#16 - Specific Reference, Must Be True

[Administrator]

Please post your questions below! Thank you!

[MountainGirl234]

Hello!

I'm having trouble distinguishing between A and D. I approached this with a "resolve" mindset. I thought that because Colwell's new test helped identify instances of V. cholera bact. then that would help explain why traditional detection methods would compute different results if that particular method didn't rely on the use of florescent lighting?

I see how A can also be true, that VC cannot always grow in a petri dish, since the cultured techniques reported fewer instances of VC in the same samples

But what makes E incorrect?

My brain is starting to spin in circles, and I think I'm overanalyzing this question...

[Robert Carroll]

Mountain,

I think you're asking only why answer choice (E) is wrong (let me know if I'm wrong). The fluorescing is part of Colwell's method of detecting cholera, but I have no idea if it is or isn't part of the petri dish culturing method, and, whether it is or isn't, it doesn't explain why Colwell's method works better. The petri dish method doesn't always grow cholera because, as the last paragraph states, dormant cholera is viable but not culturable. So a petri dish, which grows cultures, will not show growth. But Colwell's test doesn't really require cholera itself to "do" anything - cholera that's alive but won't grow, because it's dormant, will still have the antibody latch onto it.

Answer choice (E) explains why Colwell's method will work but not why petri dishes won't work in the same circumstances, so it does not resolve the paradox.

Robert Carroll

[Catallus]

What makes (D) wrong? It seems a much stronger choice than (A). (A) only tells us that V. cholerae "cannot always" be cultured (without identifying specific limitations relevant to Colwell's study), whereas (D) would give a more specific reason that would explain the 51/52 compared to 7/52 success rates: that culturing V. cholerate from water samples, as Colwell was doing in the study, doesn't work.

Re-reading the question stem, I'm thinking it might be because we're asked to infer from the passage, not just provide any explanation that could resolve the discrepancy. (D) would resolve it but isn't textually supported; we have no reason to infer (D).

[Amber Thomas]

Hi Catallus!

You're exactly right-- we have no textual support to infer answer choice D. It does explain the discrepancy, but nothing in the passage indicates that this is true. Further, if we look at lines 20-25, we can see that Colwell even suggests that the V. cholerae bacteria may not always be detectable when using petri dishes.

This can help explain why Colwell's new form of testing using antibodies and ultraviolet light yielded much higher results than traditional petri dish testing. We have textual evidence for this, and it does help to explain the discrepancy.

I hope this helps!