chlorophyll

chlorophyll , green pigment that gives most plants their color and enables them to carry on the process of photosynthesis . Chemically, chlorophyll has several similar forms, each containing a complex ring structure and a long hydrocarbon tail. The molecular structure of the chlorophylls is similar to that of the heme portion of hemoglobin, except that the latter contains iron in place of magnesium. Within the photosynthetic cells of plants the chlorophyll is in the chloroplasts—small, roundish, dense protoplasmic bodies that contain the grana, or disks, where the chlorophyll molecules are located. Chlorophyll absorbs light in the red and blue-violet portions of the visible spectrum; the green portion is not absorbed and, reflected, gives chlorophyll its characteristic color. Chlorophyll tends to mask the presence of colors in plants from other substances, such as the carotenoids. When the amount of chlorophyll decreases, the other colors become apparent. This effect can be seen most dramatically every autumn when the leaves of trees "turn color."

chlorophyll Any one of a class of pigments found in all photosynthetic organisms; the most important members are chlorophyll a (see formula) and chlorophyll b, which occur in all land plants and are responsible for their green colour. Chlorophyll molecules are the principal sites of light absorption in the light-dependent reactions of photosynthesis (see photosystems I and II). They are magnesium-containing porphyrins, chemically related to cytochrome and haemoglobin. See also bacteriochlorophyll.

chlorophyll Group of green pigments present in the chloroplasts of plants and algae that absorb light for photosynthesis. There are five types: chlorophyll a is present in all photosynthetic organisms except bacteria; chlorophyll b, in plants and green algae; and chlorophylls c, d and e, in some algae. It is similar in structure to haemoglobin, with a magnesium atom replacing the iron atom.