TYPES OF RESPIRATION 57 



formed being used as the basis of classification. Anaerobic respi- 

 ration of glucose of the alcoholic type is conventionally expressed 

 as follows: 



C 6 H 12 6 = 2C0 2 + 2C 2 H 5 OH + 25 Cal 



Alcohol 



Here again, end results alone are indicated, and no essential in- 

 formation of the steps and mechanisms involved is conveyed. 

 Moreover, this equation shows that only a portion of the potential 

 energy of the glucose molecule has been released, yet in this re- 

 spect it typifies the energy-release relationships of all other 

 anaerobically respired compounds. 



Interrelations between aerobic and anaerobic respiration. 

 It seems best at this juncture to indicate the existence of evidence 

 to show that aerobic and anaerobic respiratory processes are inter- 

 related and that both may be presumed to occur not only amono- 

 fungi but also among green plants. Once this interrelationship is 

 appreciated, it will be possible to return to the essential steps in the 

 process. Kostytchew (1927) has schematically represented the 

 relationship in the following manner: 



2C0 2 + 2C 2 H 5 OH + 25 Cal 



/ 

 Zymase 

 Intermediate prod- 7* T , 

 C 6 Hi 2 6 + Zymase -» ucts of anaerobic X ] n absence of ° 2 



respiration \ In presence of ° 2 



+ 60 2 



Xj Oxidizing-reducing enzymes 



6C0 2 + 6H2O + 673 Cal 



In this scheme the zymase complex (long believed to be a single 

 enzyme but now known to consist of glycolase, which converts 

 hexoses into methylglyoxal, carboxylase, which splits out carbon 

 dioxide from certain organic acids, and in addition certain co- 

 enzymes) is supposed to convert the hexose into labile inter- 

 mediate products as a first step in both aerobic and anaerobic 

 respiration. This change is an anaerobic one in either case, as 

 Kostytchew's scheme shows. Whether or not atmospheric oxy- 

 gen is available determines the next step and also the course of 

 the subsequent respiratory reactions. 



To support Kostytchew's theory of the course and sequence 

 of events in respiration, the following facts have been marshalled: 



