Which one of the following is the best description of the term 'ecosystem'?

Answer: (c) A community of organisms together with the environment in which they live

Ecosystem = the community (biotic) PLUS its physical environment (abiotic), working together.

The idea

Ecology is arranged in levels, each wider than the last. The word “ecosystem” is the first level that brings in the non-living part: soil, water, air and sunlight. That is the test for the right option.

Population (one species) → Community (all species) → Ecosystem (+ non-living) → Biosphere

Why the others are wrong

(a) That is a community — only the living part.

(b) That is the biosphere.

(d) Flora and fauna are just the list of plants and animals — no environment, no interaction.

The trap

(a) says “interacting”, which sounds complete. Without soil, water and sunlight, it is only a community.

Also know

The levels: organism → population (one species) → community (all species of a place) → ecosystem (community + physical environment) → biome → biosphere. An ecosystem can be as small as a pond or as large as a forest, and it can be man-made: a crop field or an aquarium.