Fotosyntézou

Fotosyntézou is the set of biochemical processes by which light energy is converted into chemical energy, enabling the synthesis of organic compounds from carbon dioxide and water. It occurs mainly in the chloroplasts of plants, algae, and some bacteria, and is driven by light absorbed by pigments such as chlorophyll a and accessory pigments. Oxygen is released as a byproduct in most oxygenic photosynthesis, shaping Earth's atmosphere.

Most photosynthesis occurs in two stages: light-dependent reactions and the Calvin cycle. In the light-dependent reactions, occurring in the thylakoid membranes, light energy drives water splitting (photolysis) to release oxygen, while electrons travel along an electron transport chain to generate ATP and NADPH. The Calvin cycle, in the stroma, uses CO2 and the energy carriers ATP and NADPH to synthesize sugars such as glyceraldehyde-3-phosphate, which can be transformed into glucose and starch.

Plants exhibit different photosynthetic strategies. The majority perform C3 photosynthesis, fixing CO2 directly in the Calvin cycle, but this can be limited by photorespiration at high temperatures. C4 photosynthesis spatially separates carbon fixation between mesophyll and bundle-sheath cells to reduce photorespiration, while CAM photosynthesis concentrates CO2 at night in arid conditions. These adaptations increase photosynthetic efficiency under varying environmental conditions.

Photosynthesis is the fundamental source of atmospheric oxygen and forms the base of most food webs. It also plays a major role in the global carbon cycle, influencing climate and biogeochemical processes. Understanding fotosyntézou informs agriculture, ecology, and efforts to develop artificial photosynthesis and sustainable energy technologies.