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(i) Assume that, GPP… (Class 12 Biology SQP 2024-25, Q21B)

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BiologyCBSE Class 12 · Sample paper, session 2024-25 · 2 marks · Very short answer

CBSE Class 12 Biology sample paper 2024-25: question 21(B)

From the official CBSE sample question paper for 2024-25, section B, question 21(B), for 2 marks. Try it first; the hints and our step-by-step solution are below.

Q21(B) · 2 marks · Very short answerCompetency-basedEcosystem

(i) Assume that, GPP Forest A = GPP Forest B = GPP Forest C, If Forest A has NPP = 1254 J/m²/day; Forest B, NPP =2157 J/m²/day; and Forest C, NPP = 779 J/m²/day, which one of these forests has maximum energy loss by respiration? Give reason.
(ii) Draw an ecological pyramid of number of the following food chains
a. Grass — Animal —Fleas on the host animal
b. Tree — Insects — Woodpecker

Source: official sample paper from cbseacademic.nic.in (PDF). See it in the full Sample paper 2024-25.

Hints

Open one hint at a time and try again before the next.

Hint 1

Rearrange NPP = GPP − R to make R the subject.

Hint 2

If GPP is the same, a lower NPP means what about R?

Hint 3

For the pyramids, count the individuals at each level: how many trees, insects or fleas there are.

Step-by-step solution

Each step shows the marks it earns, as an examiner would award them. Checked by an independent re-solve from the question paper.

  1. (i) NPP = GPP − R, so R = GPP − NPP. With GPP equal in all three forests, the forest with the smallest NPP has the largest respiratory loss. Forest C has the lowest NPP (779 J/m²/day), so Forest C loses the maximum energy by respiration.

    1 mark

  2. (ii)(a) Grass → Animal → Fleas (parasitic chain): draw three stacked horizontal bars. The bottom bar (grass) is broad because the producers are numerous. The middle bar (one host animal) is very narrow. The top bar (fleas) is broad because many fleas live on one host. The pyramid is therefore partly inverted at the top.

    ½ mark

  3. (ii)(b) Tree → Insects → Woodpecker: the bottom bar (one tree) is narrow, the middle bar (many insects) is broad, and the top bar (a few woodpeckers) is narrow. This gives a spindle-shaped pyramid of numbers.

    ½ mark

Answer: (i) Forest C (lowest NPP, so highest respiration since R = GPP − NPP). (ii) (a) broad–narrow–broad, inverted at top; (b) narrow–broad–narrow, spindle-shaped.

Where the marks are

  • Uses R = GPP − NPP to identify Forest C with reason (1 mark)
  • Correct pyramid of numbers for grass–animal–fleas (0.5 mark)
  • Correct spindle-shaped pyramid for tree–insects–woodpecker (0.5 mark)

Revise the chapter

Practise this chapterBoard-style questions from Ecosystem, one at a time, marked against the answer key and marking points.Back to the full paperSample paper 2024-25: every question, by section.

The question is transcribed from the official paper; figures are described in words. The solution, hints and chapter tag are ours. Spotted an error? Write tosupport@questionbuddy.in.