CHAPTER X 



CHEMICAL TRANSFORMATIONS IN LIVING MATTER AND ITS 



PRODUCTS 



CHEMICAL EQUILIBRIUM AND REACTION ENZYMES AND CELLS AS 

 CATALYSTS OR ENERGY TRANSFORMERS 



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 sub- 

 stances 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 reactions 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 carrying on the 

 reactions of all other cells. 



In the process of building up in the chlorophyll- bearing cell 

 the chlorophyll, or something underying it, acts as a transformer 

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

 case light energy and chemical energy) which would not occur 



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