CHAPTER SEVEN 



THE RELEASE OF ENERGY 



In order to do work, every machine in a manufacturing estab- 

 lishment must be suppHed with energy, and every Hving cell in a 

 plant requires energy for carrying on its work of repair, growth, 

 and movement. In manufacturing estabhshments the energy is 

 usually generated at one place and is then transmitted by means 

 of shafts and belts or by wires and motors to all parts of the 

 factory. It has already been shown that the plant obtains en- 

 ergy from sunhght during photosynthesis, and that this energy 

 is stored as potential energy in the food. Since the food passes 

 from cell to cell, some of the stored or potential energy finally 

 reaches every living cell of the plant. Here the energy that is 

 in the food may be liberated, or changed to free energy, and used 

 in the hfe processes of the cell, such as the synthesis of fats, 

 proteins, and other compounds. 



Respiration. A steam engine is supphed with energy by the 

 oxidation of fuel beneath the boiler that is connected with it. 

 A cell is supplied with energy by the oxidation of food within it. 

 The process by which the cells obtain energy through the oxidation 

 of foods is called respiration. In the process oxygen is absorbed 

 and carbon dioxide is given off. Respiration takes place in all 

 living cells, and to carry on this necessary process all living parts 

 of the plant must have access to oxygen. 



The substance most commonly oxidized in plants is glucose. 

 Other carbohydrates like starch are changed to glucose before 

 oxidation takes place. Fats occurring in seeds are first oxidized 

 to sugars, and the sugars may be used in building tissue or they 

 may be further oxidized to carbon dioxide and water in respira- 

 tion. Protein may be oxidized in respiration, but this does not 

 usually occur unless sugar is scarce or lacking entirely. The 

 leaves and stems of land plants obtain their oxygen from the 



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