THE ENERGETICS OF ORGANISMS 



97 



Plant oyganisms are therefore producers. Animals can only 

 utilize the already built-up proteins, fats and carbohydrates. 

 In their metabolism they oxidize and energetically degrade these 

 materials — which they cannot themselves elaborate from inorganic 

 sources. By reproduction animals can increase the mass of 

 animal organisms and tissue-substances but, in general, the 

 limit of reproductive increase is already attained. 



37^. The Bacterial-Plant- Animal Metabolism in Analogy 



WITH THE CaRNOT CyCLE. 



The working substances are O, C, N, H, S, P, etc. 

 t 



CO 



<a 



U 



(U 

 +-> 



a 



O 



"a 



a 



o 

 u 



o 



a 



-C 

 O 



t 



Energy, as 

 heat leaves 

 the cycle. 



< 



The working 

 substances 

 become 

 CO2, OH,, 

 nitrate, etc. 



Energy, as 

 solar radiation, 

 enters the cycle. 



Animal metabolism 



The working 

 substances 

 become proteins, 

 fats and carbo- 

 hydrates. 



Plant metabolism 



> Intake of Energy by the system > 



This means : 



(i) The working substances undergo cyclical changes ; 



(ii) Plants absorb energy from sunlight and this energy becomes 

 potential in the carbohydrates, etc., which are built up 

 by the rearrangements, in more complex ways, of the 

 working substances ; energy enters the cycle ; 



(iii) Animals utilize these carbohydrates as food, oxidizing 

 them to CO 2, OHo, urea, etc. ; bacteria further break 

 down the urea ; energy is dissipated and leaves the cycle. 



(iv) The COo, OHo, HNO3, etc., are again used as sources 

 of food by plants and the cycle begins again. 



38. ON THE LAWS OF CONSERVATION AND DISSIPATION 



IN ORGANISMS 



The experimental work is practically restricted to animals. 



38fl. Food Values. Small quantities of proteins, fats and 



H 



