Skip to content

Study the diagrammatic… (Class 12 Biology 2023, Q30)

questionbuddy.in/q/cbse-12-biology-2023-57-1-1-q30-diagrammatic-representation-earth-regions-marked

BiologyCBSE Class 12 · Board exam 2023, set 57/1/1 · 4 marks · Case-based

CBSE Class 12 Biology 2023: question 30

Set in the CBSE Class 12 board exam of 2023, paper 57/1/1, 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-basedBiodiversity and Conservation

Study the diagrammatic representation given below of the Earth with regions marked 'A' and 'B' respectively. Answer the questions that follow.

  1. (a)

    Write the observations made regarding the species diversity when moving from region 'A' to region 'B'. Give two reasons also.

    3 marks
  2. (b)

    Stating the reason, mention the approximate number of bird species recorded in India.

    1 mark

  3. OR

    (b)

    Name the region in the world that records the greatest biodiversity and mention why.

    1 mark

Figure in the paper: Globe with latitude lines 90° N, 60° N, 30° N, Equator 0°, 30° S, 60° S, 90° S. Region A is marked as the band from about 30° N to 30° S (tropics); region B is marked as the band from about 30° S down to 90° S (toward the south pole). See it in the official paper.

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

Hints

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

Hint 1

Recall the latitudinal gradient in biodiversity.

Hint 2

Think of climate stability, solar energy and glaciation history in the tropics versus the poles.

Hint 3

India's bird count is a little over a thousand; the most diverse rainforest is in South America.

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) Observation: species diversity decreases as we move from region A (tropics, about 30° N to 30° S) to region B (higher southern latitudes towards the pole).

    1 mark

  2. Reason 1: the tropics have a less seasonal, relatively constant and predictable environment. They have also remained undisturbed for millions of years (no frequent glaciations), giving a long time for species diversification.

    1 mark

  3. Reason 2: the tropics receive more solar energy, which gives higher productivity and supports greater diversity. Region B has less solar energy, lower productivity and less habitable land area.

    1 mark

  4. (b) India has recorded more than 1200 species of birds.

    ½ mark

  5. Reason: the Indian landmass lies largely in the tropical latitudes, which favour high diversity.

    ½ mark

  6. (b) (alternative) The Amazon rainforest in South America has the greatest biodiversity on Earth.

  7. Reason: it lies in the tropical region, with warm, stable climate, high solar energy and productivity, and a long undisturbed history.

Answer: (a) Diversity decreases from A to B, because the tropics have a stable, undisturbed environment and more solar energy/productivity; (b) >1200 bird species in India, being largely tropical; OR Amazon rainforest, being tropical

Where the marks are

  • Species diversity decreases from A to B (1 mark)
  • Any two correct reasons: constant climate/long undisturbed history, more solar energy and productivity, more habitable area (1 + 1 mark)
  • More than 1200 bird species (½ mark) because India is largely in the tropics (½ mark); OR Amazon rainforest (½ mark), being tropical (½ mark)

Revise the chapter

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