All life depends on a continuous inflow of energy. The substance of a plant or animal, or of ourselves, is held together, grown, repaired, and put into motion by means of energy derived from food. But food is manufactured only by green plants and some bacteria. When sunlight strikes a green plant growing on land or in water, remarkable events occur. In a process called "photosynthesis", the energy of light is locked into a complex molecule never found in itself in the nonliving world. This molecule, a sugar, forms the basis of most foods used by both plants and animals for their growth and activity.