Question

in his transformation experiments, which of the following results did griffith observe?
mixing a heat - killed nonpathogenic strain of bacteria with a living pathogenic strain makes the pathogenic strain nonpathogenic.
infecting mice with nonpathogenic strains of bacteria makes them resistant to pathogenic strains.
mutant mice were resistant to bacterial infections.
mixing a heat - killed pathogenic strain of bacteria with a living nonpathogenic strain can convert some of the living cells into the pathogenic form.

Explanation:

Griffith's experiment involved Streptococcus pneumoniae. He used a heat - killed pathogenic strain (S - strain) and a living non - pathogenic strain (R - strain). When he mixed them, the R - strain was transformed into the pathogenic form. This was because the heat - killed S - strain had a "transforming principle" (later found to be DNA) that altered the R - strain.

• The first option is incorrect. Mixing a heat - killed non - pathogenic strain with a living pathogenic strain would not make the pathogenic strain non - pathogenic.
• The second option is incorrect. Infecting mice with non - pathogenic strains did not make them resistant to pathogenic strains in Griffith's experiment.
• The third option is incorrect. The focus of Griffith's experiment was on bacterial transformation, not mutant mice.

Answer:

Mixing a heat - killed pathogenic strain of bacteria with a living nonpathogenic strain can convert some of the living cells into the pathogenic form.