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Industrial melanism in… (Class 12 Biology 2023, Q24)

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BiologyCBSE Class 12 · Board exam 2023, set 57/5/1 · 3 marks · Short answer

CBSE Class 12 Biology 2023: question 24

Set in the CBSE Class 12 board exam of 2023, paper 57/5/1, section C, question 24, for 3 marks. Try it first; the hints and our step-by-step solution are below.

Q24 · 3 marks · Short answerEvolution

Industrial melanism in England after 1850 is an excellent example of Natural selection. Explain how ?

Source: official question paper from cbse.gov.in (PDF). See it in the full 2023 board paper, set 57/5/1.

Hints

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

Hint 1

Compare the colour of tree bark before and after 1850.

Hint 2

Link the colour of the moth to how easily birds could spot it.

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. Before industrialisation (pre-1850): tree trunks and walls were covered with a thick growth of almost white lichens.

    ½ mark

  2. White-winged moths were camouflaged against the pale lichens, so they escaped predators and increased in number.

    ½ mark

  3. Dark-winged moths were easily seen and picked out by predatory birds, so their numbers stayed low.

    ½ mark

  4. After industrialisation: smoke and soot darkened the tree trunks, and the lichens could not grow because of pollution.

    ½ mark

  5. Dark-winged moths were now camouflaged, so they survived and increased in number.

    ½ mark

  6. White-winged moths became conspicuous and were eaten by predators, so they declined. Thus the environment 'selected' the better-adapted form, which shows natural selection.

    ½ mark

Answer: Before industrialisation, white moths were camouflaged on lichen-covered trunks and dark moths were eaten. After soot darkened the trunks, dark moths were camouflaged and increased while white moths were eaten. This change in frequency is natural selection.

Where the marks are

  • White lichen cover on tree trunks before industrialisation (½ mark)
  • White moths camouflaged and increased (½ mark)
  • Dark moths picked out by predators and decreased (½ mark)
  • Trunks darkened by soot and lichens absent after industrialisation (½ mark)
  • Dark moths camouflaged and increased (½ mark)
  • White moths eaten and decreased; nature selects the fitter form (½ mark)

Revise the chapter

Practise this chapterBoard-style questions from Evolution, one at a time, marked against the answer key and marking points.Back to the full paper2023 board paper, set 57/5/1: 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.