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Observe the population growth… (Class 12 Biology 2024, Q19)

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BiologyCBSE Class 12 · Board exam 2024, set 57/5/1 · 2 marks · Very short answer

CBSE Class 12 Biology 2024: question 19

Set in the CBSE Class 12 board exam of 2024, paper 57/5/1, section B, question 19, for 2 marks. Try it first; the hints and our step-by-step solution are below.

Q19 · 2 marks · Very short answerCompetency-basedOrganisms and Populations

Observe the population growth curve and answer the questions given below.

  1. (a)

    State the conditions under which growth curve 'A' and growth curve 'B' plotted in the graph are possible.

    1 mark
  2. (b)

    Mention what does 'K' in the graph represent.

    1 mark

Figure in the paper: Graph of population density (N) vs time (t). Curve A rises steeply exponentially, labelled dN/dt = rN. Curve B is sigmoidal and levels off at a dotted horizontal line marked K, labelled dN/dt = rN((K-N)/K). See it in the official paper.

Source: official question paper from cbse.gov.in (PDF). See it in the full 2024 board paper, set 57/5/1.

Hints

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

Hint 1

One curve keeps rising and the other levels off. What could stop a population from growing?

Hint 2

Compare the two equations: what does the factor (K−N)/K introduce?

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) Curve A (exponential, ) is possible when resources such as food and space are unlimited and there is no environmental resistance.

    ½ mark

  2. (a) Curve B (logistic/sigmoid, ) is possible when resources are limited, so competition and environmental resistance check further growth.

    ½ mark

  3. (b) K is the carrying capacity: the maximum number of individuals of a population that a given habitat can support. Beyond this limit no further growth is possible.

    1 mark

Answer: (a) A: unlimited resources, no environmental resistance; B: limited resources, with environmental resistance. (b) K = carrying capacity.

Where the marks are

  • Curve A: unlimited resources or no environmental resistance (½ mark)
  • Curve B: limited resources or environmental resistance present (½ mark)
  • K is the carrying capacity, the maximum population a habitat can support (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 paper2024 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.