Primary producers, or autotrophs, make up the first trophic level of all food webs. Autotrophs are organisms that produce their own energy from inorganic substances, such as carbon dioxide and water. The primary producers of many food webs are green plants.
Only 10 percent of the energy of the first trophic level is transferred to the next; therefore, a mere 10 percent of the energy produced by primary producers is passed on to primary consumers, or organisms that consume the primary producers. Because only a small amount of the original energy produced is retained by the primary consumers, many more primary producers must exist to support a smaller number of primary consumers.
The best-known producers are green plants. They take in energy from the sun to combine carbon dioxide and water into glucose, a sugar used as energy in many organisms. This process is called photosynthesis.
Other autotrophs use the energy in sulfur- or nitrogen-containing compounds instead of sunlight to power their energy-producing process. These autotrophs, called chemoautotrophs, make their own energy through chemosynthesis. Chemoautotrophs are usually the producers in hostile environments, such as in deep sea vents and hot springs that contain more unconventional food webs. Bacteria are the chemoautotrophs in these locations. Some of these bacteria cannot survive in the presence of oxygen, so they live where oxygen is absent.