Plants and animals live in particular habitats: for example, in an ocean, a pond or a deciduous forest. Habitats like these are eco-systems. They provide a home for various kinds of living beings that are dependent on one another. For instance, in a forest, the trees and other plants produce oxygen and regulate the water cycle. When plants die, they are decomposed by bacteria and microbes to create fertile soil upon which new trees, bushes and other plants can grow. Then there are the small and the large animals that belong to this forest eco-system. They eat, digest, spread seeds and are themselves a part of the food chain. Human beings are also part of this eco-system. They use the forest as a recreational area or because it has wood growing in it that they need.
An eco-system is delicate. It is endangered by too much interference from outside. This can happen if people cut down too many trees, build a road through the forest in the wrong place or if fields are given too much fertiliser. The balance can also be disturbed in the sea if too many fish are caught.
Human beings move in several eco-systems; unlike most animals and plants, they are not restricted to a particular area, such as a forest or an ocean. But even humans can be said to live in a large habitat, as our whole world is one huge eco-system containing all the other small and large habitats.