UNIT FOUR 



How Do the Parts of an Organism 



Work Together? 



1 How can a living thing tell what materials or organisms are suitable 



for food? 



2 How can an animal or a plant distinguish its enemies from harmless 



organisms? 



3 How perfectly are plants and animals adapted to their various ways of 



living? 



4 How does an animal meet an emergency? 



5 How do the nerves carry messages? 



6 How do plants and the animals without nerves get along? 



7 Can all animals learn from experience? 



8 Can plants learn from experience? 



9 How do living things adjust themselves to changing conditions? 

 10 How are the different parts of the body made to do teamwork? 



Conditions surrounding life are constantly changing. We say that proto- 

 plasm is sensitive, for it responds to changes in the environment. But the 

 responses of protoplasm are also adaptive. They are somehow related to 

 preventing injuries or to counteracting them, or to getting for the organism 

 substances or conditions that help to keep it alive. When food gets into the 

 mouth, for example, a new series of movements and chemical actions is 

 started. If a parasite gets into the body, a special series of actions and proc- 

 esses is started. When one runs, the body temperature rises, but the heating 

 and the chemical changes in the blood are then counteracted or balanced. 

 How does the organism meet the changes around it? Sooner or later, we 

 know, most plants and animals starve or are destroyed, for their responses 

 are not always adequate. Some part just misses, or it breaks down. 



Mankind is nevertheless impressed by the unity of the organism. An- 

 cient fables try to impress us with the importance of social co-operation by 

 comparing the community to an organism. There is the fable of the various 

 organs that went on strike. The legs remembered that they were carrying 

 the whole weight of the body, but had forgotten that they were being 

 supplied all the nourishment that they could use and were being guided by 

 the eyes and brain. Or the heart complained that it could never take time 

 out, working night and day — forgetting that it could live at all only be- 

 cause the mouth and the stomach and the liver were sticking to their jobs. 

 Such fables are repeated to teach a lesson to ordinary people or to children 



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