Passage II

Some mutations in Escherichia coli allow the bacteria to survive exposure to an antibiotic. These antibioticresistant bacteria may have a different relative fitness (a measure of survival and reproductive success) than E. coli without mutations. Scientists conducted a study to determine the relative fitness of 5 E. coli strains—1 nonmutated (Strain U) and 4 mutated (Strains W, X, Y, and Z)—when the strains were exposed for 24 hr to each of 5 different concentrations of the antibiotic streptomycin (see Table 1). The effect of the mutation in each of Strains W−Z is listed in Table 2.

Table 1 adapted from Viktória Lázár et al., “Bacterial Evolution of Antibiotic Hypersensitivity.” ©2013 by EMBO and Macmillan Publishers Limited.

10. Suppose an equal number of Strain W cells and Strain X cells were exposed for 24 hr to a streptomycin concentration of 2 μg/mL. Based on Table 1, which of Strain W or Strain X would more likely have the greater number of cells survive and reproduce?

Answer and Explanation

Your Answer is

Correct Answer is H

Explanation

According to the definition of relative fitness in the background text information, it can be seen that the larger the value, the higher the survival rate. Therefore, according to Table 1, in the case of streptomycin concentration of 2 units, Strain X is 0.8, which is greater than Strain W 0.3 , so the survival rate and reproductive rate are higher