PROBLEM I . The Part Leaves Flay 



The chlorophyll takes no part in the 

 synthesis of proteins. In fact, protein 

 synthesis takes place in all other parts of 

 the plant as well as in the leaves. It oc- 

 curs in practically all plants, whether 

 green or not green. Yet animal cells, as 

 far as we can tell, never make proteins 

 from sugar and simple mineral com- 

 pounds. 



Proteins are important for the plant. 

 As you have learned in the last unit pro- 

 tein is one of the compounds which is 

 used in making protoplasm. And without 

 the making of protoplasm there can be 

 no growth. 



Fat synthesis. Some of the sugar is 

 changed into fats. Fats, like carbohy- 

 drates, are made up of carbon, hydrogen, 

 and oxygen. Some of the oxygen is lost 

 from the sugar in the making of fats, so 

 fats have proportionately less oxygen 

 than carbohydrates. This process, too, 

 does not depend on chlorophyll; it can 

 go on in any part of the plant. In some 

 plants much fat forms and accumulates, 

 often in the fruit and seed. The kernel 

 of corn, the fruit of the olive tree, and 

 the seed of the cotton plant among many 

 other seeds and fruits contain large 

 amounts of fat (oil). 



Another use for sugar. In most plants, 

 when a certain amount of sugar has ac- 

 cumulated, it is changed into starch. The 

 starch grains in a cell are easy to recog- 

 nize. See Figure 169. This starch may 

 soon be changed back again to sugar or 

 it may accumulate in the plant. The 

 sugars which are not built up into fats 

 or proteins have another important use 

 in the plant. They are oxidized in the cell. 

 Fats and proteins may be oxidized too, 

 but generally it is sugar. 



in Making Food 



143 



Fig. 169 Cells of the potato containing starch 

 grains. From what is starch made in a potato? 



In oxidation energy is released. Some 

 of the energy released by oxidation of 

 sugar is used in making fats and proteins. 

 Other small amounts are used in assimila- 

 tion, the process of making protoplasm 

 from food. Some of the energy is lost 

 from the cells as heat. All this energy 

 comes from the oxidation of sugar in the 

 cells in every part of the plant. 



Respiration in plants. Oxidation is the 

 union of oxygen with a substance. Ox- 

 idation in the plant is called respiration. 

 If the substance oxidized is sugar, two 

 simple compounds result: carbon dioxide 

 and water as indicated in the following 

 equation. 



carbon dioxide + water 

 6CO2 + 6H„0 



Respiration goes on in all the living cells 

 all the time. As a result of photosynthesis 

 in the green parts in the daytime, there 

 is a steady production of oxygen in the 

 cells. Some of this stays in the plant and 

 combines with food in oxidation. But 

 so much is produced that it is easy to 

 demonstrate oxygen passing out of green 



Sugar -[- oxygen 



