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Observe the graph… (Class 12 Biology SQP 2023-24, Q30)

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BiologyCBSE Class 12 · Sample paper, session 2023-24 · 4 marks · Case-based

CBSE Class 12 Biology sample paper 2023-24: question 30

From the official CBSE sample question paper for 2023-24, section D, question 30, for 4 marks. Try it first; the hints and our step-by-step solution are below.

Q30 · 4 marks · Case-basedCompetency-basedOrganisms and Populations

Observe the graph given below.
The graph represents inter-specific interaction between two species of Paramecia competing for the same resource in a culture medium. Paramecium caudatum and Paramecium aurelia were grown in separate cultures as well as in mixed cultures. It was found that each species grew in numbers according to the logistic equation.

  1. a)

    Which species is competitively superior? Support it with the data provided in the graph.

    0 marks
  2. b)

    State the underlying principle for the above result and name the scientist associated with this principle.

    0 marks
  3. c)

    Explain the mechanism in which two or more species competing with each other can co - exist.

    0 marks

  4. OR

    c)

    Graphs A and B shown below depict interaction of two species. Which graph indicates Mutualism? Give reason.

    0 marks

Figure in the paper: Graph 1: number of paramecia (0-100) vs time (days, 0-18). P. aurelia alone reaches about 100 (dashed), in mixed culture about 90; P. caudatum alone reaches about 62 (dashed), in mixed culture peaks near 27 at day 5 then declines to near 0. Graphs A and B (OR part): population size vs time with species introduced at a dotted line; in A both species A and B increase after introduction; in B species B increases steeply while A stays flat then declines slightly. 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

Compare the curves of the two species in mixed culture.

Hint 2

Which principle says one competitor eventually eliminates the other?

Hint 3

Think of MacArthur's warblers for (c), or which graph shows both species benefiting.

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) P. aurelia is competitively superior.

    1 mark

  2. Evidence from the graph:

    • Grown alone, P. aurelia reaches about 100 individuals, while P. caudatum reaches only about 60.
    • In mixed culture, P. aurelia still rises to about 90, whereas P. caudatum peaks at about 27 around day 5 and then declines to almost zero.
    1 mark

  3. b) This illustrates Gause's Competitive Exclusion Principle: two closely related species competing for the same limited resources cannot coexist indefinitely, and the competitively inferior one is eliminated. The scientist is G.F. Gause.

    1 mark

  4. c) Competing species can coexist by resource partitioning. They avoid competition by feeding at different times or using different foraging patterns. For example, MacArthur's five warbler species coexist on the same tree by foraging in different parts of it.

    c) (OR) Graph A shows mutualism. After the two species are brought together, both populations increase, so both benefit (+/+). In Graph B only one species gains.

    1 mark

Answer: a) P. aurelia (about 90–100 individuals; P. caudatum falls to near 0 in mixed culture). b) Competitive exclusion principle, G.F. Gause. c) Resource partitioning (OR: Graph A, since both species increase).

Where the marks are

  • Names P. aurelia (1 mark)
  • Supports with graph data (1 mark)
  • States the competitive exclusion principle and names Gause (1 mark)
  • Explains resource partitioning / identifies Graph A as mutualism with reason (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 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.