PrepTest 104, Section 4, Question 24
Scientists, puzzled about the development of penicillin-resistant bacteria(94 more words not shown)
Which one of the following(26 more words not shown)
- AIt is a(18 more words not shown)
- BIt is a(21 more words not shown)
- CIt is a(29 more words not shown)
- DIt is the(25 more words not shown)
- EIt is a(26 more words not shown)
Reading the argument
How did these patients acquire penicillin-resistant bacteria without taking penicillin? My first thought is that they might have picked up resistant bacteria from somewhere else—another person, for example. Their own use of the drug needn't be the only possible route.
The scientists offer a different explanation. These patients have fillings containing mercury, and their bacteria resist mercury poisoning. The proposed link is genetic: the genes for penicillin resistance sit close to the gene for mercury immunity.
Now the mechanism makes sense. Mercury kills bacteria without the immunity, leaving bacteria that possess both protections room to flourish. The penicillin resistance comes along with the mercury immunity. The account doesn't require these patients to take penicillin, or require mercury to create a brand-new resistance gene in each bacterium.
What we’re looking for
The question asks about an unstated background assumption: some patients who take penicillin develop bacteria resistant to it. I'd describe that as the familiar connection that makes the opening cases puzzling. The research addresses patients who reach the resistant-bacteria outcome without taking the drug. We need an answer explaining that role, not another explanation of how the genes work.
Working the answers
- A
The passage doesn't present new findings that conclusively prove what happens in patients taking penicillin. Its problem cases are patients who haven't taken it. The background assumption helps establish why those cases call for explanation; it isn't the hypothesis this research is claimed to prove.
- B
Knowing that resistance can develop in patients taking penicillin doesn't rule it out in patients who don't take penicillin. That would turn one route to the outcome into the only possible route. The passage is specifically explaining how the outcome could occur without that exposure.
- CCorrect
Put the two facts together: resistance is associated with taking penicillin in some patients, yet the patients under investigation develop resistant bacteria without taking it. That contrast generates the question the scientists want to answer. The unstated assumption supplies the background that makes the observed case interesting.
- D
We aren't told that this is a tentative result of earlier research. More importantly, the proposed mercury explanation doesn't show the background assumption to be false. Resistance could occur in some patients taking penicillin and also occur through the described mercury-related process in patients who aren't. Explaining another route doesn't disprove the first.
- E
The scientists' proposed explanation involves genes, but the background assumption doesn't force that explanation. The initial possibility of acquiring resistant bacteria elsewhere shows why that leap would need more support. The assumption helps frame the puzzle; it doesn't conclusively establish what its solution must be.
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