AP BIOLOGY

Detailed explanation-1: -In this experiment, Griffith mixed the living non-virulent bacteria with a heat inactivated virulent form. He subsequently infected mice with this mixture and much to his surprise, the mice developed pneumonia and died. Furthermore, he was able to isolate colonies of the virulent strain from these mice.

Detailed explanation-2: -The experiments took an unexpected turn, however, when harmless R bacteria were combined with harmless heat-killed S bacteria and injected into a mouse. Not only did the mouse develop pnenumonia and die, but when Griffith took a blood sample from the dead mouse, he found that it contained living S bacteria!

Detailed explanation-3: -Statement 1-In Griffith’s experiment, when mice were injected with heat-killed R-strain and live S-strain the mice survived.

Detailed explanation-4: -Then, he mixed the heat-killed S and live R strains. This mixture was injected into mice and they died. In addition, he found living S strain bacteria in dead mice. Conclusion: Based on the observation, Griffith concluded that R strain bacteria had been transformed by S strain bacteria.

Detailed explanation-5: -So, when R-strain and heat-killed S-strain bacteria were injected separately, the mice stayed alive. But when injected together, the mice died. This was because R-strain bacteria got “transformed” into S-strain, and caused the disease. Heat-killed R-strain does not affect the mice and the mice lived.