BACTERIAL RESPIRATION 



191 



bacteria is uf the order uf 200,000 times that for man. 

 Moreover, the whole of the bacterial surface allows the 

 passage into the cell of foodstuffs, whilst in man and 

 animals the absorption of nutrients takes place through 

 only a limited part of the total surface. 



If an organism can use a given compound as a nutrient, 

 its value will depend on its calorific value. For instance, 

 it has been shown that when Aspergillus niger is grown 

 on various compounds as the source of energy and carbon, 

 the weight of mycelium grown runs parallel with the heats 

 of combustion (that is, the calorific values) of the com- 

 pounds, as may be seen from Table 16. 



Table 16 



The value of a compound as a food or energy source 

 also depends on the degree of oxidation which it under- 

 goes ; the more complete the oxidation the higher the 

 energy available. Glucose may be taken as an example, 

 and the energy liberated with var3dng degrees of oxidation 

 compared : — 



(a) Complete aerobic oxidation 



CfiHigOg+eOa > GC02 + 6H20+674Cal,s. 



Partial aerobic oxidation 



(^) 



(c) 



2C6H12O6+9O2 > 6C2H204 + 6H,0+493Calr^ 



(oxalic acid) 



Anaerobic oxidation 



(1) QHi^Oe 

 (ii) CeHi^Oe 

 (iii) CgHjoOe 



--> 2C3He03 + 22-5Cals. 



(lactic acid) 

 -^ 2C2H5OH + 2CO2 - 



(ethyl alcohol) 

 -^ 3CH3COOH + 15Cals 

 (acetic acid) 



22 Cals 



