They are the source of all the food in an ecosystem. Green plants and certain micororganisms are producers. They make their own food by using the sun's energy to produce food in a process called photosynthesis . The energy in plants is passed on when they are eaten by organisms. Organisms that cannot make their own food may eat the producers directly, or they may eat other organisms that cannot make their own food.
Producers are the source of all the food in an ecosystem.