A food chain shows the feeding relationship between different living things in a particular environment or habitat. Plants are at the bottom of a food chain because they are autotrophs that make their food from the non-living environment. Organisms that can make their own food are called producers. Consumers are animals that eat producers or other animals. The animal that eats the producer is called the primary consumer. The animal that eats the primary consumer is called a secondary consumer. The animal that eats the secondary consumer is called a third order consumer and so on to fourth, fifth, etc. The direction of arrows between the organisms shows who eats what.
Also, a food chain represents a series of events in which food and energy are transferred from one organism in an ecosystem to another. Food chains show how energy is passed from the sun to producers, from producers to consumers, and from consumers to decomposers. They also show how animals depend on other organisms for food.
In any ecosystem, many food chains overlap. Different food chains may include some of the same organisms. Several consumers may eat the same kind of plant or animal for food. When this happens, the food chain forms a food web. A food web shows how food chains are related within an ecosystem.