Final answer:
When stomata on plant leaves open, transpiration occurs, resulting in the loss of water vapor to the environment. Guard cells control this process, which is essential for photosynthesis while also being mindful of water conservation.
Step-by-step explanation:
When stomata open on the surface of plant leaves, a physiological process known as transpiration occurs. Guard cells flank each stoma and are responsible for regulating the opening and closing of the stomata. These openings are critical for the plant to take up carbon dioxide for photosynthesis and to release oxygen. However, an immediate consequence of stomata opening is the loss of water vapor to the external environment, which increases the rate of transpiration. Plants balance the necessity of open stomata for photosynthesis with the need to conserve water by closing stomata to reduce transpiration, especially under environmental conditions like high temperature, which can lead to excessive water loss.