In Your Body (Under the Microscope)

Under the Microscope

In Your

Body Sabrina Crewe Consultant: Professor Anne K. Camper, Montana State University

Copyright © 2010 by Infobase Publishing All rights reserved. No part of this book may be reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying, recording, or by any information storage or retrieval systems, without permission in writing from the publisher. For information contact: Chelsea Clubhouse An imprint of Chelsea House 132 West 31st Street New York NY 10001 Library of Congress Cataloging-in-Publication Data Crewe, Sabrina. In your body / Sabrina Crewe ; consultant, Professor Anne K. Camper. p. cm. -- (Under the microscope) Includes index. ISBN 978-1-60413-825-2 (hardcover) ISBN 978-1-4381-3369-0 (e-book) 1. Microorganisms--Juvenile literature. 2. Bacteria--Juvenile literature. 3. Microscopy-Juvenile literature. 4. Human body--Juvenile literature. 5. Microscopes--Juvenile literature. I. Title. QR57.C744 2010 579--dc22 2009050353 Chelsea Clubhouse books are available at special discounts when purchased in bulk quantities for businesses, associations, institutions, or sales promotions. Please call our Special Sales Department in New York at (212) 967-8800 or (800) 322-8755. You can find Chelsea Clubhouse on the World Wide Web at http://www.chelseahouse.com Text design by Sabine Beaupré Illustrations by Stefan Chabluk Originated by Discovery Books Composition by Discovery Books Cover printed by Bang Printing, Brainerd, MN Book printed and bound by Bang Printing, Brainerd, MN Date printed: May 2010 Printed in the United States of America 10 9 8 7 6 5 4 3 2 1 This book is printed on acid-free paper. All links and Web addresses were checked and verified to be correct at the time of publication. Because of the dynamic nature of the Web, some addresses and links may have changed since publication and may no longer be valid. Acknowledgments We would like to thank the following for permission to reproduce photographs: © Bärbel Stecher and Wolf-Dietrich Hardt, Institute of Microbiology, ETH Zurich/SNF/Stecher et al. PLoS Biol 5(10): e 244: p. 27 top; Dennis Kunkel Microscopy, Inc.: pp. 7, 11, 19, 23, 26; Science Photo Library: pp. 5 (Ralph Eagle), 8 (Power and Syred), 10 (A. B. Dowsett), 12 (David Scharf), 13 (Biophoto Associates), 14 (David Scharf), 15 (Andrew Syred), 16 (P. Motta, University La Sapienza, Rome), 17 (David Scharf), 18 (Steve Gschmeissner), 20 (P. Motta and F. M. Magliocca), 21 (F. Carpino and P. Motta, University La Sapienza, Rome), 22 (M. A. Ansary), 25 (NIBSC), 27 bottom (P. Ferguson, ISM); Shutterstock Images: pp. 4 (LeahAnne Thompson), 9 (Philip Dyer), 24 (Axel Kock), 29 (Raia).

Contents The World Inside You

4

Cells Under the Microscope

6

A Look at DNA and Genes

8

Bacteria in the Body

10

A Layer of Skin

12

Life on Your Head

14

Inside Your Mouth

16

Into the Bloodstream

18

Digesting Your Food

20

Worm Host

22

Invader Viruses

24

The Fight Against Microbes

26

Size and Scale

28

About Microscopes

28

Micro-Detective

29

Glossary

30

Explore These Web Sites

31

Index

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Some words are bold the first time they appear in the text. These words are explained in the glossary at the back of this book.

The World Inside You Take a look in the mirror. You are very familiar with what you see there—your hair, your eyes, and the shape of your body. But you probably don’t spend much time thinking about the inside of your body. Nor do you put your body under the microscope and look at it up close. If you did, you would find that your body is a world of its own. It is made up of trillions of microscopic parts called cells.

Microscopic life The cells are just the beginning, however. You may think you are the only thing living in your body, but you are not! An incredible number of microscopic living things inhabit your body along with you. Organisms are living things, and living things too small to see with the human eye are called microorganisms. These include microanimals so tiny that they go unnoticed on your skin. Even smaller are the microorganisms 

we call microbes. Microbes include bacteria, protists, microfungi, and viruses. We’ll find out about all these things in this book.

Journey around your body We are going to take a tour of the human body so you can discover the world of living things that make their homes inside you. Before we do that, let’s take a look at the cells you are made of and find out how they make you what you are.

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Micro-Fact You are made of about 100 trillion cells. And for every single one of those cells, there are ten microbes in your body!

When things are magnified, you see them in a different way. This is part of an iris, the colored part of a human eye. The blue pool at the bottom is the pupil, which is the black circle in the center of your eye that is actually a hole.

Cells Under the Microscope Cells are the units that all living things are made of. We’ll be seeing a lot of cells as we travel around the microworld of your body. That’s because all parts of you—from your hair to your toes— are a mass of microscopic cells.

Cell structure

The organelles of this human cell include the nucleus, which controls the cell. The ribosomes produce protein, which cells are made of. The mitochondria process oxygen and food to make energy for their cell.

Whether a cell is in a strand of your hair or part of a toe muscle, it has the same basic structure. You can see the basic cell parts in this diagram. cell membrane cytoplasm

nucleus

other organelles

ribosomes

mitochondria

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Micro-Fact Some human cells live for just a day, while others last for years.

The membrane holds the cell together and protects it. It is filled with a substance called cytoplasm, which contains various smaller parts, or organelles. Each type of organelle has a particular job to do to keep the cell working properly. The headquarters of the cell is called the nucleus. You’ll find out more about the nucleus soon.

These are nerve cells, or neurons— the type of cells that make up the nervous system. The nervous system carries messages around the body. Messages travel through strands that connect neurons to each other and to other parts of the body, such as muscles.

Life of a cell Things are always changing in your body. Every second, some cells are dying and others are being made. Where do the new ones come from? Many cells reproduce themselves simply by dividing. First the nucleus splits in two. Then the cell stretches in the middle and splits, with each nucleus becoming the center of a new cell. 7

A Look at DNA and Genes So how does a cell in your tongue know to look and act like a tongue cell? Why doesn’t it become a piece of knee or stomach? The answer lies inside the nucleus of every cell. Let’s take a look under the microscope.

Nucleus in control These are human chromosomes like the ones inside all the cell nuclei in your body. They have been magnified about 10,000 times. Your cells contain two sets of chromosomes, half of them from your father and half from your mother. The chromosomes carry DNA arranged in the patterns that form your own special genes.

We read earlier that the nucleus controls the cell. What does that actually mean? It means the nucleus directs the functions of the other organelles. But the nucleus also contains instructions—a type of recipe—that the cell follows when it develops. It’s how the cell “knows” what to be.

Chromosomes and DNA The packages in the nucleus that hold this vital information are called chromosomes. These are tightly coiled strings of molecules of

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a substance called DNA, which is short for deoxyribonucleic acid. DNA is made of several different chemicals.

Genes

How Small Is Small? Scientists believe that if you stretched out a string of DNA from just one chromosome, it would be about 1.25 inches (about 6 centimeters) long. That may not sound very long. But the string is packed into a chromosome only 1 micrometer wide, and 1 centimeter is 10,000 micrometers!

The way the strings of DNA are arranged is the key to making a cell what it is. In fact, DNA makes you who you are. Stretches of DNA molecules form patterns called genes. Each gene, or pattern, holds the information every cell needs to develop and function. When new cells form from existing cells, the information is passed to the new cell because the chromosomes copy themselves. Genes are passed from parents to children. Because they have similar gene patterns, people in the same family often look alike. 9

Bacteria in the Body We already read that there are different kinds of microorganisms that live in and on your body: microfungi, tiny animals, and even tinier bacteria and viruses. Let’s learn about bacteria, because we’re going to find them everywhere!

What is a bacterium? A bacterium is a living thing, like an animal. But Escherichia coli there are several important (E. coli for short) is a differences. Bacteria have bacterium that lives in only one cell, and it is people’s intestines. It is simpler than the human usually a good bacterium, but some kinds of E. coli cause one we looked at earlier. food poisoning. You can see that Unlike plants and animals, the bacterium in the center is bacteria reproduce by dividing, and it will soon separate into two cells. These bacteria simply dividing in two! have been magnified Bacteria that live in or about 26,000 times. on people absorb food from whatever part of the body they call home. This could be the oil on your skin or the food in your stomach.

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Good bacteria Bacteria can be very useful as they process their food—in fact, we couldn’t live without them. Out in the world, they digest waste, such as dead plants, and turn it into nutrients. Inside your body, many bacteria help digest your food. Groups of bacteria inside your body and on your skin also help fight off germs.

Bad bacteria Some bacteria that live on our bodies are harmful, however. Microbes that make us sick are what we call germs, but scientists call them pathogens. Several common pathogens are bacteria that find their way into or onto our bodies. They may enter in the food or water we consume, or they may be in our environment. Pathogens release chemicals that harm us instead of help us. These chemicals, or toxins, can destroy cells or cause food poisoning. 11

Micro-Fact Some bacteria can divide and multiply several times in just one hour.

This image shows several kinds of bacteria, most of which live on our skin. Many bacteria are shaped like a straight rod, while some are twisted. Others are ball-shaped. Some have flagella (little tails that help them move around). You can see that some of the bacteria in this picture are dividing to reproduce themselves.

A Layer of Skin It would be impossible for our bodies to exist without the layer of skin that covers us. Skin keeps our insides in and protects them from the Micro-Fact outside world. It is a barrier against hot and cold weather, Every square inch of water, and the knocks and skin contains 30 million bumps of daily life. cells. Between 10,000 and 1 million microbes live on each of those square inches.

Defense and attack Skin is also the first defense your body has against pathogens that attack you, such as bad bacteria. Sweat contains chemicals that help fight off pathogens. Our skin is home to about 1,000 different

Staphylococcus epidermidis bacteria live on human skin. They cluster together in colonies like the ones you see here. Staphylococci measure about 1 micrometer across. These have been magnified 8,000 times. 12

Microfungi

types of bacteria. Most are harmless, and some help protect our bodies. The bacterium Staphylococcus epidermidis, for example, lives all over the body. It can protect us from a similar bacterium, Staphylococcus aureus, which causes skin infections and other diseases.

When you see fungi growing outside, they look like plants— mushrooms are a fungi, for example. But fungi are different from plants. They spread threads called hyphae across the food source they live on. Fungi with microscopic hyphae are called microfungi. Some microfungi, like this one, live on human skin. This fungus causes athlete’s foot. You can see the hyphae (orange) spreading among the flakes of skin.

Animals on your skin There are several microanimals that can live on you or feed on your skin. These include several types of mites. The female scabies mite actually digs into the skin to make tunnels! She lays her eggs as she goes, and these eggs soon hatch to produce more mites. Scabies mites cause a rash and terrible itching. 13

Life on Your Head You probably know about lice, even though you may not have seen one. Lice are very small insects that like to live in our hair.

Dribbling lice People with lice infestations have very itchy scalps. The itch is caused by dribbling lice! To get food, lice puncture the skin of the scalp with their mouthparts and suck out blood. As they feed, lice drool liquid, which is like the saliva in your mouth. This louse dribble irritates most people’s skin and makes them itch.

Lice hold on tight by wrapping their claws around your hair. You can see that this louse has already attached an egg to the hair.

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Sticky nits Females lay eggs, called nits, once a day. They make sure the nits stick to a person’s hair by covering them with glue. The eggs look like tiny white specks, and they are just visible if you look carefully. After about a week, the nits hatch, and out come new lice.

Catching and killing lice

Micro-Monster Almost everyone has eyelash mites living in the hair follicles (tiny holes) from which their eyelashes grow. The mites feed on skin oils and the dead skin around our eyes. This picture shows the tails of eyelash mites sticking out of a follicle next to an eyelash (right). In real life, eyelash mites are 0.25 millimeters long. These have been magnified 139 times.

It’s easy to pick up lice from other kids at school if you have your heads close together. The lice simply crawl from one head to another. There are special shampoos that can kill lice. You need to use a fine-tooth comb to dislodge the sticky nits.

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Inside Your Mouth Lots of stuff gets into your body through your mouth, and a lot goes on there. It’s quite a center of microscopic activity!

Germ Barriers Your mouth has cells that are tightly packed together, which makes it hard for the pathogens you breathe in to get through to cells underneath. Your saliva, like your sweat, contains chemicals that fight pathogens.

Your tongue It’s fun to take a close-up look at your tongue. It looks pretty smooth until you put it under the microscope. Then you see that your tongue is covered in small lumps called papillae. Some contain rounded taste buds, which you use to taste your food. Other papillae are spiky and help hold onto food and move it around. The papillae also let you know if your food is too hot or too cold. In this photo of a person’s tongue, you can see the larger, rounded papillae that contain tastebuds. In between are the spiky papillae that process your food.

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Biofilm on Your Teeth Teeth are covered in hard material called enamel, which is made of calcium and other minerals. Enamel is tough so you can bite and chew food without breaking your teeth. You’ve probably heard plenty of times how important it is to keep your teeth clean. If you don’t, they get covered in plaque and start to decay. Under the microscope, we discover that plaque is actually a slimy substance, called biofilm, with bacteria in it. Some of the bacteria produce this slime to help them stick to your teeth. Some biofilm is a good thing— it protects your teeth from pathogens. But if you let too much plaque build up on your teeth, the bacteria will eat away at the enamel and cause your teeth to decay.

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Into the Bloodstream We’re going to take a look at the amazing system called the bloodstream. It is a transportation network running through your body, carrying blood to every part of you.

What is blood made of? The liquid part You can see of blood, called red blood cells and plasma, is mostly white blood cells water, but it also contains traveling through this blood vessel nutrients. The main job of in the liver. The plasma is to transport three types blood is carrying of blood cells: platelets, red blood nutrients and oxygen. cells, and white blood cells. Platelets are useful when you bleed. They thicken up, or clot, at the wound and stop the bleeding. That’s how scabs form over cuts. White blood cells are the body’s defenders against infection and sickness. We’ll learn more in a while about how they defend your body.

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Protozoa How Small Is Small? A red blood cell measures about 7 micrometers across. A drop of blood 1 cubic millimeter in size can hold about 5 million red blood cells.

Red blood cells Most of your blood cells are red blood cells, and they give your blood its color. Their job is to deliver oxygen and remove waste. When blood travels to the lungs, red blood cells pick up oxygen from the air you inhale. They travel around the bloodstream, releasing oxygen to all the cells that need it. Red blood cells also pick up waste from the cells in the form of carbon dioxide. They carry the carbon dioxide back to the lungs, where you breathe it out and get rid of it. 19

Sometimes, microbes get into our blood. They may belong to a group of organisms called protozoa, which are animal-like protists. Most protozoa catch or find food, but a few are parasites, which means they absorb food from a host. If that host is you, the protozoa are likely to make you sick. Sleeping sickness, dysentery, and malaria are all illnesses caused by parasitic protozoa. The protozoa below, in amongst red blood cells, are called trypanosomes, and they cause sleeping sickness. The green threads are their flagella.

Protozoa, such as these Giardia lambia, can live in the small intestine. Giardia lock onto the intestine wall with suckers and feed there. Unfortunately, they can make you very sick, too!

Digesting Your Food

If you’re looking for bacteria, you can be sure to find them in your colon. The colon is also called the large intestine, and it is home to more bacteria than any other part of your body.

Follow the food After you swallow your food, it heads down a tube called the esophagus to get to your stomach. Your food is churned up, or digested, in the stomach and then processed further in the small intestine. The small intestine extracts nutrients from the food and passes them into the bloodstream. 20

The colon gets the food next. By this time, what’s left is a liquid containing lumps of stuff your body can’t digest. The colon absorbs the liquid for your body to use. The rest will be turned into waste that leaves your body when you go to the bathroom. But first, the good bacteria in your colon will go to work.

Micro-Fact About 30 percent of your feces (poop) consists of bacteria from your colon.

Bacteria at work These good bacteria are often called intestinal flora. They digest food your stomach can’t handle. For example, vegetables and fruits contain nutrients we need but can’t process ourselves. The bacteria in our colon release the nutrients for us as they feed on these foods. Bacteria have other jobs in the colon, too. As they feed, they produce acids and other substances that stop bad bacteria multiplying. Intestinal flora even make vitamins for your body! A peek into the colon shows clusters of bacteria (pink) living on the intestinal wall.

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Worm Host

The mass of white-colored roundworms above was found in a section of intestine. The larvae of these worms can leave the intestine and travel around the body, causing sickness.

As you read earlier, parasites are organisms that survive in or on a host by feeding off it. Some parasites in the human body are animals. It’s hard to believe that you might actually have animals living inside you, but it’s true! Scientists say half the people in the world have worms living in them.

Roundworms Some worms are microscopic when they are larvae, or newly hatched worms. They may stay microscopic, such as the roundworms that live in your blood. Others can grow very big, such as the large roundworm. It lives in the small intestine and grows to be 1 foot (30 centimeters) long.

How Small Is Small?

Pinworms By the time you turn twelve, it’s likely you’ll have had some pinworms living in you. They feed on bacteria that live in digested food. This is the stuff that has

Pinworms can be up to 0.5 inches (13 millimeters) long. So when they come out to lay their eggs, they are visible to the human eye. 22

passed through the colon and is ready to leave your body. Yes, pinworms are worms that live in your poop. The females wriggle out at night to lay their eggs on your skin. They also deposit a substance that makes the skin itch, which is usually how people know they have worms.

Hookworms

Micro-Monster Tapeworms are parasites that people can get from dirty food or water or from meat that is not fully cooked. This tapeworm would grow by attaching to your small intestine with the hooks and suckers on its head. There, some tapeworms grow to 20 feet (6 meters) long! Some smaller tapeworms can travel anywhere in the body through the bloodstream. They can get into muscles, eyes, and even the brain.

Most worms arrive in your body in food or water, but a hookworm enters by burrowing into your skin as a larva. They get into the bloodstream, then into the intestine. The adult worm, about 0.4 inches (10 millimeters) long, feeds by sucking blood from the intestinal wall. 23

Invader Viruses Viruses are unlike other microbes. Instead of being made of living cells, they are simply Micro-Scientist a package of chemicals. Scientists who study Scientists say that they are microorganisms and cells not actually organisms, are microbiologists. Some because they can’t grow microbiologists, called or feed. Instead, they virologists, study viruses reproduce themselves by and how they damage cells invading cells of a host. The and make people sick. host could be a plant, animal, protist, or even a bacterium.

How host cells make more viruses So how does this work? You remember reading about DNA in your cells. A virus also has DNA or similar

This is a picture of what a Swine flu virus would look like if you opened it up. The coiled stuff in the center is the DNA it injects into host cells to make copies of itself. 2

material that it releases into its host. Because it has received these genetic instructions, the host cell is tricked into reproducing the virus!

These measles viruses have reproduced inside a cell and are coming out, or budding. They will travel to other cells to infect them and multiply again. Measles is very infectious and gives people a fever and a rash.

How viruses spread The newly made viruses emerge from the host and go on to infect other cells. Viruses can travel in your blood to infect other cells in your body. They can leave your body in a sneeze or a cough and travel through the air to infect other people. Viruses can also be carried around by insects.

cell

How Small Is Small?

Effects of viruses Viruses destroy the cells they invade when they multiply. As they multiply and destroy the cells, many viruses spread diseases, such as measles or flu.

Coronaviruses, which give people colds, are 100 nanometers across. You’d have to magnify them a million times to make them about the size of this period. 25

The Fight Against Microbes Virologists and other scientists have developed amazing drugs that help us fight pathogens. But some of the best defenses against viruses, bacteria, and parasites are already inside us.

Inner defenses The human body has an immune system made up in part of white blood cells called lymphocytes. These cells recognize pathogens and release chemicals to kill them. The chemicals that our body makes to protect itself are called “antibodies.” Other white blood cells, called Macrophages phagocytes, work to defend and monocytes are your body, too. Phagocytes types of phagocytes, find and eat foreign cells. which defend your body by attacking foreign cells. They also help lymphocytes In this photo, a macrophage find invaders. (blue) is engulfing E. coli bacteria (yellow). The green shape is a monocyte.

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Vaccinations Sometimes our bodies need help from outside, such as vaccinations to protect us against disease. Vaccinations work in a peculiar way. They give us a little dose of the disease we don’t want to get. It’s just enough to get the immune system working, but not enough to make us sick. The vaccine makes the immune system produce antibodies that will protect the body in the future.

Intestinal flora (the small green dashes) are battling against Salmonella bacteria (the red shapes) that are trying to attack the intestinal wall (blue). The flora are part of the body’s defense against sickness.

Antibiotics “Antibiotic” is the name we give to a drug that fights harmful bacteria. Many antibiotics are made using bacteria or microfungi. One example is penicillin, a chemical produced by the microfungi Penicillium. Penicillin and other antibiotics made from this fungus can fight a wide range of infections and illnesses. Antibiotics can kill most bacteria unless the bacteria get used to the antibiotic. If this happens, the bacteria can fight off the drug. Then the antibiotic loses its power. 27

The yellow threads are dead remains of Staphylococcus aureus bacteria (red) that have been attcked by the antibiotic drug ceftazidine.

Size and Scale In this book, we measure some things in millimeters and even smaller measurements. This is because inches are just too big for measuring microorganisms and microscopic parts of things. Millimeters are pretty small, and micrometers and nanometers are so tiny that they are impossible to see with the naked eye and hard to imagine. There are more than 25 million nanometers in just one inch! 1 inch = 25.4 millimeters 1 millimeter = 1,000 micrometers or 1,000,000 nanometers 1 micrometer = 1,000 nanometers Only the smallest of microbes are measured in nanometers. Some of these, such as viruses, have to be magnified hundreds of thousands of times before we can see them. Other microorganisms are huge compared to viruses, but we still need to magnify them to see them clearly.

About Microscopes Many of the images you have looked at were produced using an electron microscope. Electron microscopes can magnify things many thousands of times, so they are used to magnify viruses, bacteria, and tiny parts of cells. At home or in school, we use optical microscopes. They usually magnify things anywhere between 20 and 1,000 times, depending on the lenses you are using. It’s always fun to take an everyday object, like a hair from your head or a leaf from the yard, and look at it under the microscope. Some of the images we have seen are made by optical microscopes with cameras attached. 28

Micro-Detective .

Hair Stare We saw some magnified hairs earlier. Now let’s take a closer look at one of your own hairs. You will need a microscope and the help of an adult. Take a hair from your head. Ask an adult to help you cut the strand of hair at a diagonal. Now look at your hair under the microscope. You should be able to see the layer of pigment inside that gives your hair its color. If you have dark hair, ask a person who has lighter hair if you can look at one of their hairs under the microscope. If your hair is fair, compare it with someone else’s dark hair. What are the differences? What about the differences between thin and thick hair, or curly and straight hair? You could take a look at some other kinds of hair: maybe one from your eyebrow or arm, or even an eyelash. See what differences there are between them when you look at them under the microscope.

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Glossary antibiotic—medicine used to fight infections and illnesses caused by bacteria bacteria—microorganisms with only one cell that are the smallest and most numerous life-forms on Earth biofilm—film made of bacteria and other microbes that forms on surfaces in damp places cell—tiny unit that all livings things are made of chromosome—unit in the nucleus of a cell that contains strings of DNA flagella—whip-like tails that protozoa and bacteria use to swim gene—DNA patterns in chromosomes that form sets of instructions for a cell to follow hyphae—threads that most fungi use to grow and spread through their food source immune system—body’s network of cells and antibodies that fights off infection and sickness infestation—presence of a large number of pests, such as insects or bacteria larva—stage of an insect after it has hatched from an egg but is not yet an adult. Larvae is the plural of larva. microanimal—tiny bug or other animal too small to be seen clearly without a microscope microbe—microorganism that is not a microanimal. Microbes also include viruses even though they are not really organisms. microfungi—fungi that are microscopic or are made up mostly of microscopic parts. Fungi are organisms similar to plants but with no ability to make food, so they live on other organisms (living or dead). micrometer—measurement of length that is one-thousandth of a millimeter microorganism—any living thing that is too small to be seen properly without a microscope mite—tiny creature related to spiders, many of which live on animals, plants, or food 30

molecule—microscopic part that makes up all living and nonliving things. All cells are made of molecules. nanometer—measurement of length that is one-millionth of a millimeter nucleus—part of a cell that controls the cell’s form and functions nutrient—substance that is a building block for living things and helps them grow and stay healthy organelle—one of the parts inside a cell, such as the ribosome, each of which has its own function organism—any living thing, such as a plant, animal, or bacterium parasite—organism that lives on or in another living thing and feeds off it pathogen—microbe that causes sickness or disease protist—usually single-celled microorganism that lives in water or damp places protozoa—protists that are similar to animals virus—microbe that can only multiply by infecting living cells

Explore These Web Sites Cells Alive! Cell Biology http://www.cellsalive.com/toc_cellbio.htm Find out more about your body’s cells on this animated Web site. The Immune System—Defending our Bodies http://nobelprize.org/educational_games/medicine/ immunity/index.html Discover a lot about phagocytes and lymphocytes and play a game in which you can fight an invasion of bacteria! 31

Index animals, 10, 11, 22, 24 antibiotics, 27 antibodies, 26, 27 bacteria, 5, 10–11, 17, 22, 24 in colon, 20, 21, 27 Escherichia coli, 10, 26 functions of, 11, 13, 21, 27 killing, 26, 27 Salmonella, 27 shape of, 11 on skin, 11, 12 staphylococci,12, 13, 27 biofilm, 17 blood, 18, 19, 22, 23, 26 bloodstream, 18–19, 20, 23 brain, 23 cells, 5, 6–9, 16, 19, 23 bacteria, 10 blood, 18, 19, 26 neurons, 7 nucleus, 6, 7, 8 numbers of, 4, 5, 12 parts of, 6, 7, 8 viruses and, 24, 25 chromosomes, 8, 9 colon, 20, 21, 23 digestion, 11, 20–21 DNA, 8, 9, 24 eyelashes, 15 eyes, 4, 5, 23

food for bacteria, 10, 11, 21 for fungi, 13 for humans, 10, 11, 16, 20, 21, 22, 23 for microanimals, 13, 14, 15 food poisoning, 10, 11 fungi, 13, 27 genes, 8, 9 Giardia lambia, 20 hair, 4, 6, 14, 15, 29 immune system, 26, 27 infection, 13, 18, 25, 26 insects, 25 intestines, 10, 20, 21, 22, 23, 27 larvae, 22, 23 lice, 14–15 microanimals, 4, 10, 13, 22 microbes, 5, 11, 24 in blood, 19 measuring, 28 on skin, 12 microfungi, 5, 10, 13, 27 microorganisms, 4, 10 measuring, 28 microscopes, 4, 8, 16, 17, 28 mites, 13 eyelash, 15 scabies, 13

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mouth, 16 muscles, 6, 7, 23 nervous system, 7 nits, 14, 15 nutrients, 11, 18, 20, 21 oxygen, 6, 18, 19 parasites, 19, 22, 23, 26 pathogens, 11, 12, 16, 17, 26 plants, 10, 11, 24 protein, 6 protists, 5, 19, 24 protozoa, 19, 20 reproduction in bacteria, 10, 11, 21 in cells, 7 in microanimals, 13 in viruses, 24, 25 sickness, 18, 19, 20, 22, 24, 25, 27 skin, 4, 11, 12–13, 14, 23 oils, 10,15 stomach, 8, 10, 20, 21 teeth, 17 toes, 6 tongue, 8, 16 toxins, 11 vaccinations, 27 viruses, 5, 10, 24–25, 26 water, 11, 12, 18, 23 worms, 22, 23