Q21 / 200 · MHT CET - Medical 2026 (22 April Shift 2) · Biology
Which one of the following experiments by Griffith with Streptococcus pneumoniae, resulted in the death of mice due to pneumonia?
- AMice injected only with heat killed S strain.
- Correct answerBMice injected with live R strain and heat killed S strain.
- CMice injected with heat killed R as well as S strains.
- DMice injected only with heat killed R strain.
Solution
Frederick Griffith conducted a series of experiments with Streptococcus pneumoniae to demonstrate bacterial transformation.
When mice were injected with the live S strain (virulent), they died from pneumonia.
When injected with the live R strain (non-virulent), they survived.
When injected with the heat-killed S strain, they survived.
When injected with a mixture of live R strain and heat-killed S strain, the mice died. This occurred because some transforming principle from the heat-killed S strain enabled the live R strain to synthesize a smooth polysaccharide coat and become virulent.
Therefore, the injection of live R strain and heat-killed S strain resulted in the death of the mice.
Answer: Mice injected with live R strain and heat killed S strain.
When mice were injected with the live S strain (virulent), they died from pneumonia.
When injected with the live R strain (non-virulent), they survived.
When injected with the heat-killed S strain, they survived.
When injected with a mixture of live R strain and heat-killed S strain, the mice died. This occurred because some transforming principle from the heat-killed S strain enabled the live R strain to synthesize a smooth polysaccharide coat and become virulent.
Therefore, the injection of live R strain and heat-killed S strain resulted in the death of the mice.
Answer: Mice injected with live R strain and heat killed S strain.
Hence, the correct answer is option: 'B'.