CHAPTER II 



CHEMICAL TRANSFORMATIONS IN LIVING MATTER, AND ITS 

 PRODUCTS CHEMICAL EQUILIBRIUM AND REACTION- 

 ENZYMES AND CELLS AS CATALYSTS OR ENERGY-TRANS- 

 FORMERS 



THE supply of energy necessary for all the changes observable in 

 living structures arises from chemical reactions occurring in solu- 

 tion. The energy exchanges occurring in any such reaction are 

 initiated and controlled by the cell and its secretions, or the 

 substances present in the cell, acting as energy-transformers in 

 the sense indicated in the preceding chapter. In the present 

 chapter it is proposed to consider the conditions governing reac- 

 tions in solution, and as far as possible how these are modified 

 by the presence of the peculiar energy-transformers found in the 

 living cell itself or its products. 



Let us, first of all, take a general survey of the cycle of energy 

 changes which occur in living structures as matter and energy 

 are taken up from the inorganic world, sent through various 

 changes in the living cell, in which many varied forms of matter 

 are produced and different types of energy are exhibited, and 

 finally both matter and energy are returned in other forms to the 

 inorganic world. The matter involved in these changes is directly 

 or indirectly taken from inorganic sources, and the energy from 

 the light energy of the solar rays; for whether the food of an 

 animal be of animal or vegetable nature, in the first instance it 

 must have come from vegetable sources. In the green parts of 

 plants, the chemical energy is first accumulated in matter which 

 afterwards being carried to other parts of the plant, or being used 

 as the food of animals, furnishes the store of energy used in carry- 

 ing on the reactions of all other cells. 



In the process of building up of organic bodies in the chloro- 

 phyll-bearing cell the chlorophyll acts as an energy-transformer, 

 that is, it induces an interaction between forms of energy (in this 

 case light energy and chemical energy), which would not occur 



15 



