Ecosystem

16 previous-year questions from this chapter every option and the correct answer, free · where the marks are

1. Structure, productivity and decomposition

Exam focus: Net primary productivity is what's left after the plant's own respiration is subtracted from gross primary productivity — and it's this leftover, not GPP, that is actually available as food to every heterotroph in the ecosystem.

Ecosystem: Structure, Productivity and Decomposition

NCERT Wallah

Full ecosystem chapter one-shot covering structure, components, functions, productivity and decomposition, though it also extends into energy flow and pyramids, used separately for the sibling subtopic.

BotanyNEET 2025show ▾

Given below are two statements: Statement I: The primary source of energy in an ecosystem is solar energy. Statement II: The rate of production of organic matter during photosynthesis in an ecosystem is called net primary productivity (NPP). In the light of the above statements, choose the most appropriate answer from the options given below:

A.Both Statement I and Statement II are correct
B.Both Statement I and Statement II are incorrect
C.Statement I is correct but Statement II is incorrect✓
D.Statement I is incorrect but Statement II is correct

Solution

Solar energy is the primary source for almost every ecosystem (I correct). The rate of organic-matter production during photosynthesis is the gross primary productivity; NPP is what remains after respiratory loss, so II is incorrect.

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ZoologyNEET 2025show ▾

Which of the following is the unit of productivity of an ecosystem?

A. $g m^{- 2}$
B. $kcal m^{- 2}$
C. $kcal m^{- 3}$
D. $(kcal m^{- 2}) y r^{- 1}$ ✓

Solution

Productivity is the rate of biomass production per unit area per unit time, expressed in $g m^{- 2} y r^{- 1}$ or $(kcal m^{- 2}) y r^{- 1}$ .

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BotanyNEET 2023show ▾

In the equation

GPP - R = NPP

, GPP is gross primary productivity and NPP is net primary productivity.

R

here is ________.

A.Photosynthetically active radiation
B.Respiratory quotient
C.Respiratory loss✓
D.Reproductive allocation

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BotanyNEET 2023show ▾

Identify the correct statements: A. Detritivores perform fragmentation. B. The humus is further degraded by some microbes during mineralisation. C. Water-soluble inorganic nutrients go down into the soil and get precipitated by a process called leaching. D. The detritus food chain begins with living organisms. E. Earthworms break down detritus into smaller particles by a process called catabolism. Choose the correct answer from the options given below:

A.A, B, C only✓
B.B, C, D only
C.C, D, E only
D.D, E, A only

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ZoologyNEET 2022show ▾

Detritivores break down detritus into smaller particles. This process is called:

A.Decomposition
B.Catabolism
C.Fragmentation✓
D.Humification

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BotanyNEET 2022show ▾

Given below are two statements: Statement I: Decomposition is a process in which detritus is degraded into simpler substances by microbes. Statement II: Decomposition is faster if the detritus is rich in lignin and chitin. In the light of the above statements, choose the correct answer from the options given below:

A.Statement I is incorrect but Statement II is correct
B.Both Statement I and Statement II are correct
C.Both Statement I and Statement II are incorrect
D.Statement I is correct but Statement II is incorrect✓

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BotanyNEET 2021show ▾

In the equation

GPP - R = NPP

R

represents:

A.Radiant energy
B.Retardation factor
C.Environmental factor
D.Respiration losses✓

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BotanyNEET 2020show ▾

In relation to the gross primary productivity and net primary productivity of an ecosystem, which one of the following statements is correct?

A.Gross primary productivity is always less than net primary productivity
B.Gross primary productivity is always more than net primary productivity✓
C.Gross primary productivity and net primary productivity are one and the same
D.There is no relationship between gross primary productivity and net primary productivity

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2. Energy flow, ecological pyramids

Exam focus: Pyramids of numbers and biomass can both turn upside down — a single large tree supporting swarms of insects, for instance — but the pyramid of energy cannot: every trophic transfer loses energy as heat, so it stays upright without exception.

Energy Flow and Ecological Pyramids

NCERT Wallah

Dedicated lecture on energy flow (trophic levels, the 10% law, food chains/webs); the title names only energy flow, so ecological-pyramid coverage may be lighter than the flow-of-energy content.

ZoologyNEET 2025show ▾

Given below are two statements: Statement I: In an ecosystem, there is a unidirectional flow of the energy of the sun from producers to consumers. Statement II: Ecosystems are exempted from the 2nd law of thermodynamics. In the light of the above statements, choose the most appropriate answer from the options given below:

A.Both Statement I and Statement II are correct
B.Both Statement I and Statement II are incorrect
C.Statement I is correct but Statement II is incorrect✓
D.Statement I is incorrect but Statement II is correct

Solution

Energy from the sun flows one way through an ecosystem, from producers to consumers (I correct). Ecosystems obey the laws of thermodynamics; energy is lost as heat at every transfer, which is the second law at work (II incorrect).

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BotanyNEET 2024show ▾

In an ecosystem, if the Net Primary Productivity (NPP) of the first trophic level is

100 x (kcal m^{- 2}) y r^{- 1}

, what would be the GPP (Gross Primary Productivity) of the third trophic level of the same ecosystem?

A. $x (kcal m^{- 2}) y r^{- 1}$
B. $10 x (kcal m^{- 2}) y r^{- 1}$ ✓
C. $\frac{100 x}{3} (kcal m^{- 2}) y r^{- 1}$
D. $\frac{x}{10} (kcal m^{- 2}) y r^{- 1}$

Solution

By the 10% law each trophic level passes on about a tenth of its production. From a producer NPP of $100 x$ , the second level takes in $10 x$ . The official key marks $10 x$ — it treats the third level's gross intake as the energy handed on by the level below it. (Applying the 10% step once more, the third level's own NPP would be $x$ ; that is not what was marked.)

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BotanyNEET 2021show ▾

Which of the following statements is not correct?

A.Pyramid of biomass in the sea is generally inverted
B.Pyramid of biomass in the sea is generally upright✓
C.Pyramid of energy is always upright
D.Pyramid of numbers in a grassland ecosystem is upright

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BotanyNEET 2020show ▾

Match the trophic levels with their correct species examples in a grassland ecosystem.

Trophic level	Example
(a) Fourth trophic level	(i) Crow
(b) Second trophic level	(ii) Vulture
(c) First trophic level	(iii) Rabbit
(d) Third trophic level	(iv) Grass

Select the correct option:

A.(a)-(ii), (b)-(iii), (c)-(iv), (d)-(i)✓
B.(a)-(iii), (b)-(ii), (c)-(i), (d)-(iv)
C.(a)-(iv), (b)-(iii), (c)-(ii), (d)-(i)
D.(a)-(i), (b)-(ii), (c)-(iii), (d)-(iv)

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BotanyNEET 2019show ▾

Which of the following ecological pyramids is generally inverted?

A.Pyramid of numbers in grassland
B.Pyramid of energy
C.Pyramid of biomass in a forest
D.Pyramid of biomass in a sea✓

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3. Nutrient cycling

Exam focus: Sort each cycle by where its reservoir sits: carbon, nitrogen and oxygen are gaseous cycles with the atmosphere as reservoir, while phosphorus and sulphur are sedimentary, drawing from the earth's crust — phosphorus in particular has essentially no gaseous phase at all, unlike the other three.

Nutrient Cycling: Carbon and Phosphorus Cycles

PW English Medium

Covers nutrient cycling, the carbon cycle and the phosphorus cycle directly, bundled together with ecological succession and ecosystem services in the same video.

1. Structure, productivity and decomposition

Structure, productivity and decomposition

2. Energy flow, ecological pyramids

Energy flow and ecological pyramids

3. Nutrient cycling

Nutrient cycling