The New Student's Reference Work/Photosynthesis

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2890768The New Student's Reference Work — Photosynthesis

Photosynthesis (fō′tō̇-sĭn′thē̇-sĭs), the process by which green plants make sugar, starch and similar food. The materials for this are carbon dioxide and water. The former is obtained chiefly (if not exclusively) by the leaves and twigs from the air, where it constitutes three parts in 10,000. It passes through the stomata by diffusion, dissolves in the water, saturating the cell-walls, and so enters the cells. The organs by which the food is made are the minute, green bodies called chloroplasts or chlorophyll bodies, which give the plant its color. They are composed of protoplasm, which holds a green dye, chlorophyll, and are imbedded in the colorless protoplasm of those cells which lie near the surface of a plant. The chlorophyll absorbs some of the light, especially the red and yellow parts, and this energy is used (how is unknown) in the process of food-making. Even twilight (not moonlight) suffices for some photosynthesis; the amount of food made is proportional, other things being equal, to the brightness of the light. The details of the process are not known. Usually a sugar appears as the end product; this increases to a certain amount in the water of the cell; some of it is turned into starch, minute granules being formed in the chloroplasts. The food is constantly being carried away to places of use or storage. In daylight food is usually produced more rapidly than it can be disposed of; but, as photosynthesis ceases at night, the surplus is then removed. See Aëration, Chlorophyll and Stomata.