The Utilization of Foods 



83 



oxygen from the atmosphere, and the roots from the air that 

 is in the soil. Wet soils are unsuited to the growth of many 



plants, not because of the ^ ^ 



water present, but because of 

 the lack of a sufficient oxygen 

 supply for the roots. Drain- 

 age is a valuable agricultural 

 practice not only because it 

 removes excess water, but 

 also because it draws air 

 (oxygen) into the soil. When 

 the farmer breaks the crust 



on the surface, he is making it possible for more oxygen to 

 reach the roots of his crop. 



The plant and the process of respiration may be compared to 

 a manufacturing establishment and the work that goes on in it. 



The power stations are every living cell of root, stem, and 



Fig. 50. Carbon dioxid is given off from 

 the respiration of the flowers. 



The machinery 

 The fuel 

 The process 

 The product 

 The waste 



leaf, 

 is the protoplasm, 

 is foods, especially carbohydrates, 

 is the combining of food and oxygen, 

 is energy, 

 is carbon dioxid and water. 



The working hours are twenty-four a day. 



Respiration and photosynthesis contrasted. In photo- 

 synthesis, carbon dioxid and water are combined to form the 

 complex molecules of carbohydrates, and a large number of 

 atoms of oxygen are set free in the process. When, in res- 

 piration, the complex carbohydrate molecules are again 

 combined with oxygen, simple molecules of carbon dioxid 



