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(i) Compare the two… (Class 12 Biology SQP 2025-26, Q21A)

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BiologyCBSE Class 12 · Sample paper, session 2025-26 · 2 marks · Very short answer

CBSE Class 12 Biology sample paper 2025-26: question 21(A)

From the official CBSE sample question paper for 2025-26, 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

(i) Compare the two ecological pyramids of biomass I and II given below and explain the situations in which this is possible.
(ii) Construct an ideal pyramid of energy if 200,000 joules of sunlight are available.

(For Visually impaired students: (i) Compare the upright and inverted ecological pyramids of biomass and explain the situations in which this is possible. (ii) Construct an ideal pyramid of energy if 200,000 joules of sunlight is available.)

Figure in the paper: Two biomass pyramids with trophic level on left and dry weight (kg m^-2) on right. Fig. I (upright): PP 809, PC 37, SC 11, TC 1.5 (widest at base, narrowing upward). Fig. II (inverted): PC 21 (wide, top) above PP 4 (narrow, bottom). See it in the official paper.

Source: official sample paper from cbseacademic.nic.in (PDF). See it in the full Sample paper 2025-26.

Hints

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

Hint 1

Where can a small standing crop of producers support a larger crop of consumers?

Hint 2

Apply Lindeman's 10% law from the producer level upward.

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) Pyramid I (upright) belongs to a terrestrial ecosystem such as a forest or grassland. Biomass is maximum at the producer level (809 kg m) and falls through PC (37) and SC (11) to TC (1.5).

    Pyramid II (inverted) belongs to an aquatic (sea) ecosystem. A small standing crop of phytoplankton (4 kg m) supports a larger standing crop of zooplankton (21 kg m). This is possible because phytoplankton multiply rapidly and have a high turnover.

    1 mark

  2. (ii) Using about 1% capture of sunlight by producers and the 10% law at each transfer:

    Trophic levelEnergy
    Tertiary consumer (TC)2 J
    Secondary consumer (SC)20 J
    Primary consumer (PC)200 J
    Producer (PP)2,000 J
    Sunlight200,000 J

    The pyramid is always upright: a broad base of producers narrowing to the top carnivores.

    1 mark

Answer: (i) I – upright, terrestrial; II – inverted, aquatic (small phytoplankton crop supports larger zooplankton). (ii) Upright energy pyramid: PP 2000 J → PC 200 J → SC 20 J → TC 2 J.

Where the marks are

  • Compares upright (terrestrial) and inverted (aquatic) biomass pyramids with reason (1 mark)
  • Draws an upright energy pyramid with values falling by 10% at each level (1 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 2025-26: 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.