5i8 



RESPIRATION 



TABLE 52— RESPIRATORY RATIOS OF THE LEAVES OF VARIOUS SPECIES 

 (data of MAQ.UENNE AND DEMOUSSY, I9I3) 



ing upon the respiratory substrate, the completeness of the oxidation, and other 

 conditions. Many studies have been made of the respiratory quotient of 

 various plant organs. Most such investigations have dealt with germinating 

 seeds. The principal internal conditions under which it has been found that 

 the respiratory ratio of the higher green plants deviates from one are as 



follows : 



I. Respiration of Compounds Which Are Relatively Poor in Oxygen as 

 Compared with the Hexoses. — The proportion of oxygen to carbon is in- 

 variably less in fats than in carbohydrates. JVIany studies of the respiratory 

 ratio of seeds in which the stored foods are mostly in the form of oils have 

 shown that the respiratory ratio of such seeds is always less than one. The 

 following summary equation represents the complete oxidation of tri-palmitin, 

 a representative fat: 



CsiHosOe + 72.5 O2 -^ 51 CO2 + 49 H2O + 7590 kg.-cal. (approx.) 



The theoretical respiratory quotient for this compound is therefore — -• 



= 0.70, 



Respiratory ratios of less than one would result when fats are oxidized 

 whether they are used directly as the substrate, or whether, as most investiga- 

 tors believe, they are first converted into simple sugars which in turn serve 

 as the respiratory substrate. If fats are oxidized directly, it is evident from 

 the above equation that a greater volume of oxygen will be required than 

 the volume of carbon dioxide which will be released. On the other hand, 

 if the fats are first converted into simple sugars, which then serve as the 

 respiratory substrate, a considerable volume of oxygen will be utilized in 

 accomplishing this transformation, since conversion of fats to sugars is an 

 oxidation process. Transformation of fats to sugars does not result in the 

 release of carbon dioxide. This gas would be released only upon oxidation 

 of the simple carbohydrates. Hence the summation effect of these two processes, 



