Stomata are microscopic openings on the surfaces of plant leaves that allow for the easy passage of water vapor, carbon dioxide and oxygen. They are crucial to the function of leaves as photosynthesis requires plenty of carbon dioxide as well as the release of waste oxygen and excess water. "Stomata" means "mouth" in the Greek language.
While the primary site of stomata is on leaf surfaces, they are found on all above-ground parts of the plant. Each stomata is composed of two guard cells surrounding an opening known as a stoma. The number of stomata that form depends on environmental conditions, with higher light levels and moisture or lower carbon dioxide levels causing a higher density.
Stomata are capable of opening and closing in response to environmental conditions, in particular light levels, where the presence of sunlight causes them to open. Plants benefit from this since they must take in carbon dioxide for photosynthesis to convert it, together with water, into sugar, but it also places them at risk. In warmer environments, and particularly in dry air, plants lose a great deal of water through their stomata. This creates the danger of depleting a plant's water stores, which are also crucial to photosynthesis.