(a) An ecosystem is a self-sustaining, structural and functional unit of biosphere. It is an open system. it depends upon external source of energy - solar energy and includes both living and their nonliving environment. the biological communities in an ecosystem are inseparably interrelated with one another.
On the basis of natue, ecosystem may be:
.natural ecosystem
.artificial ecosystem.

(b) ponds - natural ecosystem
aquarium - artificial ecosystem.
an aquarium does not contain soil and decomposers. so they need to be cleaned everday.
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