CHAPTER I 

 ENERGY REQUIREMENTS IN CELLULAR NUTRITION* 



The formation of organic compounds from inorganic compounds 

 requires a certain amount of energy. If a certain quantity of sugar is 

 burned to carbon dioxide (CO 2 ) and to water (H 2 O), a certain amount of 

 energy is liberated in the form of heat. The heat given off in this case 

 is also a distinct product of combustion. This heat is always obtained 

 in the same amount regardless of the method chosen in burning the 

 sugar. It has been definitely determined to be 674 calories for i g. 

 molecule (180 g.) of sugar. The complete equation of sugar combus- 

 tion is therefore written 



C 6 H 12 O 6 + 1 2 O = 6CO 2 + 6H 2 O + 674 Cal. 



Consequently the same amount of energy will be needed to produce 

 sugar from carbon dioxide and water; for the law of the conservation 

 of energy requires that, if a certain process liberates a certain quantity 

 of energy, the reverse process will require the same quantity of energy. 

 Green plants get their energy from the sunlight; exactly the opposite 

 proceeds in the equation which should read from right to left; CO 2 

 and H 2 O are absorbed by the plant resulting in the formation of sugar. 

 But it is evident from the equation that CO 2 and H 2 are not sufficient 

 to produce sugar since it takes 674 calories of heat in addition. The 

 radiant energy of light is transformed by the chlorophyl granules of the 

 plant leaves into chemical energy which causes the formation of organic 

 compounds from the simple inorganic or mineral matter. Chlorophyl 

 is the green coloring substance of plants, and only green plants can use 

 the energy of sunlight for their growth. 



The growth of green plants is a storing of the energy of light in the 

 form of organic matter; their metabolism is largely synthetic, i.e., 

 building up. Plants without chlorophyl, however, like mushrooms, 

 molds, yeasts and bacteria, have to provide for their energy by some 

 other means. 



* Prepared by Otto Rahn. 



199 



