16 previous-year questions from this chapter every option and the correct answer, free · where the marks are
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.
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:
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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Save for spaced revision (free account)Solution
Productivity is the rate of biomass production per unit area per unit time, expressed in or .
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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:
The worked solution is part of a paid pack.
The worked solution is part of a paid pack.
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:
The worked solution is part of a paid pack.
The worked solution is part of a paid pack.
The worked solution is part of a paid pack.
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.
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:
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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Save for spaced revision (free account)Solution
By the 10% law each trophic level passes on about a tenth of its production. From a producer NPP of , the second level takes in . The official key marks — 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 ; that is not what was marked.)
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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:
The worked solution is part of a paid pack.
The worked solution is part of a paid pack.
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.
The worked solution is part of a paid pack.
The worked solution is part of a paid pack.
The worked solution is part of a paid pack.