phototrophy

Phototrophy is the ability of organisms to capture light energy and convert it into chemical energy, typically stored as ATP and reducing power such as NADPH, to drive cellular processes. It is one of the principal means by which organisms obtain energy, distinct from chemotrophy, which derives energy from chemical reactions. Phototrophs may also fix carbon, becoming photoautotrophs, or rely on organic carbon, as photoheterotrophs.

Oxygenic phototrophs, including plants, algae, and cyanobacteria, use chlorophyll and related pigments to drive photosystems I and II in an oxygen-generating electron transport chain. Water is split to provide electrons, releasing oxygen. The resulting ATP and NADPH fuel carbon fixation via the Calvin cycle, producing sugars and other organic compounds.

Anoxygenic phototrophs, such as purple and green bacteria, perform photosynthesis without producing oxygen. They use bacteriochlorophylls and other pigments and obtain electrons from donors like hydrogen sulfide, sulfide, or organic compounds, feeding a cyclic or non-cyclic electron transport chain and often not producing O2.

Some organisms rely on phototrophy that does not involve chlorophyll-based photosystems. Light-driven proton pumps such as bacteriorhodopsin and proteorhodopsin generate a proton-motive force to synthesize ATP, enabling photoheterotrophy in bacteria and archaea.

Phototrophy underpins primary production in many ecosystems, contributing to the global carbon cycle and supporting food webs. Evolutionarily, phototrophy has deep roots, with chloroplasts arising from endosymbiotic cyanobacteria in plants and algae. The diversity of phototrophic strategies reflects adaptations to light availability and ecological niche.