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Justify the following… (Class 12 Biology SQP 2025-26, Q33A)

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BiologyCBSE Class 12 · Sample paper, session 2025-26 · 5 marks · Long answer

CBSE Class 12 Biology sample paper 2025-26: question 33(A)

From the official CBSE sample question paper for 2025-26, section E, question 33(A), for 5 marks. Try it first; the hints and our step-by-step solution are below.

Q33(A) · 5 marks · Long answerOrganisms and Populations

Justify the following statements with suitable proof/examples: -
A. 'competition is not limited to closely related species'
B. 'competition is not always dependent on resources being limiting'
C. 'competitive exclusion occurs in nature'
D. 'competing species may evolve mechanisms for co-existence'
E. 'competition in nature comes from what is called 'competitive release''

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

Each statement matches a classic NCERT example from the chapter on organisms and populations.

Hint 2

Recall flamingoes in South American lakes, goats on the Galapagos, and warblers on a single tree.

Hint 3

For competitive release, think of the barnacles on the Scottish coast and what happens when one is removed.

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. A. Even totally unrelated species can compete for a common resource. In some shallow South American lakes, visiting flamingoes and resident fishes compete for the same food, the zooplankton.

    1 mark

  2. B. Competition can occur even when resources are plentiful. This is called interference competition: the feeding efficiency of one species is reduced by the interfering, inhibitory presence of another species, even though food and space are abundant.

    1 mark

  3. C. Gause's competitive exclusion principle states that two closely related species competing for the same limited resource cannot co-exist indefinitely; the competitively inferior one is eliminated. Example: the Abingdon tortoise of the Galapagos Islands became extinct within a decade of goats being introduced, apparently because the goats browsed more efficiently.

    1 mark

  4. D. Competing species can co-exist through resource partitioning, for example by feeding at different times or using different foraging patterns. MacArthur showed that five closely related warbler species living on the same tree avoided competition because they foraged differently.

    1 mark

  5. E. A species whose range is restricted by a competitively superior species expands its range when the competitor is experimentally removed; this is competitive release. On the rocky coasts of Scotland, the larger barnacle Balanus dominates the intertidal zone and excludes the smaller barnacle Chthamalus. When Balanus is removed, Chthamalus spreads into that zone.

    1 mark

Answer: A. Flamingoes and fishes compete for zooplankton. B. Interference competition occurs even when resources are abundant. C. Abingdon tortoise was eliminated by goats (Gause's principle). D. Resource partitioning among MacArthur's warblers. E. Balanus and Chthamalus on the Scottish coast.

Where the marks are

  • Unrelated species compete: flamingoes and fishes for zooplankton (1 mark)
  • Interference competition even when resources are abundant (1 mark)
  • Competitive exclusion: Abingdon tortoise and goats (1 mark)
  • Resource partitioning: MacArthur's five warbler species (1 mark)
  • Competitive release: Balanus and Chthamalus on the Scottish coast (1 mark)

Revise the chapter

Practise this chapterBoard-style questions from Organisms and Populations, 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.