Which is/are true regarding ecosystem?

A. Self sufficient unit

B. Cyclic exchange of materials between living beings and environment

C.  Only requirement is input of energy

D. Characterised by a major vegetation type

Ecosystem is a fairly a self-sustainable unit. The movement of nutrient elements through the various components of an ecosystem is called nutrient cycling. Ecosystems need a constant supply of energy to synthesise the molecules they require, to counteract the universal tendency toward increasing disorderliness. Each ecosystem is dominated by a certain type of vegetation.