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At a composting… (Class 12 Biology SQP 2026-27, Q33B)

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BiologyCBSE Class 12 · Sample paper, session 2026-27 · 5 marks · Long answer

CBSE Class 12 Biology sample paper 2026-27: question 33(B)

From the official CBSE sample question paper for 2026-27, section E, question 33(B), for 5 marks. Try it first; the hints and our step-by-step solution are below.

Q33(B) · 5 marks · Long answerCompetency-basedEcosystem

At a composting ground, after a community clean-up drive, large amounts of vegetable peels, garden leaves, and other organic waste are piled up. Over the next few weeks, the volume of the waste decreases noticeably.
I. Explain the sequence of processes that could have led to this transformation, and name the major organisms involved at each step. (4)
II. If a prolonged dry spell occurs during this composting period, explain how it could affect the rate of the above processes. (1)

Source: official sample paper from cbseacademic.nic.in (PDF). See it in the full Sample paper 2026-27.

Hints

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

Hint 1

This is the process of decomposition from the Ecosystem chapter.

Hint 2

There are steps from breaking into pieces, through nutrients washing down and enzymes acting, to the formation of humus.

Hint 3

Microbes need moisture to stay active.

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. Fragmentation: Detritivores such as earthworms and termites break the vegetable peels and leaves into smaller particles. This increases the surface area available for microbes to act on.

    1 mark

  2. Leaching: Water-soluble inorganic nutrients dissolve and percolate down into the soil layers, where some are precipitated as unavailable salts.

    1 mark

  3. Catabolism: Bacteria and fungi release enzymes that break the complex organic matter down into simpler inorganic substances.

    1 mark

  4. Humification and mineralisation: Microbes convert the remains into dark, amorphous humus, which resists microbial action and decomposes very slowly. Further microbial degradation of humus releases inorganic nutrients (mineralisation). Together these processes reduce the waste volume.

    1 mark

  5. II. Effect of a dry spell: Low moisture slows the activity of microbes and detritivores and reduces their enzymatic breakdown. Decomposition therefore slows down, and the waste volume falls more slowly.

    1 mark

Answer: I. Fragmentation (detritivores such as earthworms and termites) → Leaching (soluble nutrients percolate down) → Catabolism (enzymes of bacteria and fungi) → Humification and mineralisation (microbes form humus and release inorganic nutrients). II. A dry spell lowers moisture, reduces microbial activity and so slows decomposition.

Where the marks are

  • Fragmentation by detritivores, with examples (1 mark)
  • Leaching of soluble nutrients (1 mark)
  • Catabolism by bacterial and fungal enzymes (1 mark)
  • Humification and mineralisation by microbes (1 mark)
  • Dry spell lowers moisture and so slows microbial decomposition (1 mark)

Revise the chapter

  • Chapter: Ecosystem (notes, formulas, where marks are lost and every past question)
Practise this chapterBoard-style questions from Ecosystem, one at a time, marked against the answer key and marking points.Back to the full paperSample paper 2026-27: 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.