Kaplan Nursing Entrance Practice Exam 2025 – The All-in-One Guide to Exam Success!

Stomata are small openings located on the surfaces of plant leaves that facilitate gas exchange. During the day, stomata open to allow carbon dioxide to enter for photosynthesis while also permitting oxygen and water vapor to exit. At night, when photosynthesis is not occurring due to the absence of light, stomata close primarily as a strategy to prevent water loss.

When stomata remain open at night, especially in conditions of high humidity or dry air, plants can lose significant amounts of water through transpiration. Closing the stomata helps to conserve water, which is crucial for maintaining hydration and overall health of the plant. This water conservation is particularly important in environments where water availability may be limited.

Other options, such as absorbing more carbon dioxide or promoting photosynthesis, are more relevant during the day. While storing energy is an important process for plants, it does not relate directly to the closing of stomata at night. Therefore, reducing water loss is the primary reason stomata close after sunset.