A food chain is a linear sequence of organisms in an ecosystem in which nutrients and energy are transferred from one organism to another when the latter consumes the former, and are then eventually transferred to another, larger organism which consumes the latter. A food web consists of several interconnected food chains.
Every food chain has four major components. The first is the sun, which is the initial source of energy for nearly everything on the earth (except for the energy radiating from the earth's molten interior). The second is the producers, which are plants or other organisms that produce their own nutrients through photosynthesis. Consumers are all organisms that depend on plants or other organisms for food, namely herbivores (primary consumers), carnivores (secondary consumers), parasites and scavengers. Decomposers, the final stage, are organisms that obtain energy from dead or waste organic material and convert it into inorganic materials such as nutrient-rich soil.