Ecosystem

13 NEET-UG practice questions on Ecosystem, part of Botany. The first 13 are below; the first 5 with answers and explanations (tap Show answer after you have chosen), the rest in Learn with a free account.

1. Question 1 · Hard

   Which of these statements about productivity are correct? A. Secondary productivity is the rate of formation of new organic matter by consumers. B. GPP = NPP − R, where R is respiration loss. C. Annual NPP of the whole biosphere is about 170 billion tons of dry organic matter. D. The oceans account for more than half of the annual NPP of the biosphere.

   1. AB and D only
   2. BA and C only
   3. CA, C and D only
   4. DA, B and C only

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   Answer: B · A and C only

   A and C are correct. B has the terms the wrong way round: NPP = GPP − R. D is wrong because the oceans give only about 55 billion tons of the 170 billion tons, which is about one-third.

   • A: These are the two false statements.
   • C: This includes D, though the oceans give about one-third.
   • D: This includes B, which reverses GPP and NPP.

   Remember this

   NPP = GPP − R; oceans cover about 70% of the surface but give only about 55 of 170 billion tons.

2. Question 2 · Hard

   Four litter bags are buried in a decomposition experiment. Which bag will lose mass most slowly?

   1. ASugar-rich litter in cold, waterlogged soil
   2. BSugar-rich litter in warm, moist, aerated soil
   3. CLignin- and chitin-rich litter in warm, moist, aerated soil
   4. DLignin- and chitin-rich litter in cold, waterlogged soil

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   Answer: D · Lignin- and chitin-rich litter in cold, waterlogged soil

   Lignin and chitin resist decay, and low temperature and anaerobiosis inhibit decomposers. This bag has both slowing factors. Warm, moist, aerated soil and sugar-rich litter both speed decay.

   • A: Sugars decay faster than lignin under the same soil conditions.
   • B: This combines both factors that speed decay.
   • C: Warmth, moisture and air speed decay of this litter.

   Remember this

   Decay depends on litter chemistry and climate; slowest with lignin and chitin in cold, anaerobic conditions.

3. Question 3 · Hard

   A forest plot has a gross primary productivity of 5000 kJ m⁻² yr⁻¹, and the producers use 1000 kJ m⁻² yr⁻¹ in respiration. Using the 10 per cent law, how much energy, in kJ m⁻² yr⁻¹, reaches the primary carnivores?

   1. A50
   2. B40
   3. C400
   4. D4

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   Answer: B · 40

   NPP = 5000 − 1000 = 4000. Herbivores get 10 per cent, or 400, and primary carnivores get 10 per cent of that, or 40. As a check, 4000 × 0.1 × 0.1 = 40.

   • A: This starts from GPP, without subtracting respiration.
   • C: This stops at the herbivores.
   • D: This applies one transfer too many.

   Remember this

   Apply the 10% law to NPP, not GPP, once for each step up the chain.

4. Question 4 · Medium

   Match List-I with List-II. List-I (step in decomposition) A. Fragmentation B. Catabolism C. Humification D. Mineralisation List-II (event) I. Enzymes of bacteria and fungi degrade detritus into simpler substances II. Humus is degraded and inorganic nutrients are released III. Detritivores break detritus into smaller particles IV. A dark amorphous substance accumulates

   1. AA-III, B-I, C-IV, D-II
   2. BA-III, B-I, C-II, D-IV
   3. CA-I, B-III, C-IV, D-II
   4. DA-III, B-II, C-IV, D-I

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   Answer: A · A-III, B-I, C-IV, D-II

   Detritivores such as earthworms fragment detritus, and microbial enzymes carry out catabolism. Humification forms humus, and mineralisation releases nutrients from humus.

   • B: This swaps humification and mineralisation.
   • C: This swaps the detritivore step and the enzyme step.
   • D: This swaps catabolism and mineralisation.

   Remember this

   Fragmentation by detritivores, catabolism by microbial enzymes, humification gives humus, mineralisation releases inorganic nutrients.

5. Question 5 · Medium

   Why is the pyramid of biomass in the sea generally inverted?

   1. AEnergy increases at each higher trophic level
   2. BFishes do not feed in the food chain of the sea
   3. CBiomass of fishes far exceeds that of phytoplankton
   4. DBiomass of phytoplankton far exceeds that of fishes

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   Answer: C · Biomass of fishes far exceeds that of phytoplankton

   The standing biomass of fishes is greater than that of phytoplankton, so the top of the pyramid is broader than the base. The pyramid of energy remains upright.

   • A: Energy always falls at each higher level.
   • B: Fishes are consumers in the marine food chain.
   • D: This would make the pyramid upright.

   Remember this

   Biomass pyramid in the sea is inverted, but an energy pyramid is always upright.

6. Question 6 · Easy

   What share of the incident solar radiation is photosynthetically active radiation (PAR)?

   1. ALess than 50 per cent
   2. B2 to 10 per cent
   3. CAbout 70 per cent
   4. DAbout 90 per cent

   Answer and explanation in LearnFree account

7. Question 7 · Medium

   Given below are two statements: Statement I: Humus is highly susceptible to microbial action and decomposes rapidly. Statement II: In leaching, water-soluble inorganic nutrients rise to the soil surface and stay available to roots. Choose the correct answer.

   1. AStatement I is correct but Statement II is incorrect
   2. BBoth Statement I and Statement II are correct
   3. CBoth Statement I and Statement II are incorrect
   4. DStatement I is incorrect but Statement II is correct

   Answer and explanation in LearnFree account

8. Question 8 · Easy

   Detritus rich in which material decomposes most slowly?

   1. ANitrogen-rich compounds
   2. BWater-soluble sugars
   3. CLignin and chitin
   4. DNitrogen-rich compounds and sugars together

   Answer and explanation in LearnFree account

9. Question 9 · Medium

   Which statement correctly compares the two main routes of energy flow?

   1. AGrazing food chain is the major route in water; detritus food chain carries more on land
   2. BDetritus food chain is the major route in both water and land
   3. CGrazing food chain is the major route in both water and land
   4. DDetritus food chain is the major route in water; grazing food chain carries more on land

   Answer and explanation in LearnFree account

10. Question 10 · Medium

    Arrange these energy quantities of an ecosystem in decreasing order. A. Net primary productivity B. Incident solar radiation C. Photosynthetically active radiation D. Gross primary productivity

    1. AB, C, A, D
    2. BB, C, D, A
    3. CC, B, D, A
    4. DB, D, C, A

    Answer and explanation in LearnFree account

11. Question 11 · Easy

    Arrange these organisms of a grazing food chain from the first trophic level to the fourth. A. Snake B. Grasshopper C. Frog D. Grass

    1. AD, B, A, C
    2. BD, C, B, A
    3. CD, B, C, A
    4. DB, D, C, A

    Answer and explanation in LearnFree account

12. Question 12 · Medium

    Arrange the ecosystems in the table in decreasing order of net primary productivity. A. Ecosystem A B. Ecosystem B C. Ecosystem C D. Ecosystem D

    

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    1. AD, A, B, C
    2. BB, A, D, C
    3. CC, B, A, D
    4. DC, D, A, B

    Answer and explanation in LearnFree account

13. Question 13 · Medium

    Examine the four ecological pyramids in the figure. Which of them can NOT represent a real ecosystem?

    

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    1. APyramid B
    2. BPyramid A
    3. CPyramid C
    4. DPyramid D

    Answer and explanation in LearnFree account