What is the primary pigment responsible for photosynthesis?

The primary pigment responsible for photosynthesis is chlorophyll a. It sits at the center of the light-capturing machinery in oxygen-producing photosynthetic organisms, including plants, algae, and cyanobacteria.

Chlorophyll a absorbs mainly violet-blue and orange-red light. Its excited electrons help drive the electron-transfer reactions that convert light energy into chemical energy. In the reaction centers of Photosystem II and Photosystem I, special chlorophyll a molecules are known as P680 and P700 because of their peak absorption wavelengths.

Chlorophyll a is not the only pigment involved. Chlorophyll b, carotenoids, and xanthophylls act as accessory pigments, extending the range of light that can be captured and passing energy to chlorophyll a. A common mix-up is choosing chlorophyll b because it is also abundant in green plants, but chlorophyll b primarily broadens the antenna system rather than serving as the universal primary reaction-center pigment.

Plants appear green because much green light is reflected or transmitted instead of being strongly absorbed. Chlorophyll a is also widely measured in ocean science as an indicator of phytoplankton biomass.