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i-01-LBC-861740 08/20/2004 8:20 AM Page i Bill Bachmann/Rainbow i-01-LBC-861740 08/20/2004 8:20 AM Page ii Animal Diversity This Alaskan brown bear is catching a migrating salmon. This species of bear is the largest carnivore in Alaska, growing up to nine feet tall and weighing up to 1,700 pounds. All Alaskan salmon hatch in freshwater, migrate to the sea, and then eventually return to where they hatched to reproduce. Copyright © 2005 by The McGraw-Hill Companies, Inc. All rights reserved. Except as permitted under the United States Copyright Act, no part of this publication may be reproduced or distributed in any form or by any means, or stored in a database or retrieval system, without prior written permission of the publisher. The National Geographic features were designed and developed by the National Geographic Society’s Education Division. Copyright © National Geographic Society.The name “National Geographic Society” and the Yellow Border Rectangle are trademarks of the Society, and their use, without prior written permission, is strictly prohibited. The “Science and Society” and the “Science and History” features that appear in this book were designed and developed by TIME School Publishing, a division of TIME Magazine.TIME and the red border are trademarks of Time Inc. All rights reserved. Send all inquiries to: Glencoe/McGraw-Hill 8787 Orion Place Columbus, OH 43240-4027 ISBN: 0-07-861740-5 Printed in the United States of America. 2 3 4 5 6 7 8 9 10 027/055 09 08 07 06 05 04 Bill Bachmann/Rainbow i-01-LBC-861740 08/20/2004 8:20 AM Page iii Authors Education Division Washington, D.C. Lucy Daniel, PhD Dinah Zike Teacher/Consultant Rutherford County Schools Rutherfordton, NC Educational Consultant Dinah-Might Activities, Inc. San Antonio, TX Series Consultants CONTENT MATH ACTIVITY TESTERS Jerome A. Jackson, PhD Teri Willard, EdD Nerma Coats Henderson Whitaker Eminent Scholar in Science Program Director Center for Science, Mathematics, and Technology Education Florida Gulf Coast University Fort Meyers, FL Mathematics Curriculum Writer Belgrade, MT Pickerington Lakeview Jr. High School Pickerington, OH Dominic Salinas, PhD Middle School Science Supervisor Caddo Parish Schools Shreveport, LA READING Carol A. Senf, PhD School of Literature, Communication, and Culture Georgia Institute of Technology Atlanta, GA Mary Helen Mariscal-Cholka William D. Slider Middle School El Paso, TX Science Kit and Boreal Laboratories Tonawanda, NY SAFETY Sandra West, PhD Department of Biology Texas State University-San Marcos San Marcos, TX Series Reviewers Maureen Barrett Amy Morgan Darcy Vetro-Ravndal Thomas E. Harrington Middle School Mt. Laurel, NJ Berry Middle School Hoover, AL Hillsborough High School Tampa, FL Cory Fish Penn State University University Park, PA Burkholder Middle School Henderson, NV Dee Stout C ◆ iii i-01-LBC-861740 08/20/2004 8:21 AM Why do I need my science book? Have you ever been in class and not understood all of what was presented? Or, you understood everything in class, but at home, got stuck on how to answer a question? Maybe you just wondered when you were ever going to use this stuff? These next few pages are designed to help you understand everything your science book can be used for . . . besides a paperweight! Page iv Before You Read ● Chapter Opener Science is occurring all around you, and the opening photo of each chapter will preview the science