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English: Opening and Closing of Stomata 1-Epidermal cell 2-Guard cell 3-Stoma 4-K+ ions 5-Water 6-Vacuole a. Open stoma: stomata are the small pores in the epidermis of leaves. They are bordered by guard cells. The stomata open when the turgor pressure increases in the guard cells, causing the cells to buckle outward.
They help to regulate the rate of transpiration by opening and closing the stomata. Light is the main trigger for the opening or closing. [ citation needed ] Each guard cell has a relatively thick and thinner cuticle [ clarification needed ] on the pore-side and a thin one opposite it.
Stoma in a tomato leaf shown via colorized scanning electron microscope image A stoma in horizontal cross section The underside of a leaf. In this species (Tradescantia zebrina) the guard cells of the stomata are green because they contain chlorophyll while the epidermal cells are chlorophyll-free and contain red pigments.
Opening and closing of stomata by bean-shaped guard cells. Items portrayed in this file depicts. creator. some value. object of statement has role: photographer.
Stomatal conductance, usually measured in mmol m −2 s −1 by a porometer, estimates the rate of gas exchange (i.e., carbon dioxide uptake) and transpiration (i.e., water loss as water vapor) through the leaf stomata as determined by the degree of stomatal aperture (and therefore the physical resistances to the movement of gases between the air and the interior of the leaf).
The closing of the stomata is often mediated by chemical signals from the root (i.e., abscisic acid). In irrigated fields, the fact that plants close their stomata in response to drying of the roots can be exploited to 'trick' plants into using less water without reducing yields (see partial rootzone drying).
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The stomata complex regulates the exchange of gases and water vapor between the outside air and the interior of the leaf. Typically, the stomata are more numerous over the abaxial (lower) epidermis of the leaf than the (adaxial) upper epidermis. An exception is floating leaves where most or all stomata are on the upper surface.