Glucose sugar is the simplest organic molecule formed in the leaves of green plants. Glucose, and other forms of carbohydrates, are formed through the process of photosynthesis, which is the process by which plants use the energy from sunlight to combine carbon dioxide and water. These simple glucose molecules are what the plant feeds on to grow and thrive, although glucose may also be converted to starch for energy storage, or to structural carbohydrates such as cellulose or lignin.