Transpiration is the process by which leaves lose water to the environment by evaporation through openings known as stomates. The stomates are regulated by guard cells. When conditions are favorable for photosynthesis during the daytime, the guard cells open the stomates and carbon dioxide can enter the leaf to use for this process. During conditions when there is scarce rainfall, the guard cells close off the stomates. As water escapes the leaves during transpiration, it leaves room for more water to move up the xylem tubes via capillary action. This ensures a supply of water gets transported to the areas of the plant where photosynthesis occurs. Transpiration requires heat energy and wind to help water evaporate from the leaves.