ENERGY TRANSFERS AND BIOLOGICAL OXIDATIONS 159 



of reproduction, and population si/.e. Those sjjccies transferring 

 energy most efficiently and rapitUy tend to predominate in any eco- 

 logical situation. At the same time they produce the greatest changes 

 in the environment itself by markedly decreasing the available energy 

 (at least the chemical forms) and releasing large quantities of waste 

 products. 



ENERGY TRANSFERS 



As fast as energy is absorbed in the form of heat, light, or food- 

 stuffs, it is made available to the various parts of the organism. Heat 

 is transferred from molecule to molecule during the collisions resulting 

 from their kinetic motions. Those molecules heated by the environ- 

 ment thus acqtiire kinetic energy which is shared with neighboring 

 molecules after collisions. Animals utilize radiant energy, including 

 visible light, in this way by absorbing it with a gain in the kinetic 

 energy of molecules. Green plants also absorb light but are capable of 

 converting much of this absorbed energy into chemical forms instead 

 of heat. Special mechanisms (see page 206) are required for this 

 process. Chemical energy is contained in substrates or foods which 

 diffuse into or are ingested by the nonphotosynthetic species. 



The chemical energy accumulated either from photosynthesis or 

 directly from the environment is made available for the activities of 

 the organism by means of the complex array of reactions called metab- 

 olism. The activities thus powered include maintenance of tem- 

 perature, movement, growth, reproduction, repair, emission of light, 

 generation of electricity, accumulation of foods or substrates, elimina- 

 tion of wastes. The metabolic reactions involved in all these functions 

 are numerous, complex, and only partly known. Rapid progress is 

 being made but complete understanding is not in sight. Moreover, 

 different organisms possess different mechanisms in part, greatly com- 

 plicating the task. 



Energy Transfers in Metabolism 



The chemical transformations of cells include many reactions which 

 typically depend upon energy as either a reactant or a product. This 

 chemical energy is commonly referred to as free energy, symbolized by 

 the letter F. During a reaction at least part of the free energies of 

 the reactants appears in the products. The difference is the free- 

 energy change AF. Thus the reaction represented between A and B 

 to give Y and Z may be written 



