Answered

In his work with pneumonia-causing bacteria, Frederick Griffith found that a non-pathogenic strain had been transformed into a pathogenic strain. Which of the following explanations best describes the phenomenon of transformation? It refers to transfer of genetic material between bacteria through direct cell to cell contact. It refers to introduction of genetic material into animal cells. It refers to genetic material taken up from the environment through bacterial cell walls.

Sagot :

It refers to genetic material taken up from the environment through bacterial cell walls.

Answer:

The correct answer will be it refers to genetic material taken up from the environment through bacterial cell walls.

Explanation:

Frederick Griffith performed the series of experiments on Streptococcus pneumoniae bacteria and mice in 1928.

For this he used two strains of the bacteria:

1. S-strain: with polysaccharide coating which gave a smooth appearance to the bacteria and providing resistance from the immunity of the host. Thus, they were virulent strains.  

2. R-strain: without polysaccharide which were avirulent strains as they lacked smooth coating.

When he injected R bacteria with heat-killed S bacteria the mice died although R bacteria was avirulent while the virulent S strain was dead due to heat.  

He concluded that R strains have been transformed into S strain bacteria through a mechanism called "transformation" via a physiological state of cell called competence in which the living bacterial cells took the foreign DNA across their cell membrane which got incorporated into its genome through genetic recombination.

Thus, It refers to genetic material taken up from the environment through bacterial cell walls is the correct answer.

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