Plants are called producers because they make their own food through a process called photosynthesis. Using sunlight, carbon dioxide from the air, and water from the soil, they produce glucose (a type of sugar) and oxygen. This ability to create energy-rich food supports not only the plants themselves but also other organisms in the food chain. Animals and humans rely on plants either directly or indirectly for food. Because they start the flow of energy in ecosystems, plants are known as the primary producers.[tex][/tex]