Question

Assertion : In Griffith's experiment, a mixture of heat- killed virulent bacteria $R$ and live non-virulent bacteria $S$, lead to the death of mice.
Reason : 'Transforming principle' got transferred from heat-killed $R$ strain to $S$ strain and made it virulent.

• A. If both assertion and reason are true and reason is the correct explanation of assertion
• B. If both assertion and reason are true but reason is not the correct explanation of assertion
• C. If assertion is true but reason is false
• D. If both assertion and reason are false

Answer 1

Answer: (D)

When bacteria Streptococcus pneumoniae are grown on a culture plate, some produce smooth shiny colonies $(S)$ while others produce rough colonies $(R)$. This is because the $S$ strain bacteria have a mucous (polysaccharide) coat, while $R$ strain does not. Mice infected with the $S$ strain (virulent) die from pneumonia infection but mice infected with the $R$ strain do not develop pneumonia. In Griffith's experiement, some 'transforming principle', transferred from the heat-killed $S$ strain, had enabled the $R$ strain to synthesise a smooth polysaccharide coat and become virulent which must be due to the transfer of the genetic material. This is known as transformation.