1. Photosynthesis: Leaves are the primary site of photosynthesis in plants, where they use sunlight, water, and carbon dioxide to produce glucose and oxygen. 2. Transpiration: Leaves help regulate the exchange of gases and water vapor with the environment through small openings called stomata, allowing for the uptake of carbon dioxide and release of oxygen. 3. Storage: Leaves can store excess nutrients and water for later use by the plant. 4. Protection: Leaves can also provide protection for the plant by producing toxins or spines to deter herbivores, and by shading the plant from excessive sunlight.