What is an ecosystem?

The correct answer is Option (3) → Functional unit of nature, where living organisms interact among themselves and also with the surrounding physical environment.

An ecosystem has two kinds of parts: living organisms (biotic) and the physical environment, such as air, water and soil (abiotic). What makes it an ecosystem is that the organisms interact both with each other and with their physical surroundings. Ecosystems range in size from a small pond to a large forest or a sea.

Option (1) Group of interacting species at one place. — Incorrect. A group of interacting species at one place is a community. It leaves out the physical environment.

Option (2) Group of interbreeding organisms only. — Incorrect. A group of interbreeding organisms is a population of one species. It is the smallest of these levels and has no physical environment in it.

Option (3) Functional unit of nature, where living organisms interact among themselves and also with the surrounding physical environment. — Correct. This is the book’s definition. An ecosystem is a functional unit of nature in which living organisms interact among themselves and with the surrounding physical environment.

Option (4) Group of living organisms and the interactions between them. — Incorrect. Organisms and their interactions with one another form a community. Without the physical environment, it is not an ecosystem.

NCERT Extract:
Ecosystem – “An ecosystem can be visualised as a functional unit of nature, where living organisms interact among themselves and also with the surrounding physical environment. Ecosystem varies greatly in size from a small pond to a large forest or a sea. Many ecologists regard the entire biosphere as a global ecosystem, as a composite of all local ecosystems on Earth.”