The term food 
chain describes the order in which organisms, or living things, depend on each other for food. Every ecosystem, or community of living things, has one or more food chains.
Most food chains start with organisms that make their own food, such as plants. Scientists call them producers. Organisms that eat other living things are known as consumers. A squirrel that feeds on plants is called a primary consumer. A hawk that eats the squirrel and other primary consumers is called a secondary consumer.
Decomposers are often the final link in a food chain. Decomposers are bacteria and other organisms that cause decay. When plants and animals die, decomposers break down their tissues. This adds nutrients to the soil so that new plants may grow. Then the food chain begins again.
A food web is a group of food chains within an ecosystem. Most living things eat more than one type of animal or plant. So their food chains overlap and connect. For example, the hawk that ate the squirrel also may eat fish. This makes the hawk a part of two food chains, or a food web.
