(a) An ecosystem is a self-sustained unit of living things (plants, animals and decomposers) and their non-living environment (air, water and soil).
Examples: A pond is an ecosystem that includes the aquatic life (aquatic animals and plants) that live in the pond water.
A forest is an example of a terrestrial ecosystem that includes the physical environment of the forest along with the plants and animals that live in that forest.
(b) The biotic components of an ecosystem are the plants, animals and decomposers present in it.
The abiotic components of an ecosystem are air, water and soil. The abiotic components also include physical factors such as light, temperature, pressure and humidity. Inorganic substances such as carbon dioxide, oxygen, water, nitrogen, sulphur and phosphorus are also abiotic components of an ecosystem.