Importance of Transpiration to the Plant Transpiration in plants is inevitable because of the existence of numerous most cell surfaces from which evaporation occurs. Fortunately for the plant the cuticle on the leaf surface restricts water loss to the stomata. Stomata are highly sensitive to water stress and close under conditions of drought and at night when photosynthesis ceases Control of water loss is important because excessive loss can easily result in death of a plant. Given the inevitability of transpiration and its potential to harm the plant. what possible advantages does this process have for the plant? It supplies plant cells with water which: is the mediumt for many biochemical reactions; is the solvent for minerals from the soil as well as sugars from photosynthesis is an important part of photosynthesis; and helps to maintain the turgidity of cells which is needed for growth and supporting the plant. The evaporation of water from the cells requires heat energy and results in cooling of the leaves, much as the evaporation of sweat cools our skin. It has been suggested that the transpiration stream (the movement of water through the plant) is needed to distribute mineral salts throughout the plant. However, mineral supply to leaves has been found to be just as great at night as during the day.