MPSC 2026 Prelims Paper-I · Question 32 of 100

Correct — option (1), both statements are true and the Reason is the correct explanation of the Assertion. An assertion-reason question demands three separate judgements, and they must be made in order. First, is the Assertion true? An ecosystem is indeed treated as a natural resource system: it is the working unit within which soil, water, air, sunlight, minerals and living organisms are held together, and every natural resource a society draws on — food, fodder, fuel, fibre, timber, fish, fresh water — is produced by, or stored within, some ecosystem. This is why natural resource management is organised ecosystem by ecosystem: forest, grassland, wetland, coastal, agro-ecosystem. The Assertion is true. Second, is the Reason true? It states the standard definition of an ecosystem as a single unit in which the physical or abiotic environment and the biotic components exist within one framework. That is precisely what A.G. Tansley meant when he introduced the term in 1935 — a system comprising not only the organisms but the whole complex of physical factors with which they form one physical system. The Reason is true. Third, and this is the step candidates skip, does the Reason explain the Assertion? It does, and directly. The Assertion claims that an ecosystem is a resource system; the Reason supplies the ground for that claim by pointing out that the ecosystem unites the inorganic stock — the soil, water, air and minerals that are themselves resources — with the living components that capture energy and convert that stock into usable form. It is the integration of the two, in one functioning framework through which energy flows and nutrients cycle, that makes an ecosystem a resource-producing system rather than a mere inventory of separate resources. Remove either half and the claim collapses: abiotic material alone yields nothing, and organisms cannot exist without the physical environment. The Reason therefore states the very fact from which the Assertion follows, and option (1) is the answer.

• (2)Both (A) and (R) are true but (R) is not the correct explanation of (A). — This is the default landing place for a candidate who verifies both statements and then declines to test the link between them. Here the link is unusually tight: the Reason is the definition of the thing the Assertion makes a claim about, and the claim follows from the definition. Because an ecosystem unites abiotic stock with living components in one functioning framework, it produces and holds resources — which is exactly what the Assertion says. Option (2) is correct only where two independently true statements have no explanatory relation, and that is not the case here.
• (3)(A) is true but (R) is false. — Declares the standard definition of an ecosystem to be false. The Reason describes the ecosystem as one framework containing both the physical or inorganic environment and the biotic components — plants, animals, microorganisms and humans — which is the definition given in every textbook treatment since Tansley coined the term in 1935 and which Eugene Odum's work made the organising idea of modern ecology. There is nothing in it to reject, and a candidate choosing this option has almost certainly misread 'single concept' or 'single framework' as an overstatement rather than as the ordinary meaning of a system.
• (4)(A) is false but (R) is true. — Rejects the Assertion, which would mean denying that an ecosystem is a natural resource system. That denial cannot be sustained: natural resources do not exist independently of the ecosystems that generate and hold them, and the whole practice of natural resource management — of forests, grasslands, wetlands, fisheries and agro-ecosystems — is built on treating the ecosystem as the unit of the resource. A candidate may arrive here by reading 'natural resource' narrowly as mineral wealth, but even on that reading the soil and water components of the definition would keep the Assertion standing.

An ecosystem is a community of living organisms together with the non-living components of their environment, interacting as one functional unit. Its structure has two halves. The abiotic half consists of the physical and chemical factors — sunlight, temperature, rainfall, wind, soil, water, air and inorganic nutrients. The biotic half consists of producers or autotrophs, which capture solar energy through photosynthesis; consumers or heterotrophs, arranged as herbivores, carnivores and omnivores across trophic levels; and decomposers or saprotrophs, the bacteria and fungi that break dead organic matter back down into inorganic nutrients. Its functioning rests on two processes that behave quite differently. Energy flows through the system in one direction only — entering as sunlight, passing up the food chain with heavy losses at each step, and leaving as heat — so an ecosystem needs a continuous external energy supply. Nutrients, by contrast, cycle: carbon, nitrogen, phosphorus and water move between the abiotic pool and living tissue and back again, so the same atoms are used repeatedly. That combination of one-way energy flow and closed nutrient cycling is what makes the ecosystem self-sustaining, and therefore what makes it a resource system rather than a stock that is simply drawn down.

The term was introduced by the British botanist A.G. Tansley in 1935, and was developed into a quantitative science by Raymond Lindeman's work on trophic dynamics and later by Eugene Odum, whose 1953 textbook made the ecosystem the organising concept of ecology. The framing in this question — the ecosystem as a natural resource system — is the one used in resource geography and in environmental management rather than in pure ecology, and it underlies the modern vocabulary of ecosystem services, classified by the Millennium Ecosystem Assessment of 2005 into provisioning services such as food and water, regulating services such as climate and flood control, cultural services such as recreation and spiritual value, and supporting services such as soil formation and nutrient cycling. For Maharashtra, the ecosystems that recur in the syllabus are the Western Ghats forests, a global biodiversity hotspot; the mangroves and estuaries of the Konkan coast; the semi-arid grassland and scrub of the rain-shadow districts; and the agro-ecosystems of the Deccan plateau.

• The term 'ecosystem' was coined by A.G. Tansley in 1935, defining a unit that includes not only the organisms but the whole complex of physical factors forming the environment, treated as one physical system. Eugene Odum's Fundamentals of Ecology, 1953, made it the organising framework of modern ecology.
• Structure: abiotic components — sunlight, temperature, water, air, soil and inorganic nutrients — and biotic components, divided into producers (autotrophs), consumers (heterotrophs, at successive trophic levels) and decomposers (saprotrophs, chiefly bacteria and fungi).
• Function: energy flow is unidirectional, entering as solar radiation and dissipating as heat, with heavy loss at every trophic transfer — the ten per cent law associated with Raymond Lindeman's 1942 work on trophic dynamics. Nutrient movement, by contrast, is cyclic through biogeochemical cycles.
• Ecological pyramids may be of number, biomass or energy. The pyramid of energy is always upright because energy is lost at each transfer, while pyramids of number and biomass can be inverted — a single tree supporting many insects, or a small standing crop of phytoplankton supporting a larger mass of zooplankton.
• The Millennium Ecosystem Assessment of 2005 classified ecosystem services into four categories — provisioning, regulating, cultural and supporting — and this is the framework in which the ecosystem is treated as a natural resource system in policy and in economics.

• Answering an assertion-reason question after two judgements instead of three. Both statements can be true while the second explains nothing about the first; the explanatory link must be tested separately, and it is the only thing that separates option (1) from option (2).
• Treating 'natural resource' as meaning only minerals or extractable materials. In resource geography the term covers soil, water, air, biomass and the regulating functions of ecosystems, which is why the ecosystem is treated as the unit of the resource rather than as its container.
• Confusing energy flow with nutrient movement. Energy passes through an ecosystem once and is lost as heat, so a continuous external supply is required; nutrients are recycled indefinitely between the abiotic pool and living tissue. Statements that swap the two properties are a standard construction.

Assertion-reason is a favoured format for conceptual environment topics because it can test a definition and its consequence in one question. Three habits make it reliable. First, judge the Assertion alone, before reading the Reason, so that a persuasive Reason does not colour the verdict on the Assertion. Second, judge the Reason alone as a free-standing statement of fact. Third, ask specifically whether the Reason states the ground of the Assertion or merely a related truth. On ecosystems, the substantive topics that recur are the abiotic-biotic structure, one-way energy flow against cyclic nutrient movement, the ten per cent law, ecological pyramids and ecosystem services, and a candidate who can state each in one sentence can handle them in assertion-reason, statement-verification or match format alike.

No directly related past PYQ was found.

• practice — not a real PYQ

  The term 'ecosystem' was introduced into ecology by which scientist, and in which year ?

  • (a)Ernst Haeckel, 1866
  • (b)Frederic Clements, 1916
  • (c)A.G. Tansley, 1935
  • (d)Eugene Odum, 1953

  Answer(c) A.G. Tansley, 1935 — he proposed the term for a unit comprising organisms together with the whole complex of physical factors forming their environment. Haeckel coined 'ecology' in 1866, Clements is associated with plant succession and the biome concept, and Odum's 1953 textbook popularised ecosystem ecology without originating the word.

• practice — not a real PYQ

  In an ecosystem, the flow of energy and the movement of nutrients are best described as :

  • (a)Energy flow is cyclic; nutrient movement is unidirectional
  • (b)Energy flow is unidirectional; nutrient movement is cyclic
  • (c)Both energy flow and nutrient movement are cyclic
  • (d)Both energy flow and nutrient movement are unidirectional

  Answer(b) Energy flow is unidirectional; nutrient movement is cyclic. Energy enters as sunlight, passes up the trophic levels with large losses at each transfer and finally leaves as heat, so it must be continuously resupplied. Nutrients such as carbon, nitrogen and phosphorus move repeatedly between the abiotic pool and living tissue through biogeochemical cycles and are not lost from the system in the same way.