Skip to content

In an ecosystem there was… (Class 12 Biology 2026, Q21b)

questionbuddy.in/q/cbse-12-biology-2026-57-1-1-q21b-ecosystem-loss-biodiversity-due-some

BiologyCBSE Class 12 · Board exam 2026, set 57/1/1 · 2 marks · Very short answer

CBSE Class 12 Biology 2026: question 21(b)

Set in the CBSE Class 12 board exam of 2026, paper 57/1/1, section B, question 21(b), for 2 marks. Try it first; the hints and our step-by-step solution are below.

Q21(b) · 2 marks · Very short answerCompetency-basedBiodiversity and Conservation

In an ecosystem there was loss of biodiversity due to some project in that area.

  1. (i)

    How will biodiversity be affected ? (2 points)

    1 mark
  2. (ii)

    List two major causes of loss of biodiversity.

    1 mark

Source: official question paper from cbse.gov.in (PDF). See it in the full 2026 board paper, set 57/1/1.

Hints

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

Hint 1

Recall Tilman's long-term ecosystem experiments on what happens when species number falls.

Hint 2

The main causes of biodiversity loss are called the 'Evil Quartet'.

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. (i) Loss of biodiversity in the area would lead to (1) a decline in plant production and (2) lowered resistance to environmental perturbations such as drought. (A third possible effect: increased variability in ecosystem processes such as water use and pest or disease cycles.)

    1 mark

  2. (ii) Two major causes: (1) habitat loss and fragmentation, e.g. clearing forest for the project; (2) over-exploitation of natural resources. (Others: alien species invasion, co-extinction.)

    1 mark

Answer: (i) Decline in plant productivity, and lowered resistance to disturbances such as drought; (ii) habitat loss and fragmentation, and over-exploitation (also alien species invasion, co-extinction)

Where the marks are

  • Any two effects on the ecosystem (½ + ½ mark)
  • Any two of the 'Evil Quartet' causes (½ + 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 paper2026 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.