Class 12th Biology 2016 Set2 Outside Delhi Board Paper Solution
Describe the series of experiments of F. Griffith. Comment on the significance of the results obtained.
Frederick Griffith performed experiments on Streptococcus pneumonia which is responsible for causing pneumonia and mice. He observed that the bacteria produce two colonies:
(i) R strain: or rough colonies which are non-virulent.
(ii) S strain: or smooth colonies which are virulent and caused death of mice.
He observed that S cells are virulent due to production of a smooth polysaccharide coat which is absent in R- cells.
He performed the following experiment:
Mice + R-cell bacteria ----> Mice lived
Mice + S- cell bacteria ------> Mice died
Then he killed S- celled bacteria by heating which cause denaturation of its genetic material and then injected in mice.
Mice + Heat killed S- cells ------> Mice lived
Now he injected mice with heat killed S- cells and non-virulent R- cells.
Mice + Heat killed S- cells + R-cells ----->Mice died.
Then he recovered living S-cells from the dead mice.
Then he concluded that some transforming principle had been transferred from heat killed S- cell to living R- cells which enables R- cells to secrete polysaccharide coat and become virulent.
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