42 



General Botany 



the carbohydrates are transformed into glycerin, 

 with the fatty acids and forms fats and oils. 



This unites 



Fig. 24. Diagram of fat synthesis 



carbohydrate 

 carbohydrate 



■>- glycerin 

 -^ fatty acid 



fats and oils 



When fats are broken down or digested, they are changed back 

 again to glycerin and fatty acid, and may be finally altered to 

 glucose. The digestion of fats consists in forcing water into the 

 oil molecule, thus breaking it up into two or more molecules. 



C3H5(Ci8H3502)3 + 3H20 



fat water 



-^ C3H5(OH)3 + 3 HC18H35O2 



glycerin stearic acid 



In plant cells the glycerin and stearic acid may be further trans- 

 formed into sugar before leaving the cell. Compare the formula 

 of a fat with the formula of a sugar. Does it contain a larger 

 or smaller proportion of oxygen ? In changing from sugar to fat 

 is oxygen added or removed ? 



Sunlight is the direct source of energy used in photosynthesis. 

 The energy used in the transformation of the simple sugars into 

 fats and many allied compounds is derived from the oxidation 

 of a part of the sugar formed, not directly from sunlight. This 

 is discussed more fully under respiration. 



The making and use of proteins. The proteins are the third 

 class of foods. They too are constructed in large part from the 

 carbohydrates ; but their molecules are vastly more complex than 

 are the molecules of carbohydrates and fats, and they all con- 

 tain the elements nitrogen and sulfur and some of them contain 



