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Assertion (A) : Replication… (Class 12 Biology 2025, Q14)

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BiologyCBSE Class 12 · Board exam 2025, set 57/7/1 · 1 mark · Assertion-reason

CBSE Class 12 Biology 2025: question 14

Set in the CBSE Class 12 board exam of 2025, paper 57/7/1, section A, question 14, for 1 mark. Try it first; the hints and our step-by-step solution are below.

Q14 · 1 mark · Assertion-reasonCompetency-basedMolecular Basis of Inheritance

Assertion (A) : Replication of DNA takes place in S phase of the cell cycle.
Reason (R) : DNA replication and cell division cycle should be highly coordinated.

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

Source: official question paper from cbse.gov.in (PDF). See it in the full 2025 board paper, set 57/7/1.

Hints

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

Hint 1

In which interphase stage does DNA synthesis occur?

Hint 2

What would happen if DNA replicated but the cell did not divide?

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. DNA replicates in the S phase, so the Assertion is true.

  2. Replication must be tightly coordinated with the cell cycle, because failed cell division after replication leads to polyploidy. That is why replication is restricted to S phase, so R correctly explains A. Hence (A).

    1 mark

Answer: (A)

Where the marks are

  • Both true and R explains A (1 mark)

Revise the chapter

Practise this chapterBoard-style questions from Molecular Basis of Inheritance, one at a time, marked against the answer key and marking points.Back to the full paper2025 board paper, set 57/7/1: 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.