Stomata are pores surrounded by guard cells in the epidermis of the leaves and stems of plants, which can open and close. Guard cells are modified epidermal cells, which have a distinct shape and are the only epidermal cells that contain chloroplasts. Guard cells are typically bean shaped in angiosperms. The guard cell walls are unevenly thickened. The inner cellulose microfibrils are radially arranged to form inelastic hoops around guard cells. Guard cells regulate the diameter of the stomata by changing shape, widening or narrowing the gap between the pair of guard cells.
