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EXPERIMENTAL GENERAL SCIENCE 



form of energy. In the formation of ordinary foods, the 

 plant uses the water from the soil and the carbon dioxide of 

 the air. All the carbon found in plants is obtained in this way 

 from carbon dioxide. Since only the carbon is used in food 

 making, the oxygen is given off again by the plant. The 

 process of making food in this way is known as photosynthesis. 

 There are three classes of foods commonly formed by plants, 

 namely, carbohydrates, fats or oils, and proteins. The car- 

 bohydrates are most common and are represented by such 



r 



FIG. 80. Sectional and surface view of part of moss leaf showing chloro- 

 plasts. (Stevens.) 



substances as starch (CeHioOs), grape sugar (CeH^Oe), cane 

 sugar (Ci 2 H 2 2On), and cellulose (CeHioOs). In carbohy- 

 drates, the hydrogen present is always twice the amount of 

 the oxygen. Most of the oils with which we are familiar are 

 also produced by plants. These contain carbon, hydrogen, 

 and oxygen, but the oxygen is usually in smaller proportions 

 than in the carbohydrates. Proteins contain the three chem- 

 ical elements found in other foods with the element nitrogen 

 added. Protoplasm, lean meat, and albumen are examples 

 of proteins. The bodies of all animals and plants, though 



