CBSE Class 12 Biology sample paper 2026-27: question 6
From the official CBSE sample question paper for 2026-27, section A, question 6, for 1 mark. Try it first; the hints and our step-by-step solution are below.
Q6 · 1 mark · MCQMolecular Basis of Inheritance
Given below is the illustration of the different steps of experiments conducted by MacLeod, McCarty and Avery to find the chemical nature of the 'transforming principle' as DNA. Select the option that incorrectly depicts the step of the experiment.
- (A)A
- (B)B
- (C)C
- (D)D
Figure in the paper: Flowchart: heat-killed S bacteria, bacterial filtrate treated with four enzymes, then mixed with live R bacteria: A RNase → No transformation; B Protease → Transformation; C DNase → No transformation; D Lipase → Transformation. See it in the official paper.
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
The transforming principle turned out to be DNA.
Hint 2
Only an enzyme that digests DNA should stop transformation.
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.
Only DNase destroyed the transforming principle. RNase, protease and lipase did not stop transformation.
- 1 mark
So the RNase step should show 'Transformation'. Step A, which shows 'No transformation' after RNase, is therefore incorrect. Option (A).
Answer: (A)
Where the marks are
- Identifies that RNase treatment still allows transformation (1 mark)
Revise the chapter
- Chapter: Molecular Basis of Inheritance (notes, formulas, where marks are lost and every past question)
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