[Chap. XVII RESPIRATION 159 



energy that are temporarily released and actively associated with chemi- 

 cal transformations during respiration are the ones stressed in the state- 

 ment: the fundamental feature of respiration is the transfomiation of 

 energy through the oxidation of foods in living cells. Some of the partly 

 oxidized and partly reduced products formed during respiration are also 

 fundamental features. 



Respiration occurs continuously in all living active cells of plants, and 

 food and free oxygen are necessary. The few exceptions known are all 

 found among certain groups of bacteria and fungi. The food most com- 

 monly oxidized in respiration is sugar. The process is catalyzed by several 

 enzymes and there are several intermediate steps. The sugar may be 

 completely oxidized to carbon dioxide and water, or it may be incom- 

 pletely oxidized, resulting in the formation of a large variety of products, 

 among which are alcohol and organic acids. All products that are di- 

 rectly fomied by the oxidation-reduction of foods in living cells may 

 be regarded as products of respiration; their number is very large. 



When the oxidation of food is incomplete the process of respiration is 

 often referred to as fermentation. When it occurs without free oxygen 

 it is called anaerobic; with free oxvsen, aerobic. Both anaerobic and 

 aerobic respiration regularly occur in a plant. Some of the fungi (yeast) 

 and bacteria (lactic acid bacteria) are able to survive by anaerobic 

 respiration alone. 



REFERENCES 



Needham, Joseph, and David E. Green. Perspectives in Biochemistry. Cam- 

 bridge Univ. Press. 1938. Pp. 114-126. 

 Stiles, W. Respiration. Bot. Rev. 1:249-268. 1935. 



