TABLE OF CONTENTS 



Introduction: Biologists Study Aiiiuials and Plants 



JJjiit 



I. THE LIVING THINGS OF THE EARTH ARE MANY 

 AND VARIED 



14 



Problem i. What Kinds of AniTimls Inhabit the Earth? 15 



The Vertebrates i6 



The Invertebrates 39 



Problem 2. What Ki?ids of Plants hi habit the Earth? 72 



Flowerless Plants 73 



Plants with Flowers and Seeds 80" 



Problem 3. Hoiv Are Livijig Things Named and Classified? 95 



II. ALL LIVING THINGS ARE BASICALLY ALIKE 104 



Problem i. Of What Are All Living Things Composed? 105 



Problem 2. How Do Their Activities Keep Cells Alive? 118 



Problem 3. How Are the Cells Arranged in Anijnals and Plants? 129 



III. GREEN PLANTS MAKE THE FOOD USED 



BY ALL LIVING THINGS 136 



Problem i. What Part Do Leaves Play i?i Making and Using Foods? 137 

 Problem 2. What Part Do Roots and Ste?ns Play i?i Maki?ig 



and Usi?ig Food? 148 



IV. HOW A COMPLEX ANIMAL USES FOOD FOR ENERGY 



AND GROWTH 166 



Problem i. How Can We Choose Foods Wisely? 167 



Problem 2. How Does the Digestive System Make Foods Usable? 188 



Problem 3. How Are Materials Moved to and from Our 



Body Cells? 206 



Problem 4. How Are All Our Cells Provided with a Constant 



Supply of Oxygeji? 226 



Problem 5. How Does the Body Get Rid of Wastes Formed 



by Cell Activity? 237 



Problem 6. What Substances Help Regidate Cell Activities? 246 



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