Reading comp PrepTest 154 · Section 3 · Question 16

Passage

 For nearly a century after the discovery in the 1880s that a bacterium, Vibrio cholerae , causes cholera, scientists believed Remaining source text redacted.
Passage walkthrough
Passage SummaryTopic: Science

Paragraph 1
  • Paragraph note
    • A common scientific belief is discussed, and a question it leaves open is raised
  • Views, minor Meta-Structures, and the author's attitude
    • Common belief - Cholera travels via human hosts (waste into food and water supplies)
    • Question - How do spontaneous outbreaks in areas cholera was eliminated happen?
Paragraph 2.1 (Lines 12-25)
  • Paragraph note
    • A new belief is brought up and skepticism is discussed
  • Views, minor Meta-Structures, and the author's attitude
    • Rita Colwell (1970s) - Claimed to have found cholera in seawater and it can go undetected by common culture tests
    • Skepticism - "No" biologist thought it could live outside of humans, and there were no outbreaks since 1911
Paragraph 2.2 (Lines 25-39)
  • Paragraph note
    • Colwell's hypothesis is put to the test
  • Views, minor Meta-Structures, and the author's attitude
    • Colwell used a new test (antibodies/UV) and found cholera bacteria in bayous that traditional tests missed
Paragraph 3
  • Paragraph note
    • Further studies backing up/expanding on Colwell's hypothesis, and a future course of inquiry
  • Views, minor Meta-Structures, and the author's attitude
    • Tests show bacteria go into sporelike state that can't be detected using traditional tests
    • That state is more survivable
    • Question - What gets them out of sporelike state? Potential answer - Sea-surface temp spikes (e.g., Bay of Bengal)
Main Point:
There is evidence suggesting that Rita Colwell's hypothesis about "viable but nonculturable" cholera bacteria surviving in the ocean and in a sporelike state is correct, as it explains seemingly spontaneous outbreaks of the disease in areas where it has been eradicated.

Key Lines:
Lines 3-6 - Traditional scientific theory is discussed
Lines 9-11 - A question left open by this theory
Lines 12-14 - A new scientist/theory is introduced
Lines 21-24 - More on that theory
Lines 25-30 - The new theory is tested
Lines 40-42 - The new theory is expanded
Lines 49-51 - A question is posed for the new theory
Lines 51-54 - An answer is put forward

Meta-Structure:
Old Theory/New Theory - The old theory concerning the spread of cholera is shown to leave open a question that a new theory answers.

Question/Answer - Two questions are posed. The first (Lines 9-11) is broad and leads to the main point - Colwell's new theory. The second (Lines 49-50) is limited and leads to a hypothesis to be tested under Colwell's theory.

Last Thoughts:
Normally, the Author is a bit more on board with a new theory being presented. Here, there's a mix. She states that Colwell's studies "revealed" some things about V. cholerae (Line 40), but also poses Colwell's water theory as being something that isn't 100% certain ("If, as Colwell believes" in Line 54).

So we need to be careful in selecting answers that don't overshoot the Author's feelings towards Colwell's theory and pick an answer that reflects a certainty that doesn't exist.

Also, note that we split Paragraph 2 up. It was pretty long, and there was a natural breaking point between where Colwell raised her claim and people expressed skepticism, and the specific situation that allowed her to discover evidence for her hypothesis.

Question prompt

It can be inferred Remaining source text redacted.
Why the credited answer is right

Credited answer: A

The notes below walk through why it fits the stem and how to eliminate the rest.

Question Type

Science

Answer choices

  1. A
    V. cholerae cannot always Remaining source text redacted.
    Why choice A matches the stem
    Correct. Question Type:
    Paradox

    Strategy Overview:
    Head back to the relevant section and find an answer to the question

    Answer Anticipation/Relevant Lines:
    First, we have to define the discrepancy. Using Colwell's new test, cholera was found in 51/52 samples; using the old test, it was found in only 7/52 samples. That's a pretty big discrepancy!

    So we're trying to explain the different results—therefore, we want to find a relevant difference between the tests. The traditional test used culture methods, whereas Colwell's used antibodies and UV light. Also, we know that Colwell developed this new method because the bacteria ""could not always be [grown] in a petri dish.""

    So the correct answer should tie the discrepancy into the different methods, one of which is at least theorized to fail to show the bacteria sometimes.

    Answer Explanation:
    (Lines 24-25) Colwell developed the new method because she didn't believe the cholera bacterium could always be grown in a petri dish. If that's the case, then it explains why the old test showed only 7 positive results whereas her showed 51. This answer is therefore correct.

    Key Takeaway:
    RC questions are very much LR questions with a very long stimulus. Here, we approached a Paradox question as we would in LR—clearly state the paradox, and since it reflected a difference, we wanted to find an answer that highlighted a difference between the two tests.
  2. B
    V. cholerae's ability to Remaining source text redacted.
    Why choice B is not credited
    Incorrect. (Lines 30-31) Colwell's test used antibodies, so if the ability of V. cholera to bond with antibodies was limited, then her test should have shown the lower result. This answer, if anything, makes the discrepancy worse.
  3. C
    V. cholerae responds primarily Remaining source text redacted.
    Why choice C is not credited
    Incorrect. Neither test is said to feature either of these changes, so this answer is out of scope.
  4. D
    V. cholerae cannot be Remaining source text redacted.
    Why choice D is not credited
    Incorrect. There's no indication that the water from the local bayous should have had human waste in it. Even then, there's no indication that Colwell's method would be better equipped to detect V. cholera in these sources.
  5. E
    V. cholerae's cell membrane Remaining source text redacted.
    Why choice E is not credited
    Incorrect. (Lines 32-24) This can be a tricky trap answer! It seems to suggest that there might be false positives since V. cholera would fluoresce even without the antibodies from Colwell's test. However, think about that for a second—if that's the case, then it wouldn't be a false positive, as the cholera bacterium would be present! This answer doesn't explain why the cholera wasn't detected by the traditional test, so it fails to resolve the paradox.

What this tests

Question analytics

Based on historical answer selection rates for this question.

Answer choice distribution

  1. A Credited 60%
  2. B 5%
  3. C 10%
  4. D 11%
  5. E 13%

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