CBSE Class 10 Science 2022 · Paper 31/1/1 · Question 7(b)

(i) Two human-made (artificial) ecosystems: a garden and a crop field. (An aquarium is another.) (ii) A pond is a natural, self-sustaining ecosystem. Besides producers (algae and water plants) and consumers (fish and other animals), it has plenty of decomposers, bacteria and fungi, which break down dead remains and waste products into simple substances that go back into the water and are used again by the producers. Its waste is recycled and does not pile up, so the pond does not need to be cleaned by us as an aquarium does. An aquarium is a human-made ecosystem: its fish are fed by us from outside, and it has too few decomposers to break down the leftover food, excreta and dead matter as fast as they are produced, so the waste collects and fouls the water. That is why an aquarium has to be cleaned by us regularly, while a pond is not cleaned in the same manner.