Food chains and energy flow

A food chain shows who eats whom, and so how energy passes from one living thing to the next. It always starts with a producer, a green plant that makes food from sunlight. Next comes a primary consumer (a herbivore) that eats the plant, then a secondary consumer that eats the herbivore, and so on up to a top predator. At each step most of the energy is used for living or lost as heat; only about a tenth passes on. In a real habitat, food chains link together into a food web, because most animals eat, and are eaten by, more than one kind of organism.