UNIT FOUR — REVIEW • HOW DO THE PARTS 



OF AN ORGANISM WORK TOGETHER? 



Students of biology are in somewhat the same predicament as boys who 

 take clocks or cameras apart and are scolded for being "destructive". Our 

 defense, which is reasonable enough, is that we want to find out how a 

 thing works. But then we are challenged (1) to put the parts together 

 again, which is not always very difficult, and (2) to make the machine 

 work again, which is often impossible. 



Biologists have sorted out over a million distinct kinds of plants, a mil- 

 lion distinct kinds of animals. They have anatomized or analyzed animals 

 and plants into many kinds of organs and tissues. They have analyzed 

 organisms chemically into many kinds of compounds, and they have listed 

 the elements found in all organisms, as well as elements and compounds 

 found only in certain special kinds. When we try to put the pieces together 

 again, we are baffled. 



Biologists have analyzed the conditions under which various plants and 

 animals live — light, temperature, water, chemical substances, and so on; and 

 they have studied the changes in living things which result from alterations 

 in these conditions. We can take a plant or a bird away from its natural 

 surroundings and study it in the laboratory, but we cannot keep anything 

 alive apart from the environment. Organism and environment are insep- 

 arable, except in our thought about them. 



We can measure pulse rates, blood pressures, oxygen exchanges and 

 nerve impulses. Yet none of these things exists — as a living process — when 

 separated from the others. We know a great deal about muscles. But 

 muscles have meaning in "life" only in relation to other muscles, in con- 

 nection with nerves, in exact timing with blood flow or heart action or with 

 chemical changes in remoter parts of the body. However much we find out 

 about each part, we can recognize life only as a unified interaction of many 

 processes, involving all the parts. In the ameba and other one-celled or- 

 ganisms we say that the protoplasm is alive. The single cell carries on all 

 the life functions — feeding and assimilation, breathing and oxidation, move- 

 ment, excretion, sensation, reproduction. A lobster or a fish performs va- 

 rious necessary functions through various organs. This fact of having special 

 organs related to special functions has been called the physiological division 

 of labor. 



In higher animals division of labor appears gradually during develop- 

 ment. This means that digestion goes on in a living thing before it has 

 any digesting organs; breathing goes on before it has any gills or lungs; 

 excretion goes on before it has any kidneys. This idea may be easier to 

 grasp if we recall that in the evolution of society clothes were made long 



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