Stomata are epidermal structures, specific to leaves , responsible for gas exchange and transpiration . They also occur in some herbaceous branches or stems.
Each stomata has two stomatal cells ( guard cells ) elongated and reinforced in the cellulosic walls. Among the guard cells is a slit, the ostrich whose opening depends on the degree of cellular turgor.
The degree of aperture can thus be regulated by the plant, decreasing or increasing the values of transpiration. The guard cells are the only ones of the epidermis of the leaves to present chloroplasts . This is important for the opening mechanism of the grille.
Under the stomata lies a large sub-static chamber in connection with the lacunar parenchyma . This chlorophyllous parenchyme promotes total aeration of the leaf, and in it is the water vapor eliminated by the ostriches, by direct diffusion.
Most plants have stomata only in the lower epidermis of the leaves ( hypoestomatic leaves ). In many floating aquatic plants, such as victoria regia, they stay only in the upper epidermis of the leaves, which are called epiestomatic . If the leaves grow vertically, such as grasses, they occur on both sides. They are amphistomatic leaves.
Opening and closing stomata
The degree of turgidity of the guard cells is the determining factor for the opening of the stomata(When, by water entry, the cells become turgid, the walls opposite the ostiolo, thinner, yield when pressed by the vacuoles and drag the walls with reinforcement , which increases the opening of the ostium) or closure of the stomata (when the guard cells become flaccid, the reinforced walls abut and the ostium closes).
A) Turgid cells, open ostrich.
B) Wilt cells, closed ostrich.
Observe the deformation of the outer walls, without reinforcement, of the guard cells.