48 BIOLOGY 



If we analyse the various organic compounds used 

 as food, we shall see that there is a marked deficiency 

 m oxygen, although all their constituent elements have 

 a marked affinity for it. They are prevented from 

 satisfying their affinity for oxygen by the combinations 

 in which they are grouped. Now, if we make the con- 

 ditions favourable for the satisfaction of their oxygen 

 affinities new combinations are formed, and there is a 

 new grouping of the atoms, and during this process 

 heat is evolved and consequently energy is liberated. 

 We see, therefore, that the organic compounds used by 

 the organism as food are a store of potential energy, 

 which is ready to be transformed into kinetic energy 

 under certain conditions. 



Every living organism is constantly taking in oxygen 

 in the process of respiration, and this oxygen is carried 

 to the various parts of the body which are doing work, 

 and there it unites with the complex organic substances 

 which are poor in oxygen and themselves ready to unite 

 with it, and in the union kinetic energy is liberated. 



We have seen that food can be the only store of the 

 energy required by every organism for its daily life, 

 and also that by the addition of oxygen this potential 

 energy stored up in the food is transmuted to kinetic 

 energy. There are various other ways by which this 

 can be brought about, but there is no need to consider 

 them here. 



There are two other questions in relation to food that 

 we must consider first, how these organic compounds 

 are so transformed that the protoplasm may make use 

 of them, and, secondly, how these organic compounds 

 are built up. 



