The chlorophylls are used to drive photosynthesis and are the most important plant pigments. Chlorophylls occur in plants, algae, and photosynthetic bacteria. In plants and algae, they are located in the inner membranes of chloroplasts, organelles (membrane enclosed structures) within plant cells which perform photosynthesis. Photosynthesis uses the light energy absorbed by chlorophylls to synthesize carbohydrates. All organisms on earth depend upon photosynthesis for food, either directly or indirectly.
Chemists have identified more than 1,000 different, naturally occurring chlorophylls. All chlorophylls are classified as metallo-tetrapyrroles. A pyrrole is a molecule with four carbon atoms and one nitrogen atom arranged in a ring; a tetrapyrrole is simply four pyrroles joined together. In all chlorophylls, the four pyrrole rings are themselves joined into a ring. Thus, the chlorophyll molecule can be considered as a "ring of four pyrrole rings." A metal ion, such as magnesium, is in the center of the tetrapyrrole ring and a long hydrocarbon chain, termed a phytol tail, is attached to one of the pyrroles. The phytol tail anchors the chlorophyll molecule to an inner membrane within the chloroplast.
The different types of chlorophylls absorb different wavelengths of light. Most plants use several photosynthetic pigments with different absorption spectra, allowing use of a greater portion of the solar spectrum for photosynthesis. Chlorophyll-a is present in higher plants, algae, cyanobacteria, and chloroxybacteria.
Higher plants and some groups of algae also have chlorophyll-b. Other algae have chlorophyll-c or chlorophyll-d. There are also numerous types of bacteriochlorophylls found in the photosynthetic bacteria.