a How is it like other cells? b How is it different? 16 Distinguish between a neuron and a nerve.
iv
v
17 Distinguish between sensory neurons, motor neurons and interneurons.
ii
Fig 4.5.13
135
Nervous control
4.5
INVESTIGATING
Investigate your available resources (for example, textbooks, encyclopaedias, internet) to complete these tasks. 1 Research the effect of caffeine, marijuana or alcohol on the CNS. Perform a role-play to teach other students about your findings. L
5 Find out about the many young people who seriously injure their spinal cord by diving into water without knowing its depth. Many become paraplegic or tetraplegic (quadriplegic). a Investigate what tetraplegic/quadriplegic and paraplegic mean, and find out the number of diving accidents in Australia last year.
2 Research and report on one of the following disorders of the nervous system: L a Parkinson’s disease b Alzheimer’s disease c epilepsy Outline the signs, symptoms and treatments for the disorder you have chosen. 3 Find out about the blue-ringed octopus—one of the most deadly sea creatures. Investigate how its poison can paralyse the nervous system. 4 Investigate the differences in brain structure of humans, gorillas, dolphins and dogs.
4.5
b Research one such case and outline factors that led to the injury (e.g. was alcohol involved?). c Report on the person’s life since the accident and their probable life in the future. L
e –xploring To assist with the following activities, a list of web destinations can be found on Science Focus 3 Second Edition Student Lounge. • Explore interactive diagrams of the nervous system. • Perform a number of activities to test your reflexes.
PRACTICAL ACTIVITIES scalpel
sheep’s brain
1 Brain dissection Aim To investigate the structure of the brain cerebrum
Equipment • • • • • •
partly frozen lamb’s brain dissection board scalpel dissecting scissors newspapers disinfectant
cerebellum cerebrum
medulla
frontal lobe cerebellum
Method 1 Cover the workbench with a layer of newspaper and place the dissection board on it. 2 When using the scalpel, make many light cuts instead of one deep cut. When cutting, always draw the scalpel away from your hands. 3 With the edge of the scalpel, try to lift the fine membrane or skin off the brain. If successful, peel it off.
136
medulla spinal cord
Fig 4.5.15
pituitary gland
olfactory lobe
Unit 4 Separate the right and left hemispheres of the brain and remove the cerebellum and medulla. 5 If still sufficiently frozen, slice the brain into thin slices. Identify the different parts of the brain and use Figure 4.5.7 (page 132) and Figure 4.5.16 to identify any gland that is found.
4.5
thalamus (motor control, information from senses)
Questions 1 Propose reasons why a frozen brain was dissected and not a fresh brain. 2 Describe the surface and consistency of the cerebrum. 3 Describe how you identified which was the left and which was the right hemisphere.
hypothalamus (emotions, endocrine functions, motor functions, regulates food and water intake and the sleep cycle)
cerebellum
4 Compare the colour and consistency of the cerebellum with that of the cerebrum. 5 Describe the medulla.
medulla amygdala (emotion, fear, hormones)
Fig 4.5.16
hippocampus (emotions, navigation and spatial orientation, new memories)
2 A model brain Aim To construct a model of a human brain
Equipment • unpeeled orange • assorted lollies (e.g. 1 banana, 3 jubes, 1 marshmallow, 3 snakes (different colours), 1 spearmint leaf) • 2 sultanas • toothpicks • cotton buds • plastic knife • newspaper
Method 1 Peel the orange. 2 Identify the front of the ‘brain’ and attach two sultanas with toothpicks to represent the likely position of the eyes. 3 Carefully cut the orange to partly separate it into two halves/hemispheres. 4 Refer to Figures 4.5.7 (page 132) and 4.5.16 and use toothpicks to attach the following lollies in their correct place in the brain as shown in this table.
Part of the brain
Lolly
Cerebellum
Marshmallow
Medulla
Banana
Hippocampus
Spearmint leaf
Thalamus
Jube
Amygdala
Jube (different colour
Hypothalamus
Jube (different colour)
Motor cortex (motor area)
Snake
Sensory cortex (touch, smell, taste, hearing)
Snake (different colour)
Spinal cord
Snake (different colour)
5 When complete, eat your brain.
Questions 1 Identify what represented the skull in this model. 2 Identify what represented the cerebrum in this model. 3 Construct a table showing which functions are carried out by each hemisphere.
137
Nervous control
3 Brain wars: the Stroop effect Aim
3 When you succeed, record your best time.
To bluff your brain
4 Play an interactive version of the Stroop effect by visiting Science Focus 3 Second Edition Student Lounge and investigating the web destination listed.
Equipment A stopwatch
Method
Questions
1 As quickly you can, say out loud the colours you see in Figure 4.5.17. Do not say the words.
RED
1 State which hemisphere of the brain (left or right) is associated with reading and speaking language. 2 Identify which hemisphere is most associated with identifying colours (not words).
BLUE
3 Use this information to suggest why this task is difficult.
GREEN ORANGE YELLOW Fig 4.5.17
? 4 Response time
DYO
Aim To measure response times
Method Design your own experiment to measure the time taken to respond to either a visual or an auditory stimulus. For example, measure the time taken for your blindfolded partner to press a buzzer in response to the sound of a bell. Alternatively, drop a ball from a given height and measure how far it falls before your partner catches it. Determine whether repetition of the task reduces the time taken. Suggest reasons for any variations observed.
138
2 Have a classmate time you. Each time you get it wrong, start again.
4 There is a ‘battle’ going on in your brain in this task. Explain why. 5 Would you have the same problems if the names of the colours were written in a language that you do not understand?
Science Focus
Understanding memory
Prescribed focus area The nature and practice of science Most people can remember events from their distant past very clearly but often cannot remember what they did yesterday. This is because there are three types of memory: sensory memory, short-term memory and long-term memory.
Sensory memory This is the briefest form of memory, lasting for between 50 milliseconds (0.05 seconds) and four seconds. It is the memory of what has just been tasted, touched, smelled and, most importantly, seen and heard. It allows humans to remember what came immediately before when watching a film or listening to music to make it a smooth and continuous experience. It also allows humans to connect the different syllables they hear to make up sensible words. Sensory memories are quickly replaced by new sensory memories, meaning that nothing is really remembered there. Short-term memory Any sensory memory that is considered important is stored as a short-term memory. Short-term memories normally last a maximum of 30 seconds. Practise and repetition of the information increases the chance of it being remembered. Even then it might not be successful and the memory might be lost. Most people can successfully store seven pieces of information in their short-term memory. Some can store nine pieces while others struggle to store five. If given nine things to remember, then most people will forget a few while some will forget nearly all of them.
Fig 4.5.18 What a person remembers depends on how the information has been stored and in what memory. Long-term memory is vital in a test.
Science
Clip
Sparkler memory Swirl a sparkler around at night and it will ‘leave’ a trail. It doesn’t really leave a trail because nothing glowing is left behind. It’s sensory (visual) memory at work. After a very short time, this sensory memory is lost and the trail ‘disappears’.
Fig 4.5.19 You see sparkler trails because of sensory memory.
139
Short-term memory is what is used to remember the name, phone number or email address of someone just met. Remembering the number becomes more likely through: • chunking, or breaking it into smaller, easier-toremember pieces. A phone number might be broken into sets of two, three or four numbers. A set of letters might be broken into ‘words’ or a story might be made with the letters, for example, BFGLAAC 쏁 Big Friendly Prac 5 Giants Like Ants After Christmas p. 141 • repetition or replaying the number over and over, perhaps by writing it down repeatedly. Distractions interrupt repetition and replay, making it less likely that the information will be remembered • repetition of what must be remembered, but at the same time associating parts of it with dates, words or names that mean something to the person—for example, the phone number 2810 0104 might be remembered as their postcode (2810), followed by April Fool’s Day (01/04).
Information can transfer from short into long-term memory if it is repeated and replayed enough. This is why teachers get their students to repeat tasks over and over. A person will probably forget a single task but will have a better chance of remembering it if they repeat it many times. Long-term memory is: • the memory of how to do something, for example, how to swim, ride a bike or surf. People who do so when young can usually still swim, ride or surf many years later • the memory of important events in the person’s life, for example, their tenth birthday party or when they first saw a monkey at the zoo • the memory of facts, for example, that the capital of Australia is Canberra, that how a dog looks different from a cat and 5 ҂ 5 ҃ 25. Short-term memories can become long-term memories but, to be useful, long-term memories must be able to change back into short-term memories. This is called retrieval, and sometimes it can be a fuzzy process. Although a person may have remembered their tenth birthday party, their recall might have gaps in it or appear in odd orders. They may not have remembered the information correctly but it is more likely that they have not retrieved it properly. They may also have merged bits of long-term memory into a ‘new memory’. For example, Prac 6 they may clearly remember Aunty Dot at their p. 141 tenth birthday even though they know she had died by then.
Fig 4.5.20 Remembering something as complex as the order of the elements in the periodic table is easier if the information is chunked or if it is organised into ‘words’. Repetition is likely to send it into longterm memory.
Long-term memory Huge amounts of information can be stored in your long-term memory and it can stay well into old age. Elderly people often have excellent long-term memory, remembering the fine details of aspects of their youth, while forgetting much of what has just happened.
140
Fig 4.5.21 Once you know how to ride a bike, you will probably always know how to ride a bike. This is long-term memory at work.
Unit
5 What's that smell? Taste and smell are two senses rarely used in science because of their potential danger. Smell is a strong and evocative memory and in this experiment you will try and identify some common and safe smells from memory.
Aim To test the long-term memory of smells
Equipment • access to ‘secret smell’ containers (film canisters with a small ball of cotton wool with a drop or two of a scent capped to stop smells escaping) which your teacher will prepare
Method 1 In your workbook, construct a table similar to the one below. Add sufficient rows for the containers you have access to. 2 In pairs, test the smell in each container by carefully peeling back one edge of the cap and taking a small sniff. Do NOT take the lid completely off since it will let vapours escape. Container
What the group thinks it is
6 Chunking Aim To test if memory can be improved by chunking information
Equipment • three lists of ‘words’ (A, B and C) on an A4 sheet (your teacher will supply this—do not look at it until the activity begins) • access to clock or timer • paper • pen
Method 1 Place the A4 sheet face down. Do not look at it until instructed to do so. 2 When instructed, fold the sheet so that you can only see Card A, the first list of words. 3 Silently memorise the letters, words and order of words for 3 minutes or until instructed to stop. Cover the card so that you cannot see it.
3 Discuss with your partner what you think it is and where you have smelt it before, e.g. you might not know the smell of menthol but you have probably smelt it in things like Deep Heat. 4 At the end of the Prac, your teacher will read out what each small actually was. 5 Re-test the containers you identified incorrectly.
4.5
PRACTICAL ACTIVITIES
Questions 1 State how many you got correct. 2 Propose reasons why it was suggested that you discuss the smell with a partner. 3 Propose reasons why wine experts discuss the taste and smell (called the bouquet) of a wine. 4 Explain why vapours should not be left to escape, especially since they are all safe. 5 State whether your perception of the smell changed once you knew what it was. 6 The memory of a certain smell can immediately take you back to a different time and place if you smell it again. Identify a smell that does this to you. Where the group has smelt it
What it actually was
4 When instructed, begin recall by writing down everything that you remember: the letters, ‘words’ and order. Keep recalling for 2 minutes or until instructed to stop. 5 Score your memory by: • ticking every letter you got in the right place • ticking every ‘word’ you got in the right place • counting the number of ticks you have and giving yourself a score out of 58 6 Fold the sheet so that only Card B is visible and repeat the memorisation/recall. 7 Repeat for Card C.
Questions 1 Rank the cards in order from the easiest to the hardest to memorise. 2 Propose reasons why some things are easier to remember than others. 3 List other factors that might influence the speed at which you learn. 4 Use what you have found here to learn the names or symbols of the first 20 elements of the periodic table.
141
Unit
4.6
Chemical control
context
The endocrine system uses chemical messages called hormones to transfer information around the body. Hormones are responsible for controlling many processes in your body such as the storage and release of glucose into the blood.
Pituitary gland: produces the hormones: • human growth hormone (HGH), which controls cell growth and development • antidiuretic hormone (ADH), which controls water balance. Also stimulates other glands to release their hormones.
Thyroid: produces the hormone thyroxin which controls the rate of chemical reactions in cells.
Fig 4.6.1 A contraceptive pill contains synthetic female sex hormones that can control the menstrual cycle or periods.
Hormones Hormones are produced by the endocrine glands which are scattered throughout your body. Although the endocrine glands work together, they are not controlled from one central location like the nervous system. Hormones regulate functions like growth and development, water balance, sexual reproduction and the rate of chemical reactions in cells.
Pancreas: produces the hormones insulin and glucagon which both control blood glucose levels. Adrenal: produces the hormone adrenalin in readiness for flight or fight.
Ovaries (in females): produce the hormones: • oestrogen, which controls female sexual development and the menstrual cycle • progesterone, which controls the ovary and uterus in pregnancy.
Testes (in males): produce the hormone testosterone which controls male sexual development and sexual activity. Go to
Science Focus 3 Unit 5.3
Fig 4.6.2 Major human endocrine glands
142
travels in blood to hormone
receptor on target cell
Fig 4.6.3 Hormones act like jigsaw pieces and will only work if they have the correct shape to fit the receptors on the cells they must target. This image shows the jigsaw-like shape of crystals of progesterone, a female hormone that prepares the uterus for pregnancy.
4.6
Clip
making them difficult to detect. When hormones pass through the liver they are broken down and converted to relatively inactive substances, which are excreted by the kidneys. One test for pregnancy involves measuring the levels of these hormonal breakdown products in urine.
Unit
How hormones work Hormones travel to all parts of the body but only particular target cells respond to a particular hormone. Other cells are ‘blind’ to the hormone. Hormones have a specific shape that fits chemically into a receptor on the membrane of the target cell like pieces of a jigsaw. In this way, the right e hormone targets the right nc ie Sc cell with all others being blocked. The bonding of Not much there! the hormone to the The concentration of hormones receptor starts changes in in the blood is so low that it is the cell’s activities. equivalent to dissolving a sugar Hormones are secreted cube in a swimming pool! in very small quantities
Why hormones? Whereas the nervous system is Science very fast, the endocrine system acts more slowly, taking minutes, Small brain, big hours or even days for the level of testicles! a hormone in the blood to reach A team of American scientists its peak. This can be beneficial as have discovered that if a male not all responses need to be fast. animal has big testicles, then it When a hormone affects a will probably have a small cell, the response is usually longbrain. Testicles use a large lasting. If hormones acted as amount of energy to produce quickly as the nervous system, sperm and the male hormone testosterone. The brain needs a then a continuous supply of them large amount of energy too, would be needed to keep longand animals simply do not term responses going. have enough for both to be A pregnant woman, for example, big. Whereas ‘brainy’ apes would need to produce huge have testicles that make up less than 1% of their body quantities of the hormone mass, some bats with tiny progesterone. This would require brains have testicles that make a very large uterus. Hormones up 5.5% of their body mass! provide the ideal mechanism to control long-term activities such as reproduction, growth and development.
Clip
Systems working together The nervous system provides rapid messages while hormones provide slower messages. This means that the nervous and endocrine systems both respond to a stimulus. The sensation of fear, for example, involves both systems. When frightened, the nervous system sends a rapid response with messages being swiftly transferred along its neurons. The reaction is brief and almost immediate. The endocrine system also responds, but more slowly and over a longer period. Adrenalin (known as the ‘fight or flight’ hormone) is released from the adrenal glands, causing the heart to beat faster and breathing rate to increase. It also has the effect of diverting blood to the muscles, dilating the pupils, making the hairs on the skin stand on end and making the brain more alert. The body is now ready to fight or flee whatever caused the fright.
Fig 4.6.4 The hormone adrenalin gets you ready to fight or flee whatever frightened you.
143
Chemical control Thyroid-stimulating hormone The hypothalamus, pituitary and thyroid glands work together to control growth. Under instruction from the hypothalamus, the pituitary releases thyroid-stimulating hormone (TSH). This causes the thyroid gland to release thyroxin. Thyroxin controls the speed of cell reactions and therefore influences growth. A deficiency of thyroxin in infancy results in cretinism (stunted physical and mental growth). This can be cured in its early stages by administering thyroxin.
Controlling growth The pituitary gland can be considered to be the master gland, providing a vital link between the nervous and endocrine systems. The pituitary receives messages directly from the hypothalamus in the brain, it releases its own hormones and it instructs many other glands to release their hormones as well.
hypothalamus pituitary receives a message from the hypothalamus
thyroid-stimulating hormone (TSH)
stops TSH production (feedback)
thyroid gland
thyroxin produced controls chemical reactions in cells
Fig 4.6.6 Thyroxin released from the
Science
thyroid gland influences growth.
Clip
Fig 4.6.5 The pea-sized pituitary gland is located at the base of the brain.
Goitre hypothalamus
ting -stimula thyroid H) ne (TS hormo
one ic h
ado gon
an
kidney
gr
(H
ow
th
GH
)
ho
rm
on
e
rmones
go
trop
na
m
other ho
ho
r
t do
orm
rm
ic op
hu
s
s
thyroid
one
antidiuretic horm (ADH)
pituitary
e on
Iodine is an essential component of thyroxin. A deficiency of iodine can cause enlargement of the thyroid gland (a goitre). Goitres were once common in areas where the soil lacked iodine, but the use of iodised salt has largely solved this problem.
other organs e.g. mammary glands
testis
ovary
bones
Fig 4.6.7 The pituitary gland is the ‘master’ gland which stimulates other glands to secrete their hormones.
144
Unit
Controlling glucose levels Many substances must be kept at a constant level within the body. Cells need a continuous supply of glucose to produce energy, and inadequate levels may result in low energy and possible cell death. Blood glucose levels are usually maintained in a very narrow range by the action of two hormones, insulin and glucagon, both produced by the pancreas, found just below your stomach. If blood glucose levels increase, for example after eating chocolate, insulin is released. This stimulates storage of glucose in the liver, and increases uptake and use of glucose by cells. Blood glucose levels then drop, inhibiting further release of insulin. Glucagon works in a similar way. In response to low blood glucose levels, it directs the liver and cells to release glucose.
4.6
Human growth hormone Another hormone produced by the pituitary is human growth hormone (HGH), sometimes known simply as growth hormone (GH). HGH influences total body growth. Lack of HGH in childhood can lead to a form of dwarfism: although short, these people have normal intelligence and are well proportioned. If diagnosed early, injections of HGH can be given to children suffering from lack of HGH. Too much HGH in childhood leads to gigantism, producing an abnormally tall person.
Choc-N
ut Bar
food eaten blood glucose level falls feedback
rising blood glucose stimulus
glucose removed for storage response
pancreas receptor insulin released into blood hormonal relay
liver effector
Fig 4.6.9 The stimulus–response model that controls levels of blood glucose
Science
Clip
David and Goliath Fig 4.6.8 Gigantism and dwarfism can result from abnormal levels of HGH. Some giants have grown to over 2.7 metres tall, while dwarfs may be less than 0.6 metres tall.
The Jewish Torah and the Christian Bible’s Old Testament tell a story of how, in around 1000 BCE, a giant called Goliath was killed by a farmer called David who was armed only with a slingshot. There is some historical evidence that ‘giants’ existed in the region where this fight is supposed to have taken place. If Goliath was a giant, then it was probably because he had higher than normal levels of HGH when he was growing up. David went on to become king of Israel.
145
Chemical control
Diabetes Approximately one million people in Australia suffer from diabetes mellitus, a disease in which blood glucose levels are not maintained within the required range. There are two basic types of diabetics. • Type I, or insulin-dependent diabetics (around 15 per cent of cases) have a defective pancreas. High blood glucose levels result because the pancreas does not produce enough insulin. This may result in glucose in the urine as the body tries to rid itself of its excess. Long-term effects of excess glucose include damage to vital organs such as the kidneys. Treatment involves the use of daily insulin injections. • Type II, or non-insulin-dependent diabetics, do not produce enough insulin, or have cells that do not respond correctly to insulin. Treatment involves a special diet, an exercise program, use of drugs and possibly insulin injections.
Science
Clip
Too much or too little? Insulin-dependent diabetics must obtain a regular supply of insulin. They must also eat regularly. If a diabetic injects a dose of insulin (which lowers blood glucose levels) but then does not eat later, their blood glucose will fall too far. The brain will be affected, resulting in a hypoglycaemic (low sugar) episode or ‘hypo’, and possible unconsciousness. To avoid this problem, many diabetics wear an identifying label and carry a sugar source (like jelly beans) that can be taken if signs of a ‘hypo’ appear.
Prac 1 p. 148
Prac 2 p. 149
Worksheet 4.8 Chemical control
Worksheet 4.9 Hormonal control Go to
Science Focus 4 Unit 4.5
Pheromones Hormones are not the only chemicals that influence the behaviour of animals. Chemicals called pheromones may also dramatically affect behaviour. Many insects use pheromones to attract mates. Members of the opposite sex can detect pheromones in the air several kilometres away. These chemicals are effective in very small amounts. The female silk moth carries enough pheromones in her abdomen to stimulate more than one billion males! These sex-attractant pheromones act on the CNS, producing immediate behavioural changes. Other types of pheromones act more slowly, affecting growth and development. Termite queens use pheromones to stop larvae developing into new queens. Ants use pheromones to mark food trails. Use of pheromones is not restricted to insects. Larger animals convey much information with the scent of pheromones. Dogs and possums use these smells when marking out their territories by spraying urine.
146
Fig 4.6.10 Ants produce pheromones to recognise each other and to communicate.
Science
Clip
Aiming high It has been suggested that dogs can judge the size and therefore the potential danger of another dog by the height at which its urine has been sprayed up a tree. It has also been suggested that dogs wanting to create a more frightening impression try to aim as high as possible!
Unit
QUESTIONS
4.6
4.6
Remembering 1 State two reasons why the body would use hormones rather than electrical impulses to send messages.
K
2 Recall the endocrine system by matching: Gland Hormone a adrenal i oestrogen b pancreas ii adrenalin c pituitary iii testosterone d thyroid iv insulin e ovaries v ADH f testes vi thyroxin
L
N
Understanding
M
3 a Describe what hormones are. b State where they are produced. c Describe how they are transported. 4 Outline how hormones recognise their target cells. 5 Specify which endocrine gland could be called the ‘master’ gland. Explain why. 6 Listed below are several symptoms of stress caused by the release of adrenalin. Explain how each plays a role in preparing the body for action when stressed: • increased heart rate • dilation of bronchioles • glucose release from the liver • increased breathing rate 7 Describe a situation in which the response of the body is controlled by both the nervous and endocrine systems. 8 Outline the hormones involved in growth and their effect on the body. 9 Predict whether administering thyroxin would have any effect on an adult with cretinism. 10 Explain why dogs take so much interest in each other’s urine and faeces.
Applying 11 The diagram in Figure 4.6.11 shows several endocrine glands labelled using the letters K to P. Use the letters K to P to identify which gland produces a hormone that controls: a blood glucose levels b female reproductive functions c rates of chemical reactions in cells d water levels within the body e readiness of the body for action f deepening of the male voice at puberty
O P
Fig 4.6.11
12 Calculate the percentage of diabetics that suffer from Type I diabetes and the percentage that suffer from Type II. 13 Identify two examples of pheromones and describe their effects.
Analysing 14 Distinguish between a pheromone and a hormone. 15 Construct a table to compare the nervous and endocrine systems. Your table should include comparisons of the nature of the message produced, how the message is distributed, speed of delivery and length of response produced.
Evaluating 16 Propose reasons why perfume and aftershave producers carry out a lot of research into finding human pheromones.
Creating 17 Using Figure 4.6.9 as a guide, construct a flow chart to show the body’s response to a decrease in blood glucose levels. 18 Construct a sketch graph showing what happens to your blood glucose levels after you eat a lolly.
147
Chemical control
4.6
INVESTIGATING
Investigate your available resources (for example, textbooks, encyclopaedias, internet) to complete these tasks. 1 Find out more about diabetes, including: a how the insulin used by diabetics is obtained b treatments for insulin-dependent diabetics that would eliminate the need for daily insulin injections. 2 Explain the role of hormones in controlling the female reproductive cycle. How is this system of control used in the various contraceptive pills? 3 Examine the role of juvenile hormone in the moulting and metamorphosis of insects. How might knowledge of this hormone be used to control insect pests?
4.6
Plants also produce hormones. These regulate growth, flowering, fruit production and ripening, and seed germination. A response where a plant grows towards or away from a stimulus is called a tropism. Phototropism is when a plant grows towards light, a response caused by a hormone called an auxin.
Aim To investigate tropism in plants
Equipment 6 shoots of the plant Tradescantia 6 test tubes melted paraffin wax water a darkened area and a well-lit area to place plants
Fig 4.6.12 The dramatic effect of a plant hormone on plant growth
148
5 Investigate one commercial use of plant hormones, such as the use of gibberellins on grapes and in the brewing industry, the use of auxin as a rooting hormone in plant propagation, or the use of hormones to produce flowers at the ‘wrong’ time of year.
e –xploring To explore interactive diagrams of the endocrine system, web destinations can be found on Science Focus 3 Second Edition Student Lounge.
PRACTICAL ACTIVITIES
1 Plant hormones
• • • • •
4 Investigate one commercial use of pheromones—for example, the control of oriental fruit moth, which is a major pest of peach trees in Australia.
Unit
4.6
Tradescantia shoot
Method 1 Place one shoot in each of the six test tubes, add water and seal them with paraffin wax. 2 Set up three test tubes as shown in Figure 4.6.13, and place them in a well-lit area.
water
3 Set up another three test tubes as shown in Figure 4.6.13, and place them in a darkened area.
test tube sealed with paraffin wax
4 Observe any changes in the plants after two hours.
Questions 1 Sketch the shoots in the six test tubes after two hours. 2 What type of tropism is shown in the experiment? Explain your answer. 3 Explain why it was necessary to place the tubes in both light and dark. Fig 4.6.13
2 Plants and gravity
?
Design your own experiment to investigate the response of plant roots to gravity.
DYO
CHAPTER REVIEW Remembering 1 List: a the five senses b the three main regions of the ear c the five taste sensations d the two main parts of the CNS e the main parts of the brain f three hormones 2 Recall the nervous system by matching the parts of the brain to the functions listed: Part a cerebellum b medulla c meninges d cerebrum
Function i controls involuntary actions such as breathing ii centre for sight, hearing and speech iii controls muscle movements while you are cycling iv protect the brain from injury
3 a State three activities in humans that are controlled by hormones. b State one activity in plants that is controlled by hormones. 4 Recall the role of hormones by matching the hormones to the functions they control: Functions a blood glucose levels
Hormones i ADH
b female reproductive functions
ii testosterone
c the rate of chemical reactions in cells
iii insulin
d water levels within the body
iv oestrogen
e readiness of the body for action
v thyroxin
f deepening of the male voice at puberty
vi adrenalin
>> 149
Chapter review Understanding 5 Describe the function of each of the following parts of the eye: • iris • lens • retina • choroid 6 A pupil will dilate under certain conditions. Explain why and when this would occur. 7 Describe the function of each of the following parts of the ear: • eardrum • ossicles • semicircular canals 8 Explain in a sentence what happens when we smell something. 9 Describe how you could reduce the sensation of taking an unpleasant medicine. 10 Use examples to explain what is meant by:
Applying 13 Identify the parts of the tongue that detect sour tastes. 14 a State two reasons why organisms need to be responsive to their surroundings. b Explain why response to a stimulus often requires coordination. c Identify the two systems of coordination in humans. 15 a Identify four stimuli to which you respond. b State the type and location of the receptors that detect these stimuli. 16 Identify which part of the nervous system: a is the centre for decision making b controls the heartbeat c transmits messages from the PNS to the brain d receives and interprets messages from the eyes and ears 17 Glucose levels in your blood are carefully controlled so they remain within certain limits.
a a stimulus
a State the name of this careful control.
b an effector
b Explain why it is necessary to control blood glucose levels.
c a receptor d a response 11 Neurons do not touch each other. They have small gaps between them.
c Identify which coordinating system (nervous or endocrine) is most involved in controlling glucose levels. d Name the condition in which this control is defective.
a State the name of these small gaps.
Evaluating
b Describe how neural messages cross these small gaps.
18 Evaluate the importance of our senses. How would we survive without one or all of them?
12 a Clarify what is meant by a reflex action. b Identify three of your own reflex actions.
Creating
c Explain why reflex actions need to be very fast and how they achieve these speeds.
19 Construct a labelled diagram to illustrate the structure of a typical neuron. Worksheet 4.10 Wordfind
Worksheet 4.11 Crossword Worksheet 4.12 Sci-words
150
Reproduction
5
Prescribed focus area The applications and uses of science Current issues in research and development in science
Key outcomes 5.3, 5.5, 5.8.1, 5.8.4
•
Human males and females have very different reproductive systems. Each carries out a specific function and produces specific hormones.
•
The reproductive systems of males and females provide the correct environment for the sperm and egg cells they produce and the zygote that forms through fertilisation.
•
Some sexually transmitted infections are treatable while others currently have no cure.
•
When cells divide, they transfer genetic information to their daughter cells.
•
Cells reproduce in two ways, mitosis (most cells) and meiosis (forming gametes or sex cells).
•
All embryonic cells in the first stage of pregnancy are indentical. They then differentiate into different types.
Additional
Cells reproduce by dividing, allowing an organism to grow, repair itself and reproduce.
Essentials
•
Unit
5.1
context
Types of reproduction
Reproduction is the chain of events that leads to the creation of new individuals. The only way a species can survive is if some of its individuals reproduce. Reproduction also passes on genetic
Fig 5.1.1 These newborn possums snuggling in their mother’s pouch will eventually go onto reproduce themselves, giving their species some chance of survival.
Cells and reproduction All living things (organisms) are made from microscopic building blocks called cells. Cells make up all animals (including us humans), all plants and all fungi. Cells even make up organisms such as bacteria that cannot be seen with the naked eye. Almost all cells in an organism contain a nucleus. Within each nucleus are thin threads called chromosomes. Chromosomes contain all the genetic material needed to build every part of the organism and determine what each different type of cell will do. Different animals and plants have different numbers of chromosomes. Human cells, for example, contain 46 chromosomes while those of our closest relative, the
152
material from parents to their offspring. This genetic material is held within its cells. Not all living things or organisms reproduce in the same way. There are two types of reproduction: asexual and sexual reproduction. While asexual reproduction does not require sex, sexual reproduction does.
chimpanzee, have 48 chromosomes. Carp have 104, koalas have 16 and fruit flies only have 8. Pineapples have 50 chromosomes while peas have 14. Chromosomes are made up of many small segments known as genes. Genes determine every characteristic of an organism. If you have blue eyes, it is because your chromosomes carry the gene for blue eyes. Although cells contain all your genes, each type of cell uses only a few of its instructions. The blue-eye gene, for example, instructs the cells in the iris of the eye to turn blue. The same gene is, however, ‘turned off’ in cells in the heart, blood, brain, muscles and skin. Genes are made of a chemical called DNA (deoxyribonucleic acid). When cells reproduce, DNA copies itself, passing on its instructions to the newly formed cells. Reproduction passes on chromosomes, genes and DNA from parent organisms to their offspring. This ensures that each new generation is similar to its parents in the way they develop, look and act. Go to
Science Focus 4 Unit 3.1
Asexual reproduction Asexual reproduction is reproduction that does not need sex. It therefore only requires one ‘parent’ organism. Although this might seem strange, it is happening right now within your own body. All body cells reproduce in this way, during growth or to repair damage. Microbes (fungi, and single-celled organisms or protists and bacteria) reproduce this way too. So do many types of plants. In asexual reproduction, new cells are formed when older ones (called parent cells) divide to form two identical copies (called daughter cells). The cell divides by a process called mitosis.
Unit
Cytoplasm: liquid that acts as the cell’s chemical factory. The cytoplasm makes new chemicals for the cell.
Mitochondria: the powerhouses of the cell that produce energy for the cell. Plant cells only have a few while animal cells have lots.
Vacuole: stores nutrients and wastes. Plant cells have one large vacuole full of sap while animal cells have several very small vacuoles.
Animal cell
Cell wall: only found in plant cells. Includes cellulose to provide strong fibrous support. Animal cells do not need a cell wall since support is given by the animal’s skeleton.
5.1
Fig 5.1.2 The chromosomes contained in the nucleus of an animal or plant cell contain all the genetic information required to build a new organism.
Plant cell
Cell membrane: encases the cell and controls the flow of chemicals in and out of the cell.
Nucleus: the control centre of the cell. It contains long thin threads called chromosomes.
Chloroplast: only found in plant cells. Contains chlorophyll which is needed for photosynthesis.
Chromosomes: determine what a cell does and what type it is, e.g. muscle cell, redblood cell, fat cell. Most cells in the human body contain 46 different chromosomes.
Step 1: The parent cell first doubles its number of chromosomes.
Step 2: These then separate into two groups.
Step 3: A new nucleus forms around each group of chromosomes.
Step 4: The cell then divides to produce two daughter cells, each containing the same number and type of chromosomes as the parent cell.
Fig 5.1.3 Asexual reproduction occurs via a process known as mitosis. A parent cell splits into two genetically identical daughter cells.
Clones and mutants In asexual reproduction, genetic material only comes from one parent cell and so daughter cells are genetically identical to the parent cell. Cells produced this way are sometimes referred to as clones. Clones do not always look the same since the environment also affects the organism and how it grows. Two cloned trees, for example, may look very different because of different soil types, rainfall and the type of insects that eat their foliage. Occasionally a fault occurs when a parent cell splits in two. If this happens then the genes of the daughter cells will be slightly different to those of their parent cell. The copies are not exact and so the offspring can exhibit a new and unexpected characteristic. This is known as a genetic mutation.
153
Types of reproduction
Fig 5.1.4 All Granny Smith apple trees are clones of a single tree that appeared in Sydney due to a genetic mutation.
Fissure Fi
All Granny Smith apple trees can be traced back to a mutant crab-apple seedling that appeared in an orchard in Sydney around 1868. The seedling was then cloned. There are now millions of Granny Smith apple trees worldwide, all genetically identical to the original mutant tree. Likewise, all navel orange trees are descendents of a mutant orange tree that was found in Brazil in 1870.
Fission: the parent cell grows and splits across the middle to form two identical daughter cells. Bacteria and protists (single-celled organisms) reproduce by fission, as do some algae and fungi.
Fission can occur very rapidly. A single bacterium can easily reproduce to become millions under right conditions. This is why un-refrigerated food quickly goes ‘off’ and wounds easily become infected in the tropics.
Spore vessel
Advantages to asexual reproduction Asexual reproduction is useful if: • the environment is constant, the organism is suited to it and there is no advantage in changing • the species is rare and there is not much chance of meeting an organism of the same type but of the opposite sex • the organism can’t move much. Types of asexual reproduction Asexual reproduction can occur by fission, budding, spores and fragmentation followed by regeneration. Prac 1 p.159
Bud scar
Fragmentation: occurs when pieces break off from an organism. Each piece can then regenerate into a new organism. Many plants can be propagated this way. It is then known as vegetative propagation.
In this image, a new starfish is regenerating from a single leg that was torn off another starfish. Regeneration can also happen in earthworms, mushrooms and many flowering plants.
Fig 5.1.5 Asexual reproduction only needs one parent cell. Offspring are genetically identical to the parent.
154
Budding: the parent cell splits unevenly into two. One cell (the mother cell) is much larger than the other (the bud cell). These bud cells later form buds of their own.
Yeast cells reproduce by budding, as do many cnidarians such as coral, jellyfish and anemones. Yeast is important in the production of bread and alcoholic beverages.
Spores: these are reproductive cells that form inside structures called spore vessels. Spore vessels are commonly seen under the fronds of ferns. Many fungi, mosses, ferns and algae use spores to reproduce.
When released, spores are able to be spread by wind, water or other living things. When the spores reach a suitable environment, they grow and form a new organism.
Bud
Prac 2 p. 159
• when the environment changes because of daily or seasonal changes or long-term changes such as ice ages or periods of global warming. Variation allows the better adapted organisms a chance of survival when conditions change for the worse. Sometimes organisms that can reproduce sexually also have the ability to reproduce asexually.
5.1
Sexual reproduction begins when male and female sex cells (known as gametes) fuse to form a new cell called a zygote. This zygote cell then divides over and over to produce the number and variety of cells needed to form a new organism. The fusing of gametes is called fertilisation. Each gamete only carries half the number of chromosomes and cannot build the zygote by itself. Two gametes are needed to build the full number of chromosomes and fertilisation is the only way this can occur. For fertilisation to occur, both gametes must be properly formed, fully developed and released at the same time.
Unit
Sexual reproduction
Science
Clip
Male, female or both? Some animals are hermaphrodites. Hermaphrodites possess both male and female reproductive organs making them capable of selffertilisation. Often they mate with other hermaphrodites of the same species, ‘deciding’ on mating which will be male and which will be female.
Fig 5.1.7 Slugs and snails are hermaphrodites. One of these mating slugs will be acting as the male, the other the female.
Fig 5.1.6 The cells in a chimpanzee have 48 chromosomes. Twenty-four cells come from its father and the other 24 come from its mother.
Advantages to sexual reproduction A small change in the environment could easily wipe out a species if there is little variation among the individuals in the species. The species is, however, far more likely to survive if there is a lot of variation. Asexual reproduction produces offspring that are identical to their single parent cell. This makes them susceptible to extinction if unfavourable conditions occur. In contrast, sexual reproduction produces offspring that are similar, but different to their parents. The natural variation arising from sexual reproduction gives the species a better chance of long-term survival: • in environments that are unfavourable to them in some way. This allows species to colonise environments quite different to the ones that they originally came from
Plants and sex Flowers are the sexual organs of plants. A few plants, such as willows, poplars and kiwi fruit, produce flowers that are either male or female, but not both. Most flowers, however, are hermaphrodites: they contain both male and female parts. Female sex cells, called ovules, are produced in the flower’s ovaries. The male sex cells called pollen grains are produced in the flower’s anthers. Insects, birds, wind or water can all transfer pollen grain from the anther of one flower to the stigma of another (cross-pollination) or sometimes to the stigma of the same flower (self-pollination). This transfer is known as pollination. Fertilisation occurs if the pollen successfully joins with the ovule. After fertilisation, the ovule develops into a seed and in some cases forms fruit. Worksheet 5.1 Plant reproduction
Prac 3 p. 160
155
Types of reproduction The carpel (female parts of the flower)
The stamen (male parts of the flower) Anther: contains pollen. Pollen grains are the male plant gametes.
Ovary: contains the ovule structure
self-pollination cross-pollination
Ovule: a single female plant gamete is found here. Once fertilised, may form seed and eventually fruit.
petal
sepal
nectar
Filament: supports the anther
Fig 5.1.8 Most flowers are hermaphrodites, having both male and female parts. This gives them the ability to pollinate themselves.
Science
Clip
His penis on his head! A male spider has its sex organ protruding from its head. From here it can insert it easily into the right position in the female’s belly. Sometimes his ‘penis’ breaks off inside the female, leaving a plug that stops any other males from fertilising the female. The only way the female will cooperate is if the male lets her eat him during the process.
Animals and sex Most animals reproduce sexually. Males produce gametes called sperm and females produce gametes called eggs or ova (a single egg is more properly known as an ovum). Sperm and eggs are produced in structures called gonads. A male makes sperm in his testicles (more properly known as testes—a singular testicle is more properly called a testis). A sperm cell moves about by flicking its tail, which is known as a flagellum (plural: flagella).
Step 1: Parent cell with a complete set of chromosomes. The parent cell of a koala would, for example, have 16 chromosomes.
Step 2: Chromosomes double. The koala cell would now have 32 chromosomes.
Females are born with immature eggs already in place in their ovaries. Later in her life, individual eggs mature and are released into the reproductive tract. This process is known as ovulation. For humans, this process starts at puberty. Eggs carry their own store of food. They do not have flagella and cannot move about by themselves. Sperm and egg cells are formed by meiosis. This is a process where one parent cell produces four daughter cells, each daughter cell having only half the number of chromosomes of the original parent cell. For a new animal to form, a single sperm must add its chromosomes to those of an egg. In this way, the zygote has its full quota of chromosomes.
Step 3: The parent cell divides. The koala now has 16 chromosomes.
1st division
Fig 5.1.9 In meiosis, the new cells have half the number of chromosomes of the parent cell.
156
Step 4: The cells divide again. Each daughter cell has only 8 chromosomes, half the number needed to make a koala.
2nd division
Unit
5.1
Fig 5.1.10 Fish commonly fertilise outside their bodies. During spawning, the female lays her eggs and the male sheds sperm over them. After fertilisation, the eggs are left to hatch. These mandarin fish are about to spawn.
Fertilisation can be: • external—it happens outside the bodies of both the male and female • internal—it usually happens within the body of the female. After fertilisation, the new zygote will either develop inside the female or will be laid soon after as a fertilised egg.
Fig 5.1.12 Many animals have developed highly specialised penises to ensure that the sperm is delivered correctly into the female. This SEM image is of the penis of a damselfly.
Development of the embryo The cell formed at fertilisation (the zygote) is now ready to grow. It does this by mitosis, dividing over and over and doubling in number to become an embryo. If the embryo receives sufficient nourishment and is not harmed by environmental factors such as a hungry predator, it should grow to become a fully developed organism. Some organisms lay a large number of eggs at one time, but only a few will survive to adulthood. Other organisms have only one offspring at a time. Generally, organisms that provide little parental care fertilise many eggs at once. In contrast, animals that provide a lot of parental care fertilise as few as one egg at a time. Fig 5.1.11 This scanning electron microscope (SEM) image shows two mealworm beetles mating. Fertilisation is internal.
Science
Science
Pregnant males!
Virgin birth
Seahorses fertilise internally but it’s the males that get pregnant! The female inserts her oviduct tube into the male and lays her eggs inside his body where they are fertilised. The male is pregnant for several weeks until he gives birth.
In some species, an egg cell can become a new individual without ever being fertilised by sperm! This is called parthenogenesis. In aphids, unfertilised eggs all become females. In honeybees, only males result from parthenogenesis. Desert whiptail lizards only reproduce by parthenogenesis, so the entire species is female!
Clip
Clip
157
Types of reproduction
5.1
QUESTIONS
Remembering 1 State the scientific name for human gametes in: a the male
15 Identify which of the following organisms best matches the type of asexual reproduction they use to reproduce: a bacteria
i fragmentation and regeneration
b yeast
ii budding
a internally
c ferns
iii fission
b externally
d starfish
iv spores
b the female 2 Name an animal that fertilises:
3 A chimpanzee has 48 chromosomes. Specify how many chromosomes come from its mother and how many from its father.
Understanding 4 Define the following terms: a pollination b fertilisation c hermaphrodite d mutation e pollination 5 Explain how asexual reproduction is happening right now in your own body.
16 New plants are often made by taking ‘cuttings’, a small piece of the original which is then placed in soil until it forms roots. Identify what specific type of reproduction this is. 17 If a bacterial cell divides once every five minutes, calculate how many cells will be present at the end of: N a 10 minutes b 30 minutes c 1 hour d 1 day
Analysing 18 Classify the following examples of cell reproduction as either mitosis or meiosis:
6 Explain how fission is related to food going ‘off’.
a new skin cells are forming to repair a cut
7 Describe the characteristics of spores that enable them to be spread by air, water and other organisms.
b sperm cells are forming in the testes
8 Explain why sexual reproduction is the better method of reproduction in a changing environment. 9 Explain why it is best if kangaroos have only one offspring at a time. 10 Two trees have exactly the same genes. One is growing in far north NSW and the other in southern Tasmania. Explain why they look quite different from each other. 11 Fish do not provide much care to their young. Explain why it is beneficial that they fertilise many eggs at once. 12 Predict what effect overuse of insecticide will have on the reproduction of plants that are pollinated by insects. 13 Explain why nectar is located deep inside the lower part of the flower and below the anthers. 14 Many plants have brightly coloured flowers that contain sweet sugary syrup called nectar. Explain how this assists in the reproduction of these plants.
158
Applying
c white blood cells are forming to fight off infection 19 Contrast the following by listing their similarities and differences: a a plant cell and an animal cell b the four different methods of asexual reproduction
Evaluating 20 Propose a reason why earthworms and mushrooms can regenerate lost body parts but still eventually die. 21 Bacteria reproduce easily in humans. Use this information to propose which temperature best suits these bacteria. 22 Propose a reason why every cell in a human contains all the instructions needed to construct the body, yet only a few instructions are used by each cell.
Creating 23 Construct a crossword to summarise sexual and asexual reproduction. Include definitions and specific examples of the different types of reproduction.
Unit
INVESTIGATING
Investigate your available resources (for example, textbooks, encyclopaedias, internet) to complete these tasks. 1 Find information about the weather, water and food availability and healthcare of different countries. Choose a country from each continent and then use the information you find to predict which countries of the world might have: • a high rate of pregnancy • few babies dying in their first year • a high rate of women dying in childbirth.
5.1
Choose one method of propagation and attempt it at home.
e –xploring To assist with the following activities, a list of web destinations can be found on Science Focus 3 Second Edition Student Lounge. • Explore the parts of a flower and investigate how they reproduce. • Research DNA, its structure and function.
PRACTICAL ACTIVITIES
1 Asexual reproduction in plants Non-flowering plants generally reproduce asexually and it is generally a fast, easy-to-observe process
Aim To examine asexual reproduction in plants
Equipment • an onion and a potato with eyes • knife (Note: many other plants could be substituted for the onion and potato, such as strawberry runners, Chinese willow stem cuttings or orchid bulbs.)
2 Examination of spores Aim To examine spores using a stereomicroscope
Equipment • • • •
2 Find out how to take a cutting from plants in the garden and how vegetative propagation is used in agriculture.
5.1
5.1
stereomicroscope fern leaf with visible spores tweezers filter paper
Method 1 Cut the onion in half, lengthways. 2 Draw the onion, labelling the part that is connected to the roots and the part that would shoot to form a new plant. 3 Draw the potato. Identify the buds.
Questions 1 The buds of an onion can become new individuals. Explain why this is an example of asexual reproduction. 2 If the ‘eye’ of a potato is a bud, predict what might happen if you cut out a potato eye and planted it.
Method 1 Place your leaf under the microscope and examine the spore vessels. Draw a section of the leaf and describe in words what you see. 2 Use the tweezers to break open some of the spore vessels onto the piece of filter paper. Examine these under the microscope and describe them.
Questions 1 Describe how easy it was to break open the spore vessels and predict how many spores you think were in each. 2 Describe how easily you think the fern spores could be spread. 3 Identify some ways in which the spores will be spread.
159
Types of reproduction
3 Flower dissection Aim To examine the reproductive parts of a flower
!
Safety • Some plants (e.g. oleander and rhus) are known to cause allergic reactions in some people. • The sap of some plants (e.g. agapanthus) may cause skin irritation in some people.
Equipment • dissecting instruments • large flower • hand lens
Method 1 Examine your flower. How many petals and anthers does it have? 2 Carefully cut the flower so that you can see all its parts. 3 Draw the flower and label its different parts. 4 Use two different coloured pencils or highlighters to colour the male and female parts of the flower. 5 Examine the flower with your hand lens and note any unusual features. 6 Examine the flower of a different plant. List the differences and similarities that you find.
Questions 1 Assess whether the flower would have been capable of self-fertilisation. 2 Define the term hermaphrodite. 3 Assess whether the plants in Figure 5.1.13 reproduce by sexual or asexual reproduction.
Fig 5.1.13
160
UNIT
5.2
context
Human reproductive systems
Puberty is the time when your body prepares itself for reproduction. Puberty is marked by dramatic physical and emotional changes and the start of a strong sexual drive. This instinct to mate
is driven by hormones produced in the reproductive system. Males and females have very different reproductive systems producing very different cells and very different hormones.
The male reproductive system The male sex cell or gamete is sperm. Sperm are microscopic tadpole-like cells that are formed in the two testes. Most of each testis is made up of tiny, tightly coiled tubes called seminiferous tubules. Millions of sperm are formed in these tubes each day after puberty and will continue to be produced throughout a man’s adult life (the quantity of sperm produced will, however, reduce as he ages). Lining the walls of the tubules are hairlike cilia that beat back and forth, moving the sperm along to another group of coiled tubes located at the top of each testis. It is here, in the epididymis, that the
Fig 5.2.1 The human reproductive system matures at puberty due to hormonal changes.
Blladddeer:: sttorres urine rine ri ne..
Sperm duct (vas deferenns): connects teste tees to the penis. Penis: contains sponge-like tissue that fills with blood when the male is sexually aroused. The tissue expands and is harder than before, causing an erection.
Ureters: deliver urine from the kidneys to the bladder.
Epididymis: coiled tubes at the top of the testis in which sperm are stored.
Testicle or testis: made up of tiny, tightly coiled tubes called seminiferous tubules in which sperm form and mature. Testes also produce the male sex hormone testosterone.
Prostate gland, Cowper’s gland and seminal vesicle: add fluids to sperm to make semen. Not shown: Urethra: tube running the length of the penis. It empties the bladder of urine and allows the passage of semen. Scrotum: sac holding the testes.
Fig 5.2.2 The human male reproductive system
161
Human reproductive systems
The female reproductive system The female sex cell or gamete is the egg or ovum (plural: ova). Although still microscopic, a single egg is massive when compared to the size of a single sperm. Unlike a sperm cell, an egg cell has no way of moving on its own. Eggs are released after puberty by the two ovaries. The ovaries do not actually produce eggs. Instead they are a ‘store’ of immature eggs that have been in place since birth. Every 28 days or so an egg will mature in the ovary and will be released as part of the menstrual cycle. A woman is born with about 500 000 eggs in each ovary and hundreds will mature and be released between puberty and menopause. Menopause is when no more eggs are released. This usually happens between the ages of 40 and 50. Prac 1
Fig 5.2.3 Immature sperm in the seminiferous tubules in a male’s testes
Science
Clip
Hanging testicles Sperm need just the right temperature to be formed and to survive. For this reason, the testes must hang outside the body in a sac called the scrotum. This way, maximum sperm production is ensured by keeping the testes cooler than the normal body temperature of 37°C. Wrinkles in the scrotum allow it to stretch and lower the testes away from the body when too hot. When too cold, the scrotum gets even more wrinkly as the testes raise towards the warmth of the body.
sperm mature and are stored, taking several weeks to do so. On orgasm, the sperm travel from the epididymis to the penis via the sperm duct and urethra. Along the way they pass the prostate gland, seminal vesicle and Cowper’s gland which all add more fluid to the mixture. This mixture of fluid and sperm is called semen. Although both semen and urine pass along the urethra, it is not possible for both to pass through at the same time. Male secondary sexual characteristics Testes also produce the male sex hormone testosterone which gives a man secondary sexual characteristics such as: • the body becomes more muscular • the deepening of the voice at puberty • the growth of hair on the body and face • the tendency to go bald.
p. 167 Female secondary sexual characteristics The ovaries also produce the female sex hormones oestrogen and progesterone. These hormones are responsible for female secondary sexual characteristics: • the development of breasts • the menstrual cycle • less muscle and body hair than a man.
The menstrual cycle At the start of every menstrual cycle (day 1), an immature egg starts to develop. The egg is contained in a small sac of cells called a follicle. Both get bigger and bigger until, at about day 14 of the cycle, the egg becomes mature. The egg then bursts from the follicle into the ovary cavity. From here, the egg moves into the fallopian tube or oviduct, moved along by cilia and muscular contractions. While the egg is in the fallopian tube, it is capable of being fertilised. It stays there Science for about seven or eight days during each menstrual cycle, after which it travels to the You dork! uterus, regardless of whether it has been Urban legend has it fertilised or not. that dork is the From the start of every menstrual cycle, technical name for a the lining of the uterus prepares itself for whale’s penis! This receiving the fertilised egg by becoming legend seems to have thicker and with an increased blood supply. started around 1961. Dork has never meant If the egg is not fertilised by about day 25 of whale penis but it the cycle then the lining of the uterus is might describe shed as a mixture of blood, mucus and cell someone who thought debris. This shedding of the uterine lining is it did! known as menstruation or a period.
Clip
Worksheet 5.3 Ovulation
162
Clip
Ovary: releases eggs (ova) and produces the female sex hormones oestrogen and progesterone.
The smooth surface of the ovary of a three-year-old girl
Cervix: the small opening to the uterus. The cervix stretches during childbirth. During sexual intercourse, the penis does not enter the cervix or the uterus.
The much bumpier, scarred surface of the ovary of a 27-year-old woman
The surface of a woman’s ovaries are unscarred before puberty. From puberty onwards, eggs are released from follicles that form on the surface of an ovary. A scar is left behind every time an egg bursts from its follicle. By middle-age, women’s ovaries are dotted with many of these scars.
5.2
Follicles
Unit
Science
Fallopian tube (oviduct): tubes connecting ovaries to the uterus. Fertilisation occurs here. Uterus (the womb): the fertilised egg implants itself in the lining of the uterus to continue growing. The baby develops and grows here for the nine months of pregnancy.
Science
Clip
Vagina: the penis is inserted here during sexual intercourse. Sperm must swim from here to the fallopian tubes if fertilisation is to occur.
Men with breasts, women with beards Fig 5.2.4 The female reproductive system
Worksheet 5.2 Human reproductive organs
Menstruation (period): uterine lining is shed as blood, mucus and cell debris. Bleeding 28 begins 1
27
2
26
Th
4 5 6
s
23
3
enstrual C e M t 28 d yc u ay bo
A
25 24
le
22
7
21 20
Preparation of the egg: in an ovary, a follicle containing an immature egg begins to grow. The uterus lining begins to thicken.
8 e
Preparation of the uterus: 9 ti the uterus lining continues to 19 e l 10 Ferti thicken in preparation for 18 11 fertilisation. The egg moves into 17 12 16 15 14 13 the uterus. If unfertilised, the uterus lining begins to break down. m
If testosterone is given to a mature woman, then she is likely to develop many of the features that characterise males and lose many that indicate that she is female. She will grow facial and body hair, increase her muscle bulk, start to speak a little more deeply and will tend to go bald. Likewise, a mature man will need to shave less and will lose body hair and muscle bulk if he takes oestrogen. Breasts may appear, as may hair on his bald head. However, he will not develop a higher voice. His vocal cords thickened during puberty and will stay that way for life. In the sixteenth to eighteenth centuries, young boys with good singing voices were sometimes made into castrati with removal of their testes. This stopped the thickening of their vocal cords so that they retained a higher-pitched voice throughout adulthood. Castrati often performed in opera and many singing roles were written specifically for them.
Ovulation: the follicle bursts open, releasing a mature egg. The uterus lining continues to thicken.
Fig 5.2.5 The menstrual cycle
163
Human reproductive systems Science
Puberty
Clip
The reproductive organs are present from birth but they do not become fully developed or functional until puberty. Puberty is the time when males and females reach sexual maturity. Not everyone starts or finishes puberty at the same age. Girls tend to start puberty a little earlier than boys. The changes associated with puberty usually start no earlier than 10 years of age and are usually complete by 17. Changes in males at puberty
Period-free mammals Only primates such as humans, chimpanzees, orangutans and gorillas menstruate. In other mammals such as dogs, cats and horses, the unused lining of the uterus is broken down and reabsorbed by the body. The reproductive cycle in these animals is called an oestrus cycle rather than a menstrual cycle.
muscle and bone mass increases growth spurt
facial hair begins to grow voice ‘breaks’ and deepens due to a thickening of vocal cords more sweat and sebaceous oil on the skin is produced, possibly resulting in increased body odour and acne pubic, underarm, chest and leg hair grow penis lengthens and widens testes develop and begin to produce sperm At some stage ejaculation will begin. The first few times, however, there will be only fluid with no sperm as the prostate gland matures before the testes.
Fig 5.2.6 The testes secrete the hormone testosterone from the start of puberty.
Changes in females at puberty
growth spurt
Testosterone stimulates many physical and emotional changes in a boy.
pubic hair and some underarm hair develop breasts develop buttocks develop and hips become wider reproductive organs grow and mature
Menstruation begins. This first period is called the menarche. The first ovulation (release of an egg) occurs 6 to 9 months after menarche.
Fig 5.2.7 The major female hormone, oestrogen, is responsible for menstruation and for many physical and emotional changes in girls.
164
Unit
QUESTIONS
5.2
5.2
10 Identify the parts labelled a–e in Figure 5.2.9.
Remembering 1 Name the part(s) of the male reproductive system that: a produces sperm b stores sperm c add fluids to sperm 2 Name the part(s) of the female reproductive system that: a releases eggs
a b c
b is the location of fertilisation d
c is where the baby develops during pregnancy
e
3 State what semen is made up of. 4 State what menopause is. 5 Specify the hormone(s) that: a causes hair to sprout on the chest of a man b regulates the menstrual cycle
Understanding 6 Explain what is meant by ‘puberty’. 7 Explain the advantages of the testes being located outside the male body. 8 Explain how a woman’s ovaries become scarred over time.
Applying 9 Identify the parts labelled a–e in Figure 5.2.8.
Fig 5.2.9
11 Men grow beards and women grow breasts. These are secondary sexual characteristics. Identify what the primary sexual characteristics are for males and females.
Analysing 12 Contrast the changes that occur in males and females during puberty by preparing a list of similarities and a list of differences.
Evaluating 13 Evaluate the changes that happen to boys and girls at puberty. Some changes are the same. Others are very different. a Construct a Venn diagram like that shown in Figure 5.2.10. b In the diagram, list the changes that happen to boys only, the changes that happen to girls only and those that are common to both. N
a
boys
girls
b c d e
Fig 5.2.8 boys and girls
Fig 5.2.10
165
Human reproductive systems
Height (cm)
14 The graph in Figure 5.2.11 shows the average heights of boys and girls. Use it to answer the following questions. N 190 180 170 160 150 140 130 120 110 100 90 80 70 60 50
boys
15 Testosterone is a banned performance-enhancing drug in elite sports such as athletics and swimming. a Describe what testosterone does to those who take it as a drug.
girls
b Assess why it is a banned drug for sportspeople. c Men naturally have testosterone in their system. Assess what would indicate that they have been taking extra. d Some have suggested that sportspeople should be able to take testosterone. What do you think? Justify your response. 16 Assess whether it is a good or bad thing that: a men are still able to be new fathers at 100 b women rarely give birth after the age of 50
Creating 2
4
6
8 10 12 Age (years)
14
16
18 19
Fig. 5.2.11
a Specify the average height of an eight-year-old boy. b Specify the average height of an 11-year-old girl. c According to this graph, deduce the ages when puberty occurs for males and females.
5.2
17 Construct a flow chart showing what happens in the life of a sperm from production to maturity to fertilisation of an egg. 18 Construct a life-sized outline of a girl and a boy on a large sheet of butcher’s paper. a Draw and label all the parts of the reproductive systems. b Label the changes that occur to each during puberty.
INVESTIGATING
Investigate your available resources (for example, textbooks, encyclopaedias, internet) to answer the following questions. 1 Find how the reproductive systems of a platypus and a kangaroo differ from that of a human. 2 Find the rate of population growth in several countries. Which country has the highest rate and why? Which has the lowest and why? 3 Find out about China’s one child per couple policy and why more male than female babies are surviving under this policy. Evaluate the one child policy and decide whether you agree with it or not.
166
d Boys are taller than girls. Assess whether this statement is true, false or a bit of both. Justify your answer.
e –xploring To explore the human reproductive systems and the body’s changes during puberty, a list of web destinations can be found on Science Focus 3 Second Edition Student Lounge.
Unit
PRACTICAL ACTIVITIES
1 Model reproductive systems
Method
Aim
1 Construct a large, simplified diagram of either the male or the female reproductive system.
To construct a jigsaw or mobile of the male or female reproductive system
2 Cut the diagram into pieces to make either a jigsaw puzzle or a mobile to hang from the ceiling.
Equipment • • • • •
scrap A4 paper scissors coloured felt-tip pens or pencils sticky tape cotton thread or fine string
5.2
5.2
Question 1 Assess how this activity helped your understanding of how the various parts of the reproductive system were connected.
167
UNIT
5.3
Human reproduction
context
Fig 5.3.1 Every parent wishes for a healthy baby at the end of nine months of pregnancy.
Becoming pregnant Science
Clip
No need for men? In 2004, Japanese researchers made history by producing a female mouse, named Kaguya, from two female parents. They did this by using genetic techniques to modify the two parent eggs so that they would fuse together and form a zygote. It is highly unlikely that this technique will be used to make human babies in the foreseeable future.
168
Sperm and eggs Except for sperm and egg cells, all the other cells in the body reproduce by mitosis. In mitosis, the parent cell splits into two identical copies or daughter cells. The parent cell contains 46 chromosomes and so do the daughter cells. The parent and daughter cells contain all of the genetic information required to produce a new human. Sperm and egg cells are unique in that they are formed by a process called meiosis. In meiosis one parent cell produces four daughter cells. The parent cell contains 46 chromosomes but the daughter cells only contain 23 chromosomes. Each contain only half of the required genetic codes needed to make a baby. For fertilisation to occur, a complete set of 46 chromosomes is needed. This is why two cells (a single sperm and a single egg) must fuse.
During pregnancy, a single cell divides and divides to form all the cells, tissues, organs and systems required for life. A human baby normally takes about nine months to form within its mother. These nine months are known as the gestation period.
Sexual intercourse and fertilisation Sexual intercourse (copulation) allows sperm to come into contact with the female egg. During sexual intercourse, the male’s erect penis is inserted into the female’s vagina. When the male ejaculates, muscular contractions push sperm cells out from their store in the epididymis and up the sperm duct. Fluids are mixed in with the sperm as they pass the prostate gland, Cowper’s gland and seminal vesicle to form the mixture called semen. The contractions of ejaculation pump the semen from the penis and into the vagina. Once inside the vagina, the sperm use their tails to ‘swim’ towards the female’s fallopian tubes. A male will normally release between one and five millilitres of semen, containing several hundred million sperm. Only a few hundred will, however, make it as far as the fallopian tubes. Once there, sperm can live from three to five days. If they encounter an egg in this time then the sperm will surround it. However, only one sperm is capable of fertilising it. The surface of the egg
Fig 5.3.2 Sperm cells are able to move by themselves by flicking their tails.
Unit
Umbilical cord: the lifeline providing oxygen and nutrients to the embryo and removing carbon dioxide and wastes. Connects to the placenta.
Amniotic membrane: this sac holds amniotic fluid a little like a balloon holding water. Its function is to protect the embryo and later the foetus.
5.3
changes after a sperm has entered and will stop any more sperm getting in. All the other sperm will die. The newly fertilised cell is referred to as a zygote. It has all the 46 chromosomes and genetic information needed to form a new human. Zygote to blastocyst After fertilisation, the zygote begins a five-day journey to the uterus. Along the way, it divides several times, forming new cells and getting bigger until it forms a fluid-filled ball of cells known as a blastocyst. Up to now, all the required nutrients have come from the original egg. These are running out, however, and the blastocyst buries itself in the lining of the uterus to absorb nourishment from it. This is called implantation. The blastocyst produces a hormone that keeps the lining of the uterus thick and prevents menstruation. The female will have no more periods until after birth. She is now said to be pregnant. Pregnancy tests A missed period can mean pregnancy, but the only definite sign is the presence of a special hormone produced by the blastocyst. This hormone is present in a pregnant woman’s blood and urine. This hormone is detected by over-the-counter pregnancy tests.
The zygote cell has split to become four.
ovum
fully formed. Its eyes can easily be identified, as can its fingers and its brain, which does not yet fill its head cavity.
Morula: a clump of up to 80 cells, the stage before becoming a blastocyst, that is about to enter the uterus.
Zygote: begins a five-day journey to the uterus. On its way, it divides several times to form new cells.
Fertilisation: many sperm reach the egg but only one can penetrate it.
Fig 5.3.4 The body systems of this six-week-old embryo are almost
Implantation: the blastocyst buries itself in the lining of the uterus and starts to absorb nourishment from it.
Blastocyst: a ‘large’ fluid-filled ball of cells.
Fig 5.3.3 The first week from fertilisation to implantation
169
Human reproduction Embryo to foetus After eight weeks, the embryo becomes a foetus. The foetus is protected by a pool of amniotic fluid, surrounded by the amniotic membrane. Oxygen and nutrients come from the placenta via a lifeline called the umbilical cord.
The next nine months Science
Blastocyst to embryo As the cells in the implanted blastocyst multiply, they start to move around and differentiate. This means they become different from each other. After about eight weeks, the beginnings of all the major body systems have formed and the heart has begun beating. The developing baby is known in these eight weeks as an embryo. The embryo is very vulnerable, particularly to alcohol, nicotine or drugs the mother may take during that time. This is one reason why many pregnancies are miscarried (naturally terminated) in the first eight weeks.
Fact File
Stem cells All the cells in the blastocyst are identical and are known as embryonic stem cells. Stem cells have the ability to change (differentiate) into all the different types of cells that the body needs to carry out the different tasks the body needs to do. Embryonic stem cells offer a potential cure to diseases and injuries that have damaged brain and nerve cells that cannot be repaired using current medical technology.
placenta villi
umbilical cord amniotic fluid
38 week foetus endometrium (uterus wall)
plug of mucus blocking cervical canal
Fig 5.3.6 A foetus, two weeks away from birth Worksheet 5.4 Pregnancy
Weeks period of dividing zygote, implantation and beginning embryo 1
2
usually not susceptible to teratogens
embryonic period, weeks
foetal period, weeks
full term
indicates common site of action of teratogen 3
central nervous system
heart
4
5
6
7
8
9
16
20–36
38
40
brain heart eye
palate eye
arm leg
ear
ear
external genitalia
teeth
central nervous system heart arms eyes legs teeth palate external genitalia ear prenatal death
major structural abnormalities
physiological defects and minor structural abnormalities
What can go wrong
Fig 5.3.5 Development of the baby during gestation—the red dots indicate the organ or feature that can be badly
170
affected by a teratogen at that stage. A teratogen is an agent, such as a drug, that can affect the embryo or foetus.
Slapping the baby It is common in films and on TV to see a midwife or doctor slap a newborn baby’s bottom. This is to make it cry so that the lungs can be cleared of amniotic fluid.
Science
Clip
Giving birth through a ‘penis’ Female hyenas have a penislike projection that sticks out from their body as far as 18 centimetres. They urinate through this ‘penis’, mate with male hyenas through it and also give birth to their pups through it. The pups are as big as one kilogram and so it’s not surprising that the ‘penis’ often splits causing some first-time hyena mothers to bleed to death.
Twins Fraternal twins result when two separate eggs are fertilised by two separate sperm. They are the most common type of twins and don’t look any more alike than any two brothers or sisters. They can also be different sexes. Identical twins result when a single fertilised egg splits completely in two. Identical twins come from the same egg and sperm and so are genetically identical. Some scientists believe that a third type may be possible. Half-identical twins could be conceived if the mother’s egg splits before fertilisation and each half is then fertilised by a different sperm. This could explain why some fraternal twins look so alike. Conjoined twins are identical twins that are joined at some part of the bodies. It is generally thought that a single fertilised egg splits to form identical twins but for some reason the split is never completed. Another theory is that the egg splits completely but identical
5.3
Clip
Birth If all goes well, a baby is born approximately 280 days (close to nine months) after fertilisation. The cervix dilates (relaxes) to let the baby through. The amniotic membrane around the baby splits and amniotic fluid rushes out of the woman’s vagina, a moment known as ‘breaking of the waters’. The uterus contracts strongly at regular intervals. This is known as labour and eventually these contractions squeeze the baby out head first. After the birth, the placenta is delivered and the umbilical cord is cut. Your belly button marks the place where your umbilical cord was once attached. The baby starts to breathe air for the first time as it is born. Crying helps to clear fluid from its lungs.
Unit
Science
Fig 5.3.7 Identical twins result when a single fertilised egg splits completely in two.
stem cells in both twins find each other, fusing the twins back together. The occurrence of conjoined twins is rare. Some can be surgically separated, although others share vital organs making the operation either impossible or incredibly risky. Prac 1 p. 173
Science
Clip
The famous Bunker boys Conjoined twins are sometimes incorrectly known as ‘Siamese twins’ because of Chang and Eng Bunker. The boys were born conjoined in 1811 in Thailand (then called Siam) and later became famous through starring in P. T. Barnum’s travelling circus. Chang and Eng were attached at the torso, sharing some flesh and cartilage. They both had working livers but these were fused into one. Although they could be easily separated now, the operation was not possible then. Both married and together they fathered 22 children! Eventually, the extended family split. In 1874, Chang died and, within a few hours, so did Eng.
171
Human reproduction
5.3
QUESTIONS
Remembering
Applying
1 Specify the number of sperm: a released in one ejaculation
10 Identify the most dangerous time of pregnancy in terms of potential harm to the developing baby.
b that penetrate the egg
Analysing 11 Compare identical, fraternal and conjoined twins by listing their similarities and differences.
Understanding 2 Define the terms:
12 Distinguish between the following by placing them in order from smallest to biggest: blastocyst, zygote, egg, morula, sperm
a copulation b gestation 3 Match the following words with the description that best describes them: a mitosis
i most human cells have 46
b meiosis
ii between 1 and 5 mL is ejaculated
c chromosomes iii sperm and egg cells are formed this way d semen
iv all other body cells are formed this way
4 Sperm have a relatively long way to go to fertilise an egg. Describe two methods used to get there. 5 Explain how a female can become pregnant up to two days after she had sexual intercourse. 6 Describe how the foetus is protected inside the mother. 7 Explain why the foetus does not drown in the amniotic fluid. 8 A woman knows she is about to give birth when her waters break. Explain what this means. 9 Explain why it is good to hear a newborn cry loudly.
13 Distinguish between the following by placing them in order from smallest to biggest: baby, foetus, blastocyst, embryo
Evaluating 14 Refer to Figure 5.3.5 and calculate how long it takes for the following to form: N a central nervous system b external genitalia 15 A mother was drinking alcohol heavily and taking drugs at the following stages of pregnancy. Refer to Figure 5.3.5 and assess what effect her behaviour might have on the baby: a weeks 8 to 20 b weeks 4 to 5 16 When a baby is first born, the bones of the skull aren’t joined. Assess how this is helpful for the birthing process.
Creating 17 Construct a flow chart showing what happens in the development of a baby from zygote to birth.
172
Unit
INVESTIGATING
Investigate your available resources (for example, textbooks, encyclopaedias, internet) to answer the following questions. 1 a Find out what an imaging technologist does. It may be possible to interview one at a local hospital or clinic. L b Imagine you are a medical imaging technologist. Construct a diary entry for a typical day, explaining the patients you met and the tests you performed. 2 Find out about the ‘rhesus factor’ and how it can cause miscarriage during pregnancy L
b Describe how the problem is avoided using medical treatment.
5.3
5.3
c Present your information as a brochure for women who have just become pregnant.
e –xploring To explore week by week changes occuring in a baby during pregnancy, a list of web destinations can be found on Science Focus 3 Second Edition Student Lounge.
a Investigate how it affects the mother and foetus.
5.3
PRACTICAL ACTIVITIES
1 Survey of twins Aim To determine the percentage of twins in a population
Equipment • paper • pen • computer with Excel® or calculator and protractor
Method 1 In groups, construct a survey that determines:
2 Display your data as a table or spreadsheet. N 3 Calculate the percentage each group represents compared to the whole school population. N 4 Construct an accurate pie chart showing the percentages of ‘non-twins’, identical twins and fraternal twins. N
Questions 1 Describe the differences in how identical and fraternal twins are formed. 2 Explain why fraternal twins can be different sexes while identical twins are always of the same sex.
• the total number of students at your school • how many students at your school have a twin at the same school or at another school • how many of those twins are identical and how many are fraternal • how many are male and how many are female.
173
UNIT
5.4
Reproductive health
context
Our reproductive systems are vulnerable to many infections, diseases and problems. Some are deadly while others are just annoying. Some are painful while others stop some people from becoming parents. Other people are physically able to become parents but do not want to.
Fig 5.4.1 Alcohol has been shown to damage the health of an unborn child.
Contraception Science
Clip
Zap, you’re pregnant! Due to a change in circumstances, many men want to become fathers after a vasectomy. The operation can be reversed but it is rarely successful. Researchers at the University of Adelaide are currently testing a remotecontrolled valve that can be inserted into the sperm duct. The valve is the size of a rice grain and is controlled by radio waves from a ‘zapper’ like that used to lock and unlock car doors. A man with this device would have it ‘shut’ until he and his partner decide that they want to become parents. A simple zap and he’s fertile once more!
174
Contraception prevents unwanted pregnancies. Men can use a condom that also protects both the male and female from most sexually transmitted infections. A permanent method of contraception is a vasectomy, a simple operation in which a man’s sperm duct (vas deferens) is permanently cut so that sperm cannot exit the testes any more. Semen will still exit the penis on ejaculation but it will not contain sperm. All other forms of contraception are used by the female. One surgical method is ‘tube-tying’ in which the fallopian tubes are cut or cauterised (burnt) shut. The table on page 175 outlines the main types of non-surgical contraceptives, their effectiveness, advantages and Prac 1 p. 182 disadvantages.
Fig 5.4.2 If used properly, the simple condom is the only form of contraception that protects against sexually transmitted infections.
Sexually transmitted infections A range of diseases and infections can easily be passed from person to person through sexual contact. These are known as sexually transmitted infections (STIs) but are sometimes referred to as sexually transmitted diseases (STDs) or venereal diseases (VD) or are given nicknames like pox and clap. While the HIV virus and AIDS (the symptoms and infections caused by HIV) is the most feared and lifethreatening sexually transmitted infection, there are many others that can cause serious illness. Most are treatable, but all can leave permanent damage, particularly if treatment is started late. The best cure is prevention. The only way to be completely safe is to avoid all sexual contact. If you do choose to have sex, the use of condoms can greatly reduce the chances of becoming infected with some infections. Other forms of contraception, such as the Pill, give little or no protection from STIs.
Unit
Condoms
How it works Rubber sheaths that fit over the penis and stop semen entering the vagina
The Pill
Consists of hormones which stop ovulation A pill is taken at the same time each day for 21 days, followed by a seven-day break. Some pills do not require any break. Implantable hormonerelease systems are also available
Cap and diaphragm
Rubber devices that fit over the cervix that stop sperm from entering the uterus
Advantages No side-effects, although rare allergic reactions do occur
Disadvantages Reduced sensation and spontaneity
Protects against many sexually transmitted infections
Easy to use, and can protect against problems like cervical cancer May make periods lighter and improve acne
Few side-effects
They are fitted by a doctor and sit inside the uterus for up to eight years
Some shouldn’t be used by smokers or people with circulatory problems as there is a risk of blood clots This risk is reduced with some newer types. The implantable kind can produce irregular bleeding. No protection against sexually transmitted infections Reduced spontaneity Increased risk of bladder infections
Irritates the uterine lining which prevents a zygote from implanting to create a pregnancy
Once inserted, no further maintenance is required
If the condom is of high quality and is used properly, the failure rate is low Actual failure rate is higher due to unskilled use and tearing of low quality condoms
No protection against sexually transmitted infections
IUD (intra-uterine device)
Failure rate
5.4
Contraceptive
Can result in infection and heavier, painful periods
Low if taken as directed, but vomiting, diarrhoea and some antibiotics can reduce the effectiveness of the Pill
Low, especially if used with a spermicide (chemical that kills sperm) They should be replaced yearly and regularly inspected for holes or cracks Low
No protection against sexually transmitted infections
Science
Clip
Go to
Science Focus 4 Unit 4.5
Contraception throughout history! Some birth control methods used throughout history were truly bizarre. Condoms were once made of snakeskin, sheepgut or linen and were washed after use.
175
Reproductive health
Science
Clip
Poxy people! King Henry VIII of England is thought to have suffered from syphilis which may have contributed to the many miscarriages suffered by his wives and his reputed madness late in life. The American gangster Al Capone also had syphilis, eventually going mad from it and dying in prison.
Fig 5.4.3 The herpes virus is one of the most
Fig 5.4.4 A scanning electron microscope image of two
common viral pathogens in humans. It causes inflammation of the skin and mucous membranes, characterised by fluid-filled blisters.
pubic lice (crabs) on human hair—pubic lice are easily spread from person to person during sexual contact. An infestation causes severe itching and a rash.
See a doctor as soon as possible if you notice any unusual symptoms. Some diseases have few symptoms and some people will not even know they have them. Chlamydia, for example, has few symptoms but can cause infertility. Syphilis is potentially deadly and begins How it is spread
with sores called chancres. All symptoms soon disappear, however, and victims often incorrectly think they are ‘cured’. Regular check-ups can identify any problems early. Treatment for many STIs is simply a course of strong antibiotics. Symptoms
Treatment
Viral diseases HIV and AIDS
• caused by the virus HIV • needs direct exchange of body fluids • blood, semen and vaginal fluids of infected people are particularly high in HIV High risk activities: • sexual contact • sharing needles Low risk activities: • kissing • sharing coffee mugs
176
• sometimes flu-like symptoms shortly after infection, then often no symptoms for up to 10 years • eventual breakdown of immune system • results in many infections such as pneumonia • usually ends in death from these infections
• no cure likely for many years • no vaccination • some drugs can slow progress
Herpes
• related to the common cold sore • direct contact with active sore
• large cold sores or pimplelike sores on mouth, on genitals or on nearby region • fever • itching
• no cure • symptoms can be reduced with certain drugs and ointments
HPV (human papilloma virus)
• genital skin contact during sex • not spread through blood or other body fluids
• usually no symptoms • sometimes genital warts or abnormal PAP smear
• vaccination can protect from some forms • usually clears up in 1–2 years • increased risk of cervical cancer
Unit
How it is spread
Symptoms
Treatment
Gonorrhoea (the clap)
• any form of sexual contact
• may have no symptoms
• antibiotics
• can cause extreme pain when urinating in men
5.4
Bacterial infections
• can cause yellow, thick discharge oozing from penis • can cause yellow, thick discharge oozing from vagina • can cause infertility Syphilis (the pox)
• any form of sexual contact
First stage:
• enters through any break in skin
• open, painless sore called a chancre • chancre will eventually disappear
• antibiotics if detected in early stages • no treatment once final stage is entered
Second stage: • if untreated, a rash might develop Final stage (up to 10 years after infection): • loss of brain function • final and deadly infection of body organs • infection of the brain can send you ‘mad’ Chlamydia
• any form of sexual contact
• sometimes no symptoms
• antibiotics
• may cause painful urination in men • possible pus discharge from penis or vagina • can cause infertility
Insect infestations Pubic lice (crabs)
• any form of sexual contact
• itchiness where there is pubic hair, facial hair or even in eyelashes
• special lotions
• severe red rash under pubic hair • infestation may become visible
177
Reproductive health
Cancers and cysts Cancers of the reproductive system are not sexually transmitted but are leading causes of death in both men and women. Cysts are non-cancerous growths that can also hit the reproductive systems of both men and women. In men Prostate cancer is the most common cancer in men, affecting many men over the age of 50. Frequent and restricted urination are common symptoms and simple tests by a doctor will show if cancer is present. Testicular cancer affects about 550 Australian men each year making it the second most common form of cancer among young men. An unusual bump on a testicle may indicate cancer, and all boys and men should perform regular self-examinations of their testes to see and feel if there is anything strange (apart from the epididymis which is easily felt through the scrotum). If detected early enough, testicular cancer is easily treated. If detected late, then it might require an orchidectomy in which the affected testicle is surgically removed. Men can also develop cysts on their testes. In women Breast cancer is the most common cancer in women. Although it tends to affect older women more, young women can develop breast cancer, particularly if there is a family history of the disease. Women can often find any abnormal lumps in their breasts by careful self-examination. A less common form of cancer in women is cancer of the cervix. The human papilloma virus (HPV) is known to cause 70 per cent of these cancers and Australian researchers recently developed a vaccine to protect women. In 2007, the Australian Federal Government started free HPV vaccination of all girls aged 12 or older through the routine school immunisation programs. Likewise, women up to 26 years can have a free vaccination through their doctor. Cervical cancer is easily detected through regular Pap smears performed by a doctor. Women can also develop cysts on their ovaries, often causing painful periods.
A healthy pregnancy To give the baby the best chance of developing normally, a pregnant woman must pay close attention to her nutrition and her lifestyle. This is especially
178
important in the first eight weeks of pregnancy when the body systems of the embryo first develop. Nutrition During pregnancy, women may gain between 10 and 15 kilograms. Pregnant women don’t need to eat much more than usual, but it is important that all the nutritional needs of the developing baby are being met. Iron and calcium intake, for example, must be enough for both mother and child and so the mother may need to increase the amount she normally consumes. Folate is an important nutrient in the first three months of pregnancy since it gives some protection against chromosomal abnormalities in the unborn child. Most mothers easily obtain the necessary amount of folate through their normal diet although a few may need folate supplements.
Fig 5.4.5 A healthy balanced diet is essential for a pregnant woman in order to prevent birth defects.
Drugs A new baby’s blood supply is linked directly to its mother’s and so anything taken by the mother has the potential to cause harm to the developing baby. Research has shown that the incidence of babies born with some physical and/or mental defect is higher for women who smoke or drink during pregnancy than for those that don’t. These infants are also more likely to die during their first week of life. A few drinks in the early stages of pregnancy affect the baby when it is developing the most and can be enough to cause serious harm, even if the woman doesn’t drink for the rest of the nine months. Smoking affects circulation to the baby, and children of smokers are more likely to be underweight and have reduced intelligence than those of non-smokers.
Other substances that cause harm include: • legal drugs such as cortisone (which can cause deformities) and antibiotics (a cause of many problems from stained teeth to deafness) • illegal drugs such as LSD and other hallucinogens (which can increase the risk of miscarriage and deformities) and heroin (which causes the foetus to be addicted as well as the mother). These are not the only substances that can cause negative effects. It is recommended that expectant mothers avoid taking any drug, legal or illegal, during pregnancy unless it is absolutely necessary and advised by their doctor.
The eggs are collected by a needle or laparoscope and put in a salt solution
Drugs are given so that more than one egg matures
In-vitro fertilisation In-vitro fertilisation, or IVF, is one way of combating infertility. In IVF, eggs are fertilised in a container in the laboratory and not inside the woman’s body. For this reason, IVF babies are sometime called test-tube babies.
The eggs are mixed with sperm, left overnight and checked to see if they have been fertilised
The fertilised eggs are incubated for a couple of days and then implanted in the woman’s uterus
Infertility Some people want to have children but are unable to because one or both of them are infertile. Infertility can be caused by an infection or radiation, or have an unknown cause. Some people come to accept this situation or choose to adopt. Some use technology to help them have their own child.
5.4
Fig 5.4.6 Diseases such as rubella (German measles) can cause enormous deformities if contracted by a pregnant woman in the first trimester. This is why all girls are vaccinated against rubella, whereas boys are not.
Unit
In IVF, the woman’s ovaries are first stimulated to release multiple eggs instead of the usual single egg. These eggs are then retrieved from the ovary and placed in a salt solution at body temperature (37°C) until they are ready to be fertilised. Fresh sperm is then added to each egg and allowed to incubate overnight. Any fertilised eggs are allowed to develop for a couple of days in the laboratory after which several embryos will be transferred into the uterus via a small tube. While multiple embryo transfer increases the chance of success, it also increases the chance of multiple pregnancies. Women’s bodies are not built to carry more than one child at a time and multiple pregnancies pose serious risks to the mother and the developing foetuses. Such children are usually born underweight and can have many health problems.
Fig 5.4.7 The steps in one type of IVF treatment.
Science
Clip
Low sperm counts inherited Men with low sperm counts or sperm that do not swim properly are able to become fathers using an IVF technique where a sperm is injected directly into the egg. Sons born through this technique, however, often inherit their father’s infertility problems.
179
Reproductive health Science
Clip
Thalidomide The drug thalidomide was introduced in 1957 and was in wide use until the early 1960s. It was hailed as a wonder drug, a sedative that combated morning sickness, allowing a pregnant woman to have a sound night’s sleep. Morning sickness strikes in the first trimester and so this is when most women were taking it. The embryo is very vulnerable at this stage and the results of taking thalidomide were devastating. It caused terrible malformations (often shortened or absent arms and/or legs) and many deaths. In the 1990s, thalidomide was found to be effective in treating the severe weight loss that occurs in patients with diseases such as AIDS, tuberculosis (TB) and leprosy. Thalidomide has also recently shown promise as a treatment for cancer.
Fig 5.4.8 There are about 5000 people around the world who are carrying the effects of thalidomide taken during their mothers’ pregnancies.
Career Profile
Medical practitioner
Medical practitioners diagnose physical and mental illness, disorders and injuries, and prescribe treatments and medication to restore good health. Many specialise in different fields related to reproduction, including: • obstetrician/gynaecologist—provides medical care before, during and after childbirth • paediatrician—diagnoses and treats diseases of children from birth to early adolescence. A good medical practitioner is able to: • relate to and enjoy working with people • listen to others carefully • demonstrate good communication skills • apply logical and scientific thought to a problem • make observations and draw conclusions based on this information • display a high degree of motivation and self-discipline.
Fig 5.4.9 Your doctor can provide you with information on contraception, pregnancy and STIs.
180
Unit
QUESTIONS
Remembering 1 Specify what the following acronyms mean: a IUD b STIs c IVF 2 List four types of contraception, stating who uses each type and the advantages and disadvantages of each. 3 Specify the only type of contraception that gives protection against some sexually transmitted infections. 4 Name six types of sexually transmitted infections, grouping them into those which have a cure and those which do not. 5 Specify the types of cancers of the reproductive system that can be detected by self-examination. 6 List four legal drugs and four illegal drugs that are likely to harm the unborn baby.
Understanding 7 Define the following terms: a asymptomatic b chancre c cyst L 8 Past US President Bill Clinton said that he did not believe oral sex was sexual contact. In your own words, clarify what you think sexual contact means. 9 Choose an STI and describe how it is spread and how it may be treated. 10 Explain why all girls (and not boys) in secondary school are now being immunised against rubella and HPV. 11 Explain why the first eight weeks of pregnancy are more important to the baby’s future health than the remainder of pregnancy. 12 Explain why folate is important during pregnancy. 13 Explain why: a IVF often results in multiple pregnancies b it may be dangerous for a woman to proceed with a multiple pregnancy
Applying 14 Smoking constricts blood vessels and causes circulation problems. Use this information to explain how this can affect the developing foetus. 15 Identify two things that may cause infertility.
Analysing 16 The rate of adoption is going down. Analyse what might cause this and whether this is related to IVF. 17 Analyse why men are more likely to detect a sexually transmitted infection than women.
5.4
5.4
Evaluating 18 Assess each of the STIs and then order them from what you consider least worrying to most. 19 Contraception is being used more widely today than ever before. Despite this, the number of cases of most sexually transmitted infections is increasing. Propose why this may be happening. 20 Propose a reason why a pregnant woman should not do any heavy exercise in the first trimester. 21 Many people are now choosing home births rather than hospital births. Propose one advantage and one disadvantage of each. 22 Assess the importance of regular check-ups if you have multiple sex partners. 23 The National Health and Medical Research Council released their recommendations for safe alcohol consumption in 2008. The Council claims that people will suffer short or long-term damage to their health if they regularly consume over these quantities. The table below shows a comparison of the new recommendations with those published in 2001. Pregnant women (per day)
Men (per day)
Women (per day)
2001
Maximum 4 to 6 standard drinks
Maximum 2 to 4 standard drinks
Maximum 2 standard drinks per day
2008
Maximum 2 standard drinks
Maximum 2 standard drinks
No alcoholic drinks at all
(Note: 1 standard drink 쏁 1 can mid-strength beer 쏁 100 mL wine 쏁 30 mL spirits)
a Assess the drinking habits of those that you know. Do they fit within the 2001 and 2008 guidelines? b Assess the risks of a pregnant woman having the occasional alcoholic drink. c Assess whether it is realistic to assume pregnant women will have no alcohol during their pregnancy. d Propose a way in which the father could help his partner in achieving this aim.
Creating 24 Construct a flow chart showing what happens in IVF. 25 Design a poster promoting safer sex. What do you think it is and why is it important?
181
Reproductive health
5.4
INVESTIGATING
Investigate your available resources (textbooks, encyclopaedias, internet) to answer the following questions. 1 Find information about toxic shock syndrome. a What is this condition? b Why are tampons no longer likely to cause toxic shock? c Outline some alternatives to using tampons. 2 Find out about caesarean section, a process often used when birth might be particularly difficult. Find out how caesarean section relates to Julius Caesar, the Emperor of ancient Rome. 3 Find out about tests known as Pap smears, how they are carried out and how they work.
5.4
4 Find out about other reproductive problems not discussed in this unit. For example, find how ovarian cysts occur and how they are treated. Present your findings as a leaflet to be placed in a medical centre. L 5 Investigate more fully a sexually transmitted disease and outline: a the signs and symptoms b how the disease is spread c how the spread of the disease can be controlled d how widespread it is e any cures or treatments f current research into this disease. Select a way to present your information in discussion with your teacher. L
PRACTICAL ACTIVITY
1 Methods of contraception Aim To inspect and rank different forms of contraception
Equipment
Method 1 Construct a table like the one below. 2 Inspect each contraceptive device and assess them according to the criteria in the table.
Questions
• access to a selection of contraceptive devices (condom, a blister pack of the Pill, IUD, diaphragm)
1 Rank the contraceptive devices from: • most effective to least effective • easiest to use to hardest to use • easiest to obtain to hardest to obtain • cheapest to most expensive
Contraceptive device Condom Pill IUD Diaphragm
182
Used by male or female?
Effectiveness
Ease of use
Likely expense
Other comments
CHAPTER REVIEW Remembering 1 Name the type of reproduction that requires only one parent and produces offspring identical to the parent. 2 List the types of asexual reproduction and state an example of each type. 3 List the changes that testosterone causes in males at puberty. 4 Specify where fertilisation takes place in the human female reproductive system. 5 Specify how long gestation takes in humans. Give your answer in days and months. N 6 Name the parts labelled a to e in Figure 5.5.1. 7 List three things a mother-to-be could do that would harm a growing foetus.
a
d b
e
c
Fig 5.5.1
>> 183
Chapter review Understanding 8 Outline what happens in pregnancy by arranging these terms in the order in which they are happening: foetus, zygote, fertilisation, implantation, embryo, gametes 9 Recall the reproductive sustem by matching each of the following reproduction terms with its correct definition. Term
Definitions
a ova
i
ring of muscle separating uterus and vagina
b ovaries
ii
male sex organs that make sperm cells
c ovulation
iii
d oviduct
area where sperm cells are stored
v
consists of seminal fluid and sperm
f cervix
i testes
14 Identify possible career paths in the area of reproduction and associated technologies.
Analysing 16 Compare mitosis and meiosis by listing their differences and similarities. 17 Complete the following table to compare flower and human parts. Flower part
vii
area where the embryo implants and grows
Ovary
viii
k epididymis
x
the passageway for menstrual flow and birth of a baby. Sperm is also deposited here
xi xii
Human part
tube that ‘catches’ the ovum passes through the penis. Urine and sperm pass through this tube
xiii
pocket of skin that holds the testes
xiv
female sex organ that produces ova
Comparable function Production of male sex cells
Ovary Sperm
the female sex cell nourishes and activates sperm cells
l seminal fluid
184
13 Identify the scientific skills that would be useful for a career as a medical imaging technologist.
Anther
ix
n urethra
Applying
the process of releasing an ovum once a month
j scrotum
m semen
12 Explain how you can protect yourself against herpes.
vi g vagina h sperm
11 Describe the conditions needed for maximum sperm production.
15 Contrast between asexual and sexual reproduction. the male sex cell
iv
e uterus
10 Explain the advantages of a baby developing inside its mother (as in humans) and not outside (as in most fish).
Male sex cell
Ovule Male sex cells deposited here
Evaluating 18 Assess how mutations can sometimes lead to permanent improvements in a species. 19 Propose how the risk of multiple pregnancies by IVF can be reduced.
Creating 20 Construct a labelled diagram of a flower. Worksheet 5.5 Crossword
Worksheet 5.6 Sci-words
Ecosystems
6
Prescribed focus area Implications of science for society and the environment
Key outcomes 5.4, 5.10, 5.11
•
Energy is vital for all organisms and they must get it from an ecosystem.
•
Green plants get their energy from the Sun via photosynthesis and consumers get their energy by eating other organisms.
•
Water, carbon and nitrogen are all recycled via cycles specific to them.
•
Humans have affected the environment through development, pollution, overgrazing and deforestation, and by introducing animals and plants that have no natural predators.
•
Pollution is the contamination of the environment by unwanted substances.
•
Excessive use of fossil fuels has contributed to the greenhouse effect.
•
Aboriginal people have traditionally been caretakers of the land, while the first European settlers tried to dominate the environment.
Additional
Biotic refers to the living parts of the environment while abiotic refers to the non-living.
Essentials
•
Unit
6.1
context
Energy for life
The planet Earth flourishes with a rich variety and abundance of plant and animal life. Every living thing has its own particular energy requirements and will only be found in areas that meet its exact needs. Plants get their energy from
sunlight. Animals eat plants, or eat animals that once ate plants. The energy absorbed by plants from sunlight therefore passes directly or indirectly to animals and up through the food chain. Whatever the organism is, its ultimate source of energy is usually the Sun.
It came from the Sun! All the energy in an Science ecosystem begins far, far away from it. It starts in Energy the Sun. The Sun gets its energy from billions of Energy is measured in joules, abbreviated as J. nuclear explosions that happen every second on it. These explosions Science (more properly known as nuclear fusion reactions) convert Energy conversions nuclear energy into In one hour, the Sun produces massive quantities of heat more energy than all our other energy and light energy. earthly resources combined can provide in one year! Some of this heat and light eventually reaches Earth, approximately 150 million kilometres away. The Sun is the source of energy for green plants and so provides the foundation on which most food chains are built.
Fact File
Clip
Fig 6.1.1 Animals get their energy from eating plants or other animals.
Conservation of energy in an ecosystem An ecosystem is a specific area in which different organisms live and depend on one another. Everything that happens within the ecosystem involves energy since every living thing (organism) living there requires energy to grow, reproduce, respire, repair body tissues and take in food. To do this, each organism needs to be able to take in energy in some way. Within any ecosystem, energy is conserved. This means that energy cannot be created nor can it be destroyed. Energy can only be converted from one form into another. This is known as the Law of Conservation of Energy. Go to
186
Science Focus 4 Unit 6.7
Plants in an ecosystem Most food chains begin with green plants which trap energy from the sunlight that falls on them. This energy powers the chemical reaction known as photosynthesis: carbon dioxide water sunlight glucose oxygen gas 6CO2
6H2O sunlight C6H12O6
6O2
One product of this reaction is a type of sugar called glucose. Glucose is the food that plants then use to grow, flower and reproduce. In this way, plants convert light energy into chemical energy. Plants are known as producers (or autotrophs) since they produce their own food.
oxygen gas
Unit
sunlight
Consider this simple food chain.
carbon dioxide glucose to rest of plant
Green plants are known as producers since they produce their own food and energy using photosynthesis. Photosynthesis is powered by the sunlight falling on the plant.
water and nutrients
Fig 6.1.2 Plants (producers) use energy from the Sun to run the process called photosynthesis. Photosynthesis is the process by which green plants make their own food, a type of sugar called glucose.
Animals in an ecosystem Herbivores are animals that eat plants, absorbing any glucose stored in them. Herbivores are then eaten by carnivores (meat-eaters) or omnivores (eating plants and meat). Most of these animals are relatively small and soon become the food of larger animals that prey on them. All other organisms rely on the energy stored by plants to meet their energy needs. Organisms that eat plants are referred to as consumers (or heterotrophs). Whatever their food source, animals use the energy they consume to move around, repair tissue, grow, reproduce and carry out all the different functions that occur within an animal. Some animals use much of the energy they gain from food just to keep themselves warm. These animals are commonly referred to as being warmblooded but are more properly known as endotherms. Some examples are dogs, cats, mice, apes, kangaroos, echidnas, possums, birds and whales. Humans are endothermic too: we need the energy from the food we eat to keep our core body temperature at around 37°C. Other animals do not gain their warmth from the food they eat but get it instead by lying in the sunlight. These animals are known as ectotherms and their blood temperature varies throughout the day and will differ for each season of the year. Reptiles such as snakes, lizards and crocodiles are ectotherms. Ectotherms are much more efficient than endotherms in their use of food energy as they waste none of it in generating heat. All of their food energy can go into the other functions vital for life.
6.1
A simple food chain
The insect eats the green plant. In this food chain, the insect is a primary or first order consumer. First order consumers are usually herbivores, eating only plant matter.
The frog (a secondary or second order consumer) eats the insect. Second order consumers can be omnivores (which eat both meat and plants) or carnivores (meat eaters).
The snake (tertiary or third order consumer) eats the frog.
The kookaburra (fourth order consumer) eats the snake.
Fig 6.1.3 A simple food chain in an Australian ecosystem: it starts with a plant and ends with a kookaburra. The kookaburra is unlikely to be caught or eaten by anything else, making it the highest order consumer. If by chance a dingo or some other animal caught it, then that animal would be considered to be a fifth order consumer.
187
Energy for life Science
Clip
100%
Life without light Not all life on Earth depends on sunlight. In 1977, scientists found a number of places deep in the Pacific Ocean where huge tubeworms, crustaceans and octopods all survived on chemosynthetic bacteria. These special bacteria could not get their energy from sunlight as it was far too deep. The bacteria grew near ‘black smokers’, volcanic vents on the sea floor that spewed out hydrogen sulfide which they then used as their energy source.
energy from the Sun
90%
s s s
USED FOR LIFE PROCESSES EG PRODUCING FLOWERS AND SEEDS WASTE PRODUCTS EG DEAD LEAVES ARE BROKEN DOWN BY DECOMPOSERS UNUSED MOLECULES AND THE ENERGY HOLDING THEM TOGETHER ARE EXCRETED AND BROKEN DOWN BY DECOMPOSERS
10%
9%
s USED FOR LIFE PROCESSES EG ESCAPING PREDATORS s SOUND HEAT AND MOVEMENT
1%
0.9%
Fig 6.1.4 Giant tube worms in symbiosis
0.1%
s s
USED FOR LIFE PROCESSES EG MAINTAINING CONSTANT BODY TEMPERATURE !NIMALS THAT MAINTAIN A CONSTANT BODY TEMPERATURE ARE SAID TO BE ENDOTHERMIC SOUND HEAT AND MOVEMENT
with chemosynthetic bacteria
Fig 6.1.5 Only some of the energy stored in an organism is passed on in the food chain.
Energy flow Energy flows in one direction only in an ecosystem. Producers and consumers rely daily on the light energy delivered from the Sun to drive photosynthesis. The energy flow could be written as: nuclear energy (from the Sun)
light energy (from the Sun)
chemical energy
(made by producers)
chemical energy (eaten by consumers)
The transfer of energy from one organism to the next is never 100 per cent complete since energy is used at each level by the organism. Whatever energy is left over after these processes will be used to grow new cells. This energy is effectively ‘stored’ and passes on to the next level of the food chain when the animal is eaten.
Conservation of matter in an ecosystem Along with energy, matter is transferred in any food chain. While most of this material is used directly by the next organism for its own growth and survival, some is returned to the environment in the form of waste
188
products. If you look at the ecosystem as a whole, then no matter will ever be lost. It will change its form and will be spread around, but the total amount of matter will always be the same. This is known as the Law of Conservation of Mass. It states that atoms can be recycled, allowing them to be used again and again in a variety of different structures and different organisms. Antoine Lavoisier proposed one of the most fundamental laws of science—that atoms are not created or destroyed during a chemical Prac 1 reaction, but just rearranged. p. 191
Food pyramids The transfer of energy and matter within an ecosystem is inefficient with some energy and matter being lost at each level. The total number of plants in any ecosystem is huge. These plants sustain the herbivores that eat them. Each herbivore will need to eat a lot of plants to keep them alive and so there must be less herbivores in an ecosystem than there are plants. Since carnivores will eat a number of these herbivores, the number of carnivores in an ecosystem will be less than the number of herbivores.
Unit
0.1% energy 1% energy
Energy of tertiary consumers
6.1
In most ecosystems, the number of individuals at each level decreases as you move from the producers up to the higher orders of consumers. In this way, a food pyramid is formed. The plants (producers) form the pyramid’s wide base while the highest order consumer will be at its peak. The food pyramid can be built using the number of organisms at each level or their ‘dry weight’. Logically, the weight of plants in an ecosystem will be greater than the mass of the herbivores that eat them. Likewise, the weight of herbivores will be greater than the mass of the carnivores that feed on them.
Energy of secondary consumers Energy of primary consumers
10% energy
100% energy
Energy of producers
Worksheet 6.1 Energy for life Prac 2 p. 191
6.1
Fig 6.1.6 A food pyramid shows that the total amount of energy and mass at each level decreases as you go higher and higher.
QUESTIONS
Remembering 1 Specify the unit that energy is measured in. 2 List the chemicals involved in photosynthesis, giving their names and chemical formulae. 3 Recall the photosynthesis reaction by writing a word equation and chemical equation for it.
8 A food chain includes arrows. Explain what they indicate and which way they should point. 9 Describe how energy is ‘lost’ from your body. 10 Explain the Law of Conservation of: a Energy b Mass
4 Not all life needs the Sun. Specify where creatures are found that do not rely on the Sun for their energy.
11 Plants are often referred to as producers. Is this an appropriate name for them? Explain your answer.
5 Name two animals that are endothermic.
12 Discuss the advantage of a kookaburra having more than one food source (e.g. snakes and fish).
6 Referring to a food pyramid, state whether or not there would be more carnivores: a than herbivores b than plants
Understanding 7 Define the following terms: a ecosystem b producer c consumer d herbivore e carnivore f omnivore L
Applying 13 Identify a living thing that gets its energy from the Sun: a directly b indirectly 14 Refer to the food chain in Figure 6.1.5. Identify which of the organisms listed receives the highest percentage of its energy from the plant. Explain your answer. 15 Consider the following food chain: algae water snail small fish large fish kingfisher a Identify the producer. b Identify the herbivore. c Identify the third and fourth order consumers in this chain.
>>
189
Energy for life 1 6 Identify energy conversions that take place in:
23 Construct a food chain you might find in your own backyard or local park.
a the Sun b a producer c a consumer 17 In the graph in Figure 6.1.7, one line represents a snake while the other line represents a kookaburra. Identify and explain your choice using the terms endothermic and ectothermic. N
24 You are a bioscientist (a scientist who only investigates living things) on the spaceship Endeavour and have just received the first samples of life from a planet you are orbiting. It is your task to arrange them into a series of inter-linked food chains—that is, a food web. Before you begin this task:
Body temperature (ºC)
a describe the features of the planet you are orbiting. Does it have one or more suns? What is the temperature like? What about the atmosphere, water and soil types? How will these abiotic factors influence the organisms that live there?
A
B
6 a.m.
12 p.m.
6 p.m. Time
12 a.m.
Fig 6.1.7
b design six alien life forms that live there, including both plants and animals. Give the reasoning behind their order in the food chain and label them as either producers, first, second or third order consumers, or decomposers. What features, if any, do they share with their Earth counterparts? 25 A biome is an area of similar climatic conditions. Within each biome are a number of different ecosystems and food chains. Brainstorm one such food chain or web that you might find in: a b c d
the Antarctic a desert the ocean a grassland
Analysing 18 Distinguish between: a a first order consumer and a second order consumer b endothermic and ectothermic organisms 19 Distinguish between the flow of energy in an ecosystem and the flow of matter in an ecosystem, describing any similarities and differences.
Evaluating 20 Assess what would happen to all the consumers in a food chain if the Sun’s light were blocked for: a a week b a year
Creating 21 Construct a food pyramid for the following food chain: seaweed small crab lobster octopus a b c d
Estimate of the number of organisms at each level. Show with arrows where energy is ‘lost’. Label the producer. Label each consumer and its order.
22 Construct a food chain, including you. a Are you a consumer or a producer? b Are you the last organism in the chain? c Can you think of an organism that feeds on you?
190
Fig 6.1.8 Penguins live in an Antarctic biome.
For each biome: i Construct a diagram for each food chain/web, and name the producers, herbivores and carnivores. ii Compare its features with those of the other biomes, noting any similarities. iii Create a game in which individual cards have a picture of the different organisms in the food chain/web. Also include ‘arrow’ cards and cards with the words ‘producer’, ‘herbivore’ and ‘carnivore’. During the game, the cards should be arranged into the correct food chain or web. Develop the game and scoring rules.
Unit
INVESTIGATING
Investigate your available resources (for example, textbooks, encyclopaedias, internet) to examine five different samples of one of the following: • breakfast cereals • ice-creams • packaged foods (such as pies or pasties) • bread.
6.1
For each sample you investigate: a record the energy content b explain how it is different from the other samples c state the unit for the energy content listed on each pack d identify which would be the best food choice for someone who sits down all day, compared to someone who spends the day doing hard manual labour. Explain your reasoning.
6.1
6.1
PRACTICAL ACTIVITIES
1 Biomass
3 Predict the ‘dry weight’ of the plant matter. 4 Place the paper bag in a drying oven or leave in a warm place.
Biomass is the mass of living organisms in a given area or ecosystem
5 Record the mass regularly until it remains constant. This is the ‘dry weight’ of the plant mater.
Aim
6 Calculate the percentage of water in your sample using the following equation.
To investigate how biomass is determined
Equipment • beaker • electronic balance • fresh plant matter • paper bag • access to a drying oven
Method 1 Collect a beaker of fresh plant matter. 2 Place the green plant matter into a paper bag and onto a balance. Record the mass.
2 Food pyramid Aim To construct a model of a food pyramid
Equipment • ruler • calculator • strips of paper
Method 1 Use the following biomass data to construct a food pyramid Grass 400 g/ m2/Kookaburra 10 g/m2/Grasshopper 50 g/ m2
mass of dry plant matter 100 percentage of water mass of fresh plant matter
Questions 1 Compare the appearance of the green plant matter and the dry plant matter. 2 Explain why the plant material was weighed until the mass was constant. 3 Discuss why scientists compare ‘dry weight’ of organisms at each level of a food pyramid.
2 Each horizontal bar of the pyramid should be drawn to the same scale and labelled. 3 Construct the pyramid in your book.
Questions 1 Propose why you need to look at the same area for each organism. 2 Describe what your pyramid represents. 3 Construct a food chain which represents the organisms in this food pyramid. 4 Explain why the mass of each organism over the same square metre contained different amounts of matter and energy.
191
Unit
6.2
Recycling in nature
context
Science
Clip
You look like Genghis Khan! … or is it Marilyn Monroe? Although it seems impossible, some of the atoms in your body could have once been part of a great scientist like Marie Curie, an actress like Marilyn Monroe, the warrior Genghis Khan or the poet Banjo Paterson!
Fig 6.2.1 The universe started with the Big Bang 14 billion years ago. The atoms that are in your body now were there at the Big Bang. They have been recycled many, many times since and now happen to be part of you. They will continue to be recycled after you die.
Every day, atoms are recycled through the ecosystem—used again and again in the structural components of plants and animals. It is possible, therefore, that the atoms that were once part of a long extinct dinosaur may now be somewhere in your own body! You can only imagine where they will be 100 years from now.
Two types of matter Matter can take an unimaginable number of forms in an ecosystem: the petals of a rose, precious stones embedded in rock, the hard exoskeleton of a cicada and the wax in your ear are just a few examples of the forms it can take. Everything around you is made of matter which, in turn, is made up of atoms. While the same atoms are present in many different structures, each structure has its own specific combination and arrangement of them. Matter can be classified as either organic or inorganic. Both organic and inorganic matter are recycled through an ecosystem and form a series of ‘cycles’. Some cycles are simple (e.g. the carbon cycle), while others are more complex (e.g. the nitrogen cycle). All cycles rely on the flow of atoms between the biotic (living) and the abiotic (non-living) environments. The biotic environment is the living environment. It includes its plants and animals, its fungi and bacteria. Non-living things such as rock, water and the gases of the air make up the abiotic environment. In healthy ecosystems, the flow of matter between the biotic and abiotic environments remains balanced.
Organic matter
Fig 6.2.2 A perentie is a desert biome dweller. Here one is feeding on a small wallaby—‘wallaby atoms’ are soon to become ‘perentie atoms’!
192
Although the legs of a cockroach and the hairs on your head are very different, they are both built from cells made from the same basic atoms: carbon, oxygen, hydrogen and nitrogen. The only difference is that they are arranged in different ways. All living things have one vital thing in common— they are all made up from organic matter. The skin, muscles and bones that make up animals are organic, as are the fleas that live in their fur. Gum trees are living
Unit
6.2
Rose petal
Butterfly wing
Fig 6.2.4 Organic molecules always have a backbone of carbon atoms.
Inorganic matter
Fig 6.2.3 This is a close-up view of the structure of a rose petal and the structure of a butterfly’s wing. Despite their obvious differences, the same types of atoms make up both structures: both are living things and so, like all living things, contain atoms of carbon, hydrogen, oxygen and nitrogen.
All other matter is referred to as inorganic matter. Inorganic matter includes all the non-living components of the ecosystem, its rocks and minerals, the gases in the air and water and the salt in the sea. The abiotic environment is made of inorganic matter.
The water cycle and so every part of their living structure—their bark, leaves and roots—is organic too. The molecules that make up organic matter are very special in that they always contain a skeleton or backbone of carbon atoms (element symbol C). Attached to this skeleton are other atoms, usually other carbon atoms, hydrogen atoms (H), oxygen atoms (O) and nitrogen atoms (N). The basic difference is each type of organic matter is the number of each atom. The biotic environment is made up of living organisms and so is made up of organic matter containing these basic atoms.
Prac 1 p. 198
Prac 2 p. 199
Water (chemical formula H2O) is classified as an inorganic compound because it contains only hydrogen and oxygen atoms and has no carbon atoms. Of all the water on Earth, almost 98 per cent is found in the salt water of the oceans. Of the remaining two per cent, some is found in the form of atmospheric water vapour and as permanent ice deposits in parts of the Earth such as Greenland and Antarctica. Less than one per cent is available as fresh water to the organisms that live on the Earth. It is only because water is recycled that life on our planet has been able to exist for millions of years.
193
Recycling in nature The Sun is the only source of energy that powers the essential process that is known as the water cycle. Heat energy from the Sun causes water molecules to evaporate from: • moist surfaces such as the wet clothes on the line, dew on the grass and damp soil • living organisms such as plants, by transpiration (evaporation of water from plants) and animals, by sweating or panting and respiration • lakes, rivers and oceans.
energy from the Sun drives the water cycle
to land and back to the ocean.
top of ground water (the ‘watertable’)
ground water non-porous rock
Fig 6.2.5 Trees suck the water out of the ground, releasing it back into the atmosphere through their leaves in a process called transpiration.
It was observed that it would often rain after battles in which cannon fire was heavy. This was due to the release of millions of tiny carbon particles as the cannons were fired. Each of these particles acted as a nucleus around which a raindrop would form. This principle is used today in a technique called ‘cloud seeding’. Aircraft release a multitude of tiny crystals as they fly through clouds, causing it to rain.
194
groundwater
leaf
soil
Raining cannons
surface run-off
infiltration
Fig 6.2.6 The water cycle recycles water from ocean to atmosphere
roots take in water
Clip
evaporation from lakes and streams
precipitation ocean
Science
transpiration from plants
evaporation from oceans due to solar energy
water vapour exits leaf via stomata (pores)
water vapour
precipitation as rain or snow
condensation in clouds
Of these, evaporation from the oceans provides most of the water vapour present in the atmosphere. Carried by air currents, much of the water vapour falls as either rain or snow when it reaches land. This water seeps down through soil
Science
Fact File
Water • 75–80 per cent of the Earth’s surface is covered in water, mainly as oceans and seas. • The human body is approximately 60–70 per cent water. This water doesn’t just slosh around but is inside the cells that make up the body. • Ice is less dense than liquid water and so floats on top of it. • Stanislao Cannizzaro established the formula for water as H2O in 1860. • As the salt content of water increases, its boiling point increases and its freezing point decreases. This means that antifreeze in a car’s radiator gives it some protection from freezing and from boiling over.
and porous rock until it reaches a layer of nonporous rock which stops the water sinking any lower. The soil and rock immediately above this becomes saturated with water. This saturated layer is known as the water table. Eventually the water finds its way back to the sea, allowing the cycle to continue.
The carbon cycle Carbon (element symbol C) is the basic element of organic compounds. It is found in all living things and in all things that once lived but have since died. Paper and timber come from dead trees, leather from dead cows, coal, oil and natural gas from fossilised (ancient) organisms. It is present in the building blocks of living tissue such as its all important proteins. It is also found in the atmosphere. The movement of carbon atoms between the living and the non-living environment is known as the carbon cycle. Carbon enters the ecosystem Green plants need carbon dioxide (chemical formula CO2) to carry out photosynthesis, the process by which they produce glucose. Land-based (terrestrial) plants absorb the carbon dioxide they need from the atmosphere through tiny pores in their leaves called stomata. Algae inhabit the aquatic (or water) ecosystem and use their entire surface to absorb carbon dioxide that is dissolved in the water in which they float. Photosynthesis pulls apart the carbon dioxide and then combines its carbon atoms with oxygen atoms and some hydrogen atoms donated by
Unit
6.2
water molecules. The carbon is being recycled from gaseous carbon dioxide into glucose in the plant—see the following equation: carbon dioxide water sunlight glucose oxygen gas 6CO2
6H2O sunlight C6H12O6 light energy
6O2
sugars produced by photosynthesis converted into starch and stored in the plant
chlorophyll, the green pigment in plants, traps the light energy
Science
Clip
carbon dioxide from the atmosphere enters through stomata in the leaves
Purple bacteria oxygen released from the stomata in leaves
water in soil, taken in by the root hairs
Fig 6.2.7 Photosynthesis is the process that provides the foundation for most of life on Earth. Fig 6.2.8 Halobacterial ‘blooms’ in the salt field
The glucose is then eaten by other organisms. Herbivores use the carbon and other elements contained within the plant to provide for their own energy and growth requirements. Digestion in the higher order consumers, usually carnivores, converts the carbon they obtain from eating other animals into forms they can use. Omnivores convert carbon from both plant and animal sources. Carbon leaves the ecosystem Photosynthesis and digestion distribute carbon atoms among the organisms within an ecosystem. Carbon atoms are then returned to the atmosphere by: • respiration—in this process, the carbon in glucose is released back into the atmosphere as carbon dioxide: glucose oxygen carbon dioxide water energy C6H12O6 6O2
6CO2
6H2O energy
Science
Fact File
Carbon • 75 billion tonnes of carbon are turned into carbohydrates (glucose, starch) each year via the process of photosynthesis. • 500 billion tonnes of carbon is stored in the sea. • 700 billion tonnes of carbon is stored in the atmosphere.
of a lake
• animal droppings (faeces)—animal waste returns carbon to the ecosystem via the soil • decomposition of dead plants and animals and animal wastes by the action of decomposers (bacteria, fungi and worms) in the soil. Decomposers also undergo respiration, returning carbon dioxide to the atmosphere.
Halobacteria (saltloving bacteria) live in water seven times saltier than sea water. Although these bacteria are photosynthetic, they do not use chlorophyll, the green photosynthetic pigment of green plants. Instead they use retinal, the pigment found in the vertebrate eye that enables us to see. For this reason, halobacteria appear purple, not green.
Science
Clip
Killer burp On 21 August 1986, the waters of Lake Nyos in Cameroon released a massive ‘burp’ of carbon dioxide gas, suffocating almost 2000 people!
Too much CO2 The production and consumption of carbon dioxide and oxygen are linked through the processes of photosynthesis and respiration. In the past, the levels of carbon dioxide and oxygen in the atmosphere have been relatively constant, with oxygen at approximately 20 per cent and carbon dioxide at 0.04 per cent. The balance of carbon dioxide and oxygen levels has recently been upset, however, due to: • large-scale felling of rainforest trees • increased production of carbon dioxide by industry • increased burning of fossils fuels such as coal, petrol and natural gas.
195
Recycling in nature burning fossil fuels releases carbon into the air
photosynthesis removes CO2 from the atmosphere atmospheric CO2 respiration releases CO2 into atmosphere
animals gain carbon by eating plants or other animals H2O dead organisms can form fossil fuels in the Earth’s crust—coal, oil and gas
Science
Clip
Biofuels In the late 1800s, before cheaper petroleum-based diesel fuel became widely available, Rudolf Diesel created an engine that was powered by vegetable oils! One of the first diesel engines ran on peanut oil.
Science
Clip
Fertilising thunderstorms The Earth experiences an average of 16 000 000 thunderstorms each year. One hundred million tonnes of nitrogen enters the soil in this way.
196
H2O
dead organisms and their wastes are decomposed by fungi and bacteria and also release CO2 back into the atmosphere
Fig 6.2.9 The carbon cycle is a relatively simple cycle, with carbon atoms moving between the abiotic and biotic environments. Sunlight is the driving force behind it all. Go to
nitrogen into various useful nitrogen compounds. One group of those compounds is the nitrates (containing the nitrate ion NO3). These dissolve in rain droplets and fall onto the Earth’s surface to be taken up by the roots of plants. Once inside the plant, they are converted to amino acids and nucleic acids. These nitrogen compounds are then consumed by animals when the plants are eaten. The animals now have a source of nitrogen from which they can produce their own proteins and nucleic acids. Nitrogen is returned to the ecosystem as ammonia (chemical formula NH3), present in animal urine and faeces, or when dead organic matter decomposes. This ammonia is converted back into nitrates by nitrifying bacteria that are naturally present in the soil. Another type of bacteria, the denitrifying bacteria, converts these nitrates back into atmospheric nitrogen gas. Worksheet 6.2 Recycling in nature
Science Focus 4 Unit 9.2
This imbalance has contributed to what is referred to as the enhanced greenhouse effect. Most scientists agree that this is the main cause of global warming (the trend of ever-increasing average world temperatures).
The nitrogen cycle Nitrogen (element symbol N) is found in the atmosphere as a colourless and odourless gas (chemical formula N2) which makes up about 78 per cent of the air around us. Nitrogen plays an essential part in the formation of amino acids (the building blocks of protein) and nucleic acids (the building blocks of genetic material). Most organisms cannot use nitrogen when it is in its atmospheric form of N2. It needs to undergo a process called nitrogen fixation before it can be used. Most of this happens during lightning strikes. This is when the electrical energy from a storm converts atmospheric
Science
Clip
Meat-eating plants
Fig 6.2.10 Nitrogen is needed by plants to build vital amino and nucleic acids. Carnivorous plants such as the pitcher plant, Venus flytrap and sundews get their nitrogen from trapping insects.
Carnivorous plants have a unique way of getting nitrogen—they eat it! The pitcher plant, found on Cape York Peninsula, contains enzymes similar to those found in the stomachs of vertebrate animals. It obtains nitrogen by dissolving the insects that fall into it.
Unit
atmospheric nitrogen in soil spaces is converted by bacteria in root nodules into proteins which are used by the plant
dead organisms and their wastes are decomposed by fungi and bacteria. Nitrogen is released back into the soil as nitrates
nitrates used by plants soil
6.2
atmospheric nitrogen is converted to nitrates and dissolved in raindrops
atmospheric nitrogen
denitrifying bacteria in soil convert nitrates into atmospheric nitrogen
Fig 6.2.11 The nitrogen cycle is complex as it involves the interaction of many different organisms in the ecosystem.
6.2
QUESTIONS
Remembering 1 State two examples of a organic matter b inorganic matter 2 Specify the element symbols for: a carbon b nitrogen c oxygen 3 Specify the chemical formulae for: a water b carbon dioxide c ammonia 4 Recall the respiration reaction by writing a word equation and chemical equation for it. 5 List four things from which water is constantly being evaporated. 6 List three ways carbon is returned to the ecosystem. 7 Specify the form in which nitrogen exists in: a the atmosphere b the soil c urine and faeces
Understanding 8 Define the following terms: a b c d
terrestrial aquatic condensation precipitation L
9 Explain how atoms from dinosaurs could be part of your body right now. 10 Outline the conversions that occur in the water cycle. 11 Describe the role lightning has in the nitrogen cycle. 12 What would happen if all the decomposers on the Earth suddenly disappeared? Explain your reasoning.
Applying 13 Identify the element that defines an organic compound. 14 Identify where, and in what form, carbon enters a plant. 15 a Identify the process whereby plants convert carbon dioxide and water into the sugar known as glucose. b Identify the source of the energy for this process. c Identify an important gaseous product of this process. d Explain why this by-product is important. 16 Identify two acids in the human body that require nitrogen. Explain why these acids are important.
>> 197
Recycling in nature Analysing
b Most living organisms need water.
17 Classify each of the following as a biotic or an abiotic feature of the environment: water, leaf, soil, air, algae, bacteria, rock, grass, cloud, human
c The nitrogen cycle, the carbon cycle and the water cycle all support the Law of Conservation of Matter.
18 Distinguish between the different types of bacteria involved in the nitrogen cycle.
Evaluating 19 Is C6H5OH an organic or inorganic compound? Justify your answer. 20 Deduce whether the following statements are true or false. a Nitrogen and carbon atoms move between the abiotic environment and the biotic environment.
6.2
Aim To test for the presence of water in different liquids
Equipment cobalt chloride paper anhydrous copper(II) sulfate watch-glass dropper paper towels distilled water various liquids (tap water, methylated spirits, salt water, sucrose solution, acetic acid (2 M)) • unknown liquids X, Y and Z
198
21 Imagine that you are a carbon atom. Describe what you have been doing for the past 100 years. What interesting things have you been a part of, and where do you think you will go next? Construct a diagram of your life cycle so far. 22 Use a computer program such as Macromedia® Flash® to construct an animation of the carbon, nitrogen or water cycle.
e –xploring To explore interactive animations of the carbon and water cycles, web destinations can be found on Science Focus 3 Second Edition Student Lounge.
PRACTICAL ACTIVITIES
1 Testing for water
• • • • • • •
Creating
INVESTIGATING
Investigate your available resources (for example, textbooks, encyclopaedias, internet) to find how fossil fuels such as coal and oil are formed. Explain how the carbon in coal is eventually released back into the environment. Illustrate your short report with a ‘carbon cycle’ that shows the important conversions.
6.2
d Bacteria play an essential role in the continuation of life.
Method There are two simple tests that determine whether a liquid contains water. • Test 1: When water is added to anhydrous cobalt(II) chloride paper, it turns the paper from blue to pink. • Test 2: When water is added to anhydrous copper(II) sulfate, it turns from white to blue. (Note: the term ‘anhydrous’ means ‘without water’.) 1 Add 2 drops of distilled water to a small piece of anhydrous cobalt(II) chloride paper and a small sample of anhydrous copper(II) sulfate. Verify that each changes colour according to Test 1 and Test 2 above. 2 Copy the table on page 199.
Unit
Liquid tested
Copper(II) sulfate
Cobalt chloride paper
Tap water Methylated spirits Salt water Sucrose solution
Questions
Acetic acid
1 Apart from a colour change, describe what else happens when water is added to anhydrous copper(II) sulfate. 2 Identify which of the known liquids contained some water. 3 Identify which of the unknown liquids contained water. 4 Assess the importance of washing and drying the watch-glass thoroughly between each test.
Unknown X Unknown Y Unknown Z
2 Measuring the boiling point of water Aim To measure the boiling point of various samples of salt water
Equipment • • • • • • • • •
4 Add 2–5 drops of tap water and record any colour change. Record your results. 5 Wash and dry the watch-glass thoroughly. 6 Place a piece of cobalt(II) chloride paper on the cleaned watch-glass. 7 Add one drop of tap water and record any colour change. Again, wash and dry the watch-glass thoroughly. 8 Repeat steps 3–7, replacing the tap water with each of the solutions listed in the table. 9 Record your results.
6.2
3 Place one spatula of anhydrous copper(II) sulfate on a watch-glass.
Bunsen burner and mat tripod matches four 250 mL beakers measuring cylinder distilled water salt tablespoon thermometer able to record temperatures higher than 100°C or a temperature probe
2 Set up the Bunsen burner, the mat and the tripod. Light the burner. 3 Label the beakers 1 to 4. Add 150 mL of distilled water to each. 4 Heat the water in beaker 1 until it boils. Measure the temperature and record the result. (Note: place the thermometer in the water while it is still cold and heat it gradually. Allow it to cool down a little between tests.) 5 Remove beaker 1 when cool and place it to one side. 6 Add 1 tablespoon of salt to beaker 2 and stir until the salt has dissolved. Place the beaker on the tripod and continue heating until the water boils. Measure the temperature and record the result. 7 Remove beaker 2 when cool and place it to one side. 8 Repeat steps 6 and 7 with beakers 3 and 4.
Questions
Method 1 Copy the table below. Liquid Beaker 1 (distilled water) Beaker 2 (1 tablespoon salt) Beaker 3 (2 tablespoons salt) Beaker 4 (3 tablespoons salt)
Boiling temperature
1 Construct a line graph to show the relationship between the amount of salt dissolved in water (on the horizontal axis) and the temperature at which the water boiled (vertical axis). 2 Propose a reason for the results you observed. 3 Antifreeze is a solution that is often put in car radiators to stop the water from freezing in very cold weather. It is also very useful in stopping radiators from boiling in hot weather. Analyse why. 4 Analyse this statement: Impurities in water increase its boiling point.
199
context
Global warming, carbon emissions, pollution—they are in the news every day and they are all damaging the environment and the plant and animal life it supports. Humans now dominate much
were built to quickly transport them to their customers and to supply the factories with the raw materials needed to make them. New types of waste materials were released into the environment and natural habitats were destroyed as the towns became cities that then kept expanding. Human civilisation had changed forever and the environment changed with it. In the twenty-first century, some of this change has come back to hurt us: most scientists agree, for example, that the current trend in global warming has been caused by humans releasing carbon dioxide into the atmosphere. Your generation and your children and grandchildren will need to live with the climate change that is being created by all of us now. Action needs to start immediately if the future inhabitants of Earth are to have an environment that will provide for all their needs, as well as the needs of the animals and plants that (hopefully) will co-exist with them.
Fig 6.3.1 An ecosystem changes dramatically when pollutants are
For thousands of years, people were nomadic or lived and worked in small villages. Populations were small and the natural resources around them were all they needed to survive. People used simple handmade tools and lived in simple dwellings that were lit and warmed by fire. Clothes were handmade and food was either hunted or gathered from the local surroundings. The waste produced was easily absorbed back into the environment through the natural cycles. Europe (particularly Great Britain) changed forever with the Industrial Revolution that began in the mid-1700s. By 1860, many small villages had become industrial towns. Goods previously made by hand were now constructed by steam-driven machines. Machinemade goods were in demand, and roads and railways
200
World population (millions)
added to it. Many species have become extinct and many more are endangered because of the human impact on their ecosystems.
Environmental revolution
of the environment and our activities have imposed far-reaching effects on its ecosystems. There will always be a conflict of interest between production and conservation and what happens in the future depends on what the human race does now.
12 000 11 000 10 000 9000 8000 7000 6000 5000 4000 3000 2000 1000
predicted range
2050
6.3
1750 1800 1850 1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000
Unit
Human impact on ecosystems
Year
Fig 6.3.2 As the human population increases, the demands to produce food, energy and shelter and living requirements increase, resulting in a decrease in area for plant and animal habitation.
6.3
A pollutant is anything that makes the environment unfit or unhealthy for the organisms that live there. Pollutants affect the atmosphere, the land (lithosphere) and the water (hydrosphere). Although some pollutants arise from natural causes such as volcanic eruptions, they are more commonly the result of human activity. Frogs are usually the first to be affected by pollutants because they breathe using lungs and through their skin and they spend much of their life in water. Frogs provide an excellent indicator of the environmental health of an ecosystem—the more frogs, the fewer pollutants there are and the healthier the habitat.
• sediment pollution—clearing the land for housing developments and farming causes large-scale erosion. Soil particles are washed into the waterways, causing silting • inorganic chemicals—industry releases inorganic compounds directly into waterways, or into the soil where they are then carried by ground water into the waterways. Chemicals released into the atmosphere are absorbed by rain droplets and fall to Earth as acid rain. These find their way into both run-off water and ground water, eventually ending up in the rivers, bays and oceans.
Unit
Pollution
Prac 1 p. 208
Science
Clip
Fig 6.3.4 Water pollution kills fish and removes a Fig 6.3.3 Many species of frogs have already been declared extinct including the gastric brooding frog.
source of food available for people that live nearby.
Science
Clip
Shortened life span The average life span of a tree in the countryside is about 150 years. In an average city setting it is only 32 years, while in the middle of a large city it is as little as 13 years.
Water pollution Pollution in the streams, rivers, seas, lakes and oceans of the world has come from a variety of sources. • sewage—it contains contaminants such as soap, detergents and other cleaning agents from washing machines, dishwashers, baths and showers. It includes human wastes from toilets • agricultural run-off—fertilisers add large quantities of nitrogen and phosphorus to the ecosystem
Fig 6.3.5 Blue-green algae thrive in water polluted with fertiliser run-off, growing uncontrollably until they clog up rivers, dams and lakes. Blue-green algae are highly toxic and often kill the animals that live in the waterway and any others that swim or drink from it. That includes humans!
The Maccabiah Games disaster In 1997, as the Australian athletic team entered the opening ceremony of the Maccabiah Games in Israel, a temporary bridge collapsed, plunging the team into the heavily polluted Yarkon River. Two Australian athletes drowned and another two died weeks later from complications linked to pollutants in the toxic river. Dozens of other Australian athletes also suffered prolonged illness. Ten years later, the engineers who designed and built the bridge were found guilty of negligence and jailed.
201
Human impact on ecosystems Soil pollution Soil pollution is more commonly referred to as soil degradation. Over 65 per cent of soil degradation is caused by overgrazing and deforestation. Overgrazing is the degradation of land Science caused by allowing more animals to graze in an area than the area can sustain.
rain
water vapour lost through leaves (via stomata ‘pores’)
Clip
water absorbed by roots
The Easter bilby In recent years, efforts have been made to increase public awareness of the plight of the bilby by releasing chocolates in its shape at Easter time.
water leaches through soil
water travels up through trunk soil
water table
ground water non-porous rock
Fig 6.3.7 Trees act like giant straws, sucking the water out of the ground and releasing it back into the atmosphere through their leaves in a process called transpiration.
Fig 6.3.6 The native bilbies that once inhabited many Australian ecosystems are no longer able to do so due to overgrazing by introduced sheep.
Deforestation is the large-scale removal of trees to allow for more grazing land. Deforestation affects the environment in two ways: it increases the salinity of the soil and it removes its protective covering, making it more likely that large-scale erosion will occur. Trees keep the underground water table deep under the surface. When trees are removed, the water level rises, bringing with it dissolved salts. Remaining trees and plants will die if this salty water gets near the surface.
Science
Clip
Less trees, more sand! Printers and photocopiers became common in the 1980s leading to a doubling in the amount of paper being consumed each year. Non-recycled paper comes from trees, so more trees are being cut down than ever before. In Mali, the Sahara Desert has increased in size by an amazing 650 square kilometres in the last 20 years due to desertification!
Irrigation also increases the salinity of the soil since it adds water to it, making the water table rise. The process is known as salinisation. Surface vegetation holds the soil together and so its removal will increase the likelihood and severity of erosion by wind and rain. Valuable topsoil is lost, making the land useless for farming, forest plantations or even for the restoration of the original plant life. The land is devastated. Currently, about 10 per cent of the Earth’s surface has been reduced to desert and a further 25 per cent has been placed at risk. This includes a very large proportion of the Australian continent. The process of turning good land into desert is called desertification. Worksheet 6.3 Waste
Air pollution The two main sources of air pollution are motor vehicles and industry. The number of cars and trucks on the roads increases every year. They release hydrocarbons, lead (Pb), nitric oxide (NO) and carbon monoxide (CO). In the presence of sunlight, these chemicals react to form a variety of new pollutants such as ozone (O3), nitric acid (HNO3), and organic compounds such as formaldehyde. This mix of pollutants is often seen as smog. Industrial activity releases a constant stream of pollutants into the atmosphere, such as sulfur dioxide (SO2), nitrogen dioxide (NO2), carbon monoxide (CO), carbon dioxide (CO2), hydrogen sulfide (H2S), dust and smoke. These and vehicle exhaust fumes combine with water vapour in the atmosphere, only to fall back to Earth as acid rain, killing lakes, forests and the organisms that live there. Prac 2 p. 208
202
Unit
6.3
The enhanced greenhouse effect Greenhouse gases are released whenever fossil fuels such as coal, gas, petrol and oil are burnt. The main greenhouse gases are carbon dioxide (CO2), methane (CH4), nitric oxide (NO), ozone (O3) and water vapour (H2O). The amount of these gases Science in the atmosphere has increased dramatically with increased industrialisation and the trapping The disappearing Great of more heat than usual. This Barrier Reef! enhanced greenhouse effect Coral expels the algae that give leads to global warming. it colour when the sea is too The average atmospheric warm, ‘bleaching’ the reef. Although rare in the past, temperature of Earth has risen by bleaching on the Great Barrier 0.6°C over the last 100 years. This Reef now occurs every three to has sped up the melting of ice in four years and is common in glaciers in Antarctica and the reefs of 30 countries. Greenland. This additional water Repeated bleaching kills coral has made sea levels rise by several and some reefs in the Caribbean have already died. centimetres. They are expected to Some scientists expect that all rise even further if greenhouse coral reef ecosystems will be gases continue to be pumped into dead by the year 2100. the atmosphere at their current rate. Some likely results would be: • widescale flooding of coastal regions, destroying many ecosystems and their inhabitants • cities, farmland and some island nations disappearing under water, drowning their ecosystems • increased sea temperatures, destroying coral reef ecosystems that cannot tolerate changes in temperature • changes in weather patterns and storms, Prac 3 destroying many ecosystems.
Clip
Fig 6.3.8 Smog is a major concern for cities. It is caused by the action of sunlight on pollutants in the air.
Global warming The greenhouse effect The Sun delivers vast amounts of energy to Earth. Much of that energy is absorbed by the plants, rocks, buildings, roads, soil and sea, but a lot of it is released back into the atmosphere as heat. This heat would eventually escape into space if something didn’t stop it. Gases in the atmosphere reflect this heat back to the surface, effectively trapping it and keeping the atmosphere warm. These gases are known as greenhouse gases and the warming they cause is the greenhouse effect: the atmosphere acts like a giant greenhouse, keeping the temperature on Earth just right for life. Fig 6.3.9 Heat is trapped between the blanket of greenhouse gases (carbon dioxide, water vapour, methane, nitrous oxide and ozone) and the Earth’s surface, causing a global increase in temperature.
p. 209
Go to
Science Focus 4 Unit 9.2
some of the energy is reflected off atmosphere radiated energy from below
power stations: source of extra carbon dioxide
energy from Sun
exhausts from motor vehicles add to the carbon dioxide in atmosphere
heat trapped by carbon dioxide in atmosphere
burning of fossil fuels (coal, oil, etc.) also adds excess carbon dioxide to atmosphere
heat
heat radiated from land
heat radiated off sea felling of trees which would ‘lock up’ carbon dioxide
203
Human impact on ecosystems
Introduced species The wild pig, rabbit, European carp, fox, prickly pear and tamarisk tree were all brought to Australia by the early European settlers. More recently cane toads were introduced deliberately, and various seastars (starfish) were accidently Science introduced when ships pumped out their ballasts of water that contained them. Each has caused Outfoxed! huge problems for our native plants Early English settlers introduced rabbits and foxes and animals. Many are still pests so that they could continue today. Introduced species are often their tradition of hunting. referred to as exotic species. Along with feral cats, foxes Pigs were brought by the sailors have been a major cause in on the First Fleet in 1788 and were the extinctions of two thirds allowed to roam freely to forage for of the native animals in central Australia. food. Many of them ran off, and soon there were large numbers of wild pigs throughout much of Queensland and Science New South Wales. Feral pigs dig up large areas of land, damaging native plants and destroying the habitats of Take two toads with many ground-nesting birds and meals native mammals. More native animals are European carp were first threatened by cane toads. introduced into New South Wales Cane toads were introduced into Queensland, in 1935 in and Victorian fish farms in the the town of Gordonvale, to 1870s. Some escaped into the control beetles that live at waterways and by 1976, they were the top of sugarcane plants. inhabiting creeks and rivers as far Unfortunately, cane toads north as Queensland. Carp feed by live on the ground, putting taking in mouthfuls of the muddy the beetles out of reach even with a good jump! With no river bottom, then spitting it out.
Clip
Clip
natural predators, cane toads have spread across northern Australia and have reached Kakadu National Park, outside Darwin. It is expected they will devastate the native wildlife there over the coming years.
Clip
Cactoblastis and the green octopus! A variety of prickly pear cactus came to Australia with the First Fleet in 1788. Later, another introduced variety went feral. Although the pear had natural enemies in its home of South America, it had none in Australia. By the start of the twentieth century it had covered 20 million hectares and was nicknamed ‘the green octopus’! Scientists working in Chinchilla, Queensland, found that a black and yellow striped grub called Cactoblastis cactorum ate the cactus from the inside out. In 1925, the grub was released and soon the pear was decimated. The pear is spreading again, however, at an amazing rate of half a million hectares per year.
The dirt and the small organisms it contains are then suspended in the water, where the carp can catch and eat them. This method of feeding causes great damage to water plants, whose shallow root systems are made unstable because of the removal of the mud. Worksheet 6.4 Rabbit advance
Endangered species Much of Australia’s unique fauna and flora is now endangered, placing many species in danger of extinction. Once extinct, a species is lost forever from the planet. Our native wildlife is threatened by: • predation by introduced species, such as foxes and cats • competition with introduced species, such as sheep and cattle • the destruction of their habitats when houses, cities, farms, roads, mines and dams are built. The table on page 205 gives just a few of the Australian native animals and plants that are endangered or extinct.
Conservation
As destructive as the cane toad is to our Australian environment, it does have one redeeming feature: Chinese medicine manufacturers have been using it for centuries to treat cardiovascular diseases and cancer.
Fig 6.3.10 Cane toads have no natural predators in Australia and, being highly poisonous, kill any animal that attacks them or try to eat them.
204
Science
Conservation is aimed at keeping alive all the plants and animals that live together in a specific habitat, usually by keeping the habitat undisturbed and free of human interaction. Both short-term and long-term conservation actions are often required to maintain the biodiversity of a particular habitat. For example, consider the impact of an oil spill. Conservationists work hard in the short term to remove the oil from any ocean-going mammals, turtles and birds that may be affected. Steps are taken to restrict the oil from spreading further, and skimmer booms are used to remove the oil from the surface of the
Unit
Thylacine (Tasmanian tiger) died in 1936 at Hobart Zoo
Paradise parrot (1927)
Lake Pedder earthworm (1972)
Thought to be extinct
Broad-faced potoroo (last sighted 1875)
Desert-rat kangaroo (1935)
Gastric-brooding frog (1985)
Endangered possums
Leadbeater’s possum
Little pygmy possum
Mountain pygmy possum
Other endangered land marsupials
Hairy-nosed wombat
Bridled nail-tail wallaby
Gilbert’s potoroo
Endangered marine mammals
Blue whale
Southern right whale
Several dolphin species and some seals
Endangered birds
Night parrot
Helmeted honeyeater
Red-tailed black cockatoo
Southern corroboree frog
Loggerhead turtle
Grey nurse shark
Wollemi pine
Kurrajong
Davies’ waxflower
Other endangered animals Endangered plants
water. In the long term, legal action is often taken to change the laws regarding the transportation of oil, in the hope that future spills will be avoided. When we work to conserve one species in an ecosystem, we are helping to conserve all of the other species in that ecosystem because of their interactions with each other.
Science
Clip
Save the Tassie devil! Devil Facial Tumour Disease (DFTD) is a cancer that spreads like a contagious disease. Tasmanian devils engage in a power play before they mate. They scratch and bite each other and the open scars allow the disease to pass from devil to devil. A devil usually dies within a few months of the disease becoming visible. The lack of genetic diversity among Tasmanian devils means the tumour cells aren’t rejected by the animals’ immune system. In 2008, the Tasmanian devil was listed as endangered. Its long-term survival will depend on captive breeding programs of uninfected animals.
6.3
Known to be extinct
Why conserve? Humans rely on the living organisms around them. Plants provide us with the oxygen we need, as well as being food for us to eat. They are also food for the animals we eat. Plants and fungi provide the ingredients for many of the pharmaceutical drugs we use when we are ill. It is estimated that of the 400 000 to 500 000 different species of known plants on the Earth, only 10 per cent have been investigated for their chemical components. Who knows what future cures are to be found in the plants and animals we are destroying today? Worksheet 6.5 Australian plants
Fig 6.3.12 Oil spills cause a great deal of destruction to the Fig 6.3.11 A Tasmanian devil with a facial tumour
natural environment.
205
Energy for life
Case study
The northern hairy-nosed wombat
The northern hairy-nosed wombat is only found in 300 hectares of sandy countryside in the Epping Forest National Park, central Queensland. There are probably fewer than 120 left. Cattle grazing, land clearing and the introduction of species such as the rabbit and the dingo (introduced by the Aboriginal people) have devastated their numbers. To make the situation worse, the northern hairy-nosed wombat is very slow to reproduce: they have only one offspring every year and the baby takes one year to wean and three years to reach sexual maturity. To help this wombat species survive, different strategies have been suggested by scientists. • Split the colony into several groups—this will prevent the whole population from being destroyed if a fatal disease should Fig 6.3.13 The northern hairy-nosed wombat is an endangered species. threaten them. • Monitor the population carefully—scientists either • Release the offspring into suitable and protected watch the animals directly, or use methods such as habitats, where introduced species have been satellite tracking and helicopter spotting to do so. removed—captive breeding programs in zoos provide another source of wombats that may eventually be • Assist during births—it is hoped that this will prevent placed into the wild. unnecessary deaths.
6.3
QUESTIONS
Remembering 1 List three common air pollutants found in today’s industrialised cities. 2 Some pollutants become even more deadly in the presence of sunlight. List three products of the combination of air pollutants with sunlight. 3 Specify the chemical formula for the compounds: a nitric acid b carbon dioxide c methane
4 Name the following chemicals: a NO2 b CO c O3 5 List five introduced species.
Understanding 6 Define these terms: a pollutants b sewage c desertification 7 Explain why frogs are excellent indicators of pollution.
206
Unit 18 Use an example to demonstrate how advances in human technology have affected the environment.
9 Explain how the following can increase salinity of the ground water:
Analysing
a deforestation b irrigation 10 Outline the two main causes of soil degradation. 11 Explain why the greenhouse effect is a good thing while the enhanced greenhouse effect is bad. 12 Use an example to outline a problem for the Australian environment caused by an introduced species. 13 Propose reasons for the life span of a tree in the country being longer than the life span of the same species of tree in the city. 14 Describe ways of reducing the effects of global warming.
19 Contrast: a an endangered species with an extinct species b the lithosphere with the hydrosphere
Evaluating 20 Which introduced species has proven to be the most damaging and the hardest to control? Justify your answer. 21 a Explain what is meant by a ‘captive breeding’ program. b Discuss the importance of zoos and captive breeding programs for many species. c Write a letter to the editor of a newspaper to explain your views on captive breeding.
Applying
Creating
15 Use the graph in Figure 6.3.2 to predict the population expected in the year 2050. You will need to specify a range. N
22 You are a lawyer who has been asked to prosecute a company that has been caught in the act of releasing thousands of litres of poisonous waste into a local creek. Your task is to speak out on behalf of the environment and the future of the creek. Create a submission to the board of directors of the company explaining the effects of the dumping of this waste and why the company should clean up the mess. L
16 Identify the environmental threat caused by greenhouse gases. 17 Identify five sources of water pollution.
6.3
6.3
8 Explain why blue green algae are dangerous and what encourages their growth.
INVESTIGATING
Investigate your available resources (for example, textbooks, encyclopaedias, internet) to complete these tasks. 1 Research one animal and/or plant that is currently endangered. Summarise your findings, addressing the following issues: • the meaning of the term ‘endangered’ • what has caused this animal and/or plant to become endangered • the numbers left in their natural environment now • the steps being taken to increase their numbers • the expected outcome. 2 Find out about a habitat that is endangered and produce a brochure for visitors to the habitat. Choose from: a disappearing rainforests b endangered coral reefs c increasing salinity on farmlands d disappearing wetlands. L
Class debate
L
Separate the class into two groups. • Group A: those who think advances in technology should be allowed to continue in an uncontrolled fashion, with human needs and wants being more important than the health of the environment • Group B: those who think more stringent controls should be put into place to protect the environment, to the extent where technology takes a back-seat role to the needs of the environment. Students should have the opportunity to collect articles (newspapers, periodicals, internet sources) to support their views.
207
Human impact on ecosystems
6.3
PRACTICAL ACTIVITIES
1 Water pollution
Method
To investigate different methods to ‘clean’ waste water
1 Make a mixture of waste water by adding 200 mL of water to a jar and then adding 1 teaspoon of each of the following—oil, soap, grass clippings, toilet paper and strips of plastic.
Equipment
2 Shake the jar and then let it sit for several minutes.
Aim
• • • • • • • • •
jar with lid cooking oil liquid soap soil sand grass clippings toilet paper strips of plastic teaspoon
• • • • • • • • •
wire gauze blotting paper cotton wool filter funnel vinegar filter paper 3 beakers labelled A, B and C alfalfa sprouts Petri dish
3 Filter the mixture through some wire gauze into Beaker A. 4 Remove the oil from Beaker A using some blotting paper. 5 Now filter the liquid from Beaker A through some cotton wool into Beaker B. 6 Add a few drops of vinegar to Beaker B and filter through some filter paper into Beaker C. 7 Place several alfalfa seeds into a petri dish and add water from Beaker C.
Questions 1 Describe what the original waste water looked like. 2 State the purpose of each stage of the separation. 3 Explain the purpose of growing plants in the ‘clean’ water.
2 Climate in a beaker Aim
blocks of ice aluminium foil
To make a mini-climate in a bowl
Equipment • • • • • •
a large glass bowl or beaker aluminium foil ice cubes some paper or taper matches thermometer
Method
cold air forms beneath foil
thermometer
smog forms in this region smouldering paper taper at base
1 Place half a cup of water in the beaker, swirl it around to wet the sides of the beaker and then tip it out. 2 Drop a lit taper or burning piece of paper into the base of the beaker. Insert a thermometer, then cover the open top with the aluminium foil and make an indentation. Place the ice cubes in the depression you have made.
208
beaker
Fig 6.3.14
Unit
Questions 1 Propose a reason why smog occurs more in those cities that have rivers running through them than in cities that do not. 2 Smog forms more in winter than in summer. Explain why.
6.3
3 Record what happens as the air temperature inside the beaker falls due to the layer of cold air immediately under the foil. When the smoke particles and the moisture in the air get trapped together near the surface, they form smog. The smog cannot escape from the beaker, and as it cools, it falls back toward the base.
3 The inside of the beaker was wet first. Explain why. 4 Draw conclusions about the accuracy of this re-creation of city smog and a climate.
3 Simulating global warming Aim To observe the effect of an invisible ‘blanket’ on heat escape from a system
Equipment
popper A
80
70 80
straw hole
90 10 0
place thermometer in straw hole
dC
2 Place two microscope slides over the hole of one of the poppers, and stick it into place using the sticky tape, effectively sealing it. Place the thermometers through the straw holes on each of the poppers. Seal around them with sticky tape to prevent heat escaping.
dC
1 Cut a square hole in the large flat side of each of the poppers. The hole should be just smaller than the width of two microscope slides.
10 0
Method
popper B
70
small fruit juice cartons (poppers) 2 thermometers 1 pair of scissors at least 4 microscope slides sticky tape
90
• • • • •
cut a hole the width cut a hole the width of of 2 microscope slides 2 microscope slides cover with 2 microscope leave open to the air slides and stick into place
Fig 6.3.15
Questions 1 Predict the outcome of the experiment. 2 Describe what happened to the temperature inside the popper that had the microscope slides covering the hole. 3 Contrast your results with what is happening to the Earth.
3 Allow about 5 minutes for the temperature inside the poppers to stabilise. Record the temperature inside both poppers. 4 Place the poppers and the thermometers on a sunny windowsill. 5 Record the temperature inside each of the poppers every 5 minutes.
209
Science Focus
The right balance— a human problem
Prescribed focus area The implications of science for society and the environment Australia was inhabited by Aboriginal people for more than 40 000 years before the arrival of the First Fleet in 1788. They lived across the entire continent but were mainly concentrated near the coast. There was a strong spiritual aspect to their lives that was closely tied to the land and animals in the area in which they lived. This is shown through the corroboree and in the representation of animals in Aboriginal art. The Aboriginal people used their own indigenous practices to take care of the land they depended on.
understanding of its natural resources. They practised ecology in order to maintain the resources on which they depended so their lifestyle was sustainable. Aboriginal people practised burning the land, often called firestick farming. This burning cleared undergrowth, flushed out animals for hunting, and encouraged new plant growth. Regular burning resulted in some of the ancient rainforests being reduced in size and more open eucalypt forests developing.
Environmental impacts before white settlement Evidence suggests that the Aboriginal people were in tune with the natural systems and cycles of the different environments in which they lived. They used different seasonal food sources and any waste produced was biodegradable, being broken down and returned to the natural cycles. The huntergatherer lifestyle of the Aboriginal people depended on the natural environment to supply all their needs. This is why they developed a strong spiritual association with the land and an
210
Fig 6.3.16 The bush supplied the Aboriginal people with all the food
Fig 6.3.17 In traditional dance (see above), Aboriginal people dance
and materials they needed. Any waste that was produced was biodegradable and left no permanent mark on the landscape.
like their animal totems, which also appear in many forms in traditional Aboriginal art.
Fig 6.3.18 Firestick farming had many benefits for the Aboriginal people.
Fig 6.3.19 The early settlers saw the Australian landscape, animals
The early settlers: a struggle to survive When the first white settlers arrived in Australia they found a much wider range of habitats than they were used to. Most early exploration was by boat and close to the coast. This minimised travel through the bush. The plants and animals were very different and considered peculiar or strange. In the first decades, the settlers struggled to make the land produce enough food to support the growing population. This meant that settlers were forced to rely on supplies arriving from England. The land was generally described as ‘harsh and unforgiving’. Farming techniques from England were not very successful, with soil losing fertility after only a few harvests. Those who made their way into the bush found some areas with more fertile soil, but fresh water and food were hard to find. In contrast, the Aboriginal people used the same land to supply all their needs. The table on the following page shows the contrast between the attitudes of white settlers and Aboriginal people to the Australian landscape. From then until now The Aboriginal people managed to coexist with the land successfully for well over 40 000 years. After approximately 200 years of white settlement, however, modern Australians face many problems that have arisen from the exploitation of the environment.
and plants as strange. They took a long time to get used to the Australian environment.
Fig 6.3.20 The settlers cleared the land, built homes and stayed in one place planting large crops of introduced plants—a very different way of life from that of the Aboriginal people.
211
The Australian population has grown significantly and continues to grow. This and many other factors Feature
The landscape
have had an impact on the Australian landscape and its plants and animals. These factors include modern
White settlers Rugged and picturesque with much of it difficult to travel around
Their spiritual link to all that had happened and all that was to happen in the future
Needed to be cleared to allow for grazing of animals and growing of crops
It provided all their needs as they moved easily through the land, travelling from food source to food source as the seasons changed
The natural resources available from the land were there to be found and used
The plants
The animals
Property
Mostly rubbish with some that could be used for timber and a few suitable to eat
A source of food, useful materials, shelter, a home for animals
Some useful timber varieties were discovered as clearing and exploration of waterways were undertaken
The Aboriginal people had long used burning the bush as a strategy to keep the undergrowth down to allow easy movement, and to encourage new plant growth
Wild and strange, none to domesticate and not many to eat
A vital component to be nurtured and respected, a supply of food
Fish could provide food near the coast
Associated with the Dreamtime—each tribe had their own spiritual association with one of the animals found in their area
Because Terra nullius (Latin for ‘uninhabited land’) had been declared by the British Government, the land could be claimed by free settlers and provided to freed convicts
Each location had a spiritual importance to the people who lived there. Aboriginal people moved about, but on their death, their bones were buried in their traditional land. There were sacred sites, meeting places and locations where food sources were found. The individual tribes used their own land but resources were shared between tribes. The land was owned by the tribe as a whole and did not belong to any individual
Originally settlers were given land wherever they chose. All they needed to do was to clear the land to begin their farm The trees and plants needed to be removed, providing as much land for grazing or growing of crops
Land use
The Blue Mountains and Great Dividing Range
212
Local Aboriginal people
Traditional farming techniques from Britain were employed. Minerals and natural resources were sought so they could be exploited
An impassable barrier preventing access to the interior of the continent and new land to farm
There were spiritual links to the land and its animals and plants The Aboriginal people tried to maintain the land and encourage new plant growth through burning: that in turn, provided conditions where the populations of animals might increase and become available for food. Sacred areas were set aside where hunting was not allowed. These areas were often breeding grounds for animals that were used as food. These areas protected animals from extinction An area of abundant water and food with long followed paths to allow contact with the tribes who lived in inland New South Wales
farming practices, land clearing, introduced animals and plants, and the production of new non-biodegradable waste and pollution. Today, modern land use and land management practices are far more suited to Australia. Food production is generally more efficient, but still
relies on nutrients in the soil being replaced. Land clearing (habitat loss), farming and competition, or predation, by introduced species has, however, led to the extinction of many native animals and plants. Australia holds the world record for the highest recorded number of species that have become extinct. The future really comes down to the values and attitudes of the Australian people. Some still view the land in the same way as the early settlers—as a resource for humans to use or exploit. Others in the community have taken a view more closely resembling that of the Aboriginal people—viewing the land as something to be respected and conserved. We will have to find the right balance.
Fig 6.3.22 ‘Bush tucker’ sustained Aboriginal Australians for many thousands of years. Only recently have modern Australians taken any notice of it.
Fig 6.3.21 Each image suggests something about how we have affected the Australian environment. Identify what each is representing.
Fig 6.3.23 What sort of relationship do you have with the land?
213
Human impact on ecosystems
STUDENT ACTIVITIES 1 After European settlement, the bush, which had been fairly open and easy for settlers to ride horses through, started to become overgrown, making it more difficult to move about. a Outline possible reasons for the bush around Sydney becoming overgrown. Did it have anything to do with the Aboriginal people? b Firestick farming was a common practice of the Aboriginal people. Discuss the benefits of this technique. c Summarise the ways in which the Aboriginal people used the land. d Outline the problems that settlers encountered in trying to make Australia home. e Propose reasons for the settlers having such problems coming to terms with the land. f Compare and contrast the European settler and Aboriginal relationships with the land. 2 Many farming practices used by early settlers and even used today are not very good for the land. Research a problem caused by farming, such as salinity, erosion, land clearing or soil infertility, and answer the following questions. a Describe the cause of the problem. b Identify the parts of Australia where the problem exists. c Describe the effects of the problem on the land, native animals and plants. d Outline what is currently being done to help to overcome the problem. e Evaluate whether this problem can and will be fixed and give an indication of how long this may take.
214
3 European settlers introduced many animal species which have since moved into the bush to become feral animals. Research one feral animal such as the fox, rabbit, camel or pig and produce a poster to demonstrate the effects this animal can have on the environment. 4 Supply of fresh water is a big issue for modern society. The needs of a growing population must be balanced against the costs and the impact on the environment. Research this area and complete the following activities. a Outline why it is difficult to supply enough fresh water to all who need it. b Compare any water restrictions that exist in Sydney with those in a country area. c Propose some ways that enough fresh water may be supplied in the future. d Present an advertisement to help promote better water use. e As a class or group, develop a plan for managing our fresh water supply for the future. Present your plan to the local council or water board, or as a community display. 5 Explore the Aboriginal relationship with the land by researching using your available resources. Use the information you find to produce either a creative story or an artwork to illustrate the traditional relationship of Aboriginal people with the land. Your work should contrast this with the type of relationship people in modern societies have with the land. L
CHAPTER REVIEW Remembering 1 State what the arrows in a food chain show. 2 State the name given to animals that catch and eat other animals. 3 State a word equation to describe the processes of:
Applying 14 Energy and matter both flow through the ecosystem. Distinguish between them. 15 Agricultural fertilisers can damage the environment. Identify the two main elements of agricultural fertilisers.
a photosynthesis
16 Identify two major causes of increased salinity of waterways.
b respiration
17 Choose examples of pollutants in the schoolyard to demonstrate the consequences of pollution.
4 Scientists can help a small population of an endangered species to survive. List four steps that can be taken to do this.
Understanding
Evaluating 18 Deduce the meaning of the statement Lightning is a necessary danger.
5 Organisms tend to live in relatively small, localised areas. Explain why.
19 Assess why it is important to replace trees that have been cut down.
6 Determine what percentage of energy is passed on to each level of the food chain.
20 Bacteria may be small, but they have a big impact on our environment. Deduce the meaning of this statement.
7 Explain the consequences of the Law of Conservation of Energy.
21 The greater bilby lives in the desert area of Central Australia. It has an omnivorous diet (it eats both plant and animal matter). Do you think this provides the bilby with an ecological advantage compared to other animals that eat only plants or only animals? Justify your response.
8 Copy the following, modifying any incorrect statements so they are true. a The unit with which we measure energy is the joule. b Endothermic animals use most of their energy to maintain a constant body temperature. c Bacteria and fungi are decomposers that have a major role in returning atoms in the biotic environment back to the abiotic environment of the ecosystem. 9 Explain how energy is passed on from a plant to a first order consumer. 10 Define the term pollutant.
Creating 22 Construct a food chain that you might find in your local area. Label each of the organisms as either producers or consumers, and their ‘order’ in the chain. (Which ones are first order consumers? Second order?) 23 Construct an energy flow chain for your food chain. What is the original energy source? Worksheet 6.6 Crossword
11 Define the term desertification. L 12 Explain why it is important that human beings try to maintain and conserve the environments in which they live.
Worksheet 6.7 Sci-words
13 Some people buy worms to add to their soil. Describe the role worms play in the ecosystem.
215
7
Light
Prescribed focus area The applications and uses of science
Key outcomes
Additional
Essentials
5.3, 5.6.4
•
Light can be absorbed, reflected or refracted.
•
Objects are seen to be a certain colour because that colour is the only one not to be absorbed.
•
The reflection of light allows us to see objects and to determine their colour and whether they are rough or smooth.
•
Reflection off smooth surfaces allows light to form images.
•
Refraction occurs when light moves through two transparent substances of different optical denstities.
•
Refraction causes light to change speed and change direction.
•
Refraction causes many common optical illusions.
•
Lenses use refraction to focus images.
•
The lens in the eye helps focus light onto the retina, allowing us to see.
•
Scattering accounts for blue skies and red sunsets.
•
Dispersion accounts for rainbows.
Unit
7.1
context
Bending light
Light is a form of energy. You see an object because light has entered your eyes and an image of what you are looking at has formed on your retina. Although light travels in a series of straight lines to get to your eyes, it changes its direction whenever it reflects or refracts.
Reflection Reflection creates the images that you see in mirrors and extremely smooth surfaces such as highly polished tables, the panels of a freshly washed car, or the surface of a lake on a still morning. Reflection changes the direction of light: the angle a light ray makes is the same before and after reflection. This is best summarised by the law of reflection which states: angle of incidence 쏁 angle of reflection i쏁r
These angles are measured from an imaginary line called the normal, which is drawn at right angles to the surface of the mirror. Go to
Science Focus 3 Unit 7.2
Worksheet 7.1 Reflection
Fig 7.1.1 What you see is known as the image. You are the object.
Refraction Air, water, glass, diamond and Perspex are examples of transparent substances that allow light to pass through them. Light bends when it travels from one transparent substance into another. This bending is known as refraction. Refraction happens because the speed of light changes as it passes from one substance into another.
incident ray mirror
angle of incidence i angle of reflection r
light travels fast in air
glass is more optically dense than air, causing light to slow down and change direction
normal
reflected ray
Fig 7.1.2 When light reflects, the angles of incidence and reflection are the same.
Fig 7.1.3 Light slows down and refracts as it enters a glass block from air. When it exits, it speeds up and refracts once more.
217
Bending light When light enters glass from air, it slows down and bends towards the normal. As for reflection, the normal is an imaginary line drawn perpendicular to the edge of the substance it is about to enter. But when light leaves the glass block it speeds up, bending away from the normal.
light bulb
concave mirror increasing refractive index
refractive index 1.00
1.33
1.49
1.52
2.42
air
water
Perspex
glass
diamond
300
225
201
197
124
(K 1000 km/s) speed of light
red Perspex slower speed
towards the normal on entering the Perspex, and away from the normal on leaving it. The rear lenses that make up a car’s stoplights use refraction to ensure light is bent up or down, making it visible from a variety of angles.
Fig 7.1.4 Light travels at different speeds in different transparent substances. These different speeds are the cause of refraction.
Which way does it bend? Light travels fastest in a vacuum, a little slower in gases like air, slower again in liquids like water and slowest in solids like ice, glass, Perspex and diamond. The speed of light in a substance depends on the optical density or refractive index of the substance. normal s HIGHER OPTICAL DENSITY s HIGH REFRACTIVE INDEX
Fig 7.1.6 A car stoplight in action: notice how light is refracted
light ray
angle of incidence
Total internal reflection Light doesn’t always refract when it hits a boundary between two substances. When light travels from a more optically dense substance into a less optically dense one (for example, from glass into air) it sometimes reflects instead! The light is unable to escape from the substance it’s in. This phenomenon is known as total internal reflection, and happens when the angle between the light ray and the normal is greater than the critical angle. The critical angle of incidence occurs when the refracted light ray travels along the boundary between the two substances.
angle of refraction Prac 2 p. 224
s LOW OPTICAL DENSITY s LOW REFRACTIVE INDEX Skimming along the surface: the angle of incidence equals the critical angle.
Fig 7.1.5 The angle of incidence and the angle of refraction are measured from an imaginary line called the normal.
ray skims surface
When light travels from a substance to another substance with higher optical density, the light slows down and bends towards the normal. In contrast, when light travels from one substance into another substance of lower optical density (for example, from glass to air) the opposite happens—the light speeds up and bends away from the normal. There is one exception, and that is when light hits ‘head-on’, perpendicular to the boundary. The light does not bend but its speed still changes. Worksheet 7.2 Snell's law
218
‘Normal’ refraction: the angle of incidence is less than the critical angle. air
Prac 1 p. 223
total internal reflection
glass equal angles
critical angle
Total internal reflection: the angle of incidence is greater than the critical angle.
light source
Fig 7.1.7 For total internal reflection to occur, light must be travelling into a substance of lower optical density and must strike at an angle greater than the critical angle of incidence. The critical angle of incidence occurs when the refracted light ray travels along the boundary between the two substances.
total internal reflection
7.1
Fig 7.1.8 A red bike reflector in action. Reflectors used on bikes and cars are shaped at the back to ensure the angle of incoming light is always greater than the critical angle. This allows the light from the car behind to be reflected back, making the reflector appear to be shining bright red.
to provide doctors with images (magnified around four times) of the stomach and intestinal lining. Tumours that would otherwise be impossible to treat may be destroyed by laser light sent down an optical fibre cable inserted nearby. The endomicroscope produces images of body cells magnified 2000 times. Optical fibres are also increasingly being used instead of copper wire to transmit computer, video and audio data (such as telephone conversations) because they are thinner, cheaper, more durable and can carry more information. They also have increased data security and are not affected by interference from electromagnetic radiation. Fibre optic networks now connect all of Australia’s major cities.
Unit
light from a car behind
Optical fibres Optical fibres use total internal reflection to trap light within a thin, flexible strand. Optical fibres are used in endoscopes. These flexible instruments contain optical fibres and can be passed via the mouth into the lower parts of the digestive system
Fig 7.1.10 The use of an endoscope in surgery minimises the size of the cut and subsequent scar.
Refraction illusions plastic sheath
inner core
outer layer
total internal reflection
Fig 7.1.9 Optical fibres are used in decorative lights and in communication. Optical fibres use multiple total internal reflections to transmit light.
Refraction and total internal reflection can create optical illusions—causing us to see things that aren’t really there. Optical illusions are images our brain constructs based on where light appears to be coming from. This happens because our brain assumes that light always travels in perfectly straight lines, without any reflection or refraction. Refraction is also responsible for another illusion in which water appears shallower than it really is. This is evident when you look into a swimming pool. The apparent depth is less than the actual depth.
Prac 3 p. 224
Prac 4 p. 225
219
Bending light
air water apparent depth real depth image of point point
Fig 7.1.11 Refraction makes a straight ruler look very bent. Light from the lower part of the ruler is travelling into a region of lower optical density (air), and so has been bent away from the normal. The image in the water is actually an illusion.
On a hot day, total internal reflection can give the illusion of water on a hot dry road. This occurs because cool air has a higher optical density than warm air. Light coming from the sky bends away from the normal as it moves from the cool air in the upper atmosphere to the hot air near the ground. For large angles of incidence, the light from the sky and other objects is totally internally reflected within the cooler air, towards the observer. This appears similar to the reflection from the surface of a pool of water. This type of optical illusion is called a mirage.
7.1
water appears to be less deep than it really is. For someone fishing, this means that fish are deeper than they appear to be.
real cloud
cool air warm air
mirage cloud
bent rays travelling through cool and warm air
Fig 7.1.13 Air at different temperatures refracts light differently, causing a mirage.
QUESTIONS
Remembering 1 Recall the law of reflection by drawing a diagram showing a ray of light reflecting off a plane or flat mirror. Add the normal and the angles of incidence and reflection. 2 a State what is special about transparent substances. b List four examples of transparent substances. 3 Recall what refraction is by drawing a diagram showing a ray of light passing from air into glass. a Add the normal and the angles of incidence and refraction. b Indicate on your diagram which substance would have a higher optical density and which would have a higher refractive index.
220
Fig 7.1.12 Refraction makes it difficult to judge depth. From above,
4 Specify the two things that change when light refracts. 5 List at least five advantages of using optical fibre instead of copper wire for communications. 6 Specify (or draw) what happens when a light ray tries to escape from a glass block into air at an angle: a the same as the critical angle b less than the critical angle c greater than the critical angle
Unit
7 Define the terms: a refraction b total internal reflection c critical angle 8 Explain how a bike reflector can reflect light if it doesn’t contain a mirror. 9 The critical angle of incidence for light passing from diamond into air is 42°. Describe what would happen to light passing from diamond into air if it strikes the boundary at: N
14 a Copy the diagrams in Figure 7.1.15 into your workbook. b Draw a normal wherever the light rays enter a new substance. c Demonstrate what will happen to the rays as they enter and exit from the substances by continuing the ray through the shape and out the other side. a
b
c
air
air
glass
glass
water air
a 42°
water
b 50° c 35°
d
10 A mirage is created because of refraction. Describe the conditions needed for refraction to occur in air.
e Perspex
11 Identify a device that converts light into an electrical signal.
air
glass
Applying 12 Use the information in Figure 7.1.4 to predict which way light will bend when travelling from: a water to glass b glass to diamond c perspex to glass 13 Copy the diagram in Figure 7.1.14. Use a ruler to draw light rays that demonstrate why the stone appears higher than it really is.
7.1
Understanding
air
Fig 7.1.15
Analysing 15 Compare reflection and refraction by listing their similarities and differences. 16 Analyse the situation shown in Figure 7.1.16 and specify in which direction (A, B, C or D) the girl should aim her spear to hit the fish.
A B C
D
fish as seen by girl with spear
Fig 7.1.14
Fig 7.1.16
>> 221
Bending light 17 Figure 7.1.17 shows how cars ‘refract’ if they travel from bitumen into gravel or sand. Compare this situation with that of light to: a identify where the car is travelling faster b identify whether bitumen or sand has the higher ‘refractive index’ normal
20 A stomach does not contain a light source yet doctors commonly use endoscopes to look inside them. Use this information to: a propose reasons why an endoscope contains several optical fibres rather than one b explain how light gets in and out of your stomach when an endoscope is used 21 Fibre optic technology offers many advantages when used in medical applications.
bitumen
a Describe how optical fibre may be used in medical applications. b Identify the traditional medical techniques that optical fibres might replace. c Evaluate the benefits of fibre optic technology to medicine.
sand
Creating 22 The table below lists the refractive indices of several substances. a Construct a bar or column graph for these values. N b Imagine light coming from air and entering each of the substances. List the substances in order from the one that bends light the least to the one that bends light the most.
Fig 7.1.17
Evaluating
Substance
18 Evaluate whether reflection and refraction can occur at the same time.
Air
1.00
19 Scratches on the outside of an optical fibre often cause problems.
Water
1.33
Glass
1.52
a Identify what those problems may be.
Diamond
2.42
b Propose reasons why the scratches might cause problems.
Perspex
1.49
7.1
INVESTIGATING
Investigate your available resources (for example, textbooks, encyclopaedias, internet) to find out more about fibre optics such as: a how a fibre optic cable is made b some further medical applications of fibre optics. Present your work as either a role-play or presentation to be given by: L • a telecommunications engineer explaining to the board of a phone company why they should replace their old copper cables • a doctor explaining how your surgery will be performed.
222
Refractive index
e -xploring To explore refraction further, a list of web destinations can be found on Science Focus 3 Second Edition Student Lounge.
Unit
PRACTICAL ACTIVITIES
1 Measuring angles of refraction Aim To investigate the relationship between the angle of incidence and the angle of refraction
Equipment • • • • • •
light box and single slit slide 12 volt power source sheet of paper ruler polar graph paper (or protractor or Mathomat) semicircular slab of Perspex
2 Ensure an initial angle of incidence of 10°. Use two dots or crosses to mark each end of the light path and measure the angle of refraction.
7.1
7.1
Record your results in a table like the one shown here, including your results for the following angles of incidence: 10°, 20°, 30°, 40°, 50°, 60°, 70°, 80°. Angle of incidence
Angle of refraction
Angle of bending
0° 10° 20° 30°
Method
40°
1 Assemble the apparatus as shown.
50° 60°
light box
70°
single slit slide
80°
angle of incidence
Questions 1 Explain why the semicircular slab is a convenient shape to use. 2 Analyse how the angle of incidence affects the degree of bending of light.
boundary line normal angle of refraction
Fig 7.1.18
3 Construct a graph of angle of incidence versus angle of refraction for Perspex. 4 Assess how the graph would be different if a semicircular diamond was used instead. Diamond is more optically dense than Perspex.
>> 223
Bending light
2 Observing light Aim To create and observe instances of scattering, refraction and total internal reflection
Equipment • • • • • • • •
20 L rectangular fish tank or clear Perspex box HeNe laser pointer or other collimated light source filtered water milk dropper retort stand clamp boss head clamp
Method 1 Fill the fish tank with the filtered water until about ¼ full. 2 Using the retort stand, clamp the HeNe laser so that it shines the beam through the water along the length of the tank and record your observations.
3 Use the dropper to add milk to the water dropwise until you can see the laser beam. Be careful not to add too much milk or the beam will be lost. Record your observations. 4 Use the stand to direct the laser onto the surface of the water at an angle. 5 Explore what happens to the light as it enters the water as the angle of incidence is changed. 6 Explore what happens to the light reflected off the bottom of the fish tank as a function of angle. 7 Arrange the laser so that it enters the aquarium below the water level but still at a downwards angle. 8 Explore the full range of angles and record your results.
Questions 1 Analyse how the angle of incidence affects the degree of bending of light. N 2 Analyse how the angle of incidence affects the angle of total internal reflection. N 3 Explain why the results of your experiment might be different with liquids other than water. What would happen in each case if the liquid had a higher or lower refractive index?
Fig 7.1.19
3 Refraction illusions Aim To observe how refraction can change the way we view objects under water
Equipment • • • • •
224
beaker ruler water opaque bowl (e.g. ice-cream container) coin or small heavy object
Method Part A 1 Half-fill the beaker with water. 2 Place the ruler in the beaker and record your observations. 3 Change the angle of the ruler and note how this changes the apparent bending of the ruler. 4 Move the position of ruler in the beaker and note any other ways in which the ruler appears distorted. Part B As shown in Figure 7.1.20, place a coin in the bowl and have a glass of water within reach. Look at the coin and move your head until it just moves out of view. Slowly add water to the bowl and observe the coin. List your observations.
Unit 1 Analyse how the angle of the ruler affects how much the ruler appears to bend. 2 Explain why the part of the ruler under water appears bigger.
7.1
Questions
3 Explain why the addition of water brings the coin into view.
Fig 7.1.20
4 Apparent depth Aim To investigate how refraction causes depth illusions
Equipment • white paper with several parallel lines drawn on it • glass block • a pin in a cork
glass block
parallel lines
Method 1 Place the glass block on a piece of paper with some parallel lines drawn on it. 2 Hold the cork containing the pin against the block so it lines up with one of the parallel lines. 3 Move the pin up or down the block until it appears to be at the same depth as the parallel line it is lined up with. You have found the correct position if the pin and line move together when you move your head from side to side. 4 Measure the depth of the pin below the top of the block. This is the apparent depth of the glass block. 5 Measure the height of the block above the paper. This is the real depth of the glass block.
view from above apparent depth pin
real depth pin
Fig 7.1.21 Move head backwards and forwards. Pin and line should move together when the pin is at the correct position.
Questions 1 Calculate the refractive index of the block by dividing the real depth by the apparent depth. 2 Predict how the apparent depth would change if the block was replaced with water.
225
Unit
7.2
context
Focusing devices: Lenses and curved mirrors
Light rays often need to be controlled and focused to produce images in optical instruments such as microscopes, cameras and binoculars, and to change
the focus for people wearing contact lenses or glasses. We can control and focus light by using lenses and curved mirrors. Lenses use refraction to focus light. Curved mirrors use reflection.
Orientation Images can be the same way up as the original object. If so, they are referred to as being upright. Inverted images are those that have been turned upside-down.
Fig 7.2.1 Curved mirrors focus light into a point. Here an array of curved mirrors is being used to focus sunlight on a tower to boil water and generate electricity.
The language of optics Lenses and curved mirrors focus light to produce a variety of different types of images. Special terms are used to describe the images formed. Real and virtual Images are either real or virtual. Virtual images do not have light rays actually passing through them. Instead, they are found by extending the light rays until they cross. Virtual images cannot be ‘captured’ on a screen or directly on film. The image seen in the bathroom mirror is virtual. Real images are formed wherever light rays cross. Real images are difficult to see as they ‘float’ in space and need to be ‘captured’ on a wall, a sheet of paper or a screen. Once captured, they are easily seen and can actually be touched. The light energy contained in a real image will cause reactions in chemicals on photographic film which will permanently record the image. This cannot be done with a virtual image. A projector produces a real image that cannot be seen until a screen is placed in its way.
226
Magnification An image is described as enlarged if it is bigger than the original object. It is described as diminished if it is smaller. Magnification specifies exactly how enlarged or diminished the image is. To calculate magnification, divide the size of the image by the size of the object. For example, if a 2 cm object produces a 10 cm image, then its magnification is 10 쐦 2 ҃ 5 times. If the image is diminished, then magnification will be a fraction. For example, if an object is 8 cm high and the image is 4 cm, then its magnification is 4 쐦 8 ҃ ½ or 0.5.
Lenses The two main types of lenses are: • convex lenses—these curve outwards Prac 1 and are fatter in the middle p. 234 • concave lenses—these curve inwards (a little like a cave) and are thinner in the middle. Convex lens parallel rays of light F principal axis focal length Concave lens F principal axis parallel rays of light
focal length
Fig 7.2.2 The focus can be found by shining light rays directly onto the lens. The focus of a convex lens is very obvious. The focus of a concave lens is not as obvious but can be found by tracing back the refracted rays.
Prac 2 p. 235
7.2
• Real images—if the object is at a distance greater than the focal length of the lens, an inverted real image is formed. A real image can be projected onto a screen or even onto film, which will then permanently record the image.
• Virtual images—if the object is at a distance less than the focal length of the lens, a magnified, upright virtual image is formed. This image can’t be projected onto a screen.
Unit
Convex lenses Convex lenses produce two different types of images, depending on where the object is located.
Fig 7.2.3 The shape of a lens can affect its focal length.
strong lens
weak lens
short focal length
long focal length
Fig 7.2.4 A real image is
Convex lens Ray tracing diagram
formed by a convex lens when the object is beyond the focus.
What you see screen
focus focus
object
real image
real image focus object
a scale drawing that allows you to predict the size and location of the image produced by the lens
Fig 7.2.5 A virtual image
Convex lens Ray tracing diagram
What you see
virtual image
is formed by a convex lens when the object is inside the focus. This is how a simple magnifying glass works.
virtual image object focus
focus
eye traces rays back to form a virtual image
227
Focusing devices Concave lenses Concave lenses produce only upright, diminished virtual images. Ray tracing diagram
What you see
eye traces rays back to form a virtual image
object
virtual image object
focus virtual image
Fig 7.2.6 Virtual image formation in a concave lens.
Finding the focal length Rays coming into a lens from a distant object are almost parallel and form an image very close to the focus. Focal length can be found by measuring the distance from the lens to the image.
approximate focal length
distant object almost parallel rays
convex lens
real, inverted image
Fig 7.2.7 An image of a distant object can be used to find the approximate focal length of a convex lens.
Science
Clip
Worksheet 7.3 Lenses Prac 3 p. 236
Focusing devices The eye Focusing in the eye is performed in two stages by two separate lenses. Most of the focusing is performed when the light first enters the eye and passes into the cornea. The cornea is a curved transparent membrane that acts as half a convex lens. The cornea collects the light rays
228
What’s in a name? The word ‘lens’ means ‘lentil’ in Latin. Lentil seeds have the same shape as small convex lenses.
from the world around us and helps them to converge onto a second lens sitting just behind the cornea. The curvature of the second lens is adjustable and focuses the light rays on to the back of the eye where the retina detects the images and sends them to the brain.
light rays
object
Eye for an eye
cornea
The ciliary muscles stretch and relax the jelly-like lens in the human eye so it gets thinner or thicker. Its curvature therefore changes, allowing us to focus on objects at different distances.
pupil
7.2
Clip
lens
Unit
Science
image
Prac 4 p. 237
Fig 7.2.8 Light from an object is focused first by the cornea and then by the lens, which projects a real image onto your retina. The image projected onto the back of our eye is actually upside-down but our brain automatically inverts the image.
missing <<SF3_2_7_02_10>> <<SF3_2_7_02_10>>
Fig 7.2.9 A magnifying glass is a simple microscope that helps you see small objects.
Magnifying glass A magnifying glass is a simple microscope consisting of a single convex lens—allowing you to view small objects. For the magnifying glass to work, the object being viewed must be less than one focal length from the lens. However, this creates a virtual image that cannot be projected onto a screen. Therefore you need the lenses in your eye to refocus the diverging light rays to form a real image on the back of your eye—allowing you to view the magnified image.
229
Focusing devices virtual image formed by eyepiece lens convex eyepiece lens (thick) telescope F
real image formed by objective lens
convex objective lens (thin)
Fig 7.2.10 When you look through a telescope you see an image of an image.
concave mirror parallel rays of light
Telescopes Telescopes make small, distant objects appear larger. By itself, a single lens will only produce smaller images of objects a long way away. The stars and the Moon would appear even smaller! In order to produce a magnified image of such objects, two lenses are used. The objective lens in a telescope produces a real, inverted image just inside the focus of a second lens, called the eyepiece lens. The image produced by the first lens now acts as the object for the second lens. Because the first image is inside the focus of the second lens, the second image (the one seen by the telescope user) is virtual and enlarged compared to the first one. The thinner the first lens (objective lens), the larger the first image. But thin lenses have longer focal lengths—this is why telescopes are long instruments. A telescope is focused by adjusting the distance between the two lenses. The image produced by a simple telescope is upside down, but this is usually not important when viewing objects such as planets and stars.
Curved mirrors Prac 5 Curved mirrors and lenses have many p. 237 similarities. Like lenses, curved mirrors have a principal focus and a focal length. Curved mirrors can also form both real and virtual images. As a result, mirrors can also be used to magnify and project images. There are two main types of curved mirrors: • convex mirrors—these bulge out in the middle • concave mirrors—these are thinner in the middle.
230
principal axis
focus
focal length convex mirror parallel rays of light principal axis
focus
focal length
Fig 7.2.11 The focus of a curved mirror can be found by shining light rays directly onto it. The focus of a concave mirror is very obvious. The focus of a convex lens is not as obvious, but it can be found by tracing back the reflected rays.
Concave mirrors Concave mirrors produce an enlarged (magnified) virtual image of an object placed close to the mirror. These enlarged close-up views make them useful when shaving or applying makeup, or when a dentist needs to look at some tooth decay.
focus object outside the focus
7.2
object is held at a large distance from a concave mirror, a real, inverted image is produced.
Unit
Fig 7.2.12 If an
Ray tracing diagram
What you see real image
Fig 7.2.13 When an object is a very large distance from a concave mirror but directly in front of it, a very small, real image is produced at a point known as the ‘focus’.
focus
light from distant object
image of distant object
Convex mirrors Convex mirrors gather rays of light from a wide area to produce a smaller, virtual image behind the mirror. Convex mirrors are useful when a wide view is needed. They are used in shops for security across the whole store, at dangerous intersections where vision is difficult, and in some car rear-vision mirrors to give a wider view of what is behind the car. Worksheet 7.4 Mirrors Prac 6 p. 238
Prac 7 p. 238
Fig 7.2.14 A convex mirror produces a wider view than a flat mirror.
virtual image
object
focus
Ray tracing diagram
What you see
Fig 7.2.15 A convex mirror produces only virtual, smaller images.
231
Focusing devices
7.2
QUESTIONS
Remembering
a
retina
1 Recall the two main types of lenses and curved mirrors, sketching and naming each type. 2 Draw a diagram to recall how to find the focal point of a concave:
short-sightedness distant object
b
eye
long-sightedness
a mirror
retina
b lens
close object
3 Specify the two parts of the human eye that focus light.
Understanding
eye
4 Define the terms:
Fig 7.2.16
a focal length
Applying
b principal axis
10 Copy the lenses in Figure 7.2.17 and identify each as concave or convex.
c myopic d hyperopic L 5 At the movies you see real images, not virtual ones. Explain how you can tell. 6 Copy the following and modify any incorrect statements so that they become true. a Real images formed by convex lenses are always bigger than the original object. b Virtual images formed by convex lenses are always bigger than the original object. c Concave lenses can form only virtual images. d Images in a concave lens are always the right way up. e Real images in a concave lens are always the right way up. 7 Use the ray tracing diagrams (pages 227 and 228) to describe what happens to the image when a distant object is brought closer to:
Fig 7.2.17
11 Copy and complete the ray tracing diagrams in Figure 7.2.18 to demonstrate the path taken by the light rays. a
F
F
a a convex lens b a concave lens
b
8 Describe how a lens or mirror could be used to start a fire. 9 An image must be formed on the retina for it to be seen clearly. Explain how convex and concave lenses are used in spectacles and contact lenses to correct each vision defect shown in Figure 7.2.16. Illustrate your answers with a diagram.
232
F
Fig 7.2.18
F
Unit
a a convex lens
19 A curved mirror produces a large upright image when held close to an object. Identify the type of mirror it is likely to be.
Analysing 20 A convex lens can produce an enlarged image of an insect. Analyse why it can’t produce an enlarged image of the Moon.
b a concave lens 13 Convex lenses can form real images, virtual images and an unfocused blur. Identify where the object would need to be to produce each type of image. 14 A camper is using a magnifying glass to set a piece of paper on fire. Identify what type of lens is being used and what the ‘hot spot’ on the paper is an image of. 15 Demonstrate what the following terms mean by re-drawing the stick figure in Figure 7.2.19: a inverted
7.2
12 The terms diverging (moving apart) and converging (coming together) may be used to describe lenses. Identify which term applies to:
Evaluating 21 You have two lenses—one thick and one thin—to build a telescope. Propose which one you should use for the eyepiece and which one for the objective lens.
Creating 22 Construct a diagram that shows why no image is formed of an object placed at the focus of a convex lens. 23 Figure 7.2.20 shows the image of a person as seen in a dessert spoon.
b magnified c diminished
a Identify whether the spoon is acting as a lens or a mirror and whether it is convex or concave. b Use the language of optics to describe the image as fully as you can. c Construct a ray diagram showing how the image was formed in the spoon.
Fig 7.2.19
16 You look into a magnifying glass at an ant. a State whether you can touch the ant or its image. b Identify whether the image is real or virtual. 17 Calculate the magnification in each case for images produced by various lenses. N Object height
Image height
2 cm
6 cm
5 cm
20 cm
25 mm
5 mm
16 mm
4 mm
8 mm
160 mm
18 Identify which type of mirror would be best for use: a at a dangerous intersection b by a dentist
Fig 7.2.20 .2.20
233
Focusing devices
7.2
INVESTIGATING
Investigate your available resources (for example, textbooks, encyclopaedias, internet) to complete the following tasks. 1 Research the history of an optical instrument such as the telescope or camera. Include the following information:
a what causes the defect
a who invented it and when
b the symptoms displayed (include diagrams if applicable)
b what improvements have been made over the years and by whom
c any treatment(s) available to control or cure the defect.
c a diagram of the first instrument developed and a diagram of a modern version of this instrument—include a discussion of some of the differences or improvements between the original and modern versions of the instrument. Present your information in a written report that includes a timeline. L
7.2
Present your research as an information leaflet that may be found in a doctor’s surgery. L
e –xploring To explore how telescopes, microscopes, binoculars and cameras work, a list of web destinations can be found on Science Focus 3 Second Edition Student Lounge.
PRACTICAL ACTIVITIES
1 Water lenses Aim To investigate how water droplets can be used as a lens
Equipment • • • •
2 Research one type of sight defect such as long-sightedness, short-sightedness, cataracts, night blindness or colour blindness. Find out the following information:
eye dropper or pipette a printed A4 sheet of glossy paper with fonts of various sizes small beaker of water wire loop as shown in Figure 7.2.21
Method Part A 1 Use the eye dropper or pipette to place droplets of water on the printed A4 sheet. 2 Observe how the size of the droplet affects the appearance of the text below it. Part B Does it matter if a lens is hollow on the inside? Will curved surfaces with nothing (but air) in between have the same effect as a solid lens? Design your own experiment to examine these questions.
?
Questions 1 Identify if the water droplet is behaving as a convex or a concave lens. 2 Explain why text below a smaller droplet appears bigger.
Fig 7.2.21
234
DYO
Unit
7.2
2 Lenses and a light box Aim To investigate the refraction of light through various lenses
Equipment • • • •
ray box
light box and multiple-slit slide 12 volt power supply light box lenses set sheet of paper
Method lens
1 Adjust the light box (using the knob on top) to produce a wide beam of light with parallel edges on a piece of paper. 2 Direct a wide beam of light through a lens shape with no slide inserted in the light box.
Fig 7.2.22
3 Now use the slide with multiple slits to direct several parallel beams of light through the lens. Use a pencil to mark parts of the light paths. 4 Remove the lens and light box from the paper and rule the complete light paths. 5 Repeat steps 1 to 4 for several different lenses, including concave lenses. (Use a new piece of paper in each case.)
Questions 1 Describe in words the effect of: a a convex lens b a concave lens 2 Compare the light path through a wide convex lens with that through a thin one. 3 Identify whether there are any individual light rays that are not bent by the lens in each case. 4 What were the focal lengths of the lenses you used? Construct a trace or sketch of each lens and write the focal length under each one.
>> 235
Focusing devices
3 Images in a convex lens Aim To investigate the image formed by different convex lenses
Equipment • • • • • •
convex lens concave lens white card or screen plasticine or lens holder metre ruler candle or small globe with power supply
Fig 7.2.23
6 Attempt to repeat this experiment with a concave lens and record your results.
Method 1 Set up your apparatus as shown in Figure 7.2.23. 2 Determine the focal length of your lens by using it to form an image of a window 5 metres or more away on your card/ screen. Measure the distance of the image/screen from the lens—this is the focal length. 3 Use your apparatus to obtain the sharpest possible image on the screen with the candle or lamp more than two focal lengths from the lens. A darkened room will help. Copy the table below, and record your measurements. 5 Repeat for the other positions described in the table below.
Questions 1 Describe what happened as the object was brought closer to the lens. 2 Summarise the circumstances in which: a a real image (on a screen) is obtained b a virtual image (one that cannot be ‘caught’ on a screen) is obtained c no image is obtained 3 Assess whether it is possible to form a real image (one that may be ‘caught’ on a screen) using a concave lens. 4 Explain how the image changes as the object-to-lens distance is varied.
Convex lens focal length: _________ cm Object Diagram
Description of position
Object more than two focal lengths from lens
Object two focal lengths from lens
Object between one and two focal lengths from lens Object less than one focal length from lens (i.e. object inside the focal length) Object exactly at the focus (one focal length from lens)
236
Image Distance from lens (cm)
Distance from lens (cm)
Description (e.g. larger/smaller, inverted/upright)
Unit 3 Record at what point the image becomes unrecognisable.
Aim
4 Simulate an eye that is long-sighted by moving the screen towards the lens and describe what happens to the image.
To investigate the images formed by convex and concave mirrors
5 Record at what point the image becomes unrecognisable.
Equipment
6 Refocus the image then cover ¹/³ of the lens with the extra piece of card and record what happens to the image.
• • • • • •
convex lens white card or screen extra piece of card plasticine or lens holder metre ruler candle or small globe with power supply
Method 1 Set up your apparatus as shown in Figure 7.2.23 (Prac 3) so that you project a sharp, well-focused image onto the screen. 2 Simulate an eye that is short-sighted by moving the screen away from the lens and describe what happens to the image.
7 Increase the fraction of the lens that is covered by the card and record your observations.
Questions 1 Calculate the percentage difference between the focal point and the position where the image becomes unrecognisable for long- and short-sighted simulations. 2 Describe what happens to the image as more of the lens is blocked by the card. 3 Explain what this tells us about how the lens forms the image and draw a ray diagram to demonstrate your explanation.
objective lens
5 Telescopes and microscopes Aim To investigate how telescopes and microscopes form images
7.2
4 Simulating imperfect vision
translucent screen
Equipment • two convex lenses—one thin (e.g. focal length 25 cm) and one thick (e.g. focal length 5 cm) • cardboard • scissors • tracing paper or other translucent material (e.g. thin plastic from a shopping bag) • lamp • small object to view
eyepiece lens
Fig 7.2.24
Method Part A: The telescope 1 Construct and assemble the apparatus as shown in Figure 7.2.24. 2 Place the object a large distance (e.g. 1 metre) from the objective lens, and move the eyepiece lens and screen to obtain the sharpest possible image looking through the eyepiece lens. Note the size of the image compared with the object. 3 While looking through the eyepiece lens and observing the image, remove the screen. You should still see the image! Think about why.
Part B: The microscope 1 Now move the object close to the lens (but not closer than the focal length). 2 Adjust the position of the lenses to obtain an image that is larger than the object.
Questions 1 Distinguish between a telescope and a microscope. 2 Describe how the removal of the screen changes the image in Part A (step 3) above.
237
Focusing devices
6 Exploring curved surfaces: spoons Aim To explore the properties of the images reflected in the curved surfaces of spoons
Equipment
Method 1 Place the concave side of a metal soup spoon very close to your eye and describe what you see. 2 Move the spoon away from your eye and describe your observations. 3 Repeat this procedure for the convex side of the spoon.
Questions
• metal soup spoon
1 Identify when the images you are viewing are real images and when you are viewing virtual images. 2 Explain why the image in the concave side of the spoon inverts as you move the spoon further away.
7 Forming images with curved mirrors
Method Part A: Concave mirror 1 Arrange the apparatus as shown in Figure 7.2.25.
Aim
2 Move the screen until you obtain a clear image of the candle.
To investigate the images formed by convex and concave mirrors
3 Investigate the different images produced with the candle at different distances from the mirror. Is there a position where it is impossible to obtain an image on the screen? Can you see a virtual image in the mirror?
Equipment • • • •
convex mirror concave mirror candle screen
Part B: Convex mirror 1 Hold the mirror at arm’s length and look at your image. 2 Gradually move the mirror towards you, noting any changes in the image as you do so.
screen
Questions image
concave mirror
1 Explain what happens to the image as an object is brought closer to: a a concave mirror b a convex mirror 2 Identify which type(s) of image are possible in each type of mirror.
plasticine candle (object)
Fig 7.2.25
238
Unit
7.3
context
Colour
The sky is blue, sunsets are red and occasionally rainbows splash their display of colours across the sky. From a basic set of colours, other colours can be created by mixing appropriate pigments, styles and lights.
Dispersion The light from the Sun or a light globe is referred to as white light. White light is a mixture of all the colours of the rainbow. Sometimes white light is split into its component colours. This is most obvious when a rainbow forms in the sky after rain. This effect is called dispersion, and the colours of light produced are known as the visible spectrum. Dispersion occurs because the different colours of light are refracted by slightly different amounts. Red light is refracted the least. Orange light is refracted slightly less then yellow; then green, blue, indigo and finally violet light is refracted through the largest angle. Go to
Science Focus 4 Unit 7.3
Prac 1 p. 245
Fig 7.3.1 Each paint in the paintbox reflects a different colour light. Red reflects red, yellow reflects yellow and so on.
Sir Isaac Newton was one of the first people to study the properties of dispersion. In 1665 he conducted an experiment using triangular prisms to split a thin beam of white light into the colours of the rainbow. This experiment established the basic ideas that we now use to explain the many phenomena that involve light and colour. You can use these ideas to explain the colours you see when looking at objects, the sky, theatre lighting or printed photographs.
Science
Clip
Roy G who?
Fig 7.3.2 A triangular prism splits white light into the colours of the rainbow. The red light is refracted least and the violet light is refracted most with all the other colours in between.
Science
Clip
Newton’s lucky number 7 Isaac Newton first described dispersion in 1665 when he was a student at Cambridge University in England. Although the spectrum is made from an infinite number of merged colours, Newton liked the idea of seven main colours—red, orange, yellow, green, blue, indigo and violet. This was probably because he was interested in mysticism and seven was, in Newton’s time, a highly symbolic number. It has been argued that indigo was included to ‘make up the numbers’ to seven, as most people find it hard to tell blue and indigo apart.
One way of remembering the colours of the visible spectrum is imagining that the first letter of each colour is part of a name—this forms the mnemonic Roy G Biv.
239
Colour
Rainbows
Blue skies and red sunsets
Small droplets of water behave like tiny prisms in the sky. Sometimes the colours will reach your eyes after refracting and undergoing total internal reflection. Droplets higher in the sky refract red to your eyes, while green and blue go overhead. In drops lower in the sky, blue light is refracted and reflected to your eyes, but green and red light bend lower down, missing your eyes. The overall effect is that we see a primary rainbow—a band in the sky with red at the top and blue at the bottom. Sometimes a less intense secondary rainbow can be seen above a primary one. Light reaches your eyes from a secondary rainbow after two internal reflections inside each raindrop. This has the effect of reversing the colours so the bottom band is red.
Blue skies and red sunsets are caused not by refraction of sunlight, but by another phenomenon known as scattering in which molecules of gas and dust particles in the atmosphere alter the direction of light rays. Blue light is scattered more than the other colours of the spectrum, and the scattered blue rays seen against the dark background of space cause the sky to appear blue. At sunrise and sunset, when sunlight travels further through the atmosphere, almost all of the blue rays are scattered and the light that reaches us is mainly red or orange.
white light
Sun
sees red sunset
gas molecule
raindrop sees blue sky
light from Sun
Fig 7.3.4 Blue light scatters more than red light.
Colour addition primary rainbow
It is possible to mix different colours of light together by shining the coloured light sources in the same direction. Red, green and blue are known as the primary colours of light. When these three colours of light are combined they produce white light. This is the opposite to the splitting of light. When just two primary colours overlap, secondary colours— cyan, magenta and yellow—are produced. Prac 2 p. 246
raindrop white light light from Sun
blue secondary rainbow
Fig 7.3.3 How primary and secondary rainbows are formed. Note that the colours are reversed in the secondary rainbow.
240
magenta cyan white red yellow green
Fig 7.3.5 Overlapping light beams demonstrate colour addition.
Unit
7.3
1 pixel
Fig 7.3.6 Television uses a pattern of tiny pixels to generate its picture. Each pixel contains three cells, one red, one blue and one green. These cells glow when excited, either by being hit by electrons shot from an electron gun (normal TV) or an electrical current (plasma and LCD). The eyes add together the colours from the glowing cells in each pixel to contruct different colours.
Two colours of light that mix to make white light are called complementary colours. Red and cyan are complementary colours, as are green and magenta. Blue and yellow form another pair.
red filter red transmitted
white light
Colour subtraction
blue filter
If white light is passed through red cellophane it comes out red. The red cellophane is acting as a filter, absorbing and subtracting all but the red colour from the white light. All the other colours (violet to orange) are absorbed or ‘trapped’ by the chemical dye in the cellophane.
white light
blue transmitted
blue filter no light transmitted (you would perceive black)
red light
Seeing colours Colour subtraction or absorption also occurs when you look at coloured objects. When we see a red T-shirt, it’s because white light from the Sun or a ceiling light hits it and reflects red light to your eyes. The red T-shirt absorbs all other colours. Some peculiar effects can be observed when coloured objects are viewed in coloured (rather than white) light. Some of these are explained in Figure 7.3.7. To simplify explanations, consider white light to be made up of red, blue and green light only. Prac 3 p. 246
green filter yellow light
green transmitted
Fig 7.3.7 Filters allow light only of a particular colour to pass through them and absorb all other colours.
Prac 4 p. 247
241
Colour white light
white light red light reflected (all other colours absorbed) object appears red
blue light reflected (all other colours absorbed) object appears blue red light
red light reflected object appears red yellow light red light reflected (green absorbed) object appears red
red light
no light reflected object appears black
Fig 7.3.8 Coloured objects absorb some colours and reflect others.
Mixing pigments Pigments are strongly coloured substances that may be found in materials like paint and ink. These behave quite differently to light. For example, blue and yellow light mix to make white light, but blue and yellow paint mix to make green paint. When talking about paints or pigments, red, blue and yellow are primary colours. However, this should not be confused with the primary colours of light, Prac 5 which are red, blue and green. p. 248 You normally view objects in white light that is a mixture of red, orange, yellow, green, blue, indigo and violet (ROYGBIV). Paints are not perfect colours and usually reflect and absorb groups of these colours. For example: • blue paint absorbs red, orange and yellow light (ROY), but reflects green, blue, indigo and violet (GBIV) • yellow paint absorbs blue, indigo and violet (BIV) and reflects red, orange, yellow and green (ROYG) • a mixture of blue and yellow absorbs all colours that both individual paints do (red, orange, yellow, blue, indigo and violet (ROYBIV), leaving only green (G) reflected, so the mixture appears green. Mixing many different pigments will usually result in a murky dark colour. This is because most colours are absorbed by the mixture, leaving very little to be reflected. red absorbed cyan
green absorbed magenta
Fig 7.3.9 Four different candles viewed under white light and red light. blue absorbed
Science
Clip
yellow
Dark nights On a dark night the world appears to be in shades of black and white. This is because the surface of the retina on the back of our eyes is made up of two highly specialised types of cells called rods and cones. The cones are able to distinguish between light of different colours but need bright light to be activated. On the other hand, rods cannot differentiate between different colours but can work in very dim light. So when it is very dark, the cones are not strongly activated, limiting our ability to see colour.
242
Fig 7.3.10 Colour absorption in pigments
Unit
Printing
7.3
full colour electronic file
The secondary colours of light—cyan, magenta and yellow—are very important in the printing process, such as that used to print the colours in this book. They are used because they each subtract one of the primary colours. Black is also used to provide contrast and variety in shades. This set of secondary colours, together with black, is known as CYMK. The last letter in the word ‘black’, K, stands for black.
colour separations
used to make printing plates
C
Y
M
K
printing
printed page
magenta blue cyan
black green
Fig 7.3.12 Cyan, yellow, magenta and black (CMYK) are important colours in the printing process, where tiny dots of each combine to produce the colours we see in the final image.
red yellow
Fig 7.3.11 Mixing paints
Cyan, magenta and yellow are sometimes referred to as the primary colours of pigments. Secondary colour combinations give us a range of colours that can then be printed. For example, to
7.3
produce red on a printed page, magenta and yellow are combined. The magenta subtracts green and the yellow subtracts blue, leaving only red. Many desktop publishing programs can produce so-called colour separation files—four single-colour images that are transferred to plastic film used in the printing process. These images are used to control when C, Y, M or K is printed.
QUESTIONS
Remembering 1 Name two sources of ‘white’ light. 2 Name the device that Isaac Newton used to split light into several colours. 3 Name the effect where white light is split into the colours of the visible spectrum. 4 List in order the colours of the visible spectrum. 5 Name the effect which causes skies to be blue. 6 List the: a primary colours of light b secondary colours of light
7 Recall complementary colours by completing the following statements: a green light 쎵 ______________ 쏁 white light b cyan light 쎵 ______________ 쏁 white light 8 List the: a three basic colours that make up a colour TV screen b four main ink colours that must be used in a basic colour printer cartridge 9 List the colour pigments that would be mixed to produce red on a printed page.
>> 243
Colour Understanding 10 Explain why sunrises and sunsets are red or orange in colour. 11 Explain how you can tell whether a rainbow is a primary or secondary one. 12 Explain how a television screen produces colour images.
Applying 13 Diagram A in Figure 7.3.13 shows a ray of red light passing through a glass object. Identify which diagram (A, B, C or D) best shows a ray of blue light passing through the same object.
16 Three identical but differently coloured cars are parked in the sunlight. One car is white, one is green and one is black. Identify which will heat up the quickest. Explain your answer.
Evaluating 17 Propose what happens to the light energy that is absorbed by a filter. 18 Propose reasons why rainbows usually happen after a rainstorm. 19 Propose reasons why rainbows cannot be seen from all angles.
Creating 20 A stack of coloured blocks appears as shown in Figure 7.3.15 in white light. Construct a diagram and label the colour of each block when viewed in: A
B
a blue light b yellow light magenta
C
green
D
Fig 7.3.13
red
14 Copy and complete the light filter diagrams shown in Figure 7.3.14. a white light
Fig 7.3.15
21 Construct a colour wheel such as that shown in Figure 7.3.16 and study the effect of ‘mixing’ different colours in different proportions. Summarise your findings in a table. G
b blue light G c cyan light G
Fig 7.3.14
15 Identify the colour you would see when paints of the following colours are mixed: a cyan and magenta b yellow and cyan c cyan, magenta and yellow
244
Fig 7.3.16
Unit
INVESTIGATING
7.3
7.3
Investigate your available resources (for example, textbooks, encyclopaedias, internet) to complete the following tasks. 1 Find out more about how TV screens produce their colours. a What are phosphors and how do ‘normal’ colour TVs control their electron beams so that they strike just the right phosphors on the screen? b How are LCD and plasma screens different from ‘normal’ TVs and how do they produce their colours? 2 Find out how colour inkjet or laser printers work. Summarise your findings in a flow chart. L
7.3
PRACTICAL ACTIVITIES
1 Dispersion: splitting white light Aim To disperse a beam of white light into the spectrum
Equipment • • • •
triangular glass or Perspex prism light box and power supply slide with single slit white paper
Method 1 Alter the position of the light box and prism to obtain a clear spectrum. 2 Mark the ray path and position of each colour within the dispersed beam. 3 Use any other light box accessories available to try to recombine the colours into a single white ray.
Questions 1 Identify the colour that refracts: a the most b the least 2 Propose how it may be possible to recombine colours separated by a prism.
245
Colour
2 Mixing coloured light
3 Note the resulting colour in a table like the one below, and try various colour combinations.
Aim
Copy the table and record each result.
To investigate the mixing of coloured light using various combinations of coloured filters
Slide A
Slide B
Red
Blue
Red
Green
Blue
Green
Red
Cyan
Green
Magenta
Blue
Yellow
Equipment • light box and power supply • a variety of coloured slides • white paper
Method 1 Cover the end of the light box nearest the globe. 2 Place a red filter in one side of the box and a blue one in the other, using the side mirrors to reflect the coloured light onto some white paper so that they overlap.
5 Use the light box to combine three colours and record your results in a table like this. Slide A
Slide B
Slide C
Red
Blue
Green
Cyan
Magenta
Yellow
light box red slide (filter) blue slide (filter)
Result
Result
Questions 1 Identify which combinations produced white light. What do you call such combinations?
reflecting door white paper
2 The white produced was probably not quite white but was a little ‘off’. Propose why some of the results may not have been ‘perfect’.
Fig 7.3.17
3 Seeing things in a different light Aim To investigate the colour of objects when viewed under different-coloured lights
Equipment • light box and power supply • a variety of coloured slides • a variety of coloured cards (Note: the slides and cards should each be labelled with their colour.)
246
Method 1 Check that each slide and card has its colour written on it. 2 In a darkened room, use a light box and coloured slides to shine coloured light onto various coloured cards. 3 Record the appearance of the card in each case in a table like the one on the next page.
Unit
Card colour Red
Blue
Green
Cyan
Magenta
Yellow
7.3
Appearance of coloured cards in coloured light
Light colour
Red Blue Green Cyan Magenta Yellow
Questions 1 Identify which colour light needs to shine on a red card so that it appears: a red b black or very dark
4 Measuring light absorption
2 Identify examples where an object appeared quite different to its actual colour. 3 It is important to label each card with its colour. Explain why this is the case. 4 Theoretically, several combinations should have resulted in cards appearing to be pitch black. Assess why you may have seen dark colours instead.
Colour
Aim
White Red
Equipment 5 metallic cans of equal size with plastic lids e.g. coffee cans 5 thermometers coloured paint—black, white, red, blue and green timer light source e.g. the Sun or a flood lamp
Method 1 Paint the surface of the cans with the different coloured paints. 2 Put a small hole in each of the plastic lids. 3 Insert the thermometers into the cans so that each bulb is sitting approximately in the middle of the can. 4 Fill in the table below.
Colours reflected
Black
To investigate how the colour of objects affect how much light energy they absorb • • • • •
Colours absorbed
Blue Green 5 Place the painted tins in a direct light source (e.g. direct sunlight) so that they all receive equal amounts of light. 6 Measure the temperature inside each can every 5 minutes and plot your results.
Questions 1 Explain why different coloured cans may change temperature at different rates when exposed to the same light source. 2 Analyse what part of the light spectrum each of the cans will absorb and reflect. 3 Construct a graph of the temperature vs time for each of the coloured cans. 4 Assess how the colour of the can affects its ability to absorb light energy.
247
Colour
5 Mixing pigments Aim To investigate colours created by mixing paints
Equipment • a set of watercolour or acrylic paints • paint brushes • blank paper
Method 1 Experiment with mixing two colours of paints at a time. 2 Mix three different colours to see what colour results.
Questions 1 Identify what colours of light are being absorbed and reflected for different combinations of paint. 2 Explain why mixtures of three or more colours will often appear dark and murky.
CHAPTER REVIEW Remembering 1 Recall refraction by copying and completing this sentence. When a light ray travelling in air strikes a glass boundary, it bends ________ the normal. The speed of the ray in the glass is ________ than it is in air. 2 State whether the following are true or false. a Light always bends when it enters a different substance. b Images can be produced by reflection or refraction. c Light can bend due to refraction within the one substance. d Light passing from water to air will bend towards the normal. e The apparent depth of a swimming pool is less than the real depth. 3 State two uses of optical fibres. 4 Name the complementary colour to: a red b magenta 5 Name the type of image produced when an object is close to: a a concave mirror b a convex mirror 6 Name an optical device that produces: a real images for viewing b virtual images for viewing 7 State how many total internal reflections occur inside a drop of water that helps form: a a primary rainbow b a secondary rainbow
248
Understanding 8 a Describe at least two uses for optical fibres. b Outline how each use you have described may benefit society. 9 Describe the appearance of: a a green flag viewed in blue light b a blue flag viewed in red light c a cyan flag viewed in green light 10 Describe three situations in which different types of mirrors are used and why. 11 Describe how lenses and/or mirrors are used in the following technological developments: a security mirror in a shop b slide projector 12 Assess which colour light in each pair (below) refracts the most. a red or orange b blue or green c yellow or violet
Applying 13 Identify which of the following lenses are:
20 Construct ray diagrams by copying and completing the light ray in each diagram below.
a concave
a
b convex air
water
air
b
water
Fig 7.4.1 c
14 Demonstrate using a ray diagram how the virtual image produced by a magnifying glass is converted to a real image on our retina.
glass
Analysing
water
15 Analyse why red sunsets can sometimes be more impressive when there is more dust or pollution in the air than usual. 16 Analyse what type of image (real or virtual), size (enlarged or diminished) and orientation (inverted or upright) when a candle is placed: a 20 cm in front of a convex lens of focal length 10 cm b 100 cm in front of a convex lens of focal length 10 cm c 5 cm in front of a convex lens of focal length 10 cm d 5 cm in front of a concave lens of focal length 10 cm
Fig 7.4.2
21 Copy and colour each of the following colour combination diagrams to explain colour addition. a
b
magenta blue
green
yellow
Evaluating 17 A printer combines hundreds of tiny cyan dots with a similar number of yellow dots in one region of a page. Deduce what colour that part of the page will appear. 18 A fruit shop places a red light above a basket of lemons. Deduce what colour the lemons will appear to customers.
red
cyan
Light
Pigments
Creating
Fig 7.4.3
19 Construct a diagram to demonstrate how ‘ray’ tracing can be used to find a real image in: a a concave lens b a convex lens
22 Copy and complete the following diagrams involving filters. c
a white light
yellow light cyan filter
blue filter Worksheet 7.5 Crossword
b
d
magenta light Worksheet 7.6 Sci-words
red filter
white light blue filter
green filter
Fig 7.4.4
249
8
The universe
Prescribed focus area Current issues, research and development in science
Key outcomes
Additional
Essentials
5.5, 5.9.1, 5.9.3
•
The Doppler effect indicates whether an object is moving towards or away from us.
•
The huge distances in space make obtaining information about the universe very difficult.
•
Different types of electromagnetic radiation, such as radio waves, are used to obtain information about the universe.
•
Information about the movement of the stars and galaxies comes from how light changes due to the Doppler effect.
•
The Big Bang theory states that the universe exploded in all directions from a single point.
•
Stars have a life cycle from birth to death.
•
There are a number of models of the expanding universe.
•
The colour of a star, such as white and red, gives information about its age, size and distance from Earth.
•
Satellites and the Hubble Space Telescope gather information about the universe.
Unit
8.1
context
The expanding universe
The universe is expanding and has been expanding for millions of years. Scientists know this because research has shown that the stars and galaxies are moving away from us. The key
evidence they have is the Doppler effect. You have probably never seen the Doppler effect in action, but you are sure to have heard it.
The Doppler effect and sound The Doppler effect is heard whenever a car, truck or a train whiz past or when an aircraft flies overhead: the sound they make changes from a high pitch to a lower pitch as they pass you. The faster they go, the more the effect is heard. The change in pitch is most noticeable when a police car, fire truck or ambulance passes by with its siren on or when racing cars or motorbikes speed past you on a race track. The Doppler effect happens because sound transmits through the air as a series of repeated vibrations, otherwise known as a sound wave. Like all waves, sound waves have a wavelength. Wavelength is the distance between two points, identical except that they are on neighbouring repetitions of the wave. Consider an ambulance with its siren blaring. The sound waves from the siren spread evenly in all directions and so the wavelength will be exactly the same in every direction if the ambulance is not moving. You will hear the same frequency or pitch regardless of where you stand. If the ambulance is moving towards you, then it partly ‘catches up’ to the sound waves in front of it. This scrunches the sound waves closer waves stretched out, making wavelength longer and frequency (pitch) lower
Fig 8.1.2 Scientists know the universe is expanding because of the Doppler effect.
Science
Clip
Sonic boom An extreme version of the Doppler effect is heard when an aircraft travels at the speed of sound. In this case, the aircraft actually catches up with the sound waves, producing a thick band of compressed air that is heard as an explosively loud sonic boom.
waves are scrunched together, making wavelength shorter and frequency (pitch) higher
Fig 8.1.1 Sound waves with a shorter wavelength produce a higher frequency, higher pitched sound. Waves with a longer wavelength produce a lower frequency and lower pitched sound.
Fig 8.1.3 This aircraft is just breaking the sound barrier. The sound wave is so scrunched up that it compresses the moisture in the air into a cloud of ice crystals.
251
The expanding universe together, shortening the wavelength and increasing the frequency. You hear this as a high-pitched sound. As the ambulance travels away from you it ‘runs away’ from the waves behind it, stretching the wavelength and giving the siren a lower frequency or pitch. This change in wavelength and pitch is known as the Doppler effect and named after Christian Doppler (1803–1853), an Austrian physicist who described it in 1842.
The Doppler effect and light The Doppler effect also happens with light. Light also travels as a wave and a change in the colour of light can be observed if its source is moving fast towards you or away from you. If the light source is travelling towards you, then its wavelength gets scrunched up and its colour changes to become more blue. If it moves away from you, its wavelength stretches out and its colour changes to become more red. The Doppler effect is not normally noticeable: the red and blue lights on top of a police car don’t change their colour regardless of how fast the car is moving. The effect can only be observed for incredibly fastmoving light sources, such as stars and galaxies. These emit a rainbow of different light waves, each with a different colour. Physicists know this rainbow of colours (red, orange, yellow green, blue, indigo and violet) as the visible spectrum. One way of observing the visible spectrum is to pass light through a prism so that the different colours are separated as light bends or refracts. Go to
Science Focus 3 Unit 7.3
Go to
Science Focus 4 Unit 7.3
The universe is expanding Scientists use a device called a spectrometer to view the various colours (or spectrum) of a light source such as a star. Atoms in the atmosphere of stars absorb some of the light of a galaxy’s spectrum, producing dark lines within it. Stars that are moving away from us have a spectrum whose dark lines are shifted towards the red end of visible light where light has a longer wavelength. Stars that are moving towards us have a spectrum whose dark lines are shifted towards the blue, shorter wavelength end. Astronomers have studied where these dark lines occur within the spectrums emitted by stars and galaxies. They have deduced that most stars are moving very fast away from us, their dark lines being shifted towards the red end of the spectrum. This effect is called red shift, and the faster the star is travelling, the greater is its red shift. This is comparable to what you hear as an ambulance travels away from you. The faster it goes, the deeper its siren will sound: the siren has a ‘low pitch shift’. red shift
star moving away from Earth
Earth
normal
Earth
star not moving towards or away from Earth blue shift
Prac 1 p. 255
Earth
star moving towards Earth
Fig 8.1.5 A red shift indicates that a star is moving away from us. A blue shift indicates that it is moving towards us.
Science
Clip
Where did she put him?
Fig 8.1.4 A prism refracts light and separates it into the visible spectrum.
252
Edwin Hubble is best known these days for the space telescope named after him. He had two other achievements. In 1924 he proved the universe had many galaxies and not just the Milky Way (scientists now think that there are probably around 140 billion galaxies) and, in 1929, he proved that the universe was expanding. In 1953 he died of a heart attack. He was not given a funeral and his wife didn't tell anyone what she did with his body. To this day no one knows what happened to him!
Unit
past
8.1
Hubble’s law The American astronomer Edwin Hubble (1889–1953) studied the positions of the dark lines within the spectrum of light emitted by a star or galaxy. He worked out whether they are moving towards or away from us, and at what speed. In 1929, Hubble made an incredible discovery. He had been studying the dark lines emitted from different stars and galaxies and found that: • the distant stars and galaxies are moving away from Earth • the further away they are, the faster they are going. This is now known as Hubble’s law. present
Going back in time
Prac 2
p. 255 The universe must have started as something much smaller if it is still expanding. Astronomers believe that all the matter of the universe was originally so packed together that it all once fitted inside a point smaller than a proton! It then exploded out in what scientists call the Big Bang. Astronomers imagined all this expansion running in reverse, with the stars contracting until they are packed into the one spot. This spot was the beginning of the universe. This leads to some impossibly big questions. What was there before the Big Bang? Why did it blow up? What
8.1
Fig 8.1.6 The universe is expanding, just as all the raisins in a cake that is being baked move further apart as the cake ‘rises’, or dots on a party balloon become more and more separated as the balloon is inflated.
filled the rest of space? These questions have no meaning and therefore have no answers since it is thought that time and space did not exist before the Big Bang. Although there are other theories that explain the origin of the universe, most scientists believe that the Big Bang is the most likely.
QUESTIONS
Remembering 1 State whether a short or long wavelength would produce a sound of: a high pitch b low, deep pitch
Understanding 6 A car with its horn blaring approaches and passes you. Describe the change in pitch that you hear. 7 Explain why an ambulance siren sounds the same from all directions if it is not moving.
2 a Name the instrument used to view the colours of a light source.
8 Outline how scientists came to the conclusion that all matter in the universe was once packed closer together.
b State what causes light to be separated into its different colours.
9 a Name two scientists who contributed to the understanding of the origin of the universe.
3 State what produces the dark lines observed in a star’s spectrum.
b Outline their contributions.
4 Specify the shift that stars display if they are moving away from us.
10 When mosquitos fly about your head at night they display a change in shift in the sound they make. Explain what you hear in terms of the Doppler effect.
5 List the two main points of Hubble’s law.
Applying 11 Identify two examples in which you have heard the Doppler effect.
>> 253
The expanding universe 12 Identify what happens to the pitch of a sound if: a its wavelength gets longer or increases b its frequency increases c the source of the sound travels away from you
c where the pitch would be lower than normal d where the pitch would be close to normal a
13 Identify whether the voices of males or females generally have the: a higher frequency b lower frequency c longer wavelength d shorter wavelength
b
h
c
g f
d e
14 Identify whether the colour of light will shift towards the red or the blue end of the visible spectrum when: a the wavelength gets longer or increases Fig 8.1.8
b the frequency increases 15 Copy the diagram in Figure 8.1.7. Demonstrate how the sound waves behind the jet would appear by adding lines to show them.
sound waves
Analysing 17 Two identical aircraft are flying over you, one slow and one fast. Compare what you would hear. 18 Compare the density of the universe before the Big Bang with its density both just after the Big Bang and now.
Evaluating 19 A green light shines towards you. Deduce what colour you would see if it: a is not moving b moves incredibly fast away from you c moves incredibly fast towards you 20 Propose a way in which astronomers tell how fast a star is moving away from us.
Fig 8.1.7
16 The circles in Figure 8.1.8 represent sound waves generated by a moving object. Identify which label best represents: a the direction in which the object is moving b where you would hear a sound of a higher than normal pitch
8.1
21 Construct a question about the origin of the universe that is impossible to answer.
INVESTIGATING
Investigate your available resources (for example, textbooks, encyclopaedias, internet) to complete the following tasks. 1 Find out about Edwin Hubble and the telescope named after him, the Hubble Space Telescope. Gather information about: a Hubble’s involvement in space research b what the space telescope does c where it is d what Hubble’s constant is. In small groups, present your information to the class in a five-minute presentation. L
254
Creating
2 Research the sound barrier. a Specifically find out: • what problems were encountered in breaking it • the speed of sound (in km/h) • what the term ‘Mach’ means • who Chuck Yeager was and what he did. b Construct a diagram showing how the Doppler effect can cause a sonic boom. c List the commercial aircraft that once regularly travelled over Mach 1.
Unit
To explore the Doppler effect in action, a list of web destinations can be found on Science Focus 3 Second Edition Student Lounge.
8.1
8.1
e –xploring PRACTICAL ACTIVITIES
1 Using a spectroscope Aim
!
To observe the spectrum of white and coloured light
Equipment • a spectroscope
Safety Do not aim the spectroscope or look directly at the Sun. It can damage your eyes and cause permanent blindness.
Method 1 Use a spectroscope to study the spectrum of light from a light globe or from a window. 2 Sketch what you see. 3 Use your spectroscope to view coloured light from a light box containing a coloured slide or ‘filter’. Again, sketch what you see.
Questions 1 Describe the differences between the spectrum of white light and that of the coloured light. Fig 8.1.9
2 A balloon universe Aim To investigate the theory of an expanding universe
Equipment • a balloon and a pen for marking dots on the balloon
2 Construct a diagram to show how a prism can separate white light into colours.
Method 1 Mark several galaxies on an uninflated balloon. Circle one ‘galaxy’. This represents the Milky Way. 2 Blow the balloon up gradually, noting the movement of the ‘galaxies’.
Questions 1 How did the other galaxies move when comparing them to the Milky Way? 2 Predict how your answer to Question 1 would have changed if you had circled a different galaxy. 3 Evaluate how our position in the universe affects the observations we make.
Fig 8.1.10
4 Assess whether the balloon actually has a centre about which it is expanding.
255
Unit
8.2
context
The Big Bang
Years of research have given astronomers and physicists a huge amount of evidence about the universe.
This allows them to be reasonably confident of their version of the history of the universe back to a fraction of a second after the Big Bang, about 13.7 billion years ago. Before that, temperatures were so extreme that the laws of physics, as they are currently known, break down and do not apply.
The first few minutes Initially, the universe expanded Science relatively slowly. Then, within a fraction of a second, it inflated suddenly to become 100 million Birth of a universe billion billion times bigger. Scientists have a Particles of matter bumped into good picture of what particles of antimatter, happened in the Big Bang through annihilating each other and mathematical releasing a burst of light (called calculations and a photon) as they did so. experiments in When all the matterparticle accelerators. antimatter annihilations were Although not the very start, scientists finished, a relatively small believe they know amount of excess matter was left. what happened 10–43 This matter became the building seconds or one ten blocks of the universe as it is million trillion trillion known today. trillionths of a second Although only one second after it happened! old, the universe had already cooled to ‘only’ ten billion Science degrees Celsius. After three minutes, the temperature had dropped even further Watching the Big Bang to one billion degrees. At To watch the Big Bang you this temperature, particles would have needed to be called quarks clumped somewhere outside it. But there together in groups to form was nothing outside the singularity: in fact there was protons and neutrons. A less than nothing! And of proton is the centre or course you could not have nucleus of the simplest existed either, since before the atom, hydrogen, 11H. Place Big Bang there was no matter neutrons with it and you from which to build you! And time didn’t exist either! have other forms of hydrogen called isotopes.
Clip
Fig 8.2.1 The universe started as a single point and then exploded in all directions.
The Big Bang theory The universe did not exist before the Big Bang. Instead it was a single point called a singularity. Although far smaller than a proton, this singularity exploded in all directions from this single point which contained an enormous and incredibly concentrated amount of energy. At that very instant, the universe was unbelievably dense and hot (about a trillion trillion degrees Celsius). The universe continues to expand today. Under such extreme conditions, energy may be converted into mass and mass can be converted into energy. A lot of this energy stayed as energy but some of it converted into particles of matter and antimatter.
256
Clip
time = 1 billion trillionth of a second the first matter—electrons and quarks time = 300 000 years hydrogen and helium atoms form time = 1 billion years the first stars and galaxies time = 14 billion years today’s universe
The early universe was a foggy, opaque place containing energy in the form of radiation such as X-rays and light. About 300 000 years after the Big Bang, the universe had expanded so much that its temperature had dropped to around 3000°C. This resulted in electrons slowing down enough to be captured by hydrogen and helium nuclei to form new types of atoms and elements. The fog cleared as more and more particles combined to form new elements. As the universe expanded further, radiation took the form of heat, radio waves and microwaves.
8.2
Big Bang
The fog clears
Unit
Atoms of the isotope deuterium 12H (made from a one proton and one neutron) then combined to form atoms of helium 42He, made from two protons and two neutrons. The formation of chemical elements had begun!
Messages from the birth of time solar system
Science
Fig 8.2.2 From the Big Bang to our present solar system
Clip
LHC The Large Hadron Collider is a massive particle accelerator built underneath the border of Switzerland and France. When working, this accelerator will speed up particles and send them in different directions. Since the track is circular, the particles will smash into each other at speeds close to the speed of light! In this way, scientists hope to reproduce the conditions of the first second or so of the Big Bang. The first test run was held in 2008 but failed because of a problem with one of the magnetic fields that control the particles.
In 1965 physicists Arno Penzias and Robert Wilson set out to detect radio waves coming from the halo of our Milky Way galaxy. In the radio wave signals, there was a constant static or hiss. Regardless of the time of day, the time of year or the direction they were receiving their signals from, the hiss always remained the same. At first they suspected interference from cities on Earth, faulty instruments and even from ‘white dielectric material’ (known to most as pigeon-poo) on their antenna. What they were detecting were microwaves formed from the first photons of light from the very edge of the universe. The signal was from the most ancient light of all, coming from the very start of time.
Science
Clip
Annihilation!
Fig 8.2.3 It is hoped that the Large Hadron Collider will replicate the conditions of the Big Bang.
Electrons are particles of matter which are annihilated by their antimatter equivalents, positrons. There must have been more electrons than positrons at the beginning of the universe since there are so many still in existence.
257
The Big Bang
Galaxies, stars and planets
Fig 8.2.4 The satellite known as Cosmic Background Explorer (COBE) has been described as the ultimate thermometer and in 1992 produced a ‘heat’ photograph of the universe. Hotter regions show as red. Cooler appear as blue. This image shows that the universe was not the same throughout, but that matter had begun to clump together to form the seeds from which galaxies would be born.
The first galaxies formed about a billion years after the Big Bang. The gravitational forces between the swirling gas clouds would not have been strong enough to do this. Instead it’s thought that an invisible material called ‘dark matter’ (subatomic particles left over from the Big Bang) drew the clouds together until they compacted enough to form galaxies. Smaller clouds of gas collapsed even more to form the first stars. Rings of gas and dust orbiting these stars then condensed to form young planets or planetesimals. These, in turn, attracted more matter and increased in size until they finally became planets. Worksheet 8.1 Origin of the universe
Fig 8.2.5 This side-on view of a galaxy was taken by the Hubble Space Telescope.
258
Fig 8.2.6 Arno Penzias (left) and Robert Wilson (right) detected
Fig 8.2.7 A Hubble Space Telescope image of the nebula NGC 604.
background radiation left over from the very beginning of the universe.
A nebula is a swirling cloud of dust and gas. Gravity will eventually pull it together to give birth to small star clusters or young planets.
Unit
8.2
and suck in more and more matter until a final ‘Big Crunch’ will pack everything into a single black hole or another singularity. Perhaps then there will be another Big Bang and the cycle will continue. Flat universe The flat universe model states that the universe will eventually stop expanding, but never reverse.
Fig 8.2.8 At the centre of this spiral galaxy are older yellow and red stars. The outer spiral arms are more blue due to the ongoing formation of young blue stars. The arms are also very rich in interstellar dust, seen as dark areas, which may form planets around individual stars.
The future There is a lot of uncertainty about the Big Bang, how the universe started, what it is doing now and what it will do in the future. The best astronomers and physicists can do is to present a number of theories on the universe such as the following, based on evidence and mathematical models.
Accelerating universe The three models described above all expect that gravitational attraction should slow or stop the expansion of the universe and perhaps even collapse it. Recent research indicates, however, that the expansion of the universe may be accelerating due to a mysterious cosmological force that some call ‘dark energy’ which somehow overrides gravitational attraction. The existence of dark energy would complicate each of the above theories. Scientists have a long way to go before understanding the current state of the universe. Their ability to predict how it may be in the future is also nowhere near complete!
Open universe If the mass of the universe is too low, then gravity will be too weak to stop it expanding. It will continue to expand, but at a decreasing rate. Eventually the stars and galaxies will cease to shine, and it will be a dark and very cold place. Closed universe The expansion of the universe will eventually stop if it has a high enough mass and strong enough gravity. Gravitational attraction will then pull all its matter closer together, contracting the whole universe into a smaller and smaller space. Eventually everything will become superheated and atoms will disintegrate in a reversal of the Big Bang. Black holes will join together
Fig 8.2.9 An artist’s impression of the ‘Big Crunch’. The ‘Big Crunch’ is one possibility for the universe if gravity pulls it all back together again.
259
The Big Bang
8.2
QUESTIONS
Remembering
15 Identify the time when the young universe suddenly inflated.
2 State the proportion of hydrogen to helium in the universe. 3 State what the acronym COBE stands for.
16 Identify the particles that grouped to form protons and neutrons.
4 State when the first atoms began to form.
Analysing
5 List some different types of radiation.
17 Contrast the different theories of the future of the universe.
Understanding
Evaluating
6 Matter and antimatter didn’t totally destroy each other after the Big Bang. Explain why it is lucky that this didn’t occur.
18 Evaluate which theory you think is most likely to represent our future.
7 Explain why hydrogen is the most common element.
19 Another theory of the universe, called the ‘steady state’ theory, says that the universe has basically always been how it is now, with old galaxies dying and new ones being born. Assess whether you think this is more or less likely than the Big Bang theory. Justify your answer.
8 Describe what is in a hydrogen nucleus. 9 Explain why the early universe was opaque. 10 Describe the effect on the ‘fog’ of the continuing expansion of the universe. 11 Penzias and Wilson detected evidence for the Big Bang. Clarify the evidence they collected. 12 Explain how galaxies and stars are formed. 13 Explain how ‘baby planets’ become bigger. 14 If matter in the early universe was spread completely evenly, instead of in uneven clumps, predict what would not have formed.
8.2
Creating 20 Construct a timeline showing the main events of the Big Bang, including its temperature at the various key stages. Your timeline does not necessarily need to be to scale. You will find the temperatures throughout Unit 8.2. N
INVESTIGATING
Investigate your available resources (for example, textbooks, encyclopaedias, internet) to complete the following tasks. 1 Find the contribution made by scientists to the Big Bang theory. People to investigate could include Walter Adams, Ralph Alpher and Robert Dicke. Produce an information card to display your findings. L 2 Research the different possible ‘shapes of space’—closed, flat and open. Present your findings in a short written report. L 3 Research other theories of the origin of the universe. Alternatively, suggest your own. Have a class debate to discuss the arguments for and against the Big Bang theory. Different student roles may include: speakers for each team, timekeeper, chairperson and adjudicators.
260
Applying
1 State how old the universe is thought to be.
e –xploring To explore the history and timeline of the universe, a list of web destinations can be found on Science Focus 3 Second Edition Student Lounge.
Unit
8.3
context
The life of a star
Our Sun is a star. Like all stars, it is a body of gases that radiates energy. The stars you see in the night sky have not always been there. Stars are born and stars die all the time. Although it seems strange, many of the stars you see aren’t there any more. They have already died, perhaps millions of years ago!
This strange fact arises because of the huge distances involved and the time it takes for their light to get to us. Planets such as Earth are not stars since they do not radiate light energy. Planets can still be seen, however, because they reflect light from the nearest star to them.
Birth of a star Stars are not born individually, but form in groups called clusters. All stars begin in the same way, as material in a nebula. A nebula is a dense cloud of gas and dust. Inside it, denser regions collapse under the pull of their own gravity. The nebula’s gas and dust then come closer together, forming a protostar. The centre gets denser and hotter as more material is packed into the protostar. Eventually, conditions are suitable for nuclear reactions to begin. In these nuclear fusion reactions, atoms of hydrogen are fused together to form helium. Nuclear fusion reactions release vast amounts of heat and light energy and so the new star shines steadily. At this stage, a main sequence star is formed. Our own Sun is a main sequence star.
Science
Fig 8.3.1 The Sun is a star about halfway through its life.
Clip
Science
Atomic bombs
Clip
Stars use a nuclear reaction to fuse hydrogen nuclei together to form a helium nucleus. The process is known as nuclear fusion. Another type of nuclear reaction is a fission reaction. These are more common on Earth and are the reactions that run nuclear power stations. Nuclear fission reactions use a fuel of heavy elements such as uranium and plutonium and do not produce as much energy as a fusion reaction. In 1945, the Japanese cities of Hiroshima and Nagasaki were destroyed by atomic bombs that used nuclear fission. No hydrogen bomb has ever been used in war, although the armies of the USA, Russia, Great Britain, France, India, Pakistan and Israel have them.
Starry, starry night
Fig 8.3.2 A star can be thought of as billions of hydrogen bombs
About 5780 stars can be seen in a night sky without having to use a telescope. There are millions more stars than this number. The brightest star after our Sun that we can see from Earth is Sirius, also known as the Dog Star. It shines with a blue-white colour and is 6.8 light years away from Earth.
exploding every second.
261
The life of a star
Death of a star Stars have a limited amount of their hydrogen fuel and it eventually runs out. Amazing transformations then take place, depending on how big the star is.
Fig 8.3.3 New stars are produced in nebulae. This photo shows nebula NGC 1999 in the constellation of Orion.
Stars like our Sun Stars about the size of our Sun will last for around 10 billion years before they run out of fuel. The stages in their death are as follows. • The star begins to use helium as a fuel, producing carbon. • It swells up to burn any hydrogen in its atmosphere. In doing so, the star expands up to 100 times its original diameter to become a red giant. • Outer layers of the star and the carbon within them are blown away to form clouds in space which may form new stars and planets. • Without the pressure produced by nuclear reactions, the remaining centre collapses under its own gravity to form a small, very dense core called a white dwarf. A teaspoon of matter from a white dwarf could be anywhere between 5 and 10 tonnes (5000 and 10 000 kilograms). For comparison, a teaspoon of matter from our Sun would have a mass of 2.1 grams. Our Sun is about halfway through it life. In around four billion years, the Sun will swell and engulf the inner planets. Earth will be roasted to a cinder!
Fig 8.3.5 This is an optical image of stars in interstellar gas and Fig 8.3.4 A protostar about 250 000 years after it began to form
262
dust. The star Antares (centre) is a red super giant. It is several hundred times the diameter of the Sun and several thousand times the Sun’s brightness.
rotating neutron star
8.3
BEFORE
Unit
Stars much bigger than the Sun A star uses up its fuel supply much more rapidly if it has a mass 10 times that of our Sun. The star lasts only 30 million years or so and then: • it becomes a blue super giant • it expands further to form a red super giant • its inner core collapses in less than a second. This results in a massive explosion called a supernova. Matter is blasted into space and the supernova shines for about a month with the intensity of billions of stars. It is in supernovae that elements such as gold, silver and iron are formed. The remains of the star form what is called a neutron star, which has a mass three times that of the Sun but with a diameter of only 20 kilometres. The density of a neutron star is so high that a teaspoon of its matter would have a mass of around 1 billion tonnes!
beam of radio waves
Fig 8.3.7 The beam from a pulsar may be detected as it sweeps past the Earth.
AFTER
Fig 8.3.6 A star before and after exploding to become a supernova
Pulsars A pulsar is a rapidly rotating neutron star with a strong magnetic field. A pulsar emits radio waves that sweep across space as it rotates, a little like a moving searchlight. Radio telescopes detect each burst of radio waves as a pulse. Among many other tasks, the radio telescope at Parkes in central-west New South Wales explores the universe for pulsars.
Fig 8.3.8 The radio telescope at Parkes, NSW
Science
Clip
Exploding crab! The Crab Nebula is the remains of a supernova which exploded in 1054 CE. The explosion was so bright that it was seen clearly in the daylight by Chinese astronomers!
263
The life of a star
Black holes If a star is massive enough, it collapses even more than a neutron star to form a black hole—an object so dense that anything close by will be drawn into it by its overpowering gravity. The gravity of a black hole is so
strong that even light cannot escape! Black holes distort the space around them, and will often suck nearby matter into them, including other stars. As matter swirls into the black hole it becomes incredibly hot and emits tell-tale X-rays. Black holes cannot be seen directly and so astronomers detect them by observing X-ray emissions and the behaviour of nearby stars. If, for example, a star ‘wobbles’, then it may be because of a black hole nearby. Evidence suggests that a massive black hole with a mass of about 2.6 million times that of the Sun lies at the centre of our own Milky Way galaxy. Worksheet 8.2 Stars
gas from companion star
swirling gas heated to 100 million °C due to frictional effects
Science X-rays
Clip
The first black hole
Fig 8.3.9 A black hole near a companion star
8.3
The first black hole to be detected in 1971 in the Cygnus constellation was named Cygnus X-1. After its X-rays were detected, scientists noticed that a nearby star, a super giant, was orbiting the X-ray source. They calculated that the X-ray source must be around 10 times heavier than our Sun, so it could not be a normal star or a neutron star. By a process of elimination, the X-ray source must be a black hole.
QUESTIONS
Remembering
Understanding
1 Describe how a star forms.
5 Define the term ‘nebula’.
2 Name the main fuel in stars.
6 Define the term ‘pulsar’.
3 Recall the life of a star by arranging these stages of our Sun’s life in order from its earliest stage: red giant, burns hydrogen, white dwarf, burns helium
7 Explain what a black hole is and how it is formed.
4 Recall the death of a star by arranging these stages in order from the earliest stage, for a star with a mass of 10 times that of our Sun: supernova, red super giant, neutron star, blue super giant.
9 Predict what would happen if a black hole was at the centre of our own galaxy, the Milky Way.
8 Predict whether or not you could lift a sugar-sized grain of matter from a neutron star.
Applying 10 Identify the missing labels from Figure 8.3.10 which describes the death of a large star, at least 10 times the size of our Sun.
264
Unit
8.3
hydrogen runs out
'adult' star of 10 solar masses or more
Fig 8.3.10
Analysing 11 Compare what would happen to our Sun during its lifetime with the life of a star 10 times more massive.
Evaluating 12 Propose ways in which carbon and other elements in our bodies originally came from the stars.
8.3
13 Nobody has ever seen a black hole. Propose some reasons why this is so and explain how we know they exist.
Creating 14 Construct a flow chart showing the stages a star like our Sun goes through when it dies.
INVESTIGATING
Investigate your available resources (for example, textbooks, encyclopaedias, internet) to complete these tasks. 1 Find how Jocelyn Bell Burnell discovered pulsars in 1967. Write a short account of this event. L 2 Research one of the following features of the universe:
a Define what the feature is. b Describe the feature and obtain a diagram or photo of it. c Compile your work and that of other students into a booklet. Give the booklet a title such as ‘My Pocket Guide to the Universe’. L
• neutron star • pulsars • quasar • supernova • asteroids
e –xploring To explore amazing images of the universe, a list of web destinations can be found on Science Focus 3 Second Edition Student Lounge.
• meteors • black hole • comets • nova • the Milky Way galaxy.
265
Unit
8.4
context Science
Fact File
Are we alone?
Earth orbits the Sun at just the right distance to make it habitable by a variety of animals, plants and us. With so many stars and galaxies in the universe
ET ET means extraterrestrial and refers to a life from beyond Earth. Life on Earth is terrestrial.
it is highly likely that there are other planets out there that would be capable of sustaining life too. It has been estimated that there are about 50 billion stars similar to our Sun just in our immediate Milky Way neighbourhood! Other more distant galaxies would contain similar numbers, so the possibility of life out there is very high!
Long-distance space travel The closest star to Earth is the Sun and our is the only planet revolving around it that has life. Our next closest star is Proxima Centauri, part of triple-star cluster Alpha Centauri, 4.3 light years away. A spacecraft travelling at the speed of light would take just under four and a half years to get there. Unfortunately, the laws of physics do not allow things to travel at the speed of light, nor even close to it. Any mission would travel far slower and it would take about 80 000 years to get there at realistic spacecraft speeds. Even then we might not find a planet appropriate for life … we might have to go even further! Clearly this is not viable. An alternative is to send out messages at the fastest possible speed available to us—the speed of light.
Trying to make contact Fig 8.4.1 It is highly unlikely that aliens have visited Earth.
Lasers and radio waves are both examples of electromagnetic radiation. All electromagnetic radiation travels at the speed of light, considerably faster than any current spacecraft and so it offers a way to detect life elsewhere in the universe. It does this by either sending or receiving messages.
Science
Clip
War of the Worlds
Fig 8.4.2 A journalist’s impression of life on the Moon as it was supposed to have been observed by John Herschel through his telescope.
266
It was Halloween, October 1938. In the USA, radio listeners tuned in to hear that the ‘Strange beings who landed in New Jersey tonight are the vanguard of an invading army from Mars’. The Martians were ‘as high as skyscrapers’ and were gassing crowds on the streets! Thousands across the USA panicked, imagining the announcements to be real, despite four warnings that it really was just actor Orson Welles dramatising H. G. Wells’ novel War of the Worlds!
Science
Clip
False alarm In 1967, Cambridge University PhD student Jocelyn Bell thought she had discovered extraterrestrial life when she detected a strong and regular signal at a frequency likely to be used by intelligent beings. Instead of publicising her find, she investigated every possible other cause. What she had actually discovered was a star called a pulsar.
8.4
Fig 8.4.3 Pioneer 10 was launched in 1972. It passed by Jupiter in 1973 and is now out of the solar system. On board was this plaque that carried a picture message from humans to extraterrestrial life, in the event that the spacecraft was intercepted. A hydrogen molecule appears at the top, and the radiating lines show the bearings of the nearest pulsars. Figures of male and female humans are also shown. Pioneer 11 carried a similar plaque.
Unit
Proving we exist Earth is continuously emitting electromagnetic radiation in the form of TV and radio signals. To increase our chances of making contact, scientists also deliberately broadcast electromagnetic radiation in the microwave range of frequencies where background interference is less. Intelligent ETs should be able to tune into these signals and prove that we exist. More primitive ETs would not. Also, the signals may not yet have reached where ETs live, since radio and TV have only been transmitting for about 80 and 50 years, respectively. Proving they exist Scientists also scan the universe for microwave signals (and other signals) that any intelligent ETs might have sent. Any signal would need to have been sent a long time ago, however, as we have only started looking for signals recently and it takes a very long time for them to get to Earth. Who knows? Perhaps we have received a message, but are not advanced enough to recognise it. numbers 1 to 10 in binary
atomic numbers of important elements proportion of elements in our DNA
DNA double helix world population human solar system (Earth moved up slightly) outline of radio dish
Fig 8.4.5 This message was beamed from the Arecibo radio telescope towards globular cluster M13 in 1974. A series of 1679 on/off pulses was used, since you get 1679 when you multiply the two prime numbers, 23 and 73. This would give an extraterrestrial receiving the message a hint to arrange it into rows of 23 pictures, with 73 rows in total.
Fig 8.4.4 An x-ray image of the Crab nebular pulsar.
267
Are we all alone? Science
Clip
Rascally critters There have been numerous SETI projects, the first in 1960. In 1992, NASA established a SETI project only to close it down because US politicians thought it ridiculous and too expensive. As one US Congressman said: ‘We don’t need to spend millions to find these rascally creatures. Conclusive evidence of these crafty critters can be found in tabloid newspapers’. Steven Spielberg, director of ET and Close Encounters of the Third Kind, financially backed much SETI work.
SETI SETI stands for Search for Extra Terrestrial Intelligence. The SETI Institute is situated in Silicon Valley, California, USA. One of SETI’s projects in the southern hemisphere, Project Phoenix, involves the Parkes radio telescope in New South Wales.
SETI computers monitor over a thousand stars and millions of radio channels at the same time, as no one knows what frequency an ET would use. Scientists broadcast in the microwave range of frequencies, since there is less background interference in that channel. This will increase our chances of making contact. As mentioned, we have started looking for signals only recently, so the main hope may be to receive a message from an intelligent race that has been sending for a long time.
Science
Clip
UFOs and spaceships UFO is an acronym for unidentified flying object. It applies to anything in the sky that cannot be identified, whether is a strange light, a strange weather phenomenon or a stray weather balloon that doesn’t show up on radar. Although a UFO could be an alien spaceship, it is more likely to be something else!
Fig 8.4.6 The biggest radio telescope in the world—the Arecibo radio telescope in Puerto Rico, Central America
For and against There are those who think that attempting to make contact with extraterrestrials is fraught with danger. Their concerns are perhaps best summed up by the famous astrophysicist Stephen Hawking, who is quoted as saying, ‘On balance, I would rather not encounter a superior civilisation. They might wipe us out’. Dan Werthimer of project Serendip (another SETI search) puts forward the counter-argument that the notso-peaceful advanced civilisations are likely to have blown themselves up before contacting us. Worksheet 8.3 Are we alone?
Fig 8.4.7 Many people believe that other beings do exist and have visited Earth.
268
Unit
QUESTIONS
Remembering 1 List the reasons why we are unlikely ever to send a manned mission to find life elsewhere in the universe. 2 Name two ways in which we can search for extraterrestrials. 3 State what SETI is and who funds this organisation. 4 List two radio telescopes used by the SETI team.
Understanding 5 Define:
12 If only one in every 50 of the stars in the Milky Way contained an Earth-like planet, calculate how many such planets our galaxy would contain. Assume there are two billion stars in the Milky Way. N
Analysing 13 A group called SOOT (Switch Off Our Transmitters) has been proposed by a biologist who thinks we may be at risk from advanced civilisations. Analyse why switching off our transmitters would not guarantee our safety.
a a light year
Evaluating
b terrestrial
14 Propose at least two reasons why the plaque attached to the Pioneer 10 and Pioneer 11 space probes may have offended some people.
c extraterrestrial d the acronym SETI 6 Discuss the meaning of the heading for this unit, ‘Are we alone?’ 7 Explain why microwaves are preferred to radio waves when sending messages into space. 8 Describe each of the features on the Pioneer plaques and explain what each features indicates. 9 Discuss why politicians are unsupportive of SETI programs. 10 Even if SETI detects signals from an advanced civilisation, explain why this civilisation may not exist.
Applying 11 Calculate how many kilometres are equivalent to one light year.
8.4
8.4
8.4
15 Do you think extraterrestrial life exists? Justify your opinion.
Creating 16 Construct an argument for or against the statement: Aliens do exist and we should try to make contact with them. L 17 Construct a diagram for a space probe plaque clearly showing who you are and where you live on Earth. 18 You are in charge of the IETRT (International Extra Terrestrial Response Team), and must come up with a protocol for dealing with Earth’s response to the first contact with extraterrestrial intelligence. What steps should Earth follow? How should the public be handled? Who should be involved in a meeting or reply? Construct a report or essay dealing with a hypothetical situation.
INVESTIGATING
Investigate your available resources (for example, textbooks, encyclopaedias, internet) to complete the following tasks. 1 Find out about the SETI project. Find out details of its operation, what has been discovered so far and who the ‘father’ of SETI was. Present your findings to the class in a style of your choice. 2 Research Jill Tarter’s contributions to the SETI program. Tarter was rumoured to be the basis for the lead astronomer in the 1997 movie Contact starring Jodie Foster. This astronomer discovers signals from extraterrestrial intelligence and later makes contact. L
3 Examine the technical details of the Arecibo or Parkes radio telescopes and find out how it operates and what it is used for.
e –xploring To find out more about the SETI project, a list of web destinations can be found on Science Focus 3 Second Edition Student Lounge.
269
Unit
8.5
context
Using space
Entering space became a reality when the world’s first satellite, Sputnik 1, was launched by the USSR in 1957. Since then, the development of technology has enabled scientists to build more advanced telescopes that have been used to explore deeper into space. Satellites explore and collect information about Earth and its atmosphere. Experiments
can be performed in the gravity-free environment of the International Space Station (ISS). These experiments would be impossible on the surface of Earth. The International Space Station has been in orbit for more than 10 years. Space travel is currently incredibly expensive, but commercial ventures are underway that will make it cheaper for people to travel in space. As more and more countries advance their space programs, how they use space is going to become more politically, socially and economically important.
Artificial satellites
Science
Clip
Globalising communication In 1962, the USA launched the world’s first communication satellite called Telstar 1. This satellite changed communication in the world forever. Telstar 1 allowed live television pictures to be relayed across continents and could handle 600 telephone calls at a time. Today, one satellite can handle thousands of telephone circuits and television transmissions at the same time.
270
Fig 8.5.1 Is this the future of tourism?
A satellite is an object in space that travels around a larger object. The planets of our solar system are natural satellites that orbit around the Sun. Artificial satellites are sent into space on board spacecraft or rockets. Once they are in the right position they are detached from the spacecraft and most continue to orbit Earth without any assistance. Most satellites use solar energy to carry out their functions. Geostationary satellites are placed at a fixed position over the Equator, about 36 000 km above the surface of Earth. They travel at the same speed that Earth rotates on its axis and so appear to be stationary. Being fixed over one place makes geostationary satellites useful for relaying telephone, TV and the internet. Some Australian homes, for example, have satellite television. To receive a signal, each home has a small dish pointing at a geostationary satellite. Go to
Science Focus 4 Unit 7.4
Satellite remote sensing Satellite remote sensing is the use of satellites orbiting in space around Earth to observe and gather information about the Earth. To collect information, sensors use electromagnetic radiation such as visible light, and invisible ultraviolet (UV) and infra-red (IR) radiation, X-rays and radio waves. Fig 8.5.2 A geostationary satellite always stays above the same point on Earth. This makes them useful as communication satellites.
Airborne remote sensing
8.5
Satellites carry two types of sensor systems—passive and active. • Passive sensors detect and record the amount of electromagnetic radiation reflected or emitted from natural sources such as sunlight.
Unit
Fig 8.5.3 This NASA satellite is known as the multi-angle imaging spectroradiometer (MISR). It collects data about the Earth’s climate and atmosphere by measuring reflected sunlight.
• Active sensors make their own electromagnetic radiation, such as radar. They then measure the intensity of the return signal. All signals are coded as binary numbers and transmitted to ground stations as an electromagnetic signal. Remote sensing of different electromagnetic waves coming from space has provided scientists with huge amounts of information about the Earth such as: • weather patterns • temperature of the Earth and oceans • shape of the land surface • details of the sea floor as they penetrate the oceans and ice • natural phenomena such as bushfires and volcanoes • vegetation in agriculture and forestry • the ozone hole • the tracking of animals • the monitoring of pollution, algal blooms and oil spills in lakes and oceans • navigation. This information has many uses such as weather forecasting and scientific research. Satellite technology is also used by the military to monitor activities of people, organisations and countries.
Satellite remote sensing
The land: remote sensing provides data on: s FORESTS CROPS CITIES AND ROADS s SURFACE TEMPERATURE s SOIL MOISTURE s EROSION s DESERTIFICATION s THE AMOUNT OF WATER STORED AS SNOW AND ICE
The atmosphere: remote sensing provides data on: s TEMPERATURES s UPPER LEVEL WINDS s #/2 OZONE #&# CONTENT s THE SIZE OF THE OZONE HOLE s CLOUD DISTRIBUTION s THE AMOUNT OF WATER STORED AS CLOUDS
The poles: remote sensing provides data on: s ICE SHEET COVERAGE s SEA ICE DISTRIBUTION s THE AMOUNT OF ICE MELTING
Ocean buoy remote sensing
The ocean: remote sensing provides data on: s CURRENTS s TEMPERATURE AND HEAT FLOWS s EXPANSION AND RISE IN WATER LEVELS s SALINITY s COLOUR s #/2 absorption s PHYTOPLANKTON
Fig 8.5.4 Airborne, ocean bouy and satellite remote sensing allow us to study many features of the Earth.
271
Using space
Fig 8.5.5 This remotely sensed computer-generated image of the Earth is based on satellite data. It shows water (blue), bare land (brown) and vegetation (green). The ocean floor is shown by different shades of blue.
Fig 8.5.6 The ISS, photographed in 2006. The ISS is already the size of an football field and is one of the brightest objects in the sky that can be seen with the naked eye.
International Space Station: A global effort The International Space Station (ISS) is an amazing engineering and political achievement given its complexity and the number of countries involved in its construction and operation. The ISS began to be assembled in 1998 in orbit, 407 kilometres above the Earth’s surface. Over 40 missions involving the US space shuttle and Russian Soyuz and Proton rockets will be required during construction of the ISS, as well as around 1000 hours of spacewalks or EVA (extra-vehicular activity). The first spacewalk by an Australian was made by Andy Thomas in March 2001, when he assisted with some wiring and construction jobs after arriving at the ISS in the space shuttle Discovery. The construction of the ISS has been slower than expected. By July 2008, it was only 85 per cent complete. Despite setbacks, the ISS has been continually occupied since the year 2000. While on board, the long-term crews are involved in setting up and maintaining the equipment, and conducting scientific experiments. Weightlessness on the ISS Astronauts experience microgravity while on board the ISS. Microgravity is the illusion or feeling of weightlessness similar to what you feel on a roller
272
coaster when you lift out of the chair and then fall back. There is gravity at the height of the ISS. It’s just that the astronauts and the space station are accelerating towards Earth at the same speed. Microgravity allows the astronauts to seemingly float around inside the space station. In order to stop their muscles and bones deteriorating, the astronauts exercise on special equipment to keep their skeleton and muscles healthy.
Fig 8.5.7 Extended stays in space cause muscle strength and bone mass to reduce. Exercise is therefore vital for the astronauts on board the ISS. Here an astronaut is roped onto a treadmill.
Unit
Science
8.5
Fact File
The ISS Countries involved
Dimensions
United States, Russia, Japan, Canada, Brazil, and 11 countries of the European Space Agency (Belgium, Denmark, France, Germany, Italy, the Netherlands, Norway, Spain, Sweden, Switzerland, the United Kingdom)
Science
Clip
Time on the ISS
Length 110 metres, width 80 metres, mass 460 tonnes, volume 1200 cubic metres (pressurised)
Fig 8.5.8 In this experiment, 750 material
Orbit
Altitude 407 kilometres (average) at an angle of 51.6° to the equator
samples are being placed outside the ISS for 18 months to collect information about how the materials weather the space environment.
Orbital speed
3000 kilometres per hour
Power source
4000 square metres of solar panels generating 20 kilowatts
Oxygen source
Russian Elektron generator makes oxygen by splitting water into oxygen and hydrogen, supplemented by solid fuel oxygen generation (SFOG) cartridges as required. External oxygen tanks will be fitted in latter stages of construction
Heating
More than enough is provided by on board electronic equipment. Excess heat is vented to outer space
Escape vehicle
Soyuz capsule capable of transporting three people
Research and the ISS One purpose of the ISS is to study the effects of long-term microgravity on humans. This research is vital if humans are to ever to carry out long-distance travel in space. The ISS is also being used for research in fields such as life science, medicine, physics, material science, earth science, astronomy and engineering. Gravity affects the way crystals form on Earth, leading to small imperfections, but in microgravity almost perfect crystals can be made. Applications of such crystals may lead to faster computers or more effective medicines. Tissue cultures of human cells grow more quickly in space, and
studies in microgravity may lead to breakthroughs in this field. Microgravity also allows scientists to study combustion more easily, as gravity no longer forms convection currents that disturb a flame.
The ISS uses GMT (General Mean Time) to regulate its day. Since it experiences 16 sunsets and sunrises a day, the windows are covered during its ‘night time’ so that the crew can get some sleep. They wake up at 7 a.m., work for 10 hours on weekdays and five hours on Saturdays. Sundays are dedicated to rest and relaxation.
Criticism of the ISS The cost of the ISS has been estimated at over $A200 billion. Critics of the ISS say that for the contribution it has made to science, the time and money could have been better spent on other space missions that need less maintenance. This debate will continue and the future of the ISS will depend on government policy.
Space tourism Space tourism is when people who are not trained as astronauts pay to fly into space. The idea of space tourism that is open and affordable to the wider public is popular although not yet a reality. When travel into orbit becomes a commercial service, people will be able to buy a ticket and book in at an orbiting hotel. Once they get there they will be able to enjoy the view and participate in microgravity space-sport activities. Currently, NASA and most other international space agencies are not trying to promote space tourism. Tourism to the ISS Space tourism has been pioneered by the Russian Space Agency which provides limited and expensive flights to the ISS. Only six people have ever been ‘tourists’ in
273
Using space Science
Clip
Fly me to the Moon
Fig 8.5.9 Anousheh Ansari, the first
All six tourist trips to the ISS have been booked through the US company Space Adventures. Each paid around $A27 million for the privilege. The cost is now around $A38 million! All seats are fully booked until after 2009. Space Adventures is also offering flights that will orbit the Moon. The 21-day journey is likely to cost $A133 million and will not be possible until well after 2010.
space, spending about a week each aboard the International Space Station. Sixty-year-old American billionaire Dennis Tito was the first tourist in space. Tito blasted off in April 2001, accompanying a regular resupply mission. The first female space tourist was Iranian-born US citizen Anousheh Ansari. She visited the ISS in September 2006. Sub-orbital flights About eight private companies are actively exploring the possibility of cheaper, specialised tourist flights into space. Virgin Galactic is the most advanced and plans to provide regular suborbital space flights to the non-astronaut public by 2010. Their spacecraft, SpaceShipTwo, would take people to an altitude just over of 100 kilometres and allow them to experience the feeling of weightlessness for up to six minutes. By November 2007, two hundred seats on SpaceShipTwo had been sold at a starting price of US$200 000. Worksheet 8.4 Space travel
female tourist in space
Fig 8.5.10 How SpaceShipTwo is to take tourists for a quick, expensive ride into suborbital space.
Virgin Galactic’s maximum
109.7 km planned suborbital tour 99.97 km
Ansari Xprize suborbital height
99.97 km Ansari Xprize suborbital height
109.7 km Virgin Galactic’s maximum planned suborbital tour
54.86 km Space entry 54.86 km Space entry Highest manned
30.5 km balloon flight 15.2 km Concorde 0
Commercial airliners
Virgin Galactic tracker
54.86 km re-entry
Ascent to space Up to 15.2 km Release from Mothership and launch to Mach 3.
30.5 km Defeathers into glider mode Back home to collect your astronaut wings
274
Unit
QUESTIONS
Remembering
Applying
1 State what the following acronyms mean: a MISR b ISS
10 Identify how international telephone signals needed to travel before communication satellites became widely available. 11 Identify where you have felt a feeling of weightlessness.
c EVA
Analysing
d GMT
12 Compare a passive sensor with an active sensor. 13 Discuss the advantages and disadvantages of building space stations such as the ISS.
2 List two examples of: a natural satellites b artificial satellites 3 List five things that remote sensing satellites detect on Earth. 4 Name the first male space tourist and how much it cost him to be aboard.
Understanding 5 Define a satellite. L 6 Explain what a geostationary satellite is and outline its advantages for communication. 7 TV satellite dishes can be fixed in one position on the house and do not need to move. Explain why they don’t need to ‘track’ the satellite. 8 Explain why microgravity is not true weightlessness. 9 Explain how the air that astronauts on board the ISS breathe is made.
8.5
8.5
8.5
Evaluating 14 If you were a billionaire, would you pay $30 million dollars or so to travel to the ISS? Justify your response. 15 Draw conclusions about why a global effort is needed if missions such as the ISS are to succeed. 16 For a long time humans have been interested in travelling to space. Propose why. 17 Propose some of the advantages of colonies in space for the human race, world government and private industry.
Creating 18 Imagine yourself as a travel agent who markets holidays in space. Design a travel brochure or advertising campaign to sell a destination to people. Include descriptions of the sights to be seen, how you will get there, and an account of the conditions and environment there. L 19 Construct a flow chart that shows the main stages of a suborbital flight on board SpaceShipTwo.
INVESTIGATING
Investigate your available resources (for example, textbooks, encyclopaedias, internet) to complete these tasks. 1 Write a short article for your local newspaper that discusses the ethics of satellite technology. You can use the following questions to guide your discussion. L a Does satellite technology pose a threat to our personal privacy? b Should governments use satellite technology to spy on organisations and other countries? Could satellite technology be used for political gain? 2 Review a science fiction video (e.g. one of the Star Trek movies, (Mission to Mars, Galaxy Quest) and assess the scientific correctness of information and the plausibility of the technology in it. L
3 After World War Two, communist USSR (Russia) and the USA were enemies. They were constantly trying to get the upper hand politically and also in the area of science and the exploration of space. This competition was known as the ‘space race’. Find out about the events leading up to the first Moon walk.
e –xploring To explore space travel at present and its future directions, a list of web destinations can be found on Science Focus 3 Second Edition Student Lounge.
275
Science Focus
Long-distance space travel
Prescribed focus area Current issues, research and development in science It has long been a fantasy of science fiction films and novels not just to visit the other planets of the solar system, but also to travel to other stars and other galaxies. There are, however, major obstacles to long-distance space travel. Too far It is 4.3 light years from Earth to the closest star after the Sun: Proxima Centauri, in the triple star cluster Alpha Centauri. It would take 4.3 years to reach it from Earth at the speed of light—and that’s the closest star! The distances to other stars and galaxies are phenomenal and are shown in the table below. (Note: a light year is the distance light travels in a year. It is equivalent to around 9.5 trillion kilometres.)
Fig 8.5.11 Ninety-five per cent of the space shuttle’s mass at a launch is fuel, with only five per cent being shuttle! That’s just to get it into orbit! This sort of fuel use makes normal spacecraft too thirsty to travel far.
Too slow An imaginary spacecraft travelling at the speed of light would take 4.3 years to get to Proxima Centauri and 50 million years to reach the Sombrero galaxy. Current technology, however, limits spacecraft to less than 100 000 kilometres per hour or about 0.01 per cent of the speed of light. The Voyager space probes (which left the solar system in 2002) travelled at 60 000 kilometres per hour and would take 80 000 years to reach Proxima Centauri, and that’s without the extra mass of human occupants and their requirements. One possibility is to place space travellers in suspended animation and ‘wake’ them on reaching their destination. Object
New rocket technology If humans are to travel deep into space then new methods of propulsion will need to be developed.
Type
Time light takes to reach Earth (years)
Proxima Centauri
Star
4.3
Alpha Crucis
Star
230
Great Nebula
Nebula
1600
Large cloud of stars
170 000
Andromeda
Galaxy
2 million
Sombrero
Galaxy
50 million
Dorado
276
Too much fuel needed Current spacecraft must carry large amounts of fuel. To reach Proxima Centauri, the most efficient current rocket would need to carry fuel weighing more than all the mass in the entire universe! One suggestion is for a spacecraft to collect fuel as it moves. Space is not completely empty as it contains some stray atoms and subatomic particles. They could be collected using a funnel-shaped magnetic field and then be used as fuel.
Ion drives Ion-drive engines work in a similar manner to conventional rockets, but emit a stream of faster moving, positively charged xenon ions (an ion is a charged atom). Unlike conventional exhaust propulsion, ion engines emit a very small amount of mass, and take a much longer time to accelerate a craft. They are more efficient though and eventually reach much greater speeds. NASA has been working on ion-drive prototypes with a view to using them on future missions. Nuclear explosions Car engines work using a series of controlled petrol, diesel or gas explosions so a spacecraft might be able to do the same with nuclear explosions. Project Orion and Project Daedalus both imagine spacecraft powered by blasting off nuclear explosions. Orion would need three nuclear explosions every second, whilst Daedalus would require an astonishing 250 every second! The hot plasma produced would push against a giant plate attached to the spacecraft and would theoretically be capable of producing speeds of up to 10 per cent to 12 per cent of the speed of light.
Fig 8.5.13 An artist’s impression of an antimatter drive spacecraft. Scientists have estimated that only one-millionth of a gram of antimatter would be enough to power a mission to Mars!
Antimatter Atoms of antimatter have a negative nucleus surrounded by positive electrons. These are the opposite charges to normal matter. When antimatter and matter combine, they destroy each other and release huge amounts of energy. If antimatter and matter were stored in separate tanks, they could provide energy for propulsion. Some major problems must first be overcome though: less than a billionth of a gram of antimatter has only been produced and what do you store it in? Laser and light drive Light exerts pressure on anything it strikes. The effect is normally not noticeable because the pressure is so small and is overwhelmed by other factors such as air resistance and friction. In space, however, light’s pressure is more noticeable. It is possible then that large
Fig 8.5.12 An artist’s impression of an ion-drive spacecraft, its radiator fins glowing red as they radiate excess heat.
Fig 8.5.14 An artist’s impression of a spacecraft powered by its solar sail passing Jupiter and its moon Europa.
277
solar ‘sails’ could use it for propulsion. American Robert Forward suggested aiming a powerful laser mounted on an orbiting satellite at sails on a spacecraft to accelerate it to one-fifth the speed of light. Change the rules Humans have always been limited by what they know at the time and what they believe the ‘rules’ are that govern how the universe works. Humans believed the Earth was flat, the elements were earth, air, fire and water, the Sun revolved around the Earth: all these theories were wrong and eventually new ones took their place. Maybe in time some of our current theories and ‘rules’ will change too. Below are some possibilities. Although they may seem far-fetched, it’s worth remembering that many things taken for granted today (for example, aircraft, TV, nuclear energy, silicon chips, the telephone, the internet, satellites, CDs, DVDs and iPods) were once far-fetched too. Warp engines In the sci-fi series ‘Star Trek’, Captain Kirk’s Enterprise starship was able to travel faster than light, being powered by fictional warp-drive engines. This inspired Mexican physicist Miguel Alcubierre to propose that rather than change the speed of a spacecraft we may learn how to change or ‘warp’ the fabric of space and time by expanding distances behind a spacecraft, and shrinking distances in front. It’s a bit like running on a rug. If the rug is slipped backwards, then the runner gets to the other end more quickly. Fig 8.5.15 Warp drive might be fictional but at least one physicist is studying it seriously.
278
Wormholes In 1987, American astrophysicists Kip Thorne and Michael Morris proposed that there may be wormholes in space. Their idea is that wormholes could be used as ‘short cuts’ to reach places that would be impossibly far by any other routes. Although there is no evidence that wormholes exist, the laws of physics suggest they could possibly exist. Worksheet 8.5 Mir’s plunge
Worksheet 8.6 Global positioning
Fig 8.5.16 Wormholes in space may provide a short cut to reach distant stars almost instantly.
STUDENT ACTIVITIES 1 Rank the technologies presented here from least likely to most likely. 2 Write a short story that uses one of the technologies presented in this chapter to take you on a trip to deep space. What will you see, where will you go? Be imaginative, but base everything on the facts presented in this chapter. L
CHAPTER REVIEW Remembering 1 State when the ‘fog’ of the early universe cleared. 2 State whether the following are true or false. a A Formula One car’s screaming engine changes pitch from high to low as it races past your position in the grandstand.
Applying 8 Identify the first two and most abundant elements in the universe. 9 Calculate how long it would take to travel to our nearest star (Proxima Centauri, 4.3 light years away) and back, travelling at:
b Only sound can undergo a Doppler effect.
a the speed of light
c Stars moving towards us may have a spectrum shift towards the red end.
b the speed of the Voyager spacecraft N
d Hubble’s law states that stars further away from us are moving faster than those closer to us. e The universe is contracting.
Understanding 3 Explain what is meant by the Big Bang. 4 Describe how the temperature of the early universe compares with the current temperature.
10 Identify what types of celestial objects are known as ‘star nurseries’. 11 You are making a phone call to a friend. Demonstrate something that would represent interference.
Analysing 12 Analyse why scientists think there must be ‘dark matter’ in the universe. 13 Contrast the theories of the expanding universe.
5 Describe the tell-tale signs of a black hole.
Evaluating
6 Describe an area of space research:
14 Assess the value to the world of space stations such as the ISS.
a that may be conducted in space b that is conducted from Earth 7 Select two scientists mentioned in this chapter and summarise their contributions to our understanding of the universe.
Creating 15 Construct an argument for and against continuing the search for extraterrestrial life. Worksheet 8.7 Crossword
Worksheet 8.8 Sci-words
279
9
Earth’s fragile crust
Prescribed focus area The implications of science for society and the environment
Key outcomes
Additional
Essentials
5.4, 5.9.2, 5.9.4
•
Evidence suggests that the Earth’s crustal plates move over time.
•
Convection currents in the molten rock below the Earth’s surface influence what is happening on the crust above.
•
Interactions at tectonic plate boundaries may result in earthquakes, volcanoes and new landforms.
•
Natural events such as volcanic eruptions, earthquakes and tsunamis have a great impact on society and the environment.
•
Fossils form under certain conditions and can be used as a method of dating rocks.
•
The fossil record relates to the age of the Earth and the time over which life has been evolving.
•
Horizontal layers of sediments form over geological time—the oldest are at the base and the youngest at the top.
•
Information from seismic waves helps describe the Earth’s inner structure.
•
Evidence of ice ages shows that the Earth’s surface has changed over time.
•
Many scientists have contributed to our understanding of the Earth.
Unit
9.1
context
Plate tectonics
If you look at a map of the world, it appears that some coastlines could fit neatly together. Francis Bacon first noticed it in 1620: the eastern coast of America had just been mapped and seemed to fit the coasts of Africa and Europe like pieces in a jigsaw. This
observation seems to suggest something amazing—that these continents were once joined and have since moved apart!
Continents that move In 1915 Alfred Wegener proposed a radical theory. He suggested that all continents had once been joined together to form one supercontinent he called Pangaea, after a Greek word that means ‘all earth’. He suggested that this supercontinent split millions of years ago to form the continents. These continents then drifted into their current positions. Although Wegener had lots of evidence to support his ideas about drifting continents, most geologists did not take his work seriously. The evidence Wegener used in forming his theory included the following ideas. • As there was a spread of identical fossils across the southern continents, it seems they all must have started life on a single continent. They were then taken around the world when this single continent split, and the pieces drifted apart.
Fig 9.1.1 The shapes of the coasts of South America and Africa seem to match, as if they once fitted together.
Cynognathus Africa
India
Lystrosaurus
South America Australia
Antarctica
Mesosaurus
Fig 9.1.2 Alfred Wegener was not a trained geologist, but a meteorologist and astronomer, Since his expertise was in Earth’s atmosphere and weather, and in the stars, few took him seriously when he proposed his theory about Earth’s geology.
Glossopteris
Fig 9.1.3 Fossils of the same Triassic reptiles and plants have been found on all the southern continents. This migration could have happened only if the continents were joined at the time in which they lived. On splitting, the different continents then took their fossils with them.
281
Plate tectonics The rock, composition and formations of mountains in North America are similar to those of mountains across Europe and seem to have been part of the same mountain range
N
N N
common pole (roughly where Hawaii is now)
Greenland N
Iceland North America Atlantic ocean
Europe
Mountains in Africa seem to be matched in a similar way with South America
Fig 9.1.5 Magnetic particles in rocks point in the direction of the North Pole at the time of their formation. This direction will change as the rocks are shifted about.
Fig 9.1.4 The mountain ranges in eastern North America and north-western Europe are very similar in their structure and rock composition.
• Mountains across different continents can be matched in their structure, age and rock composition. This suggests that those mountains were once part of a larger mountain range spanning a supercontinent that then split into many pieces.
Science
Clip
The man from Snowy River ‘He hails from Snowy River, up by Kosciusko’s side, where the hills are twice as steep and twice as rough.’ The Snowy River valley in New South Wales/Victoria was partly formed by a glacier of 15 kilometres. Had the ‘man’ lived in the Ice Age he would have needed a snowboard instead of a horse! The closest we get to a glacier in Australia now are 30-metre deep snow patches on Mt Twynam in New South Wales. These patches are thick and heavy enough to compact to a density of about 80 per cent that of ice.
282
• Ancient glaciers have left valleys and debris across many continents, including some now too warm to produce glaciers. These continents seem to have moved from a colder climate. • Coal has been found above the Arctic Circle. Coal comes from decomposed plants and it is far too cold there now for plants to grow. These regions seem to have moved from a warmer climate where plants could grow. • As lava from a volcano cools, it adopts the magnetism of the Earth at that moment. Three-hundredmillion-year-old magnetic rocks in South and North America have been found with their north poles pointed in different directions. The magnetic alignments of ancient igneous rocks are scattered. The continents seem to have shifted so that these mini-magnets
point in mismatched directions. If the continents are put together, however, they all point in the same direction. It was later suggested that Pangaea split first into two smaller supercontinents: Gondwana (comprising Australia, Antarctica, South America, Africa and India) and Laurasia (North America, Europe and most of Asia) before breaking up again. The idea didn’t catch on at the time because it was generally thought that the Earth was solid rock. No-one could imagine how continents could move across solid rock, and what could possibly push them about. Prac 1 p. 286
Evidence from below During World War Two, the military needed accurate maps of the seabed for their submarines and landing craft and they also needed to find underwater reserves of fossil fuels to assist the war effort. Using the newly developed technology of sonar, some surprising results were found: • huge underwater volcanic mountain ranges run down the centre of the oceans, the longest being the Mid-Atlantic Ridge with a length of nearly 10 000 kilometres • incredibly deep ocean trenches exist, the deepest being over 11 kilometres • the ages of the rocks of the ocean floor vary from recent to 200 million years old, far younger than the rock of the continents • the rock of the continents is less dense than that of the ocean floor and seems to ‘float’ on it • the rocks of the ocean floor have magnetic ‘stripes’, parallel with the underwater ridges. The magnetic
Tasman Sea
new rock mid-ocean ridge new rock Key:
N
rocks have rocks have N plate movement oldest ocean rock Antarctica
Floating plates The Earth is made of layers. We live on the crust, which varies in thickness from about 11 kilometres under the ocean to an average of about 33 kilometres under the continents. Next is the 2900 kilometre thick mantle. The mantle is unusual in that the upper mantle is solid, very much like the crust. The upper mantle and crust form a rigid layer of rock known as the lithosphere. Cracks (fault lines) in the lithosphere cut it into slabs. These slabs of lithosphere are called tectonic plates. Below the lithosphere is a narrow layer of fluid-like, mobile rock called the asthenosphere. The rock here is under extreme heat and pressure and behaves like a sludgy, slow-moving liquid. The tectonic plates of the lithosphere float on the slowly moving asthenosphere. The continents sit on the plates and move with them. Imagine the asthenosphere as a bowl of thick, hot soup and the tectonic plates as pieces of toast floating on the soup. The toast will move whenever you stir the soup. Some pieces will crash against each other, some will ride up on top of others, and others will sink.
9.1
Australia
oldest ocean rock
Unit
field of the Earth has changed many times in its history, with the North Pole becoming the South Pole and the South Pole becoming the North Pole. The stripes show this reversal and indicate that the youngest rock is next to the ridges and the oldest next to the trenches.
Fig 9.1.6 The magnetic stripes of the ocean floor, south of Australia Thickness volcanic activity (island arc)
oceanic oceanic ridge crust
ocean sediment trench
continental plate
8–64 km
2300 km
rising magma
melting mantle rising magma
Crust
0
The crust is part of a zone called the lithosphere
8–64 km 2800 km
direction of movement of magma
Depth
continental crust
1400 km
Mantle 2900 km Outer core Inner core
The upper layer of the mantle is rigid and part of the lithosphere. Below this is the asthenosphere
5100 km
6400 km
Fig 9.1.7 The ocean floor is like a conveyor belt dragging new rock from mid-ocean ridges into the ocean trenches.
All this evidence suggests that the new crust is formed at mid-ocean ridges. Rock from the centre of the earth is liquid as it has a very high temperature. This is called molten rock. The molten rock cools as it hits the water of the ocean. This rock becomes solid and builds new mountains and pushes old ones out of its way. The ocean floor acts like a conveyer belt, carrying everything towards the trenches.
Fig 9.1.8 The inner structure of the Earth (not to scale)
283
Plate tectonics The theory of plate tectonics The idea of moving plates is called the theory of plate tectonics. American professor of geology Harry Hess first developed this theory in 1962. Most scientists now agree that tectonic plates exist and that they are moving. Many different theories have been proposed to explain their movement, but the truth is that nobody really knows for sure. Some theories have the plates being pulled along when they drop into a trench, while others have the spreading oceanic ridge pushing them along. Others again put it all down to tidal forces. The most commonly accepted theory is that the sea floor is moved by convection currents in the Earth’s mantle. Hot air and liquids rise and so does hot molten rock. Likewise, ‘cool’ rock drops. Heat from deep within the Earth causes the molten rock of the mantle to move upwards. When this hot mantle rock comes into contact with the relatively cold crust, it cools and sinks. Convection currents in the mantle are the result.
Alternative explanations Many scientists did not accept the theory of plate tectonics at first, especially in the old Soviet Union (USSR) of which Russia was the main part. Russia is located far from any plate boundary and so Soviet geologists at that time believed instead that the continents were stationary and were affected only by vertical movements of the Earth’s crust. More recently, the Australian geologist S Warren Carey suggested an alternative theory known as the ‘expanding Earth model’. This model suggests that the Earth was much smaller 200 million years ago. It has since expanded to its present size (the current increase in radius being 3 to 4 millimetres per year), with the expansion causing cracks in its crust. Although this model easily accounts for the break-up of Pangaea, the movement of the plates and the spreading of the ocean floor, it failed to explain the ocean trenches.
Science
Clip
Kangaroos in Antarctica? Prac 2 p. 287
Red Sea African continent
ridge
Prac 3 p. 288
India
convection currents convection currents
hot plume Mantle temperature high low
Fig 9.1.9 Rock deep in the mantle is constantly being heated by radioactive decay. Hot rock rises and cold rock drops to replace it, forming convection currents that carry the tectonic plates along with them.
284
The rocks of east Antarctica are four billion years old, making them some of the oldest rocks known on Earth. Antarctica’s fossil record is similar to Australia’s and includes dinosaurs, amphibians and marsupials from when the two continents were joined. Australia began to separate from Antarctica about 85 million years ago. Complete separation occurred about 30 million years ago. They are still moving apart at the rate of 7 centimetres a year.
Unit
QUESTIONS
Remembering 1 List five surprising facts that scientists discovered when the ocean floor was first mapped. 2 State the thickness of the: a crust b mantle c outer core d inner core
Understanding 3 Outline five pieces of evidence that suggest the continents were once joined. 4 Define the following terms: a tectonic plate b mantle c crust L
b There are similar mountain ranges in the USA and Africa, and also in Europe and South America. c Continents that do not have glaciers now have always been too warm to have them. d Coal deposits above the Arctic Circle suggest that the land floated there from warmer climates. e The rock of the ocean floor and that of the continents are the same age. f Continental rock is denser than the rock of the ocean floor. g Magnetic stripes on the ocean floor suggest that new rock is made along mid-ocean ridges.
Applying 10 Identify the land masses which are thought to have made up: a Gondwana b Laurasia
5 Explain the theory of plate tectonics.
11 Identify the locations of the oldest and youngest rocks on the ocean floor.
6 Describe what causes convection currents and where they are thought to occur.
Analysing
7 Draw a diagram to illustrate the convection currents in an oven. 8 Explain what keeps the mantle from cooling down and becoming solid. 9 Modify any of the incorrect statements so they become true and copy those that are correct. a Triassic reptiles could have swum the distances required to populate different continents.
9.1
9.1
12 The plate on which Australia sits is moving northward at about 5 centimetres per year. Calculate how far it will move in an average lifetime of 75 years. N
Evaluating 13 Temperatures along the oceanic ridges are higher than elsewhere in the ocean. Propose reasons for this. 14 Assess what would happen to the plates if the asthenosphere below them cooled and became solid. 15 The theory of plate tectonics explains why Australia once had glaciers but does not have any now. Propose another possible reason for this phenomenon.
9.1
INVESTIGATING
Investigate your available resources (for example, textbooks, encyclopaedias, internet) to complete the following tasks. 1 a Find out what one or more of these people contributed to the development of the theories of continental drift and plate tectonics. L • Alexander Du Toit • Arthur Holmes • Abraham Ortelius • Eduard Seuss • Antonio Snider-Pellegrini • Frank Taylor • Alfred Wegener b Imagine you are the person you have researched. Outline what you have discovered in a letter to send to the Geological Society of Australia.
2 Find out more about the expanding Earth theory which is an alternative to the theory of plate tectonics. a Use this theory to explain how the continents split and moved apart. b Find out more about this theory and the works of S. Warren Carey, O. C. Hilgenberg and H. G. Owen. 3 Examine what sonar is and how it measures depth. Illustrate your findings with examples.
285
Plate tectonics
9.1
PRACTICAL ACTIVITIES Method 1 Cut out the continents and arrange them to rebuild Squidgewana.
1 The planet Splatter
2 Stick the map in your workbook.
Aim
Questions
To reconstruct a supercontinent
1 Explain how each piece of evidence suggests that a supercontinent once existed.
Equipment • A4 photocopy of the map in Figure 9.1.10 or photocopy of worksheet 9.1
2 Determine whether there are any other ways the supercontinent could be arranged.
Worksheet 9.1 The planet Splatter
(Note: Splattonians think that the continents on their planet move and were once the supercontinent Squidgewana. Evidence comes from shape, magnetic fields and fossil remains of the golden splattered slug and the squidgian tinea fern.) N
N
N
Map of the Pla n et S platter
N
N Key N direction of north pole of ancient magnetic rocks fossil remains of golden splatted slug fossil remains of squidgian tinea fern
Fig 9.1.10
286
Unit
Aim To investigate the movement of convection currents
Equipment • • • • • • • • •
large (500 mL or 1000 mL) beaker potassium permanganate crystals tweezers hot plate or Bunsen burner bench mat tripod gauze mat plastic bag ice
Method Part A: Hot convection 1 Three-quarters fill the beaker with cold water.
9.1
2 Convection currents
2 With the tweezers, drop a single crystal of potassium permanganate into the centre of the beaker. 3 Gently heat the beaker on the hot plate or over the Bunsen burner. 4 Carefully observe and draw the motion of the purple stain. Part B: Cold convection 1 Three-quarter fill the beaker with cold water. 2 Put some ice in the plastic bag. 3 Use the tweezers to hold a crystal of potassium permanganate at the top of the beaker, just below the bag of ice. 4 Carefully observe and draw what happens.
Questions 1 Explain what causes convection currents. 2 Use a diagram to clarify what a ‘hot’ current does. 3 Identify the direction of a ‘cold’ current.
Part A Hot convection currents
beaker
Part B Cold convection currents plastic bag of ice
tweezers to hold crystal
hot plate
beaker of cold water
crystal potassium permanganate
Fig 9.1.11
287
Plate tectonics
3 Future Earth
2 On each sheet, draw a large arrow pointing in the direction the plate is moving.
Aim To predict possible future changes to the position of the Earth’s continents
Equipment • • • • • •
map of tectonic plates A4 sheet of paper 6 overhead transparencies overhead transparency pen or marker sticky tape photocopy of worksheet 9.2
3 Lay all the sheets on top of each other to reproduce the current map of the world. 4 Move each transparency 1 cm in the direction of the arrows. 5 Trace the new shape of the continents. Transfer the diagram to your workbook. 6 Move the transparencies 1 cm more and re-trace. 7 Do this three more times, so that you have a series of ‘maps’. 8 Mountain chains will form when a continent hits another. Mark them and give them a name. 9 Name any new seas or oceans formed.
Worksheet 9.2 Future Earth
Questions
Method 1 There are seven main tectonic plates. Trace the African plate and Africa onto a piece of A4 paper and tape it to the desk. Trace the other plates and continents onto overhead transparencies, one plate per sheet.
1 In this Prac, each plate moved at the same speed. Assess whether this is accurate in reality. 2 Predict what will happen to these bodies of water in the future: a the Mediterranean Sea b the Atlantic Ocean c the Red Sea 3 Propose the likely positions of these cities in the future: a Darwin b Tokyo c Hong Kong d Los Angeles e Rome
A4 sheet with tracing of Africa
overhead transparencies with plates, continents
shift the sheets 1 cm in the directions of the arrows
Fig 9.1.12
288
4 Propose what you would expect to happen to the climate of New South Wales in the future. 5 To compare your maps with those produced by scientists, a list of web destinations can be found on Science Focus 3 Second Edition Student Lounge.
Unit
9.2
context
At the edges
The tectonic plates move at about the rate at which your fingernails grow. For this movement to continue, new crust must be made and old crust destroyed. All this action happens at the edges or boundaries of the plates and creates the basic landscape of our world, including its volcanoes and earthquakes.
Plate boundaries The three types of plate boundaries are classified according to how they move. • Divergent or spreading boundaries are where plates move apart. They are also known as constructive boundaries as new rock is being made on the ocean floor. • Convergent or collision boundaries are where one plate collides with another. One plate slides underneath the other and then moves down into the mantle. Where the plates meet is called a subduction zone. These are destructive boundaries since rock is melted there and is returned to the mantle for recycling. • Transform or scraping boundaries are where plates scrape along each other. They are conservative boundaries since they conserve rock. They do not create or destroy it.
Fig 9.2.1 Volcanoes occur at collision boundaries. Fig 9.2.2 Tectonic plates and their boundaries: divergent, convergent and transform boundaries
North American plate
Eurasian plate
Caribbean plate Philippine plate
African plate
Cocos plate
Pacific plate
Indo–Australian plate
South American plate
N W
Nazca plate E
S collision boundaries spreading boundaries
movement not known transform boundaries
main movement directions
289
At the edges
Spreading boundaries Mapping of the ocean floor shows that some plates are moving apart at a rate of up to 20 cm a year. A huge crack or rift valley forms from a weakened line (called a fault) in the crust. The hot liquid magma forces its way up from the mantle to fill it. The magma cools and solidifies as it hits the water. This creates underwater mountain ranges like those found in the Atlantic and Pacific Oceans. This is brand new oceanic lithosphere. Older rocks crack and are squeezed out of the way as more magma moves upwards. New magma then fills Science the crack and the process repeats itself. It’s like a wound: a scab begins to repair Fire and ice the wound but any stress cracks it, Although a relatively allowing blood to ooze again. The scab small island, Iceland then needs to re-form. produces more than Most rift valleys are under water but a one fifth of the total few are on the surface. The largest is the lava output from all volcanoes around the East African Rift Valley, which is filled in Earth! It is located on parts with lakes like Lake Victoria, and in a spreading boundary other parts with huge volcanoes like Mt and is where the MidKilimanjaro. Other rift valleys pass Atlantic Ridge is through the Dead Sea (at 400 metres exposed as land.
Clip
Sea of Galilee
River Jordan
Dead Sea
Spreading boundary
Fig 9.2.4 Icelanders left their homes when the Helgafjell volcano in Iceland erupted on 24 January 1973.
below sea level, the lowest point on Earth not under an ocean) and the Sea of Galilee (209 metres below sea level). This rift valley continues into the Red Sea, indicating that it will widen and become an ocean in the future. Another rift valley is gradually splitting Iceland in two.
Collision boundaries
New oceanic lithosphere is made at the mid-ocean ridges and the old material moves away. As the oceanic plates move away from the mid-ocean ridges they collide with other oceanic plates or with continental plates. Continental plates can also hit other continental plates. Each collision creates something different. Volcanoes and trenches The rock of the oceanic plates is denser than the plates that the continents sit on. When they hit, the heavier oceanic plate is forced under the continental plate at an angle to the surface of 20° to 60°. This angled dive is called a subduction zone. Meanwhile the upper plate gets crushed, thickens and forms folded mountains along its edge. By the time the ocean plate has reached a depth of about 200 kilometres it has melted and become part of the asthenosphere once more.
Fig 9.2.3 The Sea of Galilee and the Dead Sea all lie in a giant rift valley that joins with the Red Sea.
290
Prac 1 p. 295
Worksheet 9.3 Ocean trenches
Unit
Ocean trenches form where the ocean plate drops below the continental plate.
Upper plate gets crushed, thickens and forms folded mountains along its edge.
9.2
Some water gets in through the fault and becomes steam. It is carried down into the subduction zone and makes the rock very gassy and hot.
continental plate
ocean plate
Plates do not slide easily over each other because of friction between them. When they do slip, it’s sudden and an earthquake results. earthquakes subduction zone
magma
The gassy molten rock forces its way back to the surface, perhaps to burst out as a ridge of volcanoes. Friction generated heat melts the rock as it submerges. By the time it has reached a depth of 200 km the ocean plate has become part of the mantle once more.
Fig 9.2.5 Volcanoes and trenches come from collisions between an oceanic plate and a continental plate.
Science
Clip
Really deep The Mariana Trench in the western Pacific was discovered in 1951 by the British survey ship Challenger. With a depth of 11 033 metres, it is more than six times deeper than the Grand Canyon in the USA. Mt Everest could easily sit in it, leaving plenty of room for Mt Kosciuszko to fit in as well! In January 1960, Dr Jacques Piccard of Switzerland and Lt Donald Walsh of the USA took the US Navy submersible Trieste to a depth of 10 915 metres in the Mariana Trench.
The two plates do not slide easily over each other due to friction between them. When they do slip, it’s sudden and an earthquake results. The friction also generates heat, which produces magma along the top of the oceanic plate as it submerges. The magma will try to force its way back to the surface, perhaps to burst out as a ridge of volcanoes. The Andes Mountains were formed in this way. Parallel to them is the Peru–Chile trench. Ocean trenches form where the oceanic plate drops below the continental plate. Although some of these trenches are filled with sediment, many are incredibly deep. Prac 2 Island chains p. 296 If an oceanic plate hits another oceanic plate and their densities are the same then the fastest plate sinks in the collision. Once again a subduction zone is created. The upper plate gets thicker and volcanoes form, some of which push out of the water to form islands and island chains. Examples are the islands of Japan, Indonesia, the Philippines, the Caribbean and the Aleutians.
Fig 9.2.6 Piccard and Walsh on board the submersible Trieste.
291
At the edges ocean trench island arc
Some volcanoes might rise above the water to form hidden islands and island chains.
subduction zone Upper plate becomes thicker and volcanoes form active volcano
ocean plate
ocean plate
rising magma
Scraping boundaries Plates scrape along each other along a transform boundary. These don’t make mountains or volcanoes but do produce lots of earthquakes, some very strong. Although most of these boundaries are under water, some are on land. The most important of these is the San Andreas Fault, which runs 1300 kilometres through California, USA, directly under San Francisco and close to Los Angeles. The coastline of California slips five centimetres along it every year, moving Los Angeles north and closer to San Francisco. Worksheet 9.4 Earthquakes
earthquakes melting
Worksheet 9.5 Volcanoes
Fig 9.2.7 A chain of islands forms when an oceanic plate collides with another oceanic plate.
Really big mountains When two continental plates collide, they crumple and fold. Intense heat from the collision melts some rock and forms a solid ‘mountain root’ that resists weathering. The Himalayas are the tallest range of mountains on Earth, with Mt Everest the highest mountain peak at 8848 metres. The Himalayas were formed when the plate that carries India collided head-on with the plate that carries the bulk of Asia.
mountains
continental plate tal plate
continen
Fig 9.2.9 The San Andreas Fault is a scraping or transform boundary. Movement along this boundary caused the massive 1906 and 1989 earthquakes in San Francisco.
Both plates have similar densities and neither can push the other underneath. Plates crumple, fold and push up to form mountains.
Science
Clip
Fig 9.2.8 Massive folded mountains form when continent collides with continent. Both plates have similar densities and neither can push the other underneath. Instead the plates crumple, fold and push up.
292
Climb Mt Everest soon! No dinosaur ever climbed Mt Everest, because it did not exist when they were alive. The collision of plates is still happening and is raising the Himalayas about 1 cm a year. Current mountaineers now need to climb half a metre more than the first successful climbers, Sir Edmund Hillary and Tenzing Norgay, in 1953. Every year the peak gets taller, so don’t wait: do it soon!
Unit
QUESTIONS
Remembering 1 Specify how fast tectonic plates are moving.
9.2
9.2
Applying 11 Identify the types of plate boundaries shown in Figure 9.2.10.
2 List the three types of plate boundaries. 3 State which plate is more likely to sink when the two hit each other: a the fast or the slow plate b the heavy or the light plate c the continental plate or the oceanic plate
Understanding 4 A mid-ocean ridge can be compared to a scab. Explain why. 5 Describe what happens in a subduction zone. 6 The Himalayas have a ‘mountain root’. Explain what this means and how it formed. 7 Describe what occurs at a transform boundary. 8 Describe boundaries which: a are conservative b are destructive
Fig 9.2.10
c are constructive
12 Identify the type of boundary on which the following places are situated:
d have subduction zones e form rift valleys
a Iceland
f dive into the mantle
b the San Andreas Fault
g cause trenches
c Mt Everest
h cause huge, folded mountains
d Mt Kilimanjaro
i have only sideways movement
e Lake Victoria
j form island chains
f the Dead Sea
k form mountains 9 Illustrate the following with a labelled diagram:
13 Identify the two plates that created the: a Himalayas
a spreading plate boundaries
b Andes
b oceanic plate meets continental plate
c Mid-Atlantic Ridge
c oceanic plate meets oceanic plate
d Caribbean islands
d continental plate meets continental plate
e Japan
e transform plate boundaries
f Mariana Trench
10 A plate often gets thicker when another plate is forced under it. Explain why.
g San Andreas Fault h Dead Sea
>> 293
At the edges 14 Figure 9.2.11 shows part of a spreading boundary underneath the ocean. Identify which rock (a to l) would be the same age as:
16 Currently the Red Sea is about 240 km wide and widening at about 20 cm per year. Calculate the time it will take for it to become the same width as the:
a rock a
a Mediterranean Sea (about 500 km)
b rock h
b Atlantic Ocean (6100 km)
c rock c
c Pacific Ocean (14 000 km) N
Creating land
land
e f a b c d
g h i j k l
17 Construct a four-frame cartoon to demonstrate the development of the: a Himalayas b Indonesian islands c Mid-Pacific Ridge d Andes
Fig 9.2.11
Analysing 15 a The Himalayas are growing about 1 cm per year. Calculate how much they will grow in an average lifetime. N b Calculate how long it will take for them to grow a further: i 10 m ii 100 m iii 1 km N
9.2
INVESTIGATING
Investigate your available resources (for example, textbooks, encyclopaedias, internet) to complete these tasks. 1 Using an atlas, locate the following places and information on the map. a East African Rift: use the map to find the geological features that lie on it. b Jordan Rift Valley: find what lies along it and what connects it with the East African Rift. c Iceland: find information about its eruptions and earthquakes, and how Icelanders make use of its volcanic nature as a renewable energy source. d Find the island chains that make up Japan, Indonesia, the Philippines, the Caribbean and the Aleutians. 2 Find out about ‘black smokers’ which are found on mid-ocean trenches.
294
18 A new type of power station has been developed: only 10 are needed to supply all the electricity needs of the whole world. However, they are safe, only if they are not disturbed. The United Nations will build them but it needs your advice about where to put them. No more than two can be located on any one continent, and they must be close to large population centres. You must be convincing, because California, Japan, Iceland, Indonesia and New Zealand all want them. Inquire into and draw conclusions about where the power stations should be placed. Justify reasons for your 10 choices.
e –xploring To explore animations of colliding plates, a list of web destinations can be found on Science Focus 3 Second Edition Student Lounge.
Unit
PRACTICAL ACTIVITIES
1 Plates that separate Aim To model the mid-ocean spreading of tectonic plates
Equipment • • • • •
9.2
9.2
Questions 1 Explain how this activity relates to the spreading at the mid-ocean ridges. 2 Describe what you noticed about the height of the paper as it emerged from the gap, compared to the paper further out. 3 Identify what in your model represents each of the following:
A3 sheet of paper coloured pencils or highlighters scissors sticky tape pegs
a ocean floor or plate b the water c the lava flow d gravity
Method
e mid-ocean ridge
1 Push two desks together. 2 Cut the sheet of paper lengthwise and tape the pieces together to make a long strip. 3 Fold and push both free ends of the paper up through the gap between the desks. 4 As the paper emerges from the gap, brush it down with your hand so that the paper follows the bench top.
f the magnetic strips found in rocks parallel to the mid-ocean ridges. 4 Identify which of the strips you coloured would be the ‘oldest’ rock and which the ‘youngest’ rock. 5 Identify which of these strips would be the first to be ‘swallowed’ by an ocean trench.
As each 5 cm emerges, colour or decorate each new strip of paper.
tape
colour each 5 cm strip as it emerges peg
peg
push paper up
Fig. 9.2.12
>> 295
At the edges
4 Now hold the end of one stack to keep it still. Push the other stack into it. Observe which layer climbs on top of the other. Repeat this step to confirm your observation and draw what happened.
2 Colliding plates Aim To model what happens when two tectonic plates collide
5 Finally, place a textbook on the desk and push a stack of 30 sheets into it. Observe which goes under.
Equipment • a stack of about 30 A4 pages (use recycled scrap paper) • textbook
Questions 1 Describe how the above practical activities compare with plate tectonics.
Method 1 Split the stack of A4 paper into two smaller stacks of about 15 sheets each. 2 Place each on the desk and slide them slowly into one another. 3 Observe what happens to the layers as they collide. Repeat four times to confirm your observations. Make a drawing of what usually happened.
2 State which tests simulated the following collisions: a a continental plate with another continental plate b an oceanic plate with another oceanic plate c an oceanic plate with a continental plate 3 Identify a place on Earth where each of these collision types occurs. 4 The stack of paper had obvious layers. Assess whether rock has layers, and if so explain why.
Test 1
Test 2 keep this stack still
Test 3
Fig 9.2.13
296
Unit
9.3
context
Earthquakes
The tectonic plates are constantly moving and it is at their boundaries that earthquakes happen. More than one million earthquakes occur per year. Most are so small or so far away from human
activity that they cause little if any damage. Sometimes the only people to detect them are the seismologists who use instruments to measure them.
Why earthquakes happen Tectonic plates separate, collide and scrape over each other. None of this movement is smooth, because the plates must build pressure to overcome the incredible friction forces that cause them to ‘stick’. The plates are constantly trying to move, so the release of pressure is frequent. Now imagine bending a branch. It bends fairly easily up to a point, then suddenly snaps. The vibrations you feel through your hands are the release of the stored energy in the branch. This is what happens with an earthquake. The pressure release is sudden, explosive and often catastrophic. Major earthquakes can destroy buildings, roads, services and lives. In the process they also devastate the community they hit, making many homeless and destroying the economic structure of the community.
Focus and epicentre The focus of an earthquake is the point where it begins. It is where the plates slip and it is on a fault line, usually at the plate edges. The focus can be very close to the surface or can be as deep as 200 kilometres, the depth at which the oceanic plate finally melts into the asthenosphere. The size of an earthquake does not depend on Science the focus depth. The epicentre is the point Fleas cause on the Earth’s surface that is earthquakes! directly above the focus and will In the earthquake-prone suffer the most damage. Kamchatka peninsula in An earthquake starts at its Siberia, an old tale has focus and is felt most directly the god Tuli riding with above on the surface. This is its the Earth on a sled being pulled by fleaepicentre. Seismic waves (P and ridden dogs. When they S, R and L) spread through and stop and scratch, the across Earth, spreading its Earth shakes. energy and damage far and wide.
Clip
Fig 9.3.1 Massive earthquakes devastate the cities and communities that are hit by them.
epicentre focus
R and L waves (surface waves) surface of Earth
P and S waves (body waves)
Prac 1 p. 306
Fig 9.3.2 The focus is where the earthquake starts. Seismic waves spread from here to the epicentre and beyond.
297
Earthquakes The Earth’s surface is pushed and pulled
Seismic waves
amplitude
Earthquakes release energy in the form of vibrations P S known as seismic waves, which travel through and The Earth’s around Earth. An instrument called a seismometer surface is shaken detects all these waves. The record it produces is known as a seismogram. It gives the time delay between the arrivals of each different wave type, as well as an indication of their energy. rock rock vibration The higher the amplitude of the trace on the vibration movement seismogram, the greater the energy of the earthquake. Seismic waves can be split into two categories: movement • body waves—these travel through the body of the Earth and can be either primary (P) or secondary (S) • surface waves—these travel on the A transverse wave A longitudinal or compression wave surface of the Earth and are either Prac 2 Rayleigh (R) or Love (L). Fig 9.3.4 Body waves: P and S p. 307
P waves begin arriving
S waves arrive
P and S waves
time
surface waves arrive P and S and surface waves
Fig 9.3.3 A typical seismogram, showing P and S body waves
Science
Clip
Strutt waves? The names primary and secondary make sense since that is the order in which these waves arrive. R and L waves were named after the British mathematicians who worked on the models of these waves. L waves were named after Augustus Love (1863–1940) and Rayleigh after John Strutt (1842–1919). Confused? Strutt became the third baron of Rayleigh in 1873, 12 years before he suggested they exist. Rayleigh also has craters on the Moon and Mars and an asteroid named after him.
298
Body waves Primary waves move fastest and are the first to be recorded. They are an example of longitudinal (or compression) waves. Unlike the up and down motion of water waves, these waves push and pull the material they travel through. Sound is another example of a longitudinal wave. P waves can travel through both solid and liquid rock and subject the rocks to an alternating push-pull motion, hitting the surface with an up-and-down motion.
S waves are slower than P and are the next to be recorded. They are transverse waves and have an up-down movement just like water waves. S waves travel only through solid rock. Molten rock blocks them. S waves hit the surface with a shaking or side-to-side motion. Earthquake shadows An earthquake shadow zone is where there are no P and S waves. The speeds of P and S waves depend on what they are travelling through. The denser the rock, the faster they go. The waves change speed as they pass into rock of different density. They also change direction or bend. This bending is called refraction. Refraction happens to all types of waves (water, light and sound waves) as they change speed on passing from one material to another. When an earthquake happens, seismometers around the world record all the waves that reach them. When all the seismograms are analysed, a pattern showing the spread of waves is produced. The bending of the waves and the fact that S waves will not travel through liquids causes different seismograms to record different combinations of body waves. S waves are not recorded directly opposite the epicentre of an earthquake. This suggests the core is liquid since S waves cannot travel through liquid. The paths of S and P waves are not straight. They are bent or refracted by the changes in density and temperature of the different layers of the Earth. This causes two ‘shadow zones’ where P and S waves are not recorded.
Unit
epicentre of quake
shadow zone— no P or S waves S waves are not recorded directly opposite the epicentre of an earthquake. This suggests the core is liquid since S waves cannot travel through liquid. both P and S waves arrive
The paths of S and P waves are not straight. They are bent or refracted by the changes in density and temperature of the different layers of the Earth. This causes two ‘shadow zones’.
8000
9.3
Distance from earthquake (kilometres)
both P and S waves arrive
7000 6000 5000 4000 3000 2000 1000 0
0
8.6 minutes 2 4 6 8 10 Difference in arrival times of P and S waves (minutes)
Fig 9.3.6 The difference between the arrival times of P and S waves tells us how far away the earthquake is.
Fig 9.3.5 Refraction of P and S waves and ‘shadows’ where they do not arrive
Finding the epicentre P and S waves arrive at seismometers at different times. Their speeds are well known and the distance from the epicentre can be calculated from the difference in time between their arrivals. In Figure 9.3.6, the S wave arrives 8.6 minutes after the P wave, therefore the epicentre is 7000 kilometres away. Worksheet 9.6 Earthquake epicentres
For an exact location, seismometer readings need to be gathered from three different locations. By subtracting the time of arrival of the P wave from the time of the S wave, the time difference can be found in each location. The distance from each seismometer to the epicentre is found. Circles can then be drawn from the location of each seismometer using this distance as the radius. Prac 3 p. 307 The epicentre is where the three circles intersect. h min s 10:32:09
Adelaide
Science Science
Clip
A moon made of cheese An old tale has the Moon made from green cheese. Moon rock brought back from the Apollo missions of the 1970s looks like rock but it does have some cheese-like properties! Speeds of seismic waves in moon rock range from 1.2 kilometres/s to 1.84 kilometres/s, comparing well with those found in cheese: Muenster cheese has the lowest seismic speed at 1.57 kilometres/s and Swiss cheese has the highest at 2.12 kilometres/s. In contrast, Earth rocks have speeds of 4.9 kilometres/s to 5.9 kilometres/s.
Clip
Deliberately creating earthquakes Geologists searching for minerals and fossil fuels often create ‘mini-earthquakes’ with explosives. A seismogram shows the shockwaves produced and gives information on thickness, density and position of different rock layers. This will hopefully pinpoint materials worth mining.
10:34:15
P 10:31:45
S 10:33:25
Melbourne Brisbane
10:31:06
Brisbane
10:32:16
Newcastle Sydney
Adelaide
0
500 km
Melbourne
Fig 9.3.7 Locating the epicentre: Newcastle is hit.
299
Earthquakes released by it a massive 30 times! This means that an earthquake of magnitude 8 is 10 times the size of an earthquake of magnitude 7, and has 30 times its energy. Any earthquake above 7 on the Richter scale must be considered dangerous as major damage can be expected. Luckily, such serious earthquakes are rare. The Richter scale gives no indication of the damage caused by an earthquake. Damage depends on the location of the epicentre, environment of the region, density of population, construction and design of the buildings and how long the earthquake continues to rattle everything. The Mercalli scale measures the intensity of the earthquake rather than its magnitude. The Italian scientist Guiseppe Mercalli (1850–1914) developed his scale in the 1890s before seismometers were in use. The Mercalli scale gives a better indication of the earthquake’s effects because it is based on actual observations of how and what people felt.
Surface waves Rayleigh (R) and Love (L) waves travel around the Earth, not through it. They have further to go than P and S waves and arrive after them. They are more dangerous than P and S waves, however, because their effect on the surface is more severe. Their energy radiates from the epicentre like ripples on a pond from where a stone has been dropped. R waves are rolling waves, like breakers at a surf beach. They are the slowest, but often the largest and most destructive. L waves are the fastest surface wave and have a side-to-side motion, like a moving snake.
Darwin 1979 1929
1964 1978
1906
1970
Alice Springs Bundaberg Simpson Desert 1972 1938 1918 Gayndah 1873 1937 1941 1935 Meeberrie 1941 Brisbane Geraldton 1885 Cadoux 1979 Picton Newcastle Adelaide Perth Meckering 1968 1989 1973 1954 Warooka 1902 Sydney Dalton 1949 Canberra Beachport 1897 Berridale 1959 1920 Melbourne Warnambool 1903
Carnarvon 1965
Fig 9.3.8 Rayleigh and Love waves are very dangerous and
Hobart
travel across the surface.
Fig 9.3.9 The location of major Australian earthquakes Worksheet 9.7 Waves in earthquakes Worksheet 9.8 Earthquake statistics
Measuring earthquakes Richter and Mercalli Scientists use seismometers to estimate the energy of an earthquake at its epicentre. An earthquake’s strength is measured on the Richter scale. This scale was devised in 1935 by an American physicist, Charles Richter (1900–1985). It is an open-ended scale that starts at zero. An increase of 1 on the Richter scale makes the earthquake 10 times larger, and increases the energy
300
Science
Clip
The worst ever Earthquakes were first recorded in China around 1000 BCE. The most devastating happened in CE 1556 at Hsian where most of the people had dug cave-like homes into the hills. These collapsed, burying them alive. Landslides, floods, lakes, famine and disease claimed more. A total of 830 000 are thought to have died.
Unit
9.5
Chile
1960
8.7
near Sumatra, Indonesia
2005
9.2
Alaska
1964
8.7
Alaska
1965
9.1
Alaska
1957
8.6
Tibet/India
1950
9.1
near Sumatra, Indonesia
26 December 2004
8.5
Russia
1923
9.0
Russia
1952
8.5
Indonesia
1938
8.8
Ecuador
1906
8.5
near Sumatra, Indonesia
2007
Richter 2–3 Mercalli I–II
Richter 4–5 Mercalli IV–V
Richter 5–6 Mercalli VI
Richter 6–7 Mercalli VII–VIII
9.3
The biggest quakes ever on the Richter scale
Richter 7–8 Mercalli IX–X
Fig 9.3.10 The damage at different levels on the Richter and Mercalli scales
How the Richter and Mercalli scale measure earthquakes Damage caused
Richter
Mercalli
Average number per year
Felt by seismometers only
1–2
I
More than 500 000
Felt by very few people
2–3
I–II
100 000 to 500 000
Felt by people in tall buildings; hanging objects swing, some damage
3–4
II–III
10 000 to 100 000
Felt and heard by most; parked cars rock, crockery rattles, walls crack
4–5
IV–V
1000 to 10 000
Felt by all; some panic, furniture moves, difficult to walk
5–6
VI
200 to 1000
Some panic, difficult to stand; chimneys and some buildings collapse; cracks in the ground
6–7
VII–VIII
20 to 200
General panic; deep cracks in the ground, most buildings collapse, rail lines twist, dams break
7–8
IX–X
10 to 20
Total destruction; few buildings survive, valleys fill with mud from landslides and flood
8–9
XI–XII
0 to 10
301
Earthquakes
Other earthquake nasties Aftershocks Large earthquakes have the power to move large slabs of crust and rock around. These slabs take some time to settle and cause smaller earthquakes called aftershocks. Although these are usually smaller than the first earthquake, they can be extremely dangerous, particularly if buildings were made unstable by the first earthquake.
Science
Clip
Animals predicting earthquakes? In 1975 in China, animals began to act strangely. Snakes left their burrows as if in fear and dogs barked wildly at nothing. Authorities thought the animals could sense an earthquake approaching. They warned that a major earthquake would occur in the next six months. Townsfolk were evacuated to the country. Some time later an earthquake did occur, but because of the precautions few died. Another earthquake struck two years later, killing 240 000 people. Would you trust the animals? Many animals avoided the Boxing Day tsunami in 2004 because they fled to the hills well before the first waves hit. Many animals can detect R waves and some think that this is what warned the animals to flee in 2004.
Fire Gas pipes can easily be broken in an earthquake. One spark or flame can turn the wreckage of a large earthquake into a furnace. In 1906, San Francisco was hit by a earthquake estimated at 8.3 on the Richter scale. Sixty per cent of the damaged city (520 city blocks) was burnt to the ground in the days that followed.
Tsunami An earthquake with its epicentre under the ocean floor can cause a wave to be formed. Although it may start at only two metres high, it travels at incredible speeds and increases dramatically in height as it enters shallow water. This wave is called a tsunami (pronounced soon-army). In 1998 an underwater earthquake of 7 on the Richter scale caused a 15-metre high wave to hit the north coast of Papua New Guinea, killing an estimated 3000 people. On a larger scale, a tsunami which hit Japan in 1892 killed 27 000 people. The deadliest tsunami in recorded history struck much of Asia (particularly Indonesia, Thailand, Sri Lanka and India) on 26 December 2004. The US Geological Survey estimated that the death toll was about 275 950 people. This Indian Ocean tsunami was estimated to have about 23 000 times the energy of the Hiroshima atomic bomb. The Western Australian coastline was fortunate not to feel any major effects of this tsunami.
Fig 9.3.11 San Francisco after the 1906 earthquake and subsequent fires BANDA ACEH 250 kilometres from epicentre. 30-metre waves surged 12 kilometres inland.
ANDAMAN and NICOBAR ISLANDS 400–1100 kilometres from epicentre. 20-metre waves.
PHUKET 600 kilometres from epicentre. Water receded about 200 metres before 5-metre waves surged 1–2 kilometres inland.
SRI LANKA 1600 kilometres from epicentre. Ocean receded about one kilometre before 5-metre waves reached 1–2 kilometres inland.
INDIA 1850 kilometres from epicentre. Ocean foamed before 5-metre waves raced 1–2 kilometres inland.
AUSTRALIA Over 3500 kilometres from epicentre. Waves reached the coast of Geraldton and Exmouth and the tides rose by 1.5 metres. Port Hedland and Esperance also experienced tidal surges.
302
Fig 9.3.12 One scientist’s estimation of the different heights of the waves that struck Asia on Boxing Day 2004
Unit
9.3
Devastation of the coastline in Thailand caused by the Indian Ocean tsunami of 26 December 2004
Lush vegetation and resorts on the coastline of Thailand on 13 January 2003
Fig 9.3.13 The Thai coast before and after the tsunami. Fig 9.3.14 The number of
PAKISTAN
hours it took for the 2004 Boxing Day tsunami to cross the Indian Ocean
BANGLADESH INDIA
SAUDI ARABIAOMAN Arabian Sea
Chittagong BURMA
Mumbai
YEMEN 6 hours Chennai
Indian Ocean
5 hours
4 hours
Maldive Islands 3 hours
0
SINGAPORE
2 hours 1 hour
Tsunamis can travel at 800 kilometres per hour and reach heights of 35 metres when they hit land, crashing onto the shore and sweeping everything out of their path. People in low-lying areas receive little warning because the first waves caused by the earthquake are no bigger than normal surf. The first real warning is that water rapidly gets sucked out to sea, with the main wave crashing in soon after. The sea can then die down. Survivors often move in to help search for victims and can be swept away by another large wave that follows up to an hour later.
On 28 December 2004, the Wave of Destruction website was set up to cope with the surge of traffic of videos and photos of the effects of the Indian Ocean tsunami. All personal websites around the world were taken offline.
MALAYSIA
Sumatra
Epicentre of quake Cocos Islands (Australian tsunami monitoring station)
800 km
Worksheet 9.9 Tsunami statistics
Wave of destruction Phuket Banda Aceh
SRI LANKA
Location of waves higher than 3.6 m Approximate tsunami travel times, moving at about 800 km/h
Clip
THAILAND
Andaman Islands
SOMALIA
Science
INDONESIA Jakarta
Major tsunami 2004
Indian Ocean
about 280 000 people killed
1998
Papua New Guinea
about 3000 killed
1976
South-west Philippines
about 8000 killed
1964
Alaska
120 killed
1960
Chile
about 1500 killed
1896
Japan
at least 27 000 killed
1883
Explosion of Krakatoa volcano
more than 36 000 killed
1755
Portugal
more than 60 000 killed
303
Earthquakes
9.3
QUESTIONS
Remembering 1 List two reasons why most earthquakes are not felt. 2 List the main types of seismic waves. 3 State which of the seismic waves, P, S, R or L: a are the most dangerous b are up-down waves c are compression waves d pass through the Earth e are the fastest f are the last to arrive g are like surf h travel like a snake i cannot travel through liquid 4 A tremor is an earthquake that can be felt but does little damage. Specify what its value would probably be on both the Richter and Mercalli scales.
Understanding 5 Explain why friction exists at plate boundaries. 6 Use friction to explain what causes an earthquake. 7 Outline the evidence that suggests that the Earth’s core is liquid. 8 Specify the maximum depth the focus can be below the surface. Explain why it can be no deeper. 9 At what value on the Richter scale would you call an earthquake ‘serious’? Explain why you chose this number.
b An earthquake of strength 5 on the Richter scale is double the strength of a 4. c Earthquakes are caused by plates slipping. d The focus of an earthquake is the exact point where an earthquake starts. e Tsunamis are huge when in deep water.
Applying 16 Use a diagram to demonstrate how S waves change an up-down movement in the rock into a side-to-side movement of the surface. 17 Identify examples of: a a longitudinal wave b a transverse wave
Analysing 18 Distinguish between the epicentre and the focus of an earthquake. 19 a Contrast L waves and R waves. b Draw diagrams to demonstrate the action of L and R waves. 20 Distinguish between: a body and surface waves b a longitudinal and a transverse wave 21 Calculate the distance from the epicentre if the time between the P and S waves arriving is:
10 Aftershocks are often more dangerous than the first earthquake. Explain why this is the case.
a 4.0 minutes
11 Explain what causes a tsunami to form and why they are so dangerous to those living on coastlines.
c 3.5 minutes
12 Australia has few earthquakes, yet our neighbours Papua New Guinea and New Zealand have lots. Use the theory of plate tectonics to explain why. 13 Explain where you would need to be for the P and S waves to arrive at almost the same time. 14 Explain what a single seismogram tells us about an earthquake. 15 Copy the following and modify any incorrect statements so they become true.
304
a Aftershocks are huge waves caused by earthquakes.
b 2.2 minutes d 8.1 minutes N 22 Calculate the length of time between the arrival of the P and S waves if the epicentre is this far away: a 6000 kilometres b 1500 kilometres c 3300 kilometres d 900 kilometres N 23 Complete the information about a number of earthquakes given in the table on page 305. To calculate column 4, convert the seconds into a decimal by dividing by 60. N
Unit
Arrival time of S waves (h:min:s)
10:24:00
10:32:00
04:48:20
04:52:50
2:55:21
3:01:21
7:37:03
7.42:33
14:08:34
14:11:46
20:21:02
20:25:50
Time difference (min:s
Time (min)
4:30
30 쎵 60 쏁 0.5 so time is 4.5 min
05:45:10
Distance of epicentre (km)
9.3
Arrival time of P waves (h:min:s)
5.0
11:34:30
6:30
08:12:56
2500
15:21:04
5800
Evaluating 24 There are many video clips or photographs of the effects of tsunamis, but not many of the actual tsunami. Propose an explanation for this.
25 Super quakes are ones that are more than 8 on the Richter scale. a Evaluate the damage that can be expected when superquakes hit. b State how often they occur per year.
9.3
INVESTIGATING
Investigate your available resources (for example, textbooks, encyclopaedias, internet) to complete the following tasks. 1 Find out more about the 1989 Newcastle earthquake—the most devastating earthquake in recent times in Australia. Find out its strength, damage and injury/death toll. Present your findings in an official written report to be sent to the government. L
e –xploring To explore animations of seismic activities and pictures of earthquakes, a list of web destinations can be found on Science Focus 3 Second Edition Student Lounge.
2 a Research in groups how engineers and architects design buildings to withstand earthquakes. b Japanese traditional architecture is designed to withstand frequent earthquakes. Investigate why this type of architecture is ideal for an earthquake-prone country. 3 Examine what you should do if an earthquake hits. Present your findings in an illustrated poster.
305
Earthquakes
9.3
PRACTICAL ACTIVITIES
1 Slinky springs Aim
move hand side to side
waves
paper
To model the movement of P and S waves
Equipment • • • • •
slinky spring dense slinky (smaller diameter) string sticky tape paper
Method
keep hand stationary stick small sheet of paper to spring
move hand in and out
Tape a small piece of paper to the slinky. Part A: Transverse waves 1 Lie the slinky along the floor. Hold the spring at both ends, stretching it lightly. One person should hold their end still at all times. 2 Move one end sideways so that a ripple-like wave moves down the spring. 3 Construct a diagram showing the movement of the paper and in which direction it moves down the spring. 4 Test bigger and smaller waves. Compare their speeds and ‘height’ or amplitude. Part B: Longitudinal waves 1 Quickly move one end of the spring in and out about 30 cm. A compression should move down the spring. Describe what happened to the paper. Part C: Waves in different densities 1 Attach the heavy, smaller slinky to the bigger one and repeat the above experiments. Compare your observations on speed and size when the wave travels from big to small diameter and vice versa. 2 Repeat step 1 above, but attach a piece of string instead of the smaller diameter spring.
306
waves spring
paper
keep hand stationary
Fig 9.3.15
Questions 1 Identify the direction of movement of the paper in the slinky when: a a transverse wave moved along it b a longitudinal wave moved along it 2 Imagine you are an ant standing on the piece of paper in each case. Describe what you would feel. 3 Identify which part of the experiment (A, B or C) best represents: a a P wave b an S wave c an L wave
Unit
9.3
2 Build a seismometer
Questions
Aim
1 Identify which movements caused the seismometers to work.
To construct a working model of a seismometer
2 Explain why the graph didn’t stop after the earthquake did.
Equipment • • • • • •
retort stands bossheads and clamps springs heavy weight adhesive tape felt pen
spring
paper
Method 1 Construct the device shown in Figure 9.3.16.
weight
2 Slowly pull the paper while creating ‘earthquakes’ by thumping the bench on top and at the end.
tape felt pen touching paper
Fig 9.3.16
3 Locating the epicentre Aim
15:06:47
To locate the epicentre of an earthquake
Cairns
Broome
Equipment
15:07:41
• compass • ruler • photocopy of Worksheet 9.11
Alice Springs Brisbane
Worksheet 9.11 Locating the epicentre
h min s 15:13:11
Perth 15:17:47
Adelaide 0
Method
P
1000 km
S
1 Calculate the difference in time between the arrival of the P and S waves for each seismogram.
Fig 9.3.17
2 Use the graph in Figure 9.3.6 to find the distance the epicentre is away from each location.
Questions
Sydney Canberra Melbourne 15:10:37
Hobart
3 Paste the photocopy supplied into your workbook.
1 Locate the epicentre of the earthquake.
4 Use a compass to draw three circles on it with radii equivalent to these distances.
2 Locate its focus.
5 The epicentre is the point or small area where the circles intersect. Mark the point or area (it should be reasonably small) where the three circles intersect.
15:13:49
3 Calculate the time between the arrival of the P and S waves in Broome. N 4 Check an atlas to locate the town most likely to be affected by the earthquake.
307
Unit
9.4
context
Volcanoes
A small volcanic island called Krakatoa, located west of Java in Indonesia, erupted in 1883 and caused the largest explosion ever experienced in the recorded history of humans.
Fig 9.4.1 In the 120 years or so since Krakatoa destroyed itself, pressure from below has steadily built a new island of Krakatoa. The new island has small, regular eruptions.
Science
Clip
Dead or alive? All volcanoes can be classified as either active or dormant. Active volcanoes erupt regularly. Dormant volcanoes are ‘sleeping’—volcanic activity is still present but they have lasted 20 to 5000 years without an eruption. Dead volcanoes are those that cannot erupt. They are often classified as extinct and have had no eruptions for the last 25 000 years.
308
The volcano caused a noise so loud that it could be heard clearly 5000 kilometres away. It also completely destroyed itself, produced waves 40 metres high that travelled for 16 kilometres and killed 36 000 people.
Fig 9.4.2 Ash from Mt Pinatubo in the Philippines blocked the Sun for many days in 1991.
Volcanoes everywhere
Just like a pimple!
There are about 1500 potentially active volcanoes around the world, with some erupting each day. Eruptions are often not noticed, however, as many of these active volcanoes lie under water. These eruptions produce about three-quarters of the total lava erupting from volcanoes each year. There are no active volcanoes in Australia. Mt Gambier in South Australia last erupted about 4600 years ago and can probably be said to be extinct. A long period of inactivity does not always mean that a volcano is extinct. Mt St Helens in the USA was dormant for 123 years until it erupted violently in 1980, blowing 400 metres off its top and killing 57 people.
Most volcanoes occur at the edges of the tectonic plates. Pressure from gases in the mantle squeezes the molten rock upwards. The surface of the Earth can swell like a big pimple until it cannot take any more pressure. It then explodes with lava, ash and steam bursting through the surface. Eruptions may come from a single vent, or from a group of vents. Others take place from long cracks called fissures. The table on page 309 can be used to determine the temperature of the lava.
Science
Clip
Volcanoes in space At 24 kilometres high and with a base spanning a distance equal to that from Sydney to Melbourne, the largest volcano in the solar system discovered so far is Olympus Mons on Mars.
Temperature Above 1150°C
Yellow
1000–1150°C
Orange
900–1000°C
Red
500–900°C
Black
Less than 500°C
9.4
White
Unit
Colour of lava
Science
Clip
Unexpected turbulence Fig 9.4.3 Hot lava and ash spurts from this erupting volcano.
In 1982 a British Airways Boeing 747 flying from Kuala Lumpur to Perth flew through an ash cloud from the eruption of Mt Galunggung in Java. The dust jammed all four engines and the aircraft dropped without any power for many minutes before they could be re-started. Volcanic ash is not visible to radar so the pilots had little warning.
sulfide (rotten egg gas) and steam. Lava flows down the volcano at speeds of less Most volcanoes just release clouds of steam, gas (called than 10 kilometres per hour and slowly fume) and ‘smoke’. The smoke is made up of fine rock cools to form solid rock. dust or ash and rock. Hot volcanic ash, steam and gases Magma is molten rock that forms in a magma form a fast-moving (often 200 kilometres chamber deep under the surface of the earth. per hour) cloud that can reach incredible It is lighter than the surrounding rock because it is heights. Krakatoa’s cloud is estimated to full of gas. The pressure pushes it up until it bursts out have reached a height of 80 kilometres! from a vent. The ash is carried by the winds and When magma reaches the surface it is called lava. eventually settles back to Earth as a thick Lava is made up of magma and gases such as hydrogen blanket. The ash from the 1994 eruption of Mt Tavurvur in Papua New Guinea crushed the nearby town of Rabaul. dust, ash, steam and gas In 79 CE the people of Pompeii, Italy, suffocated on the ash from Mt Vesuvius and were then buried by it! Ash from Mt St Helens landed up to 500 kilometres away. Rain often then turns the ash into a lahar, a river of mud that can devastate anything downstream from it. volcanic bombs Volcanic ash can also travel the Earth in lava the jet-stream winds that exist 30 kilometres side vent up. Here the ash blocks the Sun, making the central vent planet cooler and producing spectacular sunsets. Ash from the 1991 eruption of Mt Pinatubo in the Philippines is thought to have blocked four per cent of the sunlight reaching Earth that year and the dust from Krakatoa changed the colour of Earth’s crust Earth’s crust the sky in England, 10 000 kilometres away!
Volcanic material
magma chamber
Fig 9.4.4 Lava flowing from a volcano
309
Volcanoes
Science
Clip
Why live next door to a volcano? Across the world, about 500 million people live uncomfortably close to active volcanoes. Why? One reason is that volcanic materials break down to form fertile soil that yield good crops for farmers. Living near an active volcano is obviously risky, but it is often the only livelihood available. For this reason, vulcanologists are constantly trying to predict future eruptions of the world’s active volcanoes.
Fig 9.4.5 Mt Pinatubo erupts in 1991.
Gas explosions can destroy parts of a volcano, with large pieces blown out as solid rock, called volcanic bombs. Volcanic bombs also form when hot lava is thrown into the air, landing great distances from the crater. The rock can also block the vent until the gases build enough pressure to clear it once more with another large explosion.
9.4
Prac 1 p. 312
Prac 2 p. 313
QUESTIONS
Remembering 1 State the number of volcanoes in the world and how many of them are active. 2 State what Krakatoa was, what it is now, and why it is famous. 3 State the location of an Australian volcano that is probably extinct.
Understanding
7 Define the following terms: a lava b the magma chamber c lahar d fume e jet stream 8 Copy the following and modify any incorrect statements so they become true.
4 Explain why erupting volcanoes are sometimes not able to be seen.
a Lava is not the same as magma.
5 Explain why volcanoes are more likely to be found at the edges of tectonic plates than in the middle of them.
c Volcanic ash moves more slowly than lava.
6 a Explain why volcanic ash clouds rise. b Describe three different situations in which volcanic ash can be dangerous.
310
Worksheet 9.10 Labelling a volcano
b A dormant volcano is a live volcano. d White lava is hotter than red. e Ash clouds do not travel far.
Unit
Creating
9 Identify five different volcanic materials. 10 Identify what a volcanic bomb is and three ways it can form. 11 Identify what causes the smell that is always around volcanoes and hot springs.
Analysing
16 Construct a timeline of major volcanic eruptions in the last century. N 17 Mt Bigbang is going to erupt in the next day or two. A group of technicians are staying in the area to monitor the eruption. You are a seismologist about to warn the technicians going into the area. Design a presentation that will describe what:
12 Distinguish between a fissure and a vent.
a dangers they may encounter
13 The sound of the Krakatoa explosion took four hours to travel 5000 kilometres across the Indian Ocean. From this information, calculate the speed of sound using the formula: N
b volcanic material that may be coming their way
speed (kilometres/hour) 쏁
distance (kilometres) time (hours)
9.4
Applying
c precautions they should take L 18 Use a scale of 1 cm: 1000 m to construct a diagram of: a Centrepoint tower (305 m) b Mt Everest (8848 m)
Evaluating
c the ash cloud of Krakatoa
14 The edge around the Pacific is often called the ‘Ring of Fire’. Propose a reason for this.
(Hint: you will not be able to do this in your workbook!)
d the height at which commercial aircraft fly (10 000 m) N
15 Justify why volcanic areas are also areas of great earthquake activity.
9.4
INVESTIGATING
Investigate your available resources (for example, textbooks, encyclopaedias, internet) to complete the following tasks. 1 Find where Krakatoa (or Pulau Rakata) is located. On a copy of the map, draw the 5000 kilometre radius circle in which its eruption could be heard. N
e –xploring To explore photos and information about volcanic eruptions, a list of web destinations can be found on Science Focus 3 Second Edition Student Lounge.
2 Research the Roman god Vulcan, from whose name the word volcano comes. Find out what he did and where he was supposed to live. 3 Find out about one major volcanic eruption. Imagine yourself as a reporter and present your findings in a newspaper article. Include: a the date of the eruption b what warnings there were that an eruption was coming c the types of volcanic material the volcano expelled d the damage it caused. L
Fig 9.4.6 The ash cloud from the 1980 eruption of Mt St Helens, USA. The Mt St Helens blast ripped the trees from all the surrounding hills and devastated more than 400 square kilometres.
311
Volcanoes
9.4
PRACTICAL ACTIVITIES Method
1 Volcanic clouds
1 Three-quarter fill the large beaker or container with cold water.
Aim
2 Put 2–3 drops of food dye in the 100 mL flask.
To investigate the formation of volcanic clouds
3 Fill the flask to the very top with hot water (the hotter the better, but take care).
Equipment • • • • •
4 Seal the flask with the stopper.
large beaker pneumatic trough or transparent jar 100 mL flask, rubber stopper with hole food dye hot and cold water
5 Place your finger over the hole and lower the flask carefully into the container of cold water until it is completely submerged. 6 Carefully remove your finger and observe the motion of the hot coloured water.
pneumatic trough or large beaker
Questions 1 Construct a diagram of what you observed. 2 State whether hot water rises or falls when it mixes with cold water.
cold water
hot green
4 Predict what you think would happen when hot ash from a volcano mixes with cold air.
coloured water
5 Propose a likely reason why this happens.
Fig 9.4.7
312
3 Identify what the coloured and clear water represent in this model of a volcano.
Unit
Method 1 In a group, design a 3D model of a volcano. You will need to estimate the length, breadth and height of the volcano. Make accurate and detailed drawings of your design and include the scale of the model.
Aim Build a scale model of a volcano
Equipment • • • • • • •
cardboard scissors blades glue chicken wire newspaper clay
• • • • • •
9.4
2 Build a 3D model of a volcano
2 Write a plan of how you will build a 3D model of a volcano. Your plan should include each person’s task, how long it will take, materials you will need and where you will get them.
plasticine string wood different colours of paint paint brushes ruler
3 Show your design and plan to your teacher before you start building your model. Make changes that will improve your design and plan. 4 Construct your model.
Questions 1 Evaluate your model and how well you worked together. 2 What would you do differently if you could plan and make your model again?
Fig 9.4.8 Some of the materials and tools for making a model of a volcano
313
Unit
9.5
context
Landscaping the crust
The Earth’s crust is built up in layers. The oldest rock is the deepest and the youngest rock and sediment from erosion are on the very top. These layers were originally flat and horizontal but
have since been cracked and folded by plate movement and punctured by volcanoes. Weathering and erosion further shape the landscape to form the land we live on today.
normal fault
reverse fault
Fig 9.5.1 Mt Fujiyama in Japan is a composite volcano made from layers and layers of lava.
Faulty landscaping Faults are fractures in the Earth’s crust caused by the extreme forces from the slow movement of rock in the asthenosphere. Faults can be: • normal • reverse • transcurrent. Normal and reverse faults These faults are roughly vertical and are formed by forces pulling the crust apart (normal fault) or by compressing the crust (reverse fault). Movement along them is roughly up-down, creating a fault scarp. If the rock is hard and weathering slowly, a cliff will form. If the rock is soft, erosion will wear it down to a gentle rise. Sometimes two faults allow a block of rock to thrust up to form a horst or sink down to form graben or rift valleys.
314
transcurrent fault
Fig 9.5.2 Faults are fractures along lines of weakness in the Earth’s crust. The arrows show likely movement.
Transcurrent faults These faults are horizontal and movement along them is in a sideways direction. No mountains are formed but the movement shatters rock along the fault. Smaller rock is easier to weather than larger rock, so heavy erosion creates troughs that often fill with water to form lakes and inlets.
Folding When continental plates collide, the rock of the Earth’s crust is subjected to extreme pressure, both horizontally and vertically. Under these conditions rock acts like modelling clay and begins to buckle and fold without breaking (scientists call this plastic behaviour).
Unit
9.5
hard rock
soft rock
Fig 9.5.3 Normal faults can erode into different landscapes depending on the hardness of the rock.
horsts horsts
graben
weathers to
graben graben
Fig 9.5.4 Horsts and graben are blocks of rock with faults on two sides. The Spencer and St Vincent gulfs in South Australia are examples of horsts and graben (in these cases filled with water). Erosion sometimes moulds them into parallel mountain ranges.
Fig 9.5.5 A transcurrent fault nearly splits Scotland in two. It is partly filled with water and includes the very deep lake, Loch Ness.
The rock can be folded to build mountain ranges or hills. The folded rock can form an arch (called an anticline) or a trough (called a syncline) or may even fold over another fold (called an overfold). Erosion can wear away exposed soft rock or can level the folded layers. When new sediments are laid down on top of these old and eroded folds, an unconformity is created. anticline
overfold
syncline Prac 1 p. 320
Fig 9.5.6 Many mountains and hills are just layers of rocks that have been folded under intense pressure and heat. Synclines, anticlines and overfolds can occur when rock buckles under intense pressure and high temperature.
315
Landscaping the crust
Volcanic landscapes
erosion of folds
Volcanic mountains can be formed in three different ways.
new rock unconformity old rock
Fig 9.5.7 Erosion exposes layers of folded rock and allows new
Shield cones The biggest volcanoes form well away from the boundaries of the tectonic plates and are what vulcanologists call shield cones. These get bigger every time an eruption takes place, with lava cooling as it slowly slides down its sides. The slopes are very gentle and the volcano resembles a shield lying on the ground. Their eruptions are rarely life-threatening but large lava flows do destroy property and agricultural lands. Mauna Loa on Hawaii is an active shield volcano.
layers to be laid on top.
Cinder cones Cinder cones are very common and relatively small, rarely exceeding 300 metres in height. These are piles of hot rock and cinders that spewed out of the vent, only to fall back around it. Composite cones Volcanoes formed above the subduction zones at the edges of tectonic plates are called composite cones. These erupt with explosive force because the magma is too thick to allow the easy escape of volcanic gases. It’s like putting your thumb over an opened bottle of soft drink and shaking it. The release of the magma is the same—violent and messy.
Fig 9.5.8 Uluru (formerly known as Ayers Rock) is the massive tip of a fold formed when layers of sandstone were folded 300 million years ago. The folding was so severe that the layers are 80° to the horizontal.
Science
Clip
Tourist drives to top of world’s tallest mountain! Mauna Loa on the island of Hawaii rises 9169 metres directly from the ocean floor. It is therefore a much higher mountain than Mt Everest at 8848 metres. Only 4169 metres of Mauna Loa is above water, however, and it has a road all the way to the top!
Fig 9.5.9 Mt Kilauea in Hawaii is a cinder cone. The helicopter gives an idea of the size of the volcano and the lava flow.
316
Unit
9.5
volcano extrusive igneous rock
Fig 9.5.10 Volcanic plugs are the remnants of extinct volcanoes. All that now remains is the solidified core of magma. The rest of the volcano has weathered and eroded away. They form spectacular mountains such as this one known as Wollumbin (formerly Mt Warning) which towers over the Tweed Valley on the north-east coast of NSW. The Warrumbungles in western NSW are also volcanic plugs.
Plugs and other intrusions Magma is filled with gases and will always try to force its way up. Sometimes it breaks the surface to explode from a volcanic vent. Magma often cools before it gets to the surface, sometimes in the vent of a dying volcano. Over the years the softer rocks of the walls erode away, leaving a volcanic plug where the vent once stood. If the magma cools below the surface it is called an igneous intrusion. Each igneous intrusion depends on where it eventually cools. Some different types are: • dyke • sill • batholith • laccolith. Prac 2 p. 321
lava
dyke
sill intrusive igneous rock
magma
Fig 9.5.11 Magma and lava form different features depending on where cooling takes place.
Although the hot spot never changes position, the plate above does, carrying the islands to the west. Hawaii is directly over a hot spot now and it too will eventually move in this direction. An underwater volcano called Loihi is already forming east of Hawaii and will become the newest island in the chain. The Australian territories of Heard Island and Lord Howe Island were once located over hot spots. An active line of hot spots is at a latitude of about 40°S, passing under Victoria, Bass Strait, Tasmania and the Tasman Sea. Luckily, its activity is confined to minor earthquakes with epicentres east of Flinders Island.
Science
Clip
Blacksmiths make lava In ancient Greece it was thought that the god of fire, Hephaestus, lived under Mt Etna in Sicily. Here he made weapons for the gods. When he hammered the red-hot iron, fire flicked out of the volcano above.
Moving volcanoes Volcanoes are usually located at the weak edges of tectonic plates. Some volcanoes are nowhere near an edge but are directly over hot spots or plumes. Although there is no obvious weakness in the plate above it, the magma has so much pressure that it can force its way through. The islands of Hawaii are 3200 kilometres from the nearest plate boundary. Underwater volcanoes formed over a hot spot, eventually rising above sea level to form islands. All are different ages. In the west is Kauai, the oldest at 5.5 million years. The youngest is the ‘big island’ of Hawaii, which began forming 700 000 years ago. It is still being extended by lava flows from the continually erupting Mt Kilauea.
Kauai (5.5 million years old)
Oahu Maui (2.5 to 4 million (750 000 to years old) 1 million years old)
Hawaii (brand new to 700 000 years old)
Pacific plate moves hot spot
Fig 9.5.12 Hawaii’s islands are moving west as the plate moves.
317
Landscaping the crust A few hot spots are on land, the largest being Yellowstone National Park in the USA. Here the magma boils underground water that then forces its way to the surface as geysers, steaming lakes and mud pools.
Treasure from below
Fig 9.5.13 Water superheated by the magma below can form spectacular geysers such as this one.
9.5
QUESTIONS
Remembering 1 List three types of faults in the Earth’s crust. 2 State the properties of something that shows plastic behaviour.
Understanding 3 Fault scarps are often very rounded and not sharp like cliffs. Explain why. 4 Horsts and graben exist along the mid-ocean ridges, where new crust is being made. Explain why.
8 Illustrate how Uluru could have formed from a fold. 9 Arrange the letters of the different layers and features shown in Figure 9.5.14 in the order in which they occurred. A B C D
5 Describe what conditions are needed to make rock act in a plastic way.
Fig 9.5.14
6 Outline evidence that indicates that the Hawaiian Islands are moving westwards.
Applying
7 Illustrate with a diagram how hot-spot islands can move and how their volcanoes die.
318
Many natural resources of energy and minerals are found near present or past plate boundaries. Fossil fuels (oil, coal and natural gas) are usually found near weaknesses in the crust. Plate boundaries, smaller faults, folds, hot spots and even the craters of extinct volcanoes have all been found to have stores of fossil fuels. Fossil fuels are plant and animal matter that has decomposed to form a tar-like compound called kerogen. Over millions of years it forms other compounds called hydrocarbons, which is the actual energy store in the fuel. The intense pressures and heat at the weak spots may provide just the right conditions to do the job. Weak spots may also provide a more porous or sponge-like rock for oil to be squeezed into. Ore deposits are also associated with magma bodies that have solidified, causing the metallic minerals to form rich mineral veins. As the global population rises and industrialisation increases, the world’s demand for minerals and energy will grow enormously. This will require an improved knowledge of the relationship between plate tectonics and natural resources.
10 Australians use the natural gas stored deep under Bass Strait. Identify what weakness in the Earth’s crust may have contributed to this gas being available here.
Unit 17 Construct diagrams of how shield, cinder and composite volcanoes are formed.
Analysing
18 The Warrumbungles in western NSW are volcanic plugs. Construct a series of diagrams to demonstrate how they formed.
12 Use diagrams to distinguish between: a a normal and a transcurrent fault b a fault and a fold
9.5
Creating
11 Identify and label the faults, anticlines, synclines and unconformities in the landforms in Figure 9.5.15.
19 Imagine that all the tectonic plates are moving faster than ever before. What would have taken millions of years is now happening in a single day. Australia’s north-west coast is heading for the underbelly of China and Darwin and Hong Kong are about to join.
c a syncline and an anticline d kerogen and hydrocarbons 13 Distinguish between: a a plug and a dyke b a shield and a cinder cone volcano c horsts and graben
Evaluating 14 Propose two possible reasons why fossil fuels are found at weak spots in the crust. 15 Assess the conditions needed for volcanoes to form away from plate boundaries. 16 New Zealand has huge mountains in its South Island and active volcanoes in A the North Island. Propose how these B features were formed.
You are the information officer for the State Emergency Services and have the job of providing information to the citizens of Darwin. You must: • explain why the plates are shifting • describe what the climate will do • describe what events can be expected before the collision • describe what will happen once the continents collide • construct a list of relatively safe cities in Australia and overseas to evacuate to. Create a set of information sheets, a PowerPoint presentation or a script for a TV announcement. Be imaginative, but base all descriptions on what you know about tectonic plates and their boundaries. L
C D E F G
Fig 9.5.15
H I K
J
9.5
INVESTIGATING
Investigate your available resources (for example, textbooks, encyclopaedias, internet) to complete the following tasks. 1 Find out about hot spots that can produce basalt plains instead of mountains. Investigate how they form and where they are located. 2 Find out more about the islands of Hawaii. a Trace a map of Hawaii and its position in the Pacific Ocean. b On each island, locate the volcanoes and label them as active or dead.
3 Investigate the natural gas reserves of Bass Strait. What else is found there, how is it tapped and what processing is needed?
e –xploring To explore animations of the different types of faults, a list of web destinations can be found on Science Focus 3 Second Edition Student Lounge.
c Indicate where Loihi is likely to be and where future islands may form.
319
Landscaping the crust
9.5
PRACTICAL ACTIVITIES 5 Once again use the hacksaw blade or wire to cut in the direction shown by the arrows in each diagram. This is our ‘erosion’.
1 Faults and folds
6 For each feature, draw a cross-section or side view after ‘erosion’. Colour the layers appropriately.
Aim To model faults and folds in the land
7 Look down on the feature as if you are travelling over it in an aircraft. Draw what you see.
Equipment • modelling clay in four colours • a rolling pin • fine wire or a hacksaw blade
Questions 1 Identify which geological feature created the layers in Figure 9.5.17 when seen from the air.
Method 1 Roll the modelling clay flat into 1 cm layers. 2 Make a layered ‘cake’ with the modelling clay. 3 Copy the table below into your workbook. 4 Model each feature shown in the table. To make faults, cut the cake in the direction of the arrows with the hacksaw, or hold the wire tightly with two hands and cut down through it.
a
Fig 9.5.17
c
b
d
Fig. 9.5.16
Geological feature
Syncline (downward fold)
Anticline (upwards fold)
Overfold
Normal fault
Transcurrent fault
Horsts and graben
320
What to build
Before erosion
After erosion
Aerial view after erosion
Unit
9.5
2 Shaping volcanoes Aim To examine the angle of repose of different types of volcanoes
Equipment • • • • • •
funnel retort stand bosshead and clamp 1 sheet of graph paper ruler with millimetre markings materials such as fine sand, coarse sand, flour, fine blue metal screenings, candles (old stumps will do) • matches • protractor • access to a scientific calculator (Note: when material piles up into a cone, the angle that the side makes with the horizontal is called the angle of repose.)
retort stand graph paper
candle
Method graph paper
Part A 1 Set up the funnel as shown in Figure 9.5.18. 2 Place your finger over the end of the funnel and fill with fine dry sand. Remove your finger quickly and let the sand run out. 3 Measure the height of the mound. Use the graph paper to estimate the diameter of its base. Calculate its radius.
height
4 Construct a scale diagram of the side-view (cross-section) of the mound. 5 Use a protractor to measure the angle that the sand makes with the horizontal. 6 Another way is to use trigonometry. Follow these steps. a On your calculator, divide the height of the mound by its radius. The answer should be less than 1. b Push the tan–1 button (push the inverse or shift button first!). c The answer is the angle of repose of the sand. N
angle of repose
radius
Fig 9.5.18
Questions 1 Explain what type of volcano you built in parts A and B. 2 Arrange the materials in order from smallest to largest angle of repose.
7 Put the angle on your diagram.
3 Assess why the angles might differ between materials.
8 Repeat the experiment and calculations for the other samples of sand, flour and blue metal screenings.
4 State whether bigger ‘volcanoes’ have different angles to smaller ‘volcanoes’ of the same material.
9 Make bigger ‘volcanoes’ using two funnel-loads of material and calculate the angle of repose for each.
5 Design and test a model for a composite volcano.
? DYO
Part B 1 Repeat the experiment but make the cone with melted candle wax. Drip a small amount of wax onto the graph paper and allow it to cool. 2 Drip more and more wax, allowing it to cool each time. 3 Calculate the angle of repose of the wax.
321
Unit
9.6
context
Geological time
People have long wondered about how old the Earth is and how it has changed since it began. Using biblical records, some believe that the Earth was created in around 4004 BCE, which makes the planet about 6000 years old. Growth rings in trees have been used to trace
back further in time than this. More recently, other methods have been used to estimate the ages of rocks in the Earth’s crust and how different organisms have changed, developed and died out over millions of years. Scientists now estimate the Earth to be between 4.5 and 4.7 billion years old!
• bones, teeth, shell or a complete skeleton • a mould in the exact shape of the animal. The mould sometimes fills naturally with quartz, limestone or other natural chemicals that harden to form a cast. Occasionally opal fills the mould! If the mould is empty then plaster or molten plastic can be added to make an accurate cast or model of the animal • a footprint or footprints. These can also be filled to make a cast • a mineral petrified ‘replica’ of the bone, shell or even wood. Minerals sometimes slowly replace the original material as it decays away, leaving a stone replica of it. This is called petrification • a ‘picture’ of the animal or plant. Heat may burn away everything except black carbon, which is left as a ‘picture’ of the organism. A carbonised fossil has been formed. Fig 9.6.1 Fossil remains are usually the only evidence scientists have of past life forms. This perfectly preserved baby mammoth was deep-frozen in the permafrost in northern Russia until it was discovered in 1989.
Go to
Science Focus 4 Unit 5.3
Fossils The story of life on Earth is told by its fossils. Palaeontology is a branch of geology that studies them. A fossil is evidence of past life found in a rock—usually sedimentary rock. This evidence may be: • part of an animal or a complete animal preserved by a rare freak of nature. Ancient insects have been found trapped in amber (sap from a plant). Woolly mammoths have been found in frozen soil in Siberia in Russia, so perfectly preserved that they still have flesh, hair and stomach contents! Sabre-tooth tigers have been found in tar pits in Los Angeles and even human bodies have been found preserved in ice or the mud of bogs
322
Fig 9.6.2 An insect trapped in amber
Prac 1 p. 328
Unit
9.6
need to be discovered and then recognised as important. Most fossils will be buried too deeply and too remotely to ever be discovered—others might be discovered by someone who doesn’t understand or care about what they are seeing.
9.6.3 These dinosaur footprints were found in Queensland and have been dated at around 100 million years old.
Fig 9.6.4 The bones of an Icthyosaurus have been replaced by minerals to form this fossil.
a An ammonite dies and falls to the bottom of the sea where it is covered by sediments and protected from being eaten by other animals. The soft parts of its body decay, leaving just the shell.
b More and more sediment covers and squeezes the shell. The shell may remain or be replaced with minerals such as quartz or limestone that seep into it in solution before the original shell dissolves.
c After millions of years, movement in the Earth’s crust may thrust the layer of sedimentary rock containing the fossil upwards to form part of a mountain range.
d Weathering and erosion may eventually wear away some of the rock to expose part of the fossil. Fossils are often found in road cuttings or quarries.
Science
How fossils form Fossils only form under special conditions that preserve the shape of the original organism for long enough for some impression to be left behind. Two specific conditions are: • quick covering of the organism in sediment (dust, sand or mud) that prevents weathering • exclusion of oxygen and bacteria, thereby preventing decay. Finding fossils of long-extinct organisms is extremely rare since most animal and plant remains are crushed or decay too quickly for them to be preserved in the rock they are to become part of. Otherwise, they have died where the rock is of the wrong type for fossil formation. Even when fossils are formed, they can be destroyed by later folding and faulting of the landscape. They then
Clip
Wrong end!
Fig 9.6.5 These ammonite fossils are casts of
In 1870, dinosaur hunter Edward Drinker Cope wrote a report about a plesiosaur— what is known today as a long-necked, short-tailed dinosaur. Cope made an embarrassing error, however—he put the head at the wrong end, to construct a short-necked, longtailed dinosaur!
animals that lived about 100 million years ago. They probably formed via the steps shown.
323
Geological time
Dating fossils Index fossils When a hole is dug, the oldest soil and rocks will generally be at its base while the youngest will be at the very top. Logically, the oldest fossils will normally occur in the lowest layers. Some fossils lived over a comparatively short period of time and were widespread. These fossils are known as index fossils and provide a convenient method of determining the age of that layer of rock. The presence of different species of ammonite, for example, can be used to date various layers of rock around the world to within a million years or so. The presence of more primitive ammonites indicates that a region is older than one Prac 2 containing more evolved ammonites. p. 328
Fig 9.6.7 Fossil tracks in sandstone dated to 1.2 billion to 2 billion years ago
Radioactive dating Rocks contain radioactive substances that gradually change or decay into other substances over a long period of time. For example, uranium is a radioactive substance found in many rocks that slowly changes into lead over time. By comparing the amount of uranium and lead in a rock, the age of the rock may be determined. This type of radioactive dating is used to determine the ages of fossils more than 100 million years old. Using this technique, tiny sand grains found in Western Australia have been estimated to be 4.25 billion years old. A radioactive form of carbon found in plants and animals may also be used to date fossils less than 70 000 years old. Prac 3
Science
Clip
First animal life In 2002, a research team found fossil tracks, similar to those left by corals or worms in sandstone from the Stirling Range, about 400 kilometres southeast of Perth. These rocks are believed to date back to between 1.2 billion and 2 billion years. This would make the fossils twice as old as the generally accepted scientific age for animal life on Earth.
p. 329
Creation of rock Ratio 100% U, 0% Pb
Ratio 50% U, 50% Pb
Ratio 25% U, 75% Pb
U U U U U Pb U Pb U Pb U Pb Pb Pb Pb U U U U Pb U 713 713 Pb U Pb Pb U Pb U U U U U U U million Pb U Pb U million Pb Pb Pb U years years Pb U Pb Pb U Pb U U U Pb U U U U U U Pb U U Pb Pb Pb Pb U Pb Pb U U U U Pb U Pb Pb Pb Pb U Pb U Pb U U U U U Pb Pb U Pb U U U U U U U Pb Pb Pb Pb Pb Pb Pb Pb U U U U U U U U U U Pb Pb Pb U
Fig 9.6.8 Radioactive decay can help determine the age of a rock Fig 9.6.6 A human fossil plaster cast—this unfortunate person died under a layer of volcanic ash after Mount Vesuvius erupted in 79 CE.
324
containing a fossil. Uranium (symbol U) decays to form a new element, lead (Pb). Older rocks will have more lead and less uranium than younger rocks.
Era
Period Quaternary
Cenozoic (recent life) Tertiary
Life
9.6
Scientists now believe the Earth to be about 4.5 billion years old. If the complete history of the Earth were condensed into a year, modern humans (Homo sapiens) would have appeared only in the last five minutes of the year. It is no wonder there is still much to be learned about the past! Despite this, rocks and fossil records have enabled scientists to piece together a history of the Earth in various stages, called eras. Each era is divided into periods.
Many of the animals that evolved over the ages no longer exist—dinosaurs are perhaps the most famous example. In the history of the Earth there have been several times when mass extinctions have occurred in a relatively short space of time. Each extinction allowed other species to emerge and dominate their environment. For example, around 250 million years ago, the trilobites died out and crustaceans became abundant—today, there are over 30 000 species of crustaceans. One, the horseshoe crab, bears some resemblance to the trilobite. A summary of this time scale is shown in the following timeline.
Unit
The geological time scale
Millions of years ago (mya)
Humans (Homo sapiens)
0–2
Mammals and birds become dominant after extinction of the dinosaurs
2–65
Final period for dinosaurs Cretaceous
Small mammals, flowering plants
65–144
Tyrannosaurus lived around 65–68 mya Mesozoic (middle life) Jurassic
Triassic Permian Carboniferous Palaeozoic (ancient life)
Apatosaurus (formerly Brontosaurus) lived around 150–156 mya Dinosaurs and tiny mammals Modern insects New mountains, deserts
144–208
208–248 248–290
Reptiles evolve from amphibians
290–362
Many types of fish, first land animals, amphibians, tree-sized land plants
362–408
Early simple land plants, first insects
408–438
Ordovician
Fish, corals, molluscs
438–505
Cambrian
Worm-like creatures, first vertebrates—eel-like animals, animals with shells (e.g. trilobites)
505–570
Single-celled animals, early sea plants, fungi
570–2700
First signs of life—algae and bacteria
2700–3500
Devonian Silurian
Proterozoic (earlier life) Precambrian
Plant-eating dinosaurs abundant, flying reptiles, first birds
Archaeozoic (primitive life) Azoic (without life)
No life Earth still cooling after its creation
3500–4600
325
Geological time
Fig 9.6.9 This trilobite fossil is 5 cm long and between 250 and
Fig 9.6.10 The horseshoe crab is thought to be a distant relative
400 million years old.
of the trilobite.
9.6
QUESTIONS
Remembering 1 State how old scientists currently believe the Earth to be. 2 List the following eras in order, starting with the most recent: Palaeozoic, Archaeozoic, Cenozoic, Azoic, Proterozoic, Mesozoic. 3 List the periods that make up the Mesozoic era.
c Soft-bodied animals are less likely to form fossils than animals with shells or skeletons. d Fossils are found only under oceans or other bodies of water. e Generally speaking, lower layers of rock in a region contain older fossils. f Fossils of complete animals do not exist.
Understanding
Applying
4 Copy and complete this table.
7 Identify how trees can be used to trace back through time. Period
Span (millions of years)
Quaternary Tertiary
2 63
8 Identify what uranium changes into over time. 9 Identify which radioactive substance may be used to date plant and animal fossils. 10 Identify an example of an index fossil. 11 Identify the period in which: a reptiles evolved b Tyrannosaurus lived c land plants appeared
5 Define the term fossil.
d bacteria evolved from a ‘chemical soup’ in the oceans
6 Copy the following statements into your workbook, modifying any incorrect statements so they are true.
e birds appeared f plant-eating dinosaurs had their heyday
a A dinosaur footprint is not a fossil.
g fish appeared on Earth
b Minerals may replace the shell or bone of an animal to make a fossil.
h sea plants appeared i flying reptiles first existed j dinosaurs last lived
326
Unit 18 Assess what may have happened long ago to produce the tracks in Figure 9.6.10.
b Use arrows to indicate the reign of the dinosaurs and when humans appeared.
9.6
12 a Demonstrate the first three eras and the periods they contain on a scaled timeline.
c Explain why it would be difficult to extend the timeline to include the Precambrian era.
Evaluating 13 Evaluate whether radioactive dating could be used to date a 100 000-year-old fossil. 14 Propose two reasons why a species may become extinct. 15 Older fossils can sometimes be found in rock above newer fossils. Justify how this can be. 16 Rock containing fossils of sea life can be found in areas far from the ocean. Assess how this can happen.
Fig 9.6.11
17 In the year 79 CE, Mount Vesuvius erupted, burying the cities of Herculaneum and Pompeii under molten rock and mud flows. Lava hardened around the human and dog victims. When the bodies rotted away they left human- and dog-shaped spaces, which were later discovered. Propose a method that would produce accurate models of these victims.
Creating
9.6
19 Examine different fossils. Construct a series of sketches that shows what the original animal or plant may have looked like and indicate when it lived.
INVESTIGATING
Investigate your available resources (for example, textbooks, encyclopaedias, internet) to complete the following tasks. 1 Find out about one famous palaeontologist, such as Mary Anning (British), Edward Drinker Cope (USA), or current-day dinosaur hunters such as Patricia Vickers-Rich (Australian) and Ron Clark (South African). Prepare a profile about them, including dates and their contribution to science. L 2 a Find what is meant by the term ice age and when they occurred.
3 Investigate the diprotodon and the giant short-faced kangaroo—two examples of Australian megafauna that lived between 40 000 and 1 600 000 years ago. a Find out more about these and/or other Australian megafauna. b Explain some of the theories as to why these animals became extinct.
b Watch the movie Ice Age and evaluate whether the conditions shown are accurate.
327
Geological time
9.6
PRACTICAL ACTIVITIES
1 Inspecting fossils
• the name of the fossil/skull/skeleton
Aim
• the approximate age or era from which it came
To make detailed observations of different fossils
• what type of fossil it is (remnant, cast, mould, carbonised etc.)
Equipment • • • •
access to a fossils kit a range of skulls and/or skeletons grey-lead pencil eraser
Method 1 Carefully inspect one of the fossils, a skull or a skeleton. 2 In your workbook, carefully sketch what you are inspecting. Include the main features and do not worry too much about all the finer details.
2 Dinosaur fossils Aim To make a fossil of a dinosaur
Equipment • • • • • • • •
clay or modelling clay (to make a mould) a pin a probe or blunt pencil tracing paper or photocopy of the skeleton on page 329 rolling pin or piece of dowel cardboard or shoe-box lid plaster mix water
Method 1 Trace the skeleton shown in Figure 9.6.11 (your teacher may provide a photocopy). 2 Roll out a layer of modelling clay about half a centimetre thick, large enough for a copy of the skeleton.
328
3 Next to your sketch, list the following information if known:
4 Select another fossil/skull/skeleton and repeat.
Questions 1 Identify the conditions that would destroy a skull or skeleton in the wild. 2 Explain how a cast would be made of a fossilised footprint. 3 Identify examples of current-day animals and plants that are unlikely to ever form fossils. Explain why you chose those organisms.
3 Transfer a copy of the skeleton to the modelling clay by pushing a pin through the copy at key points to mark the shape and use a probe to form an impression of the skeleton. 4 Place the modelling clay in a shallow cardboard tray or shoe-box lid that is at least 3 cm deep. 5 Mix up a thick plaster paste, fill the impression with it and allow it to dry overnight. 6 Carefully remove the cast of the ‘fossil’.
Questions 1 If this was a real fossil, propose what material would replace the modelling clay/plaster mix. 2 You have actually made two types of artificial fossil. Describe each one. 3 Identify an example of something more likely to make each type of fossil.
Unit
9.6
3 ‘Radioactive’ cubes Aim To model the radioactive decay of uranium
Equipment • • • •
50 or more small wooden cubes each with one face marked (e.g. with a dot) a cup graph paper
Method 1 Make sure one face of each cube has a distinctive mark (e.g. a dot or a ‘6’).
Number of ‘atoms’ remaining
Fig 9.6.12
Number of tosses
Fig 9.6.13
Questions
2 Imagine that each cube represents an atom of radioactive uranium. These atoms emit invisible particles as they change into lead. Shake the ‘uranium’ cubes in a cup and tip them carefully onto a desk.
1 Plot a graph showing the amount of ‘uranium atoms’ left after each toss. Draw a smooth curve like the one in Figure 9.6.12 through the middle of the group of plotted points. This is called a ‘curve of best fit’. N
3 Cubes that land with the distinctive face uppermost are said to have ‘decayed’ into lead. Remove these from the pile and put them to one side.
2 Use your curve of best fit to determine the number of tosses taken for the original amount of ‘uranium’ to halve. This is called the ‘half-life’. N
4 Count and record how many ‘uranium’ cubes are left (e.g. subtract the number of ‘lead’ cubes that were removed).
3 Compare the half-life for your experiment with that obtained by other groups.
5 Collect the remaining ‘uranium’ cubes and repeat steps 2 and 3 until no ‘uranium’ cubes remain.
4 Try to find out the half-life of real radioactive uranium.
329
Chapter review
CHAPTER REVIEW Remembering 1 Name the scientist who proposed there was once a supercontinent called Pangaea.
12 Explain how slipping plates: a cause earthquakes b often allow volcanoes to appear
2 List the evidence to support his theory.
13 Draw and label a transverse wave.
3 State the theory of plate tectonics.
14 Explain what magma is and why it gets squeezed to the surface as shown in Figure 9.7.2.
4 State at what depth the subduction zone is completely molten and returns to the asthenosphere. 5 State what scientists measure to tell the approximate age of a rock.
Understanding 6 Explain why the Earth’s plates are like toast on soup. 7 Describe how magnetism in rocks suggests that: a the continents were once joined b the ocean floor is spreading 8 Describe how convection pushes tectonic plates around. 9 Earthquakes occur mainly at plate boundaries. Explain why. 10 Describe three different ways in which mountain ranges can form. 11 Describe any volcanic material visible in Figure 9.7.1.
Fig 9.7.2
15 Explain why the temperature near the ceiling of a room is always hotter than that at floor level. 16 P and S waves are refracted. Illustrate what this means. 17 Use a diagram to explain why: a the Mediterranean Sea is being slowly squeezed shut b the Atlantic Ocean is getting wider c the Himalayan mountains are getting higher 18 Explain why volcanic ash rises in the atmosphere. 19 A map of the world in the future will be different to the one we know now. Outline how it will be different and explain why.
Fig 9.7.1
330
Applying
Analysing
20 Identify the waves detected by a seismometer and in what order they will be detected.
27 Distinguish between the theory of continental drift and the theory of plate tectonics.
21 Identify which seismic waves produce these motions at the Earth’s surface:
28 Distinguish between a fault and a fold.
a side-to-side b up-down c rolling 22 Identify which statements are true or false. a The mantle is where most volcanic and earthquake activity occurs. b The crust is thickest under the continents. c Scientists who study earthquakes are called seismologists.
29 a Analyse how the upper mantle can be solid but still able to move. b Identify other substances that are like this. 30 Analyse how density affects the movement of plates.
Evaluating 31 Pangaea is Greek for ‘all earth’. Justify why this is a good name for the original supercontinent and identify the names of its ‘offspring or children’.
d A seismogram shows where an earthquake is.
32 Assess why the mysteries of the ocean floor weren’t discovered until the late twentieth century.
e A tsunami is a wave caused when the epicentre is under the ocean.
33 The ocean floor has been likened to a conveyer belt. Assess why.
f Magma rises because it is full of gas.
34 Propose an easy way of remembering what P, S, R and L waves do.
g A dead volcano will never erupt again. 23 Identify where on Earth the longest mountain range and the highest mountain range are. 24 a Identify which types of animals are more likely to form fossils. b Explain why this is the case. 25 Identify which eras occurred in the following periods: a Silurian b Cambrian c Tertiary d Jurassic
35 Assess why magma rises. 36 Propose why the sides of a cinder cone are steeper than those of a shield volcano.
Creating 37 Construct an argument, based on scientific findings, explaining why the Earth cannot be 6000 years old. Worksheet 9.12 Crossword
Worksheet 9.13 Sci-words
26 Identify a life form that existed in each of the following times: a Devonian b Archaeozoic c Quaternary
331
Ask Sci Q Busters team Foiled again! Squeaky sand Mosquito time Cracking knuckles Saucy stuff
Foiled again!
Squeaky sand
Mosquito time
Foiled again! Hi Q Busters, I have always wondered why aluminium foil is shiny on one side and dull on the other. When mum wraps something for cooking she always puts the shiny side inwards. When I asked her why she said ‘that’s how my mum did it’. First of all, why does aluminium foil have a shiny side and a dull side. And second of all, is there any scientific reason for putting the shiny side inward when cooking? Thanks, Selena Hi Selena, The answer to the first question had us stumped. So, like good scientists we had to do some research. It turns out to be very simple. In the final stage of making aluminium foil, it passes through two rollers as two thicknesses of foil are pressed together. The sides facing each other come out with the dull finish, while the sides in contact with the rolls come out shinier. This process is actually called doubling—making two sheets of foil at once, which is cheaper and quicker. For the second part of your question, we need to look at the science of heating. The shiny side of just about anything is a slightly better reflector of heat than the dull side. Therefore, scientifically, to keep things cold, put the shiny side on the outside—that will reflect incoming heat. To keep things warm, face the shiny side inward towards the hot food—to reflect the heat that is trying to escape back into the food. A more technical answer should look at how something can be heated. There are three methods for heat energy to move: • conduction • convection • radiation. Let’s look at cooking some fish on a BBQ grill. First we wrap it in foil, but which way to face the foil? Put the shiny side inwards? Okay, let’s look at what happens to the heat when we do that. Conductive heating happens when the hot grill is in direct contact with the foil. This depends on the thermal conductivity of the foil (how well heat
332
moves through the material). This is the same no matter which side faces out. Convective heating occurs when hot air moves around the foil. This will be limited by the heat transferred to the fish bundle by the air moving around it and by the temperature difference between the foil and the hot air. This is the same no matter which side faces out. Radiant heating is the absorption of infrared radiation (IR radiation) by the fish bundle from the flames or volcanic rocks of the BBQ. The radiation will act just like light. So if the foil is placed shiny side out it would act like a mirror. But we want to transmit as much IR through the foil as possible! To do that the best way, the dull side should be outward facing to minimise the reflection of IR radiation. In reality, the difference is really, really tiny. Happy cooking! The Q Busters team
Squeaky sand Hi Q Busters, I’m an obsessive surfer. Every day when I run down to the surf the sand makes a squeaking sound when my feet hit it, but only on the dry part. What’s going on here? Dave Hi Dave, The sand does seem to sing or squeal when we push our feet into it. So what’s the science behind it? There are a few requirements for the sand to squeal like this and they include: • smooth well-rounded sand grains • sand all of a similar size • very dry and loosely packed sand. The strange squeaking noise is caused from the friction of the layers of sand rubbing against each other. If it’s packed too tightly it won’t move enough and if it’s too wet the grains will be lubricated.
The sounds produced are at very high frequencies— between 450 and 2500 hertz and lasting for a very short time—roughly a quarter of a second. The sand has to be mainly made up of quartz. This means that polluted sand will not squeak. There’s a beach in Victoria in the Wilsons Promontory National Park actually called Squeaky Beach. It’s also a very good surfing beach. Happy squeaking! The Q Busters team
Mosquito time Hi Q Busters, The other day after school at cricket practice a mosquito, or a lot of them, bit me hundreds of times. I got itchy bite marks all over and the more I scratched them the worse they became. Why do mosquitoes need blood? Hope you know the answer to this and can share it with me. James Hi James, For starters, here’s an interesting fact: it’s only the females that need the blood, and they only need it when they want to lay eggs. At this time, they need a very high protein meal—and that means you. When a mosquito bites you, it inserts a long hollow tube like a needle. It’s actually called a proboscis. It goes into your skin and probes around until they find a blood vessel. It’s usually a capillary they find and then they can start sucking out your blood. Its next trick is to stop the blood from clotting, because if it goes all thick they can’t suck it up.
So they inject about 20 different proteins into your skin near the bite to stop this happening. This lets the mosquito have a nice dinner without you knowing it’s there. The problem is that the mosquito leaves small amounts of its saliva in the wound. This means that when the mosquito has flown away, your body’s immune system begins reacting to that foreign protein. This is when it becomes itchy. The Q Busters team
333
Ask Sci Q Busters team Foiled again! Squeaky sand Mosquito time Cracking knuckles
Cracking knuckles
Saucy stuff
Cracking knuckles Hi Q Busters, I have this friend who sits next to me and he is always cracking his knuckles. It’s very annoying—and you should hear the teacher go off! When I asked the teacher the other day about what causes the knuckle noises, all of the others in the class decided cracking their fingers would be a great idea. We all got detention and our teacher wouldn’t give me an answer. Can you please help? Thanks, Radhika
Saucy stuff Hi Radhika Inside each of your finger joints there is a little sack filled with a liquid. This liquid is called synovial fluid and it’s there to lubricate your joint, letting it slide easily. It also carries nutrients along with gases, such as oxygen, nitrogen and carbon dioxide. When you stretch the finger joint backwards, you also stretch the sack, making it larger. This creates a lower pressure in the fluid, which causes the
gases dissolved in the fluid to come out. The rapid expansion and breaking of the small gas bubbles causes the cracking sound. You will also know that once you crack them you can’t crack them again straight away. This is because your knuckle fluid must re-dissolve some more gases. Hope this helps! The Q Busters team
334
Saucy stuff Hi Q Busters, When I try to put tomato sauce on my meat pies I always have a fight with a tomato sauce bottle and it always wins. It wins because no matter what I do I always end up with a big puddle of sauce on my plate that is three times more than I want. Why is this and how can I beat the bottle? Thanks, Alicia
Hi Alicia,
Imagine that the particles in the tomato sauce are built like a house of cards. They will stand upright so long as there is no sideways force put on them. Tomato sauce is actually what’s called a colloidal suspension. When a sideways force is applied, it acts more like a liquid. As with the cards the suspended particles lose their grip on one another and fall over. Toothpaste is also thixotropic. It is much like a solid when left alone. But when you squeeze it, you apply a sideways force through the tube and it flows much like a liquid.
Now there are things that behave in the opposite way. These are called dilatant materials. These substances get harder when you apply a force. A really fascinating example of a dilatant material can be made by mixing cornflour with water. You can do this at home, as long as you clean up the mess. Start by mixing a small amount of cornflour in a bowl. When you do, you’ll notice a problem when you start mixing in the water. The cornflour immediately turns to an almost solid paste. Keep adding water and stirring until you have a thick, smooth mixture. As you stir, it will clump like a solid. But when you leave it, it will look wet, and when you pour some out of the bowl, it will pour like very thick paint. You can also make it up fairly thick and bounce it like a ball. Now hold it in your hand and slowly move it back and forth. Notice how it now spreads out into a squishy, thickish puddle that runs through your fingers. Happy saucing! The Q Busters team
+
Tomato sauce is a thick paste, not quite a solid, but certainly thick enough that it won’t flow out of a new bottle. However, if you shake the bottle, it then behaves more like a liquid, and will pour. These mixtures that appear to change their behaviour have a special name. They are called thixotropic fluids.
–
+
Subject
Got a question? Email the Sci Q Busters team at:
[email protected]
335
Index Numbers in bold refer to key terms in bold type in the text
A abiotic 192 Aboriginal people 210–12 accelerating universe 259 accommodation (eyes) 106 acetylcholine 131 acid rain 202 acidic substance 91 acids 88–93 actinides 41–2 active sensor 271 adrenal 142 aftershock 302 agricultural run-off 201 air pollution 202 airbags 76 alchemists 62 alkali metals 56 alkaline 56 alkaline earths 57 allotropes 57 Alpha Centauri 266 amber 322 amino acids 196 ammonite fossils 323 amniotic fluid 170 amniotic membrane 169, 170 angle of incidence 217–18 angle of reflection 217 animal droppings 195 animal eyes 105 animals 187 anions 84 anther 156 anthropometry 3, 7 anticline 315 antimatter 256, 277 anvil (ear) 113 aqua regia 93 aquatic 194 aqueous 68 Aristotle 62 arteries 129 artificial elements 63 artificial satellite 270 asexual reproduction 152–4 asthenosphere 283 atomic bombs 261 atomic mass 63 atomic number 36, 42, 48 atoms 35–7, 41–3, 47–9, 192–4, 257
336
auditory canal 112–13 auditory nerve 113 Australia 210–12 autotrophs (plants) 186 axon 130
B backbone 134 bacterial infections 177 basal cell carcinoma 120 bases 90–93 basic substance 91 Bertillon system 4 Big Bang 253, 256–9 Big Crunch 259 binocular vision 104 biofuels 196 biological evidence 21, 22 biometric facial recognition 4 bionic ear 114 biotic 192 birth 171 black hole 264 bladder 161 blastocyst 169, 170 blood glucose 145 blue shift 252 blue super giant 263 body waves 298–9 boiling point 49, 56–8 bonded 37 boundaries (plate) 289 brain 129, 131–2, 144 brain damage 133 brittle 49 budding 154
C cancers 178–9 carbon 193–5 carbon cycle 194–5 carbon emissions 195–6, 200, 202–4 carbonates 92–3 carbonised fossil 322 carnivores 187 cast 322 cations 84 caustic 90 CCTV 23 cell membrane 153 cell wall 153 cells 152 Cenozoic Era 325 central nervous system (CNS) 129–34 cerebellum 132
cerebrospinal fluid (CSF) 134 cerebrum 132 cervix 163 chancres 176 chemical change 67–70 chemical combination 74–6 chemical combustion 74–6 chemical control 142–6 chemical decomposition 74–6 chemical energy 186 chemical equations 68–70 chemical formula 37 chemical properties 62 chemical reactions 43, 67–70 chlamydia 177 chlorophyll 195 chloroplast 153 chromatography 13 chromosomes 152, 153 chunking (memory) 140 cilia 161 cinder cones 316 circumstantial evidence 21 clones 153 closed universe 259 clusters (stars) 261 CNS (central nervous system) 129–34 cochlea 112 collision boundaries 289 colloidal suspension 335 colour 239–43, 252–3 colour addition 240–41 colour blindness 104 colour subtraction 240–41 colour vision 104 combination reactions 74–6 combustion reactions 74–6 comparison microscope 21 complementary colours 241 composite cones 316 composite drawings 3 compounds 36–7 compression (wave) 298 concave lens 226–30 concave mirror 218, 230–31 concentrated 91 concentration 91 condoms 175 conductive heating 332 conductors 48 cones (retina) 104 conjoined twins 171 connecting neurons 130 conservation 204
D Dalton, John 62 dark energy 259 dark matter 258 daughter cells 152 decomposition 75, 195 decomposition reactions 75–6 decomposition temperature 76 deforestation 202 dendrites 130 denitrifying bacteria 196–7 dermatitis 120 desertification 202 deuterium 257 diabetes mellitus 146 diaphragm (contraception) 175 diatomic 74 diatoms 22 dilatant materials 335 dilute 91 diminished (image) 226 dispersion 239 divergent boundaries 280 DNA 6–7, 14, 22, 152 Dobereiner, Johann 62 dopamine 131 Doppler effect 251–2 doubling 332 dry weight 189 ductile 48 dull 49
E ear 112–14 ear protection 114 eardrum 112–13 early settlers 211 Earth, structure 281–303 earthquake shadows 298–9 earthquakes 297–303 ecosystems 186–213 ectotherms 187 effector 125–6, 129, 134, 145 eggs (reproduction) 156, 162–3, 168– 70, 179 ejaculate 164, 168 electromagnetic radiation 266 electron configuration 43, 82 electron shells 43 electronic evidence 23–4 electrons 35, 43, 48 elements 35–7, 36, 56–9, 257 embryo 157, 169–170 embryonic period 170 encephalins 131 endangered (species) 204 endocrine glands 142 endocrine system 143 endoscope 219 endothermic 70 endotherms 187 energy 70, 186–9, 203, 217, 256 energy flow 188 energy levels 43 enhanced greenhouse effect 196, 203 enlarged (image) 226 environmental impact, Aboriginals 210–12 environmental revolution 200 epicentre 297, 299, 302 epididymis 161 era (time) 325 erosion 314–16, 323 eruption (volcanic) 308 EVA (extra-vehicular activity) 272 evidence 20–26 exotic species 204 exothermic 70 expanding universe 251–3 extinction 204 extraterrestrial life 266–8 eye defects 106–7 eye, the 103–8 eyewitnesses 20
F facial recognition 3 fallopian tube 162, 163 false negatives 4 false positives 4 families of elements 56–9
fault (earth) 290, 292, 314–15 fault scarp 314 feedback 125–6 female reproductive system 162–3 femur 7 fertilisation 155, 168–9 fibre analysis 21 fingerprints 4–5, 20 first order consumer 187 fission (cells) 154 fission reaction (nuclear) 261 flagella 156 flagellum 156 flat universe 259 flavour 118 floating plates 283 fluoresce 13 fluorescing inks 14 focal length 228, 230 focus (earthquake) 297 focusing devices 226–31 foetal period 170 foetus 170 folate 178 folded (rock) 292, 314–315 follicle 162 food chain 187 food pyramid 188–9 forensic pathologist 2 forensic science 2 forgery 2, 13–14 fossil formation 323 fossil fuels 196, 203, 318 fossils 281, 322–6 fourth order consumer 187 fragmentation 154 frames (video) 23 fraternal twins 171 freckles 120 fume (volcano) 309
Index
conservation of matter 188 conservative (boundaries) 289 conserved 186 constructive boundaries 289 consumers (organisms) 187 continents 281–3 contraception 174–5 control and sense 103–46 convective heating 332 convection currents 284 convergent boundaries 289 convex lens 226–30 convex mirror 231 coordination 125 copulation 168 cornea 103–4 corpses 7 corrosive 88 counterfeit 13 crime scene units 2 critical angle 218 cross-pollination 155 crust (Earth) 283, 309, 314–18 curved mirrors 226–31 cyan 240–43 cysts 178 cytoplasm 153
G galaxies 251–3, 258–68 gametes 155 gas 68 genes 152 genetic identification 6 geological time 322–6 geostationary satellite 270 global warming 196, 200, 203 glucagon 145 glucose 145, 186, 187 goitre 144 gonads 156 Gondwana 282 gonorrhoea 177 graben (valley) 314–15 greenhouse effect 203 greenhouse gases 203 groups 41, 43, 82
337
H haemorrhage 133 half-identical twins 171 halogens 58 hammer (ear) 113 handwriting analysis 12 hard water 81 hearing 112–14, 129 hearing aids 114 heat 129, 203, 256 helium 257 hemispheres (brain) 132 herbivores 187 hermaphrodites 155 herpes 176 heterotrophs 187 history of science 62–3 HIV/AIDS 176 homeostasis 125 homicide 2 hormones 142–4 horsts 314–15 hot spot 317 HPV (human papilloma virus) 176 Hubble Space Telescope 258 Hubble’s law 253 human growth hormone 145 human reproductive systems 161–71 hydride ion 48 hydrocarbons 318 hydrogen 193, 256 hydrogen ion 48 hydrogen sulfide 309 hydrosphere 201 hydroxides 92 hyperopia 107 hypothalmus 144
I identical twins 171 identification and forensics 2–8 Identikit 3 igneous intrusion 317 implantation 169 impotence 132 impressions 22 incontinence 132 index fossils 324 indicator 91 infections 177 infertility 179 inner ear 112 inorganic chemicals 201 inorganic matter 193 insulators 49 insulin 145 intaglio printing 14 International Space Station (ISS) 272–3 interneurons 130
338
introduced species 204, 213 inverted 226 in-vitro fertilisation 179 ion-drive 277 ionic liquids 81 ions 47–9, 81–3, 277 iris 103–4 island chain 291–2 isotopes 256 IUD (contraception) 175
J jet-stream winds 309
K kerogen 318 Krakatoa 308
L labour (childbirth) 171 lahar 309 land clearing 213 lanthanides 41–2 laser surgery 108 latent fingerprints 20 lattice 37 Laurasia 282 lava 282, 308, 309, 317 Law of Conservation of Energy 186 Law of Conservation of Mass 188 lens 103 lenses 226–31 LHC (Large Haldron Collider) 257 light 217–43, 251–3, 277 liquid 68 lithosphere 201, 283 litmus 91 longitudinal (wave) 298 long-term memory 140 Love (L) waves 300 lustrous 48
M magenta 240–43 magma 290, 309, 317–18 magma chamber 309 magnesium chloride 84 magnetic stripes 283 magnification 226 magnifying glass 229 main sequence star 261 male reproductive system 161–2 malleable 48 mantle (Earth) 283–4 mass number 36 matter 192–4, 256–8 medulla 132 meiosis 156, 168 melanoma 120 melting point 49, 56–8
memory 139–40 Mendeleev, Dmitri 62 meninges 134 menopause 162 menstrual cycle 162–3 menstruation 162 Mercalli scale 300–301 Mesozoic Era 325 metalloids 41–2 metals 41–2, 48–9, 93 Meyer, Julius 63 microgravity 272 microprinting 14 Mid-Atlantic Ridge 282 middle ear 112–13 mirage 220 mitochondria 153 mitosis 152, 168 mixture 37 molecule 37 moles 120 molten 283 molten salts 81 Moseley, Henry 63 motor neurons 130 mountains 282–92, 323 multiple sclerosis 132 mutation 153–4 myelin 130 myopia 107
N nebula 261 negative (charge) 35 negative ion 47, 84 nerves 130–33 nervous control 129–34 nervous system 129–34 neuron 130 neurotransmitters 130–32 neutral 35, 90 neutral substance 91 neutralisation 90, 92 neutron star 263 neutrons 35, 256 Newlands, John 62 Newton, Sir Isaac 239 nitrates 196 nitrifying bacteria 196 nitrogen 193 nitrogen cycle 196–7 nitrogen fixation 196 noble gases 42, 47, 59 non-biodegradable 213 non-metals 41 non-metals 48–9 non-porous 20 non-spontaneous 70 noradrenalin 131
O oblique lighting 13 ocean floor 282–3 ocean plate 290–91 ocean trench 283, 291 odontology 7 oestrogen 162 olfactory cell 117 olfactory nerve 117 omnivores 187, 195 open universe 259 optic nerve 104 optical density 218 optical fibres 219 optical illusion 219 optically active devices 14 optics 226–31 orbits 104 ore deposits 318 organic matter 192 organisms 124, 152 organs 129 outer ear 112 ova 156 ovaries 142, 144, 155, 156, 162–3 overfold 315–16 overgrazing 202 oviduct 162, 163 ovulation 156, 163 ovules 155 ovum 156, 162 oxides 92 oxygen 193
P P waves 298–9 palaeontology 322 Palaeozoic Era 325 pancreas 142, 145 Pangaea 281 papillae 118 paraplegia 132 parent cells 152 parthenogenesis 157 passive sensor 271 penis 161 Penzias, Arno 257–8 period (elements) 41, 43 periodic table 35–7, 41–3, 47–9, 62–3 periods (time) 325 peripheral nervous system (PNS) 130
petrification 322 petrified 322 pH scale 91 pheromones 146 phlogiston 75 photographic identification 3 photon 256 photosynthesis 186, 194–6 physical change 67 physical evidence 20 physical properties 62 pigments 242 Pill, the (contraception) 175 pimples 119 pinna (ear) 113 pituitary gland 142, 144 pixels 241 placenta 170 planetesimals 258 planets 258–68 plants 155–6, 186–7, 196–7, 212 plate boundaries 289 plate tectonics 281–4, 317 plates 281–303 plume 284, 317 PNS (peripheral nervous system) 130 pollen 155 pollen grains 155 pollination 155 pollutant 201 pollution 195–6, 200–205 polyatomic ions 82 polymer film 14 poor conductors 49 population growth 200 porous 20 positive (charge) 35 positive ion 47, 84 Precambrian Era 325 precipitate 69, 80 precipitation 80 precipitation reactions 80–84 pregnancy 168–71 pregnancy test 169 pregnant 169 presbyopia 107 primary colours 240 primary consumer 187 primary rainbow 240 primates 4 principal focus 230 print analysis 12 printing 243 proboscis 333 producers (plants) 186–7 products 68 progesterone 162 protists 154 protons 35, 256
protostar 261 Proxima Centauri 266 psychology 2 puberty 164 pubic lice 177 pulsar 263 pupil 103–4
Index
normal (fault) 314–15 normal (light) 217 nuclear energy 186 nuclear fission 261 nuclear fusion 186, 261 nucleic acids 196 nucleus (atoms) 35 nucleus (cells) 152
Q quadriplegia 132
R radiant heating 332 radiation 203, 332 radio telescope 263 radioactive 324 radioactive dating 324 radioactive decay 324 rainbows 240 ray tracing diagram 227–8 Rayleigh (R) waves 300 rays 217–19 reactants 68–70 reactions 67–70, 74–6, 80–84 real image 226, 227 receptors 118, 125–6, 134, 145 red giant 262 red shift 252 red super giant 263 reflection 203, 217 reflex action 134 reflex arc 134 refraction 217–20, 298 refraction illusions 219–20 refractive index 218 remote sensing 270–72 repetition (memory) 140 retroactive interface 3 reproduction 152–80 reproductive health 174–80 respiration 195, 196 respond 124 responding 124–6, 145 retina 103–4 retrieval (memory) 140 retroactive interference 3 reverse (fault) 314 Richter scale 300–301 rift (valley) 314 rift valleys 290 rock composition 282, 315–16 rods (retina) 104
S S waves 298–9 salinisation 202 salts 80, 81–3 satellite 270 scattering 240 SCI (spinal cord injuries) 132–3
339
science history 62–3 scraping boundaries 289 second order consumer 187 secondary colours 240 secondary consumer 187 sediment pollution 201 seismic wave 297–298 seismogram 298 seismometer 298 self-pollination 155 semen 162 semi-metals 48–9 seminiferous tubules 161 sense and control 103–46 sense receptor 125 sensory memory 139 sensory neurons 130 SETI 268 sewage 201 sexual intercourse 168 sexual reproduction 155–7 sexually transmitted infections 174–7 shadow zone 299 shells 43 shield cones 316 short-term memory 139 sight 103–8, 129 simple ions 82 singularity 256 skin cancer 119 skin conditions 119–20 skull 134 smell 117, 129 sodium chloride 84 soil degradation 202 soil pollution 202 solar system 257 solid 68 solute 69 solution 69 solvent 69 sound 112–14, 251–2 sound level 114 sound wave 251 space tourism 273 space travel 266, 276–8 spectrum 252 sperm 156, 161, 168–70, 179 sperm duct 161 spina bifida 133 spinal cord 129, 132–4 spinal cord injury 132 spine 134 spontaneous 70 spores 154 spreading boundaries 289 squamous cell carcinoma 120 stars 251–3, 258–68, 276
340
stimulus 124, 134 stimulus-response 125–6, 145 stirrup (ear) 113 stomata 194 striations 22 stroke 133 strong acids 88–93 strong bases 90–93 Strutt waves 298 subduction zone 289, 290 sub-orbital flight 274 Sun 261 sunlight 186–8, 194–5, 203, 239 supercontinent 281–3 supernova 263 surface waves 298 synapses 130–31 synclines 315 synovial fluid 334 syphilis 177
T taste 118, 129 taste buds 118 tectonic plates 283 telescopes 230 teratogen 170 terrestrial 194 tertiary consumer 187 testes 142, 156 testis 144, 156, 161 testosterone 162 tetraplegia 132 thalidomide 180 theory of plate tectonics 284 thermal decomposition 76 thermolysis reactions 76 third order consumer 187 thixotropic fluid 335 thyroid 142, 144 thyroid-stimulating hormone 144 thyroxin 144 tidal surge 302–3 time, geological 322–6 tinnitus 113 tongue 118 tool mark 22 total internal reflection 218 touch 118, 129 transcurrent (fault) 314–15 transform boundaries 289 transition elements 41–2 transition metals 42, 59 transpiration 194, 202 transverse (wave) 298 trenches 290–91 tsunami 302–3 twins 171
U umbilical cord 169, 170 unconformity 315 universal indicator 91 universe, the 251–74 upright (image) 226 urethra 161 use of space 270–74 uterus 163
V vagina 163 variation 155 vasectomy 174 vegetative propagation 154 vent (volcano) 308, 309 viral diseases 176 virtual image 226, 227 visible spectrum 239, 252 volcanic ash 289, 309 volcanic bomb 309, 310 volcanic material 309 volcanic plug 317 volcanoes 289–92, 308–10
W warp engines 278 warts 120 water 194 water cycle 193–194 water pollution 201 water table 194 wavelength 251 weak acid 88–93 weathering 314, 323 Wegener, Alfred 281 weightlessness 272 white dwarf 262 white light 239–42 white settlement 210–12 Wilson, Robert 257–8 word equation 68–70, 74–6 wormholes 278 wounds 25
Y yellow 240–43
Z zygote 169
