Question

In his work with pneumonia-causing bacteria and mice, Griffith found that ______.

Options

• The polysaccharide coat of R cells caused pneumonia.

• Some heat-stable chemical from S cells was transferred to R cells to transform them into S cells.

• Heat-killed S cells were able to cause pneumonia only when they were transformed by the DNA of R cells.

• The protein coat from smooth (S) cells was able to transform rough (R) cells.

Answer 1

In his work with pneumonia-causing bacteria and mice, Griffith found that some heat-stable chemical from S cells was transferred to R cells to transform them into S cells.

Explanation:

Frederick Griffith’s 1928 experiment demonstrated the process of bacterial transformation. He observed that when heat-killed, virulent S-strain bacteria were mixed with live, non-virulent R-strain bacteria and injected into mice, the mice developed pneumonia and died. Because the heat-killed S cells alone could not cause the disease, he concluded that a “transforming principle”, a heat-stable substance, had passed from the dead S cells into the live R cells. This substance provided the R cells with the genetic instructions to develop a protective polysaccharide coat, effectively transforming them into pathogenic S cells. Although Griffith did not identify the chemical nature of this principle, later research confirmed it was DNA.