fotosynteesin

Fotosynteesin, commonly known in English as photosynthesis, is the process by which light energy is converted into chemical energy in plants, algae, and some bacteria. During photosynthesis, chloroplasts containing chlorophyll capture light, driving reactions that store energy in carbohydrate molecules. Oxygen is released as a byproduct.

Most photosynthesis consists of light-dependent reactions that take place in the thylakoid membranes, producing ATP and NADPH while splitting water to release O2. An electron transport chain creates a proton gradient, and ATP synthase uses this gradient to generate ATP. NADP+ is reduced to NADPH, which provides reducing power for carbon fixation.

The light-independent reactions, or the Calvin cycle, occur in the stroma. Using ATP and NADPH, CO2 is fixed into sugars, ultimately forming triose phosphates such as glyceraldehyde-3-phosphate, which can be converted to glucose, sucrose, and starch.

Overall, the general chemical equation is often summarized as: 6 CO2 + 6 H2O + light energy → C6H12O6 + 6 O2. The process is the primary source of organic matter for almost all organisms, and it is responsible for the release of most atmospheric oxygen.

Variations of photosynthesis include C3, C4, and CAM pathways, which optimize carbon fixation under different temperatures, light intensities, and water availability. Chloroplast pigments include chlorophyll a and b and carotenoids, which expand the range of light absorbed.