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Assertion (A) : Decomposition… (Class 12 Biology 2023, Q15)

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BiologyCBSE Class 12 · Board exam 2023, set 57/5/1 · 1 mark · Assertion-reason

CBSE Class 12 Biology 2023: question 15

Set in the CBSE Class 12 board exam of 2023, paper 57/5/1, section A, question 15, for 1 mark. Try it first; the hints and our step-by-step solution are below.

Q15 · 1 mark · Assertion-reasonCompetency-basedEcosystem

Assertion (A) : Decomposition process is slower if detritus is rich in lignin and cutin.
Reason (R) : Decomposition is largely an oxygen requiring process.

  1. (A)Both (A) and (R) are true and (R) is the correct explanation of (A).
  2. (B)Both (A) and (R) are true, but (R) is not the correct explanation of (A).
  3. (C)(A) is true, but (R) is false.
  4. (D)(A) is false, but (R) is true.

Source: official question paper from cbse.gov.in (PDF). See it in the full 2023 board paper, set 57/5/1.

Hints

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

Hint 1

List the factors that affect the rate of decomposition.

Hint 2

Chemical composition and oxygen supply are two separate factors.

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. Lignin and chitin-rich detritus decomposes slowly, so (A) is true. Decomposition is also largely an oxygen-requiring process, so (R) is true.

    ½ mark

  2. The slow rate in (A) is due to the chemical nature of the detritus, not the need for oxygen. So (R) does not explain (A). Hence option (B).

    ½ mark

Answer: (B)

Where the marks are

  • Both true, R not explanation (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 paper2023 board paper, set 57/5/1: 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.