In terrestrial plants, gaseous exchange occurs mainly in leaves and to a lesser extent in the roots and stems. In leaves, the structures involved in gaseous exchange are stomata and spongy mesophyll tissues.
The stoma comprises of a stomatal pore and two specialized guard cells. The guard cells are structurally adapted by having chloroplasts, thicker, inelastic inner walls and thinner and elastic outer walls.
The stomata mostly opens during the day. They open when the guard cells are turgid.When the guard cells are flaccid, the thinner outer wall shrinks. The inner thicker walls curvature reduces causing the stomata to close.
