What causes the stomata on a plant to open?
Stomata open when the guard cells become turgid. When are the stomata usually open? The guard cells become turgid when it is light and there is plenty of water in the soil. What happens when stomata open? The problem which the plant has to juggle is that of trying to let CO2 in (for photosynthesis) whilst holding on to as much water as possible. The physics of the processes mean that the plant loses about 500 molecules of water (by transpiration) for every molecule of CO2 that comes in. The closing of the stomata slows BOTH processes. The clever thing is that the plant opens its stomata at a time when the most CO2 will get in for each molecule of water lost. For example, the stomata are closed at night when CO2 is not needed and open stomata would simply loose water. It seems that light causes ions to be pumped into the guard cells. This results in water entering the guard cells by osmosis. Hydrogen ions, Potassium ions and Chloride ions are important, but sucrose concentration in the
