SURVEY QUESTIONS 



Why do you chew food ? What do we mean by the term " digestion " ? 

 Do you know what does the digesting of food? Do plants digest their 

 foods ? Where do we digest foods ? How and why do we digest foods ? 

 Do you know how to avoid having indigestion ? 



Photo by H. Armstrong Roberts 



UNIT XII 



HOW FOOD IS PREPARED FOR BODY USE 



Preview. It seems a far cry from the chemistry laboratory, 

 with its bottles and test tubes, its acids and its bases and all of 

 the complicated formulae that we see in chemistry books, to our 

 own digestive tract. But to the physiologist the human body 

 is a marvelous chemical laboratory which in the complexity 

 of its working makes our science laboratory in school seem very 

 insignificant. We have learned that organic food substances are 

 found in the leaves of plants. This food has to be taken to other 

 parts of the plant in order to be used. Before it can be trans- 

 ported from one part of the plant to another, it has to be made 

 soluble so that it can pass from one cell to another by the process 

 of diffusion through a cell membrane. This change of food from 



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