Biology · Ecosystems · NEET
Species composition and stratification. Species composition means the list of all plant and animal species found in that ecosystem (found by identifying and counting them). Stratification means the vertical distribution of species in different layers. NCERT states these are the two main structural features, so NEET expects both.
Productivity, decomposition, energy flow, and nutrient cycling. NCERT lists exactly these four. A memory hook is PDEN. Do not confuse these with the biotic components (producers, consumers, decomposers) which are part of the structure, not the function.
Species composition is part of the STRUCTURE. Students often mix this up. Structure answers 'what is present and how is it arranged' (species composition and stratification). Function answers 'what processes are happening' (productivity, decomposition, energy flow, nutrient cycling).
Stratification is the vertical distribution of different species occupying different levels (layers). NCERT gives a forest example: trees occupy the top layer, shrubs the second layer, and herbs and grasses occupy the bottom layer. It is a structural feature, not a function.
They are biotic COMPONENTS, so they are part of the structure of the ecosystem (along with abiotic components like air, water, soil). The functional processes are productivity, decomposition, energy flow, and nutrient cycling. NEET often traps students who label the four functions as 'producers, consumers, decomposers' - that is wrong.
Because within it, living organisms interact among themselves and with the physical (abiotic) environment, and these interactions drive processes like energy flow and nutrient cycling that keep the system self-sustaining. NCERT defines an ecosystem as a functional unit of nature.
Try the real previous-year questions from this chapter — each with the answer and a full solution.
An ecosystem is a structural and functional unit of nature where living organisms interact among themselves and with the surrounding physical (abiotic) environment.
Species composition is the identification and enumeration (counting) of all the plant and animal species present in an ecosystem. It is one of the two structural features.
In a forest, trees occupy the top vertical layer, shrubs occupy the second layer, and herbs and grasses occupy the bottom layer. This vertical layering is stratification.
Productivity, decomposition, energy flow, and nutrient cycling. Use the hook PDEN to recall them.
They are linked. NCERT treats the ecosystem as one structural and functional unit. But for exam listing, structure = species composition + stratification, and function = the four processes (PDEN).
