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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 32 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. 5 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 6 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 8 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