AP BIOLOGY

Detailed explanation-1: -In 1928, in an attempt to develop a vaccine against pneumonia, Frederick Griffith became the first to identify bacterial transformation, in which the form and function of a bacterium changes. Both virulent and avirulent Streptococcus pneumoniae were under his study.

Detailed explanation-2: -Experiment: Griffith injected both S and R strains to mice. The one which was infected with the S strain developed pneumonia and died while that infected with the R strain stayed alive. In the second stage, Griffith heat-killed the S strain bacteria and injected into mice, but the mice stayed alive.

Detailed explanation-3: -Griffith’s Experiments First, Griffith took a culture of the S strain, heated the cells to kill them, and then injected the heat-killed bacteria into laboratory mice. The mice survived, suggesting that the cause of pneumonia was not a toxin from these disease-causing bacteria.

Detailed explanation-4: -Griffith developed the concept of the transforming principle. The prinicple was able to transform a non-pathogenic bacteria into a pathogenic strain. Changing phenotype is one of the characteristics of the hereditary material. Griffith called the factor that changed the phenotype the tranforming principle.