Rose Johnson - Discoveries in Life Science That Changed the World

Published in 2015 by The Rosen Publishing Group, Inc.

29 East 21st Street, New York, NY 10010

2015 Brown Bear Books Ltd

First Edition

All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted in any form or by any means, without the prior written consent in writing from the publisher.

Library of Congress Cataloging-in-Publication Data Johnson, Rose, 1981- author.

Discoveries in life science that changed the world / Rose Johnson.

pages cm. -- (Scientific breakthroughs)

Audience: Grades 5 to 8.

Includes bibliographical references and index.

ISBN 978-1-4777-8607-9 (library bound)

1. Life sciences--History--Juvenile literature. 2. Discoveries in science--Juvenile literature. I. Title.

Q126.4.J64 2015

570.9--dc23

2014027233

Editor and Text: Rose Johnson

Editorial Director: Lindsey Lowe

Childrens Publisher: Anne ODaly

Design Manager: Keith Davis

Designers: Lynne Lennon

Picture Researcher: Clare Newman

Picture Manager: Sophie Mortimer

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All artwork: Brown Bear Books

Manufactured in the United States of America

Picture Credits

t=top, c=center, b=bottom, l=left, r=right.

FC, isak55/Shutterstock; , Karelnoppe/ Shutterstock.

Contents

Introduction

Life science is the study of the most complicated things in the universe-living things. It investigates how life forms survive and where they came from.

A s far as we know, Earth is the only planet to have life on it. This one planet has more than 8 million species of complex life, and perhaps millions more of simpler bugs and germs. An individual organism can be made up of trillions of cells all working together to keep the body alive. The human brain alone is thought to have more interconnections in it than there are stars in the Universe.

Being alive

Nevertheless, life scientists have discovered that all life works according to the same basic rules. To be alive, an object must be able to move, at least a little. It must have a source of energy to drive its body processes. It must be able to respond to its surroundings, and above all it must be able to reproduce, to make a copy of itself.

The tiger is one of the biggest hunters on Earth and also one of the rarest.

Most of the life forms on Earth are trees and other plants. For every pound of animal on Earth, there are 1,000 pounds of plant.

Ecosystems

No organism lives by itself. There are always other life forms competing for food and other resources. Life science investigates how communities of organisms, or ecosystems, work. This knowledge is used to protect wildlife as it is threatened by human activities.

Natural history

Understanding how animals and plants live today also helps life scientists to figure out where they came from. It is thought that life has existed on Earth for 3.6 billion years, and 99 percent of the organisms that ever lived are now gone forever!

Many organisms are too small to see. Nearly 2,500 of these algae would just cover a dime.

Using Microscopes

The invention of the microscope revealed just how complex a living body is, and it showed that some organisms are too small to see with the naked eye.

T he microscope was invented at the end of the 16th century, around the same time as the telescope. Both instruments work in a similar way, using a pair of lenses to magnify an image. Microscopes make a very small object appear much larger. One of the first people to look at living things through a microscope was the English scientist Robert Hooke (16351703).

Robert Hooke used his microscope to investigate the intricate structure of living things such as the compound eye of a fly.

Microscopic world

Hooke made many drawings of the plant and animal features he saw. He published them in a book called Micrographia in 1665. Hookes main discovery was that bodies were made of tiny units. He called them cells, after the little rooms that monks (and convicts) lived in. A few years later the Dutch scientist Anton van Leeuwenhoek (16321723) used a microscope to discover what he called animalculesmicroscopic, single-celled organisms such as bacteria and protists.

An electron microscope image of the underside of a sunflower leaf shows tiny spikes that make the leaf feel rough to the touch.

IMPLICATIONS

The first microscopes used light to make images. There is a limit to the size of object you can see with a light microscope, and many of the objects inside cells are too small to see. In the late 1920s, more powerful microscopes were invented. They used beams of particles called electrons, which could magnify things 100,000 times more than light. Electron microscopes have shown that cells are filled with even tinier structures called organelles.

Classifying Life

One of the main aims of life science is to organize living things into related groups. The system used today was devised in 1735 by Carl Linnaeus.

CARL LINNAEUS

Linnaeus was born in Sweden in 1707. He learned Latin before he could speak Swedish. Latin was the language of science in those days, and he used it as the language for his taxonomy system. Linnaeus published his taxonomy system in 1735 as the book Systema Naturae (meaning natures system). Linnaeus then became a college professor. He died in 1778.

T he field of life science that classifies organisms is called taxonomy. Linnaeuss taxonomy classified animals into groups according to how they looked.

Groups within groups

Linnaeus developed a hierarchy of groups that was able to show how closely related any two organisms were. The largest grouping was the kingdom. All life was split between the animal kingdom and plant kingdom. (Fungi, bacteria, and other microorganisms were not really understood at that time, but they now form their own kingdoms.)

These three life forms, the bird, mushroom, and moss all belong to separate kingdoms.

Linnaeus used these drawings of animal anatomy to show how each group of animals shared particular features.

Smaller groups

The kingdoms were organized into classes. Animal classes included the mammals, birds, and insects. A class was subdivided into orders: Humans and monkeys were in the primate order, while lions and bears were in the carnivore order. Next came a family, followed by a genus, and finally every organism belonging to a species, the smallest grouping. Linnaeus gave every species two names. For example, a lion is