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The movement of… (Class 12 Biology SQP 2026-27, Q18)

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BiologyCBSE Class 12 · Sample paper, session 2026-27 · 2 marks · Very short answer

CBSE Class 12 Biology sample paper 2026-27: question 18

From the official CBSE sample question paper for 2026-27, section B, question 18, for 2 marks. Try it first; the hints and our step-by-step solution are below.

Q18 · 2 marks · Very short answerEvolution

The movement of landmasses over geological time changed the distribution and evolution of animals. Explain this idea using two examples from different regions of the world.

Source: official sample paper from cbseacademic.nic.in (PDF). See it in the full Sample paper 2026-27.

Hints

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

Hint 1

Think of one case where two continents joined and one case where a continent stayed isolated.

Hint 2

Recall the examples in NCERT's evidences of evolution and adaptive radiation: South American mammals and Australian marsupials.

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. South America: South America once had native mammals resembling the horse, hippopotamus, bear and rabbit. When continental drift joined South America to North America, these animals were overridden and replaced by the North American fauna.

    1 mark

  2. Australia: Australia stayed isolated after continental drift. Many different marsupials evolved from a common ancestral stock within this island continent (adaptive radiation). They survived because there was no competition from other (placental) mammals.

    1 mark

Answer: (1) Joining of South and North America let North American fauna override South American mammals. (2) Isolation of Australia allowed marsupials to radiate from one ancestor without competition from other mammals.

Where the marks are

  • South American mammals overridden by North American fauna after the continents joined (1 mark)
  • Australian marsupials radiated from a common ancestor in isolation, with no competition (1 mark)

Revise the chapter

  • Chapter: Evolution (notes, formulas, where marks are lost and every past question)
Practise this chapterBoard-style questions from Evolution, one at a time, marked against the answer key and marking points.Back to the full paperSample paper 2026-27: 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.