What occurs when stomata close during photosynthesis?

• A. It increases CO2 uptake but reduces water loss.
• B. It has no effect on photosynthesis.
• C. It increases transpiration.
• D. It conserves water but limits CO2 uptake.

Answer: (D)

Stomata are the tiny openings that allow gases to diffuse in and out of the leaf. When they close, water vapor can’t escape as readily, so the plant conserves water and reduces transpiration. However, closing the openings also blocks the entry of carbon dioxide needed for photosynthesis. With less CO2 available in the leaf, the rate of photosynthesis drops because the Calvin cycle has less carbon to fix into sugars. So stomatal closure saves water but limits CO2 uptake, creating a trade-off between surviving drought and maintaining high photosynthetic activity.