Chlorophyll is a pigment found in the chloroplasts of plants that absorbs the wavelengths of light required to convert water and carbon dioxide into chemical energy during photosynthesis. Molecules of chlorophyll are arranged around the photosystems embedded in the chloroplasts' thylakoid membranes. There can be several hundred chlorophyll molecules per photosystem.
A pigment is a molecule that will absorb a specific range of light wavelengths while reflecting those not included. The pigment chlorophyll a, one of two types of chlorophyll found in plants, absorbs light primarily at the wavelength of 430 nm (blue), and to a lesser extent, at the wavelength of 662 nm (red). Chlorophyll a absorbs light poorly in the electromagnetic spectrum occupied by the color green, so it is reflected back and gives plant tissues containing the pigment their green appearance.
Because it contains a fat-soluble phytol chain, chlorophyll can remain embedded within a lipid membrane. The portion of the chlorophyll structure extending past the membrane is the part that absorbs the light energy. A porphyrin ring serves as the central part of a chlorophyll molecule. This consists of a magnesium ion encircled by fused rings of nitrogen and carbon. Those organisms, such as plants, that use chlorophyll for photosynthesis represent the source of nearly all the oxygen (O2) found in the Earth's atmosphere.