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Analyse the following… (Class 12 Biology 2025, Q18A)

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BiologyCBSE Class 12 · Board exam 2025, set 57/1/1 · 2 marks · Very short answer

CBSE Class 12 Biology 2025: question 18(A)

Set in the CBSE Class 12 board exam of 2025, paper 57/1/1, section B, question 18(A), for 2 marks. Try it first; the hints and our step-by-step solution are below.

Q18(A) · 2 marks · Very short answerCompetency-basedEcosystem

Analyse the following ecosystems and discuss, which will be more productive in terms of primary productivity :
A young forest, a natural old forest, a shallow polluted lake.

Source: official question paper from cbse.gov.in (PDF). See it in the full 2025 board paper, set 57/1/1.

Hints

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

Hint 1

Primary productivity depends on how much producer biomass is capturing sunlight.

Hint 2

Compare the number and variety of producers in each ecosystem, and think about what pollution does to the producers in a lake.

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. The natural old forest will be the most productive.

    ½ mark

  2. It has a large standing biomass of producers and high biodiversity, with a multi-layered canopy. It therefore traps more solar radiation and stores it as organic matter, giving high primary productivity.

    ½ mark

  3. A young forest is still developing. It has fewer and smaller trees, so it captures less solar radiation and its productivity is lower.

    ½ mark

  4. A shallow polluted lake has few producers, a lot of dead organic matter and poor light and oxygen conditions. Its productivity is therefore the least of the three.

    ½ mark

Answer: Natural old forest is the most productive (more biomass and biodiversity trap more solar energy); the young forest and the shallow polluted lake are less productive.

Where the marks are

  • Chooses the natural old forest as most productive (½ mark)
  • Reason: high biomass/biodiversity traps more solar energy (½ mark)
  • Young forest has fewer trees, so less energy is captured (½ mark)
  • Polluted lake has few producers and much dead matter, so low productivity (½ mark)

Revise the chapter

Practise this chapterBoard-style questions from Ecosystem, one at a time, marked against the answer key and marking points.Back to the full paper2025 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.