Question 77·Medium·Command of Evidence
Asha Kwon and colleagues studied a gene called blaX in a common bacterium. Some bacteria carry blaX, while others do not. The researchers predicted that blaX helps bacteria survive exposure to an antibiotic because it is associated with a protein that breaks the antibiotic down. To test this idea, they compared bacterial growth for two strains: one with a working copy of blaX and one in which blaX had been disabled.
Which choice best describes data in the graph that support the researchers’ prediction?
For Command of Evidence questions tied to a graph, restate the conclusion in your own words, then scan the graph for the specific comparison that would most directly support it. Prioritize evidence that shows the clearest, most relevant contrast (often at extremes like the highest dosage), and choose the option that summarizes that strongest pattern rather than a minor or less relevant detail.
Hints
Focus on what would count as support
The prediction is about survival in the presence of the antibiotic. Look for where the graph shows differences between strains when antibiotic concentration is above 0.
Compare at the highest concentration
Check what happens at 20 mcg/mL for each strain. Which strain still has substantial growth?
Choose the most complete description
Prefer the option that summarizes the overall trend across multiple concentrations, not just a single point or a situation without antibiotic.
Step-by-step Explanation
Identify the claim being supported
The researchers’ prediction is that blaX helps bacteria survive exposure to the antibiotic, so the strongest evidence will show a growth advantage for the blaX strain when antibiotic is present, especially at higher concentrations.
Compare the strains at higher antibiotic levels
At 10 and 20 mcg/mL, the blaX strain’s cell density remains relatively high, while the blaX-disabled strain drops to much lower values (near zero at 20 mcg/mL). This difference directly supports the idea that blaX improves survival under antibiotic stress.
Select the option that describes that pattern
The choice that best captures the widening growth gap as antibiotic concentration increases is: As antibiotic concentration increases, the strain with a working copy of blaX maintains a much higher cell density than the strain with blaX disabled, especially at 20 mcg/mL.