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Given below is a pyramid… (Class 12 Biology 2026, Q21a)

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BiologyCBSE Class 12 · Board exam 2026, set 57/1/1 · 2 marks · Very short answer

CBSE Class 12 Biology 2026: question 21(a)

Set in the CBSE Class 12 board exam of 2026, paper 57/1/1, section B, question 21(a), for 2 marks. Try it first; the hints and our step-by-step solution are below.

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

Given below is a pyramid found in an ecosystem, where each bar represents the standing crop available in the trophic level.

  1. (i)

    Identify the kind of pyramid and with the help of an example explain the conditions where this kind of pyramid is possible in nature.

    1 mark
  2. (ii)

    Write any two limitations of ecological pyramids.

    1 mark

Figure in the paper: Inverted pyramid of two bars: the upper bar labelled PC (primary consumer) is wider than the lower bar labelled PP (primary producer). See it in the official paper.

Source: official question paper from cbse.gov.in (PDF). See it in the full 2026 board paper, set 57/1/1.

Hints

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

Hint 1

The bars represent standing crop. Which ecological quantity is that?

Hint 2

Think of a producer that is small in mass at any moment but multiplies very fast.

Hint 3

For limitations, consider food webs, decomposers and omnivores.

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) Because the bars show standing crop and the consumer bar is wider than the producer bar, this is an inverted pyramid of biomass.

    ½ mark

  2. Such a pyramid occurs in aquatic ecosystems such as the sea. There, a small standing crop of phytoplankton reproduces very fast and supports a larger standing crop of zooplankton or fish.

    ½ mark

  3. (ii) Any two limitations: (1) It does not account for the same species occupying two or more trophic levels. (2) It assumes a simple food chain and cannot accommodate a food web.

    1 mark

  4. (Another accepted limitation: saprophytes or decomposers are given no place in the pyramid, though they play a vital role in the ecosystem.)

Answer: (i) Inverted pyramid of biomass, e.g. in the sea a small standing crop of phytoplankton supports a larger standing crop of zooplankton or fish; (ii) it ignores species at more than one trophic level, and it cannot show food webs (or it omits saprophytes)

Where the marks are

  • Identifies an inverted pyramid of biomass (½ mark)
  • Correct condition or example, e.g. phytoplankton supporting zooplankton or fish in the sea (½ mark)
  • Any two limitations (½ + ½ 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 paper2026 board paper, set 57/1/1: 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.