A food chain is a way to show how energy and nutrients are passed from one organism to another in the ecosystem. Plants (producers) are at the base. Herbivores (primary consumers) eat the plants, then carnivores (secondary consumers) eat the herbivores. There might be tertiary consumers that eat the carnivores, and so on. Decomposers break down the remains of dead organisms, returning nutrients to the soil, which in turn nourishes the plants, restarting the cycle.