What happens to oxygen that cells don't need?

When plants produce oxygen, particularly during the process of photosynthesis, any excess oxygen that is not used by the plant cells for respiration can diffuse out of the plant through small openings called stomata. These stomata are primarily located on the underside of leaves and allow for gas exchange; they enable oxygen, as well as carbon dioxide, to move in and out of the plant. This mechanism is essential for maintaining the balance of gases in the atmosphere and ensuring that the oxygen released during photosynthesis is available for other organisms, including humans, to use.

The other options do not accurately reflect the fate of excess oxygen in plants. While oxygen is indeed a byproduct of photosynthesis, it is not used as a raw material in the process itself, nor is it converted into glucose or stored in roots under normal circumstances. The primary role of the roots is to absorb water and nutrients from the soil, not to store gases like oxygen.