Photosynthesis, in general, is the reverse of respiration, in which carbohydrates are broken down to release energy. These are also known as autotrophs, since they make their own food. Producers are able to harness the energy of the sun to make food. They make up the bulk of the food chain or web. In short, consumers are every organism that eats something else.
Primary consumers are the herbivores, and are the second largest biomass in an ecosystem.
This continues with tertiary consumers, etc. These are mainly bacteria and fungi that convert dead matter into gases such as carbon and nitrogen to be released back into the air, soil, or water. Fungi, and other organisms that break down dead organic matter are known as saprophytes . Even though most of us hate those mushrooms or molds, they actually play a very important role. Without decomposers, the earth would be covered in trash.