Final answer:
Guard cells regulate the opening and closing of stomata on plant leaves. They control gas exchange and the intake of carbon dioxide needed for photosynthesis. Environmental factors influence the opening and closing of guard cells.
Step-by-step explanation:
Guard cells are specialized cells found in pairs in the epidermis of plant leaves. Their role is to regulate the opening and closing of stomata, which are small pores on the leaf surface. Stomata allow for gas exchange and control the intake of carbon dioxide needed for photosynthesis and the release of oxygen and water vapor. The opening and closing of guard cells is influenced by various environmental factors such as light intensity, leaf water status, and carbon dioxide concentrations.