Question

In Lederberg’s replica plating experiment what shall be used to obtain streptomycin resistant strain………………..
A. Minimal medium and streptomycin
B. Complete medium and streptomycin
C. Only minimal medium
D. Only complete medium

Answer 1

Hint: The experiment named the replica plating experiment was done by Esther and Joshua Lederberg to show that mutations are random and are not directed. The main hypothesis of the experiment was that the antibiotic resistant strains of bacteria which are surviving the antibiotic application, were having the resistance before itself and it is not due to the exposure.

Complete answer:
Let us know the procedure of the experiment. In this experiment, the bacteria are spread on an original plate and are allowed to produce some colonies. These colonies were stamped into a new plate containing the antibiotic streptomycin. A cloth is first placed on the original plate by which some of the bacterial colonies are stamped to it, when the same cloth is put over the other plate, the colonies get transferred. All the transferred colonies on the new plate survived even after exposure to antibiotics. So by this, scientists concluded that the colonies on new plates were already having resistance to antibiotics and they did not develop the resistance as a result of exposure to antibiotics. In this experiment, selective growth media is used which means the media contains some inhibitors that inhibit the growth of microbes and is said to be minimal media because it does not contain all the nutrients required for microbial growth. So, by this we can conclude that both minimal media and streptomycin were used.

Hence the correct answer is option A.

Note:
By this experiment, the scientists concluded that mutations are random and can occur by chance when there is any change in the environment and this is in accordance with Darwin's theory. He also proved that mutant strains were better in adapting to the environmental changes.