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2 Photo Credits: Cover: Bill Curtsinger/Getty Images; 2 (br) Dan Dalton/Getty Images; 3 (tr) Frans Lanting/Corbis, (cl) Jack Milchanowski/Visuals Unlimited, (br) Arthur Morris/ Visuals Unlimited; 4 (b) Getty Images; 5 (t) Floresco Productions/Corbis, (cr) Getty Images; 6 (tl) Ray Kachatorian/Getty Images, (tr) Gio Barto/Getty Images, (br) Jonathan Nourok/PhotoEdit, (bl) Vario images GmbH & Co.KG/Alamy; 7 (tr) Frans Lanting/Corbis, (cr) Jack Milchanowski/Visuals Unlimited, (br) Arthur Morris/Visuals Unlimited, (tc) Burke/ Triolo Productions/Getty Images, (tcl) Klein/Hubert/Peter Arnold, Inc.; 8 (bl) John Anderson/Animals Animals - Earth Scenes; 9 (c) Bruce Coleman, Inc., (cl) E. A. Janes/Age Fotostock, (cr) Cheryl Ertlet/Visuals Unlimited; 13 (cr) Brian Sullivan / Visuals Unlimited; 14 (br) Rachel Weill/Getty Images; 16 (b) Michael Gadomski/Photo Researchers, Inc.; 18 (b) Bernard Photo Productions/Animals Animals - Earth Scenes; 19 (c) Nigel Cattlin/ Photo Researchers, Inc.; 20 (bl) Photodisc Red (Royalty-free)/Getty Images, (br) E.A. Janes/Age Fotostock America, (tl) Jane Burton/Bruce Coleman, Inc., (tr) Photodisc Green (Royalty-free)/Getty Images; 21 (cl) Dwight Kuhn, (cr) Dwight Kuhn, (br) Patti Murray/ Animals Animals - Earth Scenes,(bl) Dwight Kuhn; 22 (br) SuperStock; 23 (tl) Zigmund Leszczynski/Animals Animals - Earth Scenes, (br) Norbert Rosing/Getty Images; 24 (bl) Tom Brakefield/Corbis, (r) Cosmos Blank/Photo Researchers, Inc.; 25 (tl) Rubberball/ Getty Images, (tr) David Zelick/Getty Images, (cl) Photodisc/Getty Images, (bc) Photodisc/Getty Images; 26 (cl) Dwight Kuhn, (cr) Dwight Kuhn, (br) Patti Murray/ Animals Animals - Earth Scenes, (bl) Dwight Kuhn; 27 (tl) Naturfoto Honal/Corbis, (tr) John M. Burnley/Photo Researchers, Inc., (bl) Frank Greenaway/Getty Images, (br) Joe McDonald/Animals Animals - Earth Scenes, (bg) Richard Cummins/Superstock. If you have received these materials as examination copies free of charge, Harcourt School Publishers retains title to the materials and they may not be resold. Resale of examination copies is strictly prohibited and is illegal. Possession of this publication in print format does not entitle users to convert this publication, or any portion of it, into electronic format.

3 Copyright by Harcourt, Inc. All rights reserved. No part of this publication may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopy, recording, or any information storage and retrieval system, without permission in writing from the publisher. Requests for permission to make copies of any part of the work should be addressed to School Permissions and Copyrights, Harcourt, Inc., 6277 Sea Harbor Drive, Orlando, Florida Fax: HARCOURT and the Harcourt Logo are trademarks of Harcourt, Inc., registered in the United States of America and/or other jurisdictions. Printed in the Mexico ISBN-13: ISBN-10:

4 trait heredity gene A trait is a characteristic that makes one living thing different from another. An attached ear lobe is a trait that some people have. Heredity is the process by which traits are passed from parents to offspring. Eye and hair color are a result of heredity.

5 A gene is the basic unit of heredity. Genes carry instructions for how a living thing will grow and develop. Genes determine the shape of these birds beaks.

6 The main idea is what the text is mostly about. Details tell more about the main idea. Look for details about what traits are and how they are passed on from parents to offspring. When living things reproduce, they make more of their own kind. Offspring tend to look like their parents. This is because they have similar traits. A trait is a characteristic that makes living things different from each other. Heredity is the process by which traits are passed on from parents to their young.

7 A gene is the basic unit of heredity. Genes carry instructions. They tell what traits a living thing will have. Every human has the same number and kind of genes. But the instructions on the genes are different from person to person. This mix of instructions causes people to have different traits. Your genes come from your parents. You get the same genes from each parent. You get one set of instructions for every gene from each parent. Tell how a girl could look like both her mother and her father.

8 Thousands of traits make you who you are. Some traits are determined only by genes. These traits include eye and hair color. Other traits come from things in your life. These things could be where you live and things you do. You can learn to speak because of certain genes. But the words you speak are learned from others.

9 Some behaviors are not learned. These behaviors are because of heredity. Some animals, like turtles, hatch from eggs. They do not have their parents there to help them. They are born knowing how to survive. Other animals have more to learn. The young animals depend on their parents. These animals have inherited traits to help them survive, but they have to learn how to use the traits. They have to learn from their parents and other adults. Give an example of a trait determined by genes and one resulting from a mix of heredity and things in your life.

10 Genes affect your eye color. But this color may vary from that of your parents. This is because eye color is caused by many genes from both parents. Your eyes might be brown or blue or green. They might be some combination of colors. The genes for eye color can combine in many different ways. Very few people have exactly the same eye color. Look at your eyes in the mirror. What color are they? You can make the color of your eyes look different for a while with colored contact lenses, but you cannot change your eye color.

11 Some traits can change because of the way you live. For example, genes carry information about your height. However, your height also depends on the way you eat. A poor diet could limit your growth. A healthful diet and activity can help your body grow as much as possible. Why might there be different hair colors in the same family? 1. are determined by genes and also by a mix of heredity and where you live. 2. The basic unit of heredity is the. 3. Your genes come from both of your. 4. Eye color can because there are many possible gene combinations.

12 life cycle photosynthesis Photosynthesis is how plants make food.

13 A life cycle is all of the stages a living thing goes through. This diagram shows the life cycle of a tomato plant.

14 A sequence is the order in which things happen. Look for the sequence of stages in the life cycles of plants. When you face the sun on a bright day, what do you feel? That warmth is energy from the sun. Almost every living thing depends on energy from the sun to survive. Plants use the light energy of the sun directly. They use photosynthesis to turn light energy from the sun into chemical energy. Plants turn water and carbon dioxide into sugar and oxygen.

15 Plants use the sugar for food. They release the oxygen into the air around them. Plants use the food for energy. They use some of the energy and store the rest. Other organisms feed on plants. They eat the stored energy in plants to survive and grow. Without plants, these organisms could not survive. How do humans depend on the energy of the sun to survive?

16 A life cycle is all the stages a living thing goes through. Different living things have different life cycles. A flowering plant has four stages in its life cycle. Germination is the first stage. Germination happens when a seed gets what it needs to begin to grow. Roots and a stem push out of the seed. A seedling is the second stage. A seedling is a young plant. Flowering is the third stage. Flowers make pollen. Pollen contains sperm cells. Birds, insects, and wind carry pollen to other plants. Sperm cells join with egg cells inside the flowers. Then new seeds form.

17 Fruiting is the fourth stage in the life cycle of a flowering plant. Seeds form inside the fruit. The ripe fruit falls to the ground or is eaten. Some seeds are scattered far from the parent plant. When these seeds get what they need, they begin to grow. A new life cycle begins. Tell whether flowers or roots grow first.

18 Plants reproduce in different ways. Some new plants grow from spores, not seeds. Mosses and ferns have similar life cycles. First, spores drop onto damp ground. There they grow into tiny plants. These tiny plants make sperm and egg cells. Next, the sperm and egg join, and a small plant begins to grow. The plant grows until it is an adult. Spores form and are released. The life cycle begins again. Tell what happens after spores from a fern plant drop onto damp ground.

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20 Most new plants grow from seeds. But plants can grow from other plant parts, too. In this kind of growth, an egg and a sperm do not join to make a new plant. Sometimes new plants grow from stems. The stem of the parent plant sends out runners. New plants grow from the runners. Strawberry plants grow from runners. Many grasses grow from runners, too.

21 Some plants grow from a part of a stem called a tuber. White potatoes are tubers. An onion bulb is a kind of stem. If you cut an onion, you will see a small plant growing inside. Grafting is another way to grow new plants. Part of one kind of fruit tree can be grafted, or attached to, another tree. The grafted part will grow on the new tree. Does the runner or the new strawberry plant grow first? 1. A living thing s includes all the stages in its life from beginning to end. 2. Before a seed can begin to grow, conditions must be right for to happen. 3. After a seedling grows, begin to form which will make pollen. 4. After an egg and sperm cell join in a flower, new begin to form.

22 direct development metamorphosis Direct development is a kind of growth in which a living thing gets larger, but its basic body parts do not change. A dog s life cycle is an example of direct development.

23 Metamorphosis is a kind of growth in which major body changes take place during an animal s life cycle. A moth s body completely changes several times during its metamorphosis.

24 When you compare and contrast, you tell how things are alike and different. Look for ways to compare and contrast animal life cycles. Animals have life cycles. Different animals have different kinds of life cycles. Most animals are alike in one way. Most of them come from an egg that has joined with a sperm cell. Most mammals grow and develop inside their mothers. The mother cares for her young after birth. Mammals called marsupials are different. They are very tiny when they are born. They develop more in the mother s pouch. Kangaroos are marsupials.

25 Most birds lay eggs in nests. A young bird develops within the egg. Most birds care for their young until they can fly. Most reptiles also lay eggs. When they hatch, most young reptiles live on their own. Amphibians and most fish lay eggs in water. Fish hatch and look like their parents. Most young amphibians do not look like adults. After hatching, they usually go through several complete changes in their bodies. Many insects also go through body changes as they grow. Tell how bird and reptile life cycles are the same and different.

26 Animals grow and develop in different ways. One kind of growth is called direct development. In direct development, a living thing gets larger, but its body parts do not change. Cats, spiders, and humans all go through direct development. Some animals molt as they grow. This means they shed their covering. Both reptiles and insects molt. Animals grow at different rates. A fruit fly is an adult in about ten days. A dog takes about three years. A human takes much longer.

27 The human life cycle has four stages. They are infancy, childhood, adolescence, and adulthood. You were an infant from birth to two years. During this time, your body size changed. You learned to walk and talk. Now you are in childhood. You are growing. You are learning new things. You will be an adolescent next. This will happen when you are a teenager. Your body will develop. You will continue to learn. When you reach adulthood, your body will be fully developed. You will have reached your full height. What differences are there in the stages of childhood and adulthood?

28 Direct development describes many animals life cycles. But some animals develop differently. In metamorphosis, major body changes happen. Insects and most amphibians go through metamorphosis. There are two types of insect metamorphosis. A moth goes through complete metamorphosis. The stages are egg, larva, pupa, and adult. Grasshoppers go through incomplete metamorphosis. The young insects look like adults when they hatch. But they do not have all the adult body parts.

29 Frogs and some other amphibians also go through complete metamorphosis. A frog begins life as an egg. A tadpole hatches from the egg. It has gills and a tail. It lives in water. As it develops, it grows legs. It loses its tail and develops lungs. As an adult frog, it lives on land. Compare the life cycle of a moth to that of a grasshopper. 1. Almost all animals develop from a sperm cell that has joined with an. 2. Marsupials are different from other mammals because their young develop in a. 3. All children are older than and younger than adolescents. 4. Before an egg turns into an adult moth, it must first be a and then a pupa.

30 GLOSSARY direct development (duh REKT dih VEL uhp muhnt) a kind of growth in which an organism gets larger but doesn t go through other changes gene (JEEN) the basic unit of heredity heredity (huh RED ih tee) the process by which traits are passed from parents to offspring life cycle (LYF CY kuhl) all the stages a living thing goes through metamorphosis (met uh MAWR fuh sis) major changes in the body form during the development of an animal photosynthesis (foht oh SIN thuh sis) the process that plants use to make sugar trait (TRAYT) a characteristic that makes one organism different from another

31 1. Explain why people in a family have many similar traits. Then tell why some traits are different. 2. Explain how most of your traits develop. Choose a plant. Create a poster showing the plant s life cycle. 1. Use a diagram to explain how the plant grows and develops during its life cycle. 2. Write several questions that can be answered by looking at your poster. Share them with a partner. Draw or take photos of people in your community. Arrange your pictures to show a human life cycle. Use them to explain this cycle to a family member. Tell what stage each family member is at in this cycle.

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