Leaves need oxygen and carbon-dioxide (for photosynthesis). How do they get these gases?
Plants get carbon dioxide from the air through their leaves. The carbon dioxide diffuses through small holes in the underside of the leaf called stomata. It also allows the oxygen produced in photosynthesis to leave the leaf easily. The exchange of oxygen and carbon dioxide in the leaf (as well as the loss of water vapor in transpiration) occurs through pores called stomata.