Which one of the following is NOT a functional unit of an ecosystem?

The correct answer is Option (1) → Stratification

An ecosystem has a structure and it works as a unit. The structure includes the species present and how they are arranged; the vertical arrangement of species in layers (trees on top, then shrubs, then herbs and grasses) is stratification. The ecosystem functions as a unit through four processes: productivity, decomposition, energy flow and nutrient cycling.

Option (1) Stratification — Not a functional unit of an ecosystem. Stratification is part of the structure of an ecosystem, the way species occupy different vertical levels. It is not a process.

Option (2) Energy flow — A functional unit of an ecosystem. Energy flows one way, from the sun to producers and then to consumers.

Option (3) Productivity — A functional unit of an ecosystem. Productivity is the rate at which producers make organic matter.

Option (4) Decomposition — A functional unit of an ecosystem. Decomposition breaks dead matter into simple inorganic substances.

NCERT Extract:
Ecosystem – Structure and Function – “… Identification and enumeration of plant and animal species of an ecosystem gives its species composition. Vertical distribution of different species occupying different levels is called stratification. For example, trees occupy top vertical strata or layer of a forest, shrubs the second and herbs and grasses occupy the bottom layers. The components of the ecosystem are seen to function as a unit when you consider the following aspects: (i) Productivity; (ii) Decomposition; (iii) Energy flow; and (iv) Nutrient cycling.”