Ecosystems and their parts

Your body's digestive system is many parts working together: mouth, stomach, intestines. An ecosystem is the same idea for nature: all the living things in an area, together with the non-living things around them, working together and depending on each other.

Take a pond:

The plants need sunlight, water and carbon dioxide to make food; the fish need the plants and the oxygen; the water's temperature affects them all.

Forests, ponds and lakes are natural ecosystems. Gardens, crop-fields and aquariums are human-made. How can you tell? Nobody goes into a forest to add manure, but a farmer must water, weed and fertilise a field, and an aquarium's water must be changed.

Every living thing in an ecosystem has a role:

Even vegetarians are consumers: spinach and dal come from living plants.

Decomposers are the quiet heroes. When a plant or animal dies, bacteria and fungi break its body down into simple substances that go back into the soil. Plants take these up again. Without decomposers, dead bodies and wastes would pile up and the soil would run out of what plants need.

"Why must an aquarium be cleaned, but not a pond?" An aquarium is a small, incomplete ecosystem with too few decomposers. Uneaten food and the fishes' wastes build up faster than they are broken down, and the water turns dirty. In a pond, the decomposers keep up.