What is a food chain?

A food chain describes the flow of energy through an ecosystem, from the organisms that capture energy to those that consume them. It begins with producers, usually plants or algae, which make their own food from sunlight through photosynthesis. Primary consumers, or herbivores, eat the producers, and secondary and tertiary consumers, the predators, eat other animals. Finally, decomposers such as fungi and bacteria break down dead matter and return nutrients to the soil. At each step, only about 10 percent of the energy is passed on, with the rest lost as heat, which is why food chains rarely have more than four or five links. In reality, most organisms eat and are eaten by many species, so overlapping food chains form a complex food web.