The mechanism and reasoning for how this movement reduces water loss for plants is not fully known. However, one known mechanism is the closing of the stomatal pores which are the mouths of the plant in which gas exchange occurs. It takes in carbon dioxide which is important for photosynthesis. This movement of the stomatal pores is done by the guard cells that surround the pores. When there is not enough water in the air, the guard cells well release K+ ions into surrounding cells, and this causes water to move out of the guard cells. After the water is moved out the guard cells shrink in size as well as the stomata pores, and this prevents water from escaping through the pores. This information was obtained through Yahyai’s research on the starfruit tree’s response to differing soil water depletion levels. Trees were grown in a greenhouse, and there were four levels of soil water depletion. Stomatal response, CO2 levels, and transpiration were recorded and then analyzed.