Explanation

(i) The term ‘ecosystem’ was coined by Sir AG Tansley (1935) to describe the whole complex of living organisms living together as a sociological units and their habitats (ii) The entire biosphere is referred to as global ecosystem, which consists of several local ecosystems of earth. The size of the ecosystem varies from small pond to a large forest or sea (iii) Vertical distribution of different species occupying different levels is called stratification, $e.g.,$ in a forest ecosystem, trees occupy top vertical layer, shrubs the second and herbs and grasses occupy the bottom layers