stomatal density 2.3.2

• a guard cell is a cell that is either side of the stomata that controls the opening of the stomata
• the guard cells close the stomata when: there is a high concentration of CO2 inside the leaf, there is not much sunlight (night) and if the plant cannot afford to lose any more water eg cacti
• the cell wall of the guard cell is thicker on the inside so when the cell swells, the stomata opens
• 1 cm^2 = 100mm^2