Question

A series of experiments were conducted by Frederick Griffith in 1928, on transforming principle with:

• A. Streptococcus pneumoniae
• B. Escherichia coli
• C. Bacillus thuringiensis
• D. Salmonella typhimurium

Answer 1

The Correct Option is A

Frederick Griffith's experiments were pivotal in understanding the phenomenon of bacterial transformation. He studied different strains of Streptococcus pneumoniae, specifically the virulent (pathogenic) strain and the non-virulent (avirulent) strain.

In his experiments, Griffith observed that when he injected mice with the heat-killed virulent strain of Streptococcus pneumoniae, the mice remained healthy and survived. Similarly, when he injected mice with the live avirulent strain, the mice also remained healthy.

However, Griffith discovered something intriguing when he injected mice with a mixture of the heat-killed virulent strain and the live avirulent strain. The mice became sick and died, and upon examination, he found live virulent bacteria in their bodies. This led Griffith to propose the concept of transformation, where the genetic material from the heat-killed virulent strain somehow transformed the avirulent strain into a virulent form.

Answer 2

Frederick Griffith conducted a series of experiments in 1928 on the transforming principle using Streptococcus pneumoniae (pneumococcus) bacteria. He worked with two strains of S. pneumoniae:

Smooth strain (S strain) – Virulent and caused pneumonia in mice due to the presence of a polysaccharide capsule.

Rough strain (R strain) – Non-virulent and did not cause disease, as it lacked the protective capsule.

Through his experiments, Griffith demonstrated that when heat-killed S strain bacteria were mixed with live R strain bacteria, the R strain transformed into the virulent S strain, indicating the presence of a "transforming principle." This laid the foundation for the discovery of DNA as the genetic material.