A food chain is a model that shows how energy flows between living things. You can think of animals and plants in the same food chain as all living in the same neighborhood, which scientists call a habitat, and they all have a job to do. Interacting with each other day in and day out. Together, they form a kind of system. A self-contained collection of different things that all work together as a whole. And they also interact with the nonliving stuff around them, like the water, the air, the ground and the sun. Put it all together and what do you get? A special system called an "ecosystem". And food chains show us what eats what in an ecosystem.