Which gas do plants absorb from the atmosphere during photosynthesis?

Plants absorb carbon dioxide from the atmosphere during photosynthesis.

Carbon dioxide enters a plant mainly through microscopic openings called stomata, usually found on leaves. Inside chloroplasts, the carbon from CO₂ is fixed during the Calvin cycle and used to build carbohydrates such as glucose. Water supplies hydrogen and electrons, while light provides the energy that drives the overall process.

The familiar summary equation is carbon dioxide plus water plus light energy producing carbohydrate and oxygen. Oxygen is released mainly because water is split during the light-dependent reactions; it is not simply the oxygen atom from incoming carbon dioxide being “breathed out.” This is one of the most common misunderstandings about photosynthesis.

Photosynthesis also explains why plants are important in the global carbon cycle. Plants, algae and cyanobacteria convert atmospheric carbon into organic matter, which can later become food, wood or other biomass. Jan Ingenhousz’s experiments in 1779 showed that plants need light to carry out this process, helping establish the modern understanding of photosynthesis.