Chlorophyll

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Chlorophyll
Chlorophyll, the pigment found in plants, some algae, and some bacteria that gives them their green color and that absorbs the light necessary for photosynthesis. Chlorophyll absorbs mainly violet-blue and orange-red light. The great abundance of chlorophyll in leaves and its occasional presence in other plant tissues, such as stems, causes these plant parts to appear green. In some leaves, chlorophyll is masked by other pigments. In fall, chlorophyll wanes in the leaves of trees, and other pigments predominate.

Chlorophyll is a large molecule composed mostly of carbon and hydrogen. At the center of the molecule is a single atom of magnesium surrounded by a nitrogen-containing group of atoms called a porphyrin ring. The structure somewhat resembles that of the active constituent of hemoglobin in the blood. A long chain of carbon and hydrogen atoms proceeds from this central core and attaches the chlorophyll molecule to the inner membrane of the chloroplast, the cell organelle in which photosynthesis takes place. As a molecule of chlorophyll absorbs a photon of light, its electrons become excited and move to higher energy levels (see Photochemistry). This initiates a complex series of chemical reactions in the chloroplast that enables the energy to be stored in chemical bonds.

See also: Algae; Lichens; Photosynthesis; Leaves

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