CBSE Class 10 Science 2017 · Paper 31/1/3 · Question 3

A lake is an ecosystem because its living organisms, producers (phytoplankton and water plants), consumers (zooplankton, fish) and decomposers (bacteria, fungi), interact with one another and with the non-living parts of their surroundings (water, sunlight, temperature, dissolved gases and minerals). It is a natural ecosystem because it forms and sustains itself by natural processes, with its nutrients recycled by decomposers; people do not create or maintain it, as they do a garden, a crop field or an aquarium.