Plants produce their own food through the process of photosynthesis, which occurs in their leaves. Photosynthesis requires light, air, and water. During photosynthesis, plants use light to produce glucose from carbon dioxide and water, and release oxygen as a byproduct. Glucose provides energy for the plant to grow. Plants produce enough glucose during photosynthesis to meet their needs both during the day and at night or on cloudy days, storing any excess glucose.