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The graphs below show… (Class 12 Biology SQP 2023-24, Q25)

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BiologyCBSE Class 12 · Sample paper, session 2023-24 · 3 marks · Short answer

CBSE Class 12 Biology sample paper 2023-24: question 25

From the official CBSE sample question paper for 2023-24, section C, question 25, for 3 marks. Try it first; the hints and our step-by-step solution are below.

Q25 · 3 marks · Short answerCompetency-basedEvolution

The graphs below show three types of natural selection. The shaded areas marked with arrows show the individuals in the population which are not selected. The dotted vertical lines show the statistical means.

  1. a)

    What names are given to the types of selection shown in graphs A, B and C.

    0 marks
  2. b)

    After the selection has operated for several generations in the above populations indicated as Graph A, B and C, graphically illustrate the probable results.

    0 marks

Figure in the paper: Three bell curves of number of individuals vs character. Graph A: both extreme tails shaded. Graph B: only the left tail shaded. Graph C: the central region around the mean shaded. See it in the official paper.

Source: official sample paper from cbseacademic.nic.in (PDF). See it in the full Sample paper 2023-24.

Hints

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

Hint 1

Look at which parts of each curve are shaded (eliminated).

Hint 2

Ask yourself: are the extremes, one extreme, or the middle being removed?

Hint 3

After the removal, where will most individuals lie in each population?

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) Graph A: stabilising selection (both extremes removed). Graph B: directional selection (one extreme removed). Graph C: disruptive selection (the mean/intermediates removed).

    1½ marks

  2. b) Probable results after several generations, described as graphs:

    • Graph A (stabilising): the curve becomes narrower and taller, with the same mean. More individuals now have the mean character value.
    • Graph B (directional): the whole curve, with its peak and mean, shifts to the right (away from the eliminated left tail).
    • Graph C (disruptive): the curve splits into two peaks at the two extremes, with a dip at the original mean.
    1½ marks

Answer: a) A: stabilising, B: directional, C: disruptive. b) A: narrower, taller peak at the same mean; B: peak shifted to the right; C: two peaks at the extremes.

Where the marks are

  • Correctly names all three types of selection (1.5 marks)
  • Correct resultant curves for A, B and C (0.5 × 3 = 1.5 marks)

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 paperSample paper 2023-24: 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.