It is the source of all energy.
A living organism can either make its own food or depend on others to make food for them. For example green plants produce their own food from a process called photosynthesis. They use the chloroplasts in their cells to capture energy in sunlight. They combine it with water and carbon dioxide from the air to produce sugars for themselves. Green plants are therefore known as producers or autotrophs. Bacteria can also make their own food or breakdown food.
