In botany, a stoma (also stomate; plural stomata) is a pore, found in the leaf and stem epidermis that's used for gas exchange. The pore is formed by a pair of specialized parenchyma cells known as guard cells which are responsible for regulating the size of the opening. Air containing carbon dioxide and oxygen enters the plant through these openings where it's used in photosynthesis and respiration, respectively. Oxygen produced by photosynthesis in the spongy layer cells (parenchyma cells wit… (More on Stomata)