CHAPTER XIV 



PLANT PHYSIOLOGY 



PLANTS AND ANIMALS COMPARED 



In the discussion just concluded we have endeavored to 

 show how the living cell, and thus the organism as a whole, 

 utilizes food materials for the production of the energy neces- 

 sary for its living processes, and by a study of the animal body 

 to explain the chemical changes that take place in the trans- 

 formations of this food until it is finally oxidized and the energy 

 liberated. 



We shall now study the plant organism to find out how, by 

 means of its distinctive physiological processes, the three essen- 

 tial organic food constituents, carbohydrates, fats and proteins, 

 are formed and the plant structure built up. 



Similarity of Plants and Animals. — In our study of animals 

 and the physiological processes by which they utilize their 

 food we grouped the chemical reactions taking place under two 

 heads, viz. digestion and metabolism. Digestion may be con- 

 sidered as a preliminary change taking place in the food material 

 outside of the real body proper, that is, in the digestive tract. 

 By means of this change the mixed food substance is brought 

 into the particular condition necessary for absorption and 

 metabolism. After the digested food material is absorbed into 

 the body proper it undergoes more or less complicated changes 

 embraced in the term metabolism. During the period of 

 metabolism the food performs its two functions, viz. it is built 

 up into body substance or it is oxidized and yields energy. 

 These two functions eventually become one, for the body sub- 

 stance, in most part, is, sooner or later, metabolized further 

 and finally oxidized with the liberation of energy. 



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