leaf shown via colorized electron microscope image]] In botany, a "stoma" (also stomate; plural stomata) is a tiny opening or pore, found mostly on the underside of a plant leaf and used forgas exchange. The pore is formed by a pair of specialized sclerenchyma cells known as guard cells which are responsible for regulating the size of the opening. Air containing carbon dioxide enters the plant through these openings where it gets used in photosynthesis and respiration. Oxygen produced by photosynthesis in the parenchyma cells (parenchyma cells with pectin) of the leaf interior exits through these same openings. Also, water vapor is released into the atmosphere through these pores in a process called transpiration. Dicotyledons usually have more stomata on the lower epidermis than the upper epidermis. Monocotyledons, on the other hand, usually have the same number of stomata on the two epidermes.

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