During the day, plants produce oxygen by splitting water molecules in the light-dependent reactions of photosynthesis.
Light-dependent reactions occur in thylakoid membranes of chloroplasts and begin with the absorption of light energy. This energy (together with water and photosystems) is used for the production of ATP and the reduced electron carrier NADPH which are necessary for the next stage of photosynthesis. Oxygen is released.
At the same time, plants use cellular respiration to produce some of the carbon dioxide needed by the light-independent reactions to make sugars.
Cellular respiration is a chemical reaction of plants where they use glucose and oxygen to produce carbon dioxide and water and release energy.
During the night, plants produce carbon dioxide, but not oxygen because only cellular respiration takes place.
There is no sunlight at night, so only the cellular respiration occurs.
