The right answer is photosynthesis.
Plants absorb CO2 from the air by photosynthesis as they grow. The carbon is then stored in the plants. At the end of the crop cycle or at the end of the season for perennial crops, the residues return to the soil. After the degradation of these, the carbon is organized to give more and more complex molecules and more and more stable.
In the short carbon cycle that spans less than a century and affects the balance of CO2 in the atmosphere, three basic reactions must be distinguished:
Photosynthesis: Plant photosynthesis consists in reducing the carbon dioxide in the atmosphere by the water absorbed by the roots using solar energy captured by the leaves, in the presence of mineral salts, with the release of oxygen, to produce carbohydrates.
Respiration: It is the opposite of photosynthesis: it transforms all organic matter into CO2, from O2 free oxygen. The equation of respiration can be summarized as:
(CH2O) n + n O2 → n (CO2 + H2O)
Fermentation: It happens in
* An aerobic environment (presence of oxygen) produces carbon dioxide
* And in an anaerobic environment (absence of oxygen) methane (the simplest hydrocarbon, with a single molecule of carbon).
