Photoautotrophs

Photoautotrophs are organisms that obtain energy from light and carbon from inorganic sources, typically carbon dioxide, to synthesize organic matter. They form the base of most ecosystems by providing the organic compounds used by heterotrophs and, in many lineages, by releasing oxygen through photosynthesis.

In plants, algae, and cyanobacteria, light energy is captured by chlorophyll and other pigments and converted into chemical energy via a two-photosystem electron transport chain. Oxygenic photosynthesis uses water as an electron donor, splits water in photosystem II, and releases oxygen. The resulting ATP and NADPH power the Calvin cycle, fixing CO2 into sugars that can be respired or built into biomass.

Some bacteria perform anoxygenic photosynthesis, using pigments such as bacteriochlorophyll and electron donors other than water, producing organic matter without releasing oxygen.

Photoautotrophs are diverse, including land plants, a variety of algae, and cyanobacteria, inhabiting aquatic and terrestrial environments from oceans to soils. They show adaptations such as C4 and CAM metabolism in arid or high-light environments to conserve water. They are central to primary production and drive global carbon and oxygen cycles, supporting life by converting light energy into chemical energy.