Trophic levels provide a structure for understanding food chains and how energy flows through an ecosystem. At the base of the pyramid are the producers, who use photosynthesis or chemosynthesis to make their own food. Herbivores or primary consumers, make up the second level. Secondary and tertiary consumers, omnivores and carnivores, follow in the subsequent sections of the pyramid. At each step up the food chain, only 10% of the energy is passed on to the next level, while approximately 90% of the energy is lost as heat.