In a series of experiments, Griffith infected mice with nonvirulent R-strain bacteria and highly virulent S-strain bacteria. Heat-killed S bacteria were nonvirulent. However, the nonvirulent heat-killed S bacteria and the nonvirulent R bacteria together produced a virulent mixture. What did this demonstrate?
A. The molecules present on the outside of bacteria determine whether it's virulent or nonvirulent.
B. A transforming principle in the S bacteria allowed the nonvirulent R strain to become virulent.
C. The translation of proteins, carbohydrates, lipids, and DNA is important in determining bacterial virulence.
D. The S-strain bacteria had not been killed completely.

In the transformation experiments, conducted by Fredrick Griffith in 1928, he observed that heat-killed S-strain bacteria injected into mice did not kill them. When he injected a mixture of heat-killed S and live R-bacteria, the mice died. He concluded that the R-strain bacteria had somehow been transformed by the heat-killed S-strain bacteria. This occurred perhaps due to absorption of some transforming principal or substance by rough type bacteria from heat killed smooth bacteria. It had enabled the R-strain to synthesize a smooth polysaccharide coat and become virulent. This must be due to the transfer of the genetic material. However, the biochemical nature of genetic material was defined not from his experiments.

shimaaelaraby shimaaelaraby · Answer 2 · 2019-07-21T19:05:51+02:00

Answer:

the correct answer is :

B. ( A transforming principle in the S bacteria allowed the nonvirulent R strain to become virulent.)

Explanation:

According to Griffith's experiment, he used two strains of (Streptococcus pneumoniae ) which is bacteria infect mice causing pneumonia.

First strain: type |||-S (Smooth) bacteria, this bacteria is virulent, it has the ability to kill mice because it covers itself with smooth polysaccharide capsule that resist the immune system of mice, and this ability is according to the genetic traits inside its DNA.

Second strain: type ||-R (Rough) bacteria, this bacteria is non-virulent, it doesn't have this protective capsule so the immune system can resist it and it can't kill the mice on their own.

Steps of experiment :

Griffith killed the |||-S. by heat
The remains of killed |||-S where added to the ||-R. bacteria
He injected the mice with this mixture of ( heat-killed |||-S and ||-R )

Observation:

The mice all died, However the virulent |||-S strain bacteria killed by heat

Conclusion:

The DNA of the |||-S strain bacteria survived the heat and transformed to ||-R, this means somehow, type |||-S bacteria still alive inside the type ||-R.
This process called transforming principle, that allowed the nonvirulent R strain to become virulent.