oxygenische

Oxygenic is an adjective used to describe processes that produce molecular oxygen (O2) as a by-product. In biology, it is most commonly applied to oxygenic photosynthesis, the form of photosynthesis that uses water as an electron donor and releases O2 into the atmosphere.

In oxygenic photosynthesis, light energy is captured by two photosystems (PSII and PSI) within the photosynthetic membranes. The oxidation of water at PSII releases electrons, protons, and oxygen. The excited electrons travel through an electron transport chain, generating ATP and NADPH, which power the Calvin cycle that fixes carbon dioxide into sugars. This pathway is central to the energy and carbon economy of many organisms.

Organisms that perform oxygenic photosynthesis include cyanobacteria, algae, and green plants. Cyanobacteria are ancient contributors to photosynthesis and are linked to the Great Oxygenation Event, a major increase in atmospheric oxygen about 2.4 billion years ago. The photosynthetic organelles of plants and algae, chloroplasts, are believed to have originated from endosymbiotic cyanobacteria.

Oxygenic photosynthesis contrasts with anoxygenic photosynthesis, carried out by some bacteria that do not split water and therefore do not release oxygen. These organisms use alternative electron donors, such as hydrogen sulfide or organic compounds, and often produce sulfur or related compounds instead of O2.

The concept of oxygenic processes is fundamental in studies of Earth's early atmosphere, photosynthetic biology, ecology, and global biogeochemical cycles.