INTRODUCTION 



The series of priming reactions and synthetic mechanisms described in 

 Part Three of this book give some idea of the chemical processes occurring 

 in the biosphere. Superimposed on this general background there are 

 many variations, simplifications or amplifications arising from the differen- 

 tiation, adaptation and evolution of both the cells and the organism. 

 Without them life would become extinct. 



Each organism is a link in a food chain whose beginning varies according 

 to the particular association of living creatures. In a pond, bacteria and 

 other micro-organisms are at the beginning of the chain. Crustaceans 

 feed on the micro-organisms and themselves act as food for aquatic insects 

 that, in turn, are eaten by fish. The dead bodies of the latter serve to 

 nourish bacteria. Animals feeding on plants are the prey of carnivorous 

 animals, that are themselves eaten by other carnivores. This concept of 

 food chains demonstrates how the macromolecules in the cells of an 

 organism can serve as food to other organisms which begin by hydrolysing 

 them with the aid of the arsenal of hydrolases so liberally distributed 

 throughout the biosphere. In this way one part of the biosphere serves to 

 feed the other part. However, if each portion of the biosphere was 

 nourished solely by the consumption of another portion, life would be 

 progressively stifled and would disappear in a very short time. In the same 

 way as for the metabolism of a single organism the metabolism of the 

 biosphere implies an entry and an exit of matter and energy. This 

 continuous exchange with the surroundings constitutes the general 

 metabolism of the biosphere which is dealt with in Part Six. 



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