Question 1

Which experimental result from the Luria-Delbrück fluctuation test provided evidence for the spontaneous mutation hypothesis in bacteria?

Accepted Answer

There was a high fluctuation in the number of resistant colonies among different plates.

Question 2

A prototroph is defined as a bacterial strain that:

Accepted Answer

Can synthesize all essential organic compounds and grow on minimal medium.

Question 3

Which of the following best describes an auxotroph?

Accepted Answer

A mutant bacterium that requires a specific nutrient supplement to grow.

Question 4

During which phase of bacterial growth does the population increase exponentially?

Accepted Answer

Log phase

Question 5

Which of the following statements about spontaneous mutations is TRUE?

Accepted Answer

They occur naturally and randomly, independent of external factors.

Question 6

If a bacterial culture is plated on medium containing a bacteriophage, and resistant colonies appear, what does the spontaneous mutation hypothesis predict about the timing of these mutations?

Accepted Answer

Mutations occur before exposure to the phage, during normal growth.

Question 7

Which of the following equations best describes exponential bacterial growth during the log phase?

Accepted Answer

$$N_t = N_0$ e$$^{rt}$$

Question 8

A researcher observes that the number of phage-resistant colonies varies greatly between replicate plates, even though all conditions are kept constant. What is the most likely explanation?

Accepted Answer

Mutations occur spontaneously and randomly before exposure to the phage.

Question 9

Which of the following is NOT a characteristic of induced mutations?

Accepted Answer

They occur naturally and randomly during DNA replication.

Question 10

In a fluctuation test, which result would support the adaptive mutation hypothesis?

Accepted Answer

A low and consistent number of resistant colonies among plates.

Question 11

A bacterial strain is able to grow on minimal medium containing only glucose and inorganic salts. After exposure to UV light, some cells can no longer grow unless the medium is supplemented with tryptophan. What term best describes these mutant cells?

Accepted Answer

Auxotrophs

Question 12

Which of the following best explains why the stationary phase occurs in bacterial growth?

Accepted Answer

Nutrients become limited and waste products accumulate, slowing growth.

Question 13

If a mutation occurs in a bacterial cell during the lag phase, what is the likely outcome for the progeny of that cell during the log phase?

Accepted Answer

All progeny will inherit the mutation.

Question 14

Which of the following statements about the difference between prototrophs and auxotrophs is correct?

Accepted Answer

Auxotrophs have lost the ability to synthesize one or more essential compounds.

Question 15

Which of the following is a direct consequence of spontaneous mutation in a bacterial population?

Accepted Answer

Genetic variation arises even in the absence of selective pressure.

Question 16

A culture of E. coli is grown in minimal medium. After several generations, a few cells are able to grow on medium containing a bacteriophage. According to the spontaneous mutation hypothesis, what is the most likely explanation?

Accepted Answer

Resistant mutants arose randomly before exposure to the phage.

Bacterial Mutation and Genetic Variation: Mechanisms and Experimental Evidence

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