CHAPTER III 



RESPIRATION OF PLANTS 



19. Importance of Respiration in the Life of the Plant and 

 the Nature of the Process. — Respiration is a process that has 

 long been closely connected with life. Respiration is essentially 

 the oxidation and decomposition of complex organic compounds, 

 principally carbohydrates into simpler substances such as carbon 

 dioxide and water. It may be expressed by the following general 

 reaction : 



CeHiaOe + 6O2 -> 6CO2 + 6H2O + 674 cal. 



This reaction shows that oxygen absorbed from the air par- 

 ticipates in this oxidation and that the chief product of this 

 reaction is carbon dioxide gas liberated into the surrounding 

 atmosphere in exchange for an equal volume of oxygen absorbed. 

 This exchange of gaseous oxygen and carbon dioxide is the most 

 prominent and most easily demonstrated external manifestation 

 of respiration. Later on, it will be sho\Mi (Art. 21) that it is 

 the quantitative changes in the surrounding atmosphere and 

 not inside the living object that are used in most of the methods 

 of studying the intensity of respiration. 



The physiological significance of respiration is not determined 

 merely by this external manifestation of a definite gas exchange. 

 The process of respiration is the liberation of energy connected 

 with the oxidation of organic substances. All the vital functions 

 of the organism, such as growth and the movements connected 

 with growth, and different kinds of reactions accompanying 

 synthetic processes all require energy, just as it is required by 

 motors in a factory. This energy is obtained from the oxidation 

 of carbohydrates. However, unlike the burning of fuels in 

 factory furnaces, in protoplasm the chemical energy of oxidation 

 is directly transformed into other forms of chemical energy; and 

 only after the physiological process has been completed, does it 

 appear in the form of heat energy. These internal transforma- 



82 



