Green plants release oxygen during oxygen-producing photosynthesis. The oxygen comes from water molecules split during the light-dependent reactions, rather than directly from carbon dioxide.
The basic process
When light reaches photosynthetic machinery, reactions help separate electrons and protons from water. Oxygen is generated as a byproduct. Other reactions then use energy and electrons to help fix carbon dioxide into sugars.
Why the balanced equation is useful
A simplified overall expression is carbon dioxide plus water plus light energy yielding sugar and oxygen. It summarizes the inputs and outputs, but many individual chemical steps occur between them.
Plants also consume oxygen
Plant cells perform respiration, including at night. A healthy plant in good light can produce more oxygen through photosynthesis than it consumes, but net gas exchange varies with species and conditions.
Can one houseplant supply all the air in a room?
No. A few indoor plants should not be treated as a substitute for building ventilation. Their oxygen production under normal indoor conditions is modest compared with the air exchange needed for healthy indoor environments.
Frequently asked question
Do all organisms that photosynthesize release oxygen?
No. Some photosynthetic bacteria use processes that do not produce oxygen.
Sources and further reading
See this university, government or veterinary source for more information.
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