chlorophyl

Science Dictionary
chlorophyll   (klôr'ə-fĭl)  Pronunciation Key 
Any of several green pigments found in photosynthetic organisms, such as plants, algae, and cyanobacteria. At its molecular core, chlorophyll has a porphyrin structure but contains a magnesium atom at its center and a long carbon side chain. Chlorophyll absorbs red and blue wavelengths of light, but reflects green. When it absorbs light energy, a chlorophyll molecule enters a higher energy state in which it easily gives up an electron to the first available electron-accepting molecule nearby. This electron moves through a chain of acceptors and is ultimately used in the synthesis of ATP, which provides chemical energy for plant metabolism. Plants rely on two forms of chlorophyll, chlorophyll a (C66H72MgN4O5) and chlorophyll b (C66H70MgN4O6), which have slightly different light absorbing properties. All plants, algae, and cyanobacteria have chlorophyll a, since only this compound can pass an electron to acceptors in oxygen-producing photosynthetic reactions. Chlorophyll b absorbs light energy that is then transferred to chlorophyll a. Several protist groups such as brown algae and diatoms lack chlorophyll b but have another pigment, chlorophyll c, instead. Other closely related pigments are used by various bacteria in photosynthetic reactions that do not produce oxygen. See more at photosynthesis.

Our Living Language  : From its name, one might think that chlorophyll has chlorine in it, but it doesn't. The chloro- of chlorophyll comes from the Greek word for "green"; chlorophyll in fact is the chemical compound that gives green plants their characteristic color. The name of the chemical element chlorine comes from the same root as the prefix chloro-, and is so called because it is a greenish-colored gas.
The American Heritage® Science Dictionary
Copyright © 2002. Published by Houghton Mifflin. All rights reserved.
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