14 FOUNDATIONS OF BIOLOGY 



oxidizable and richer in potential energy. Fats represent 

 a synthesis of an acid (fatty acid) and glycerine. Examples 

 are butter and all oils of plant or animal origin. 



Thus proteins, carbohydrates, and fats represent large 

 classes of substances which are distinctly characteristic of 

 living matter, not being found in nature except as the result 

 of protoplasmic activity; although biochemists now can 

 artificially synthesize certain fats and carbohydrates as well 

 as the amino acid constituents of some proteins. Proteins 

 undoubtedly play the most important part in the organiza- 

 tion of protoplasm, while the carbohydrates and fats contrib- 

 ute largely to the supply of available energy. However, it is 

 impossible to draw a hard and fast distinction in regard to 

 their respective contributions because, for example, as we 

 shall see later, carbohydrates form the foundation upon 

 which proteins are synthesized by green plants. 



Proteins, carbohydrates, and fats are frequently referred 

 to as the foodstuffs, but it will be recognized that while, in a 

 way, they constitute the chief groups, all the constituents 

 of protoplasm must be available. Accordingly, inorganic 

 salts, water, and free oxygen are really foodstuffs. Further- 

 more, recent investigation has disclosed another class of 

 organic substances which are absolutely necessary for the 

 constructive phases of protoplasmic activity. These are 

 termed VITAMINES and must be classified as accessory food 

 substances, although as yet little is known in regard .to their 

 chemical structure or mode of action. And then, finally, on 

 the border line of food substances may be mentioned a great 

 group of organic catalyzers, called ENZYMES, which play a 

 major role in metabolism. But, when all is said, our knowl- 

 edge of the chemical complexities of protoplasm affords no 

 adequate conception of how they are related to the phe- 

 nomena of life. This is beyond present-day biology. 



