X Tciblc of Contents 



Unit 



V. WHY Ll\ ING THINGS BEHAVE AS THEY DO 260 



Problem 1. What Arc the Simplest Forms of Bcl^avior in Animals? 261 

 Problem 2. What Makes Coinplex Behavior Possible iji 



Many-celled Animals? 269 

 Problem ^. Hove Does the Behavior of Complex Ani/nals Differ 



from That of Simpler Forms? 286 



Problem 4. Hov: Do Plants Respojid to Their Enviroiimoit? 301 



VI. CONSTANT CARE IS NEEDED FOR MAINTAINING 



OUR HEALTH 310 



Problem 1. Hove Are Our Bodies Protected against Microorga/nsi/is? qii 

 Problem 2. ]]'hat Have Scientists Learned about Conqneriiiir 



Sovie Covnnon Diseases? 320 



Problem 3. {Optional) How Have Recent Discoveries Changed 



Some of Our Ideas about Disease? 338 



Problem 4. Hove Do We Attevipt to Stop the Spread of Disease? 343 



Problem 5. Ho\e May We Achieve Better Health for All? 359 



Ml. HOW IJ\ ING THINGS AFFECT ONE ANOTHER 372 



Problem i. TF/m? Makes Possible the Continued Existence of Plants 



and Anntials? 373 



Problem :. What Are Our Relationships to Other Organisms? 381 



Problem ^ Hove Do We Try to Solve Our Insect Problevis? 389 



P1UIBLEM 4. Why Must We Practice Conservation? 399 



\ III. now ANIMALS AND PLANTS MAKE MORE OF THEIR 



OWN KIND 410 



Problem 1. Hov: Do the Simple Anii/ials and Plants Reproduce? 411 



Problem 2. How Do the More Complex Annuals Reproduce? 421 



Problem ^ Hove Do the More Complex Plants Reproduce? 438 



IX. THE ORGANISM IS THE PRODUCT OF ITS HEREDITY 



AND ITS EN \' I RON Ml- NT 454 



Problem i. Why Do Off spring Resemble Their Parents? 455 

 Problem 2. Hov: Can Some of the Differences between Parents 



and Offspring Be Explained? 464 



Problim 3. How Can New Hereditary Characters Appear? 479 

 Problem 4. How Does the Environment Affect the Characters of 



an Organism? 485 



