For nearly a century after the discovery in the 1880s that a bacterium

Question

For nearly a century after the discovery in the
1880s that a bacterium,  Vibrio cholerae , causes cholera,
scientists believed that it traveled to new geographic
regions only via human hosts and that
  (5)   epidemics typically occurred when the bacteria spread
through contamination, by human waste, of food and
unchlorinated water supplies. But scientists wondered
where the bacteria went during the many years between
epidemics. How could the disease arise seemingly
  (10)   spontaneously around the world, often where it was
thought to have been eradicated?

In the 1970s, microbiologist Rita Colwell’s
claim that she had isolated . cholerae from the
Chesapeake Bay in the eastern United States met
  (15)   with great skepticism, as no biologists believed
V. cholerae could persist without a human host, and
no cholera outbreaks were occurring anywhere near
the Chesapeake. Indeed, there had been no cholera
epidemics anywhere in the United States since 1911.
  (20)   But, noting that most historic cholera outbreaks have
happened along seacoasts, Colwell suspected that
V. cholerae could somehow survive in seawater and
that perhaps the bacteria were not always detectable by
traditiona! culture methods—that is, that they could not
  (25)   always be cultured (i.e., grown) in a petri dish. Later
that decade, a small cholera outbreak near New Orleans
in the southern United States allowed Colwell to test
this hypothesis. She used a new detection method on
water from the local bayous from which people with
  (30)   cholera had eaten crab. This method uses an antibody
that latches onto a key component of the bacterium’s
cell membrane. Linked to that antibody is a molecule
that fluoresces bright green under ultraviolet light if the
V. cholerae bacterium is present. Her tests showed
  (35)   that the bacteria were in the bayous. Furthermore, in
a study in Asia, Colwell’s antibody test detected the
bacteria in 51 of 52 suspect water samples, whereas
culture techniques found them in only 7 of the same
52 samples.

(40)   Colwell’s further studies revealed that V. cholerae,
like some other bacteria, goes into a dormant, sporelike
state when environmental conditions do not favor
reproduction; in this state, the bacterium’s metabolic
rate plummets and the bacterium shrinks some
  (45)   15- to 300-fold. It stops reproducing and therefore
cannot be cultured. This “viable but nonculturable”
state, says Colwell, functions as a survival mechanism,
enabling V. cholerae to persist in a wide range of
conditions and habitats far from human hosts. Though
  (50)   no one knows exactly what conditions awaken
V. cholerae from dormancy, Colwell notes that seasonal
peaks in sea-surface temperatures in the Bay of Bengal
in south Asia correlate closely with peaks in that
region’s cholera cases. If, as Colwell believes, the
  (55)   bacteria are persisting in the water all along, it is
possible that changes in seawater temperature or
salinity are what enable them to spread among
humans again.    1 
 1. The passage provides information that is most helpful in answering which one of the following questions?

(A) Why did Colwell suspect that the ocean served as the environmental reservoir for V cholerae?
(B) What other bacteria are capable of entering a dormant state similar to that of V cholerae?
(C) Does ultraviolet light as used in Colwell's test have any effects on the reproduction of V cholerae?
(D) Is V cholerae harmful to shellfish that transmit it?
(E) How does Colwell intend to determine the conditions that awaken V cholerae from dormancy?

2 
 2. The passage suggests that biologists were skeptical of Colwell's claim to have isolated V cholerae from the Chesapeake Bay because they believed that

(A) V cholerae could not always be cultured in a petri dish
(B) V cholerae bacteria were unable to persist in seawater
(C) V cholerae bacteria were unculturable in their dormant state
(D) Colwell's new method of detecting V cholerae was flawed
(E) the only V cholerae bacteria in Chesapeake Bay were to be found in crabs

3 
 3. It can be inferred from the passage that which one of the following best explains the discrepancy in the findings reported in the last sentence of the second paragraph?

(A) V cholerae cannot always be grown in a petri dish.
(B) V cholerae's ability to bond with antibodies is limited.
(C) V cholerae responds primarily to changes in temperature and salinity.
(D) V cholerae cannot be cultured using samples taken from sources other than human tissue or waste.
(E) V cholerae's cell membrane normally contains a molecule that fluoresces under ultraviolet light.

4 
 4. The passage suggests that if V cholerae bacteria undetectable by traditional culture methods inevitably caused cholera in humans who ingested them, then which one of the following is most likely to be true?

(A) Human antibodies that usually latch onto V cholerae's cell membrane were unable to do so in these cases.
(B) The human body's temperature is the temperature the ocean must reach to awaken V cholerae bacteria from their dormant state.
(C) In their dormant state, V cholerae bacteria are able to survive in chlorinated water systems.
(D) The infected humans had been infected with cholera at some point earlier in their lives.
(E) The human body is an environment in which dormant V cholerae bacteria can awaken.

5 
 5. Which one of the following is most strongly supported by the passage?

(A) V cholerae bacteria in the Bay of Bengal are more likely to be detectable by traditional culture methods when sea-surface temperatures there are at seasonal peaks.
(B) When the salinity of seawater in the Bay of Bengal decreases, V cholerae bacteria are likely to reproduce there and cause cholera outbreaks.
(C) Although V cholerae can persist in seawater, it still requires human hosts in order to spread along a seacoast.
(D) Bacteria that are taken from a human host are harder to detect using traditional culture methods than are bacteria taken from seawater.
(E) Antibodies are less likely to bond to the cell membrane of V cholerae when the bacterium is in a dormant state.

6 
 6. Which one of the following most accurately expresses the main purpose of the final paragraph of the passage?

(A) to identify future directions for research within a field of study and describe the obstacles that researchers will need to overcome
(B) to answer a question raised earlier in the passage and provide new evidence that gives rise to further questions
(C) to evaluate the effect an innovative methodology described earlier in the passage is likely to have on future research
(D) to offer recommendations concerning future uses of an innovative methodology described earlier in the passage
(E) to enumerate the effects of a biological phenomenon described in the previous paragraph and describe the limits of current knowledge regarding it

7 
 7. The passage suggests that Colwell most likely holds which one of the following views regarding V cholerae?

(A) In most cases, V cholerae bacteria do not travel to new locations via human hosts, but rather move through the ocean.
(B) In most cases, V cholerae requires a human host in order to awaken and return from dormancy to a culturable state.
(C) Cholera outbreaks are never caused by the introduction of active V cholerae bacteria into a new location, but rather by V cholerae awakening from dormancy.
(D) Use of Colwell's new detection technique on the water samples she obtained from the Chesapeake Bay would have revealed the presence of V cholerae.
(E) Water samples from coastal regions throughout Asia, if subjected to Colwell's new detection technique, would reveal the presence of V cholerae.

Sajjad1994 · Answer

Explanation

4. The passage suggests that if V cholerae bacteria undetectable by traditional culture methods inevitably caused cholera in humans who ingested them, then which one of the following is most likely to be true?

Difficulty Level:   650-700

Explanation

The passage describes microbiologist Rita Colwell's research on Vibrio cholerae and its ability to persist in the environment in a dormant, spore-like state. Colwell's studies revealed that V. cholerae can enter a  "viable but nonculturable"  state, where it cannot be detected by traditional culture methods. This state allows the bacteria to survive in various conditions and habitats far from human hosts.

Let's analyze each answer choice in light of the passage:

(A)  The passage does not provide information about the effectiveness of human antibodies in latching onto V. cholerae's cell membrane.

(B)  The passage does mention seasonal peaks in sea-surface temperatures in the Bay of Bengal correlating with peaks in cholera cases, but it does not specify that the ocean temperature must reach a particular level to awaken V. cholerae.

(C)  The passage does not provide information about the ability of dormant V. cholerae bacteria to survive in chlorinated water systems.

(D)  The passage does not suggest that the infected humans had been infected with cholera at some point earlier in their lives.

(E)  The passage implies that dormant V. cholerae bacteria can persist in the water and suggests that changes in seawater temperature or salinity might enable them to spread among humans again. This aligns with the idea that the human body is an environment in which dormant V. cholerae bacteria can awaken.

Therefore, the most likely answer is  (E)  - the human body is an environment in which dormant V. cholerae bacteria can awaken, based on the passage's discussion of the bacteria persisting in water and the potential role of changes in seawater conditions in enabling their spread among humans.

Answer: E

DmitryFarberMPrep · Answer

#7

This one relies on our understanding of the main point. The passage starts with a belief long held by scientists. If you've done a few RC passages by now, you should know what's coming: the belief will be questioned or overturned! Sure enough, that's what happens. People thought cholera could only be passed via contamination from human hosts, but that didn't explain how cholera could pop up spontaneously in new locations. Colwell figured that cholera must be able survive in the sea, and that's what she found. After devising a new test, she was able to determine that cholera was present, and that it was hanging out in a dormant state until it could find new human hosts.

Main Point? Colwell showed that, contrary to prior opinion, cholera can survive in seawater without a human host.

So now let's do #7.

First, cut A and C. She's telling us what  can  happen, not what usually or always happens. She isn't saying that the old idea about humans spreading cholera is wrong, or that every outbreak of cholera follows upon a period of dormancy.

B is talking about how dormancy ends, but the passage tells us that "no one knows exactly what conditions awaken V. cholerae from dormancy."

D and E are saying that she thinks her test would find cholera in specific locations. So where does she expect to find it? We know that she thought she found cholera in the Chesapeake Bay, but no one believed her. So presumably she'd think that her new test would have revealed the presence of cholera. D is a match!

E is too broad: would water samples from "throughout Asia" really all have cholera? We know there have been outbreaks in Asia, and she found cholera in almost all of the suspect water samples she tested, but that doesn't mean that if she just randomly tested water samples, they'd have cholera. It's like the difference between testing patients who show symptoms that suggest a certain illness and getting a positive result and testing  random  patients and expecting a positive result.

Sajjad1994 · Answer

Explanation

5. Which one of the following is most strongly supported by the passage?

Difficulty Level:   700

Explanation

(A)  The passage does mention that seasonal peaks in sea-surface temperatures in the Bay of Bengal correlate closely with peaks in cholera cases. It is reasonable to infer that higher temperatures might affect the detectability of the bacteria by traditional methods. Therefore,  option (A)  is supported by the correlation between sea-surface temperatures and cholera cases.

(B)  The passage does not provide information about the relationship between the salinity of seawater in the Bay of Bengal and the reproduction of V. cholerae. This option makes an assumption not supported by the information provided.

(C)  This statement contradicts the information in the passage. The passage suggests that V. cholerae can persist in seawater in a dormant state, enabling it to survive in various conditions and habitats far from human hosts.

(D)  Similar to option (C), this statement contradicts the information in the passage. It implies a dependence on human hosts for the spread of V. cholerae along a seacoast, which is not consistent with the dormant state mentioned in the passage.

(E)  Partially correct.

Answer: A

Sajjad1994 · Answer

Explanation

6. Which one of the following most accurately expresses the main purpose of the final paragraph of the passage?

Difficulty Level:   650-700

Explanation

(A)  This option doesn't accurately capture the main purpose of the final paragraph. While the paragraph discusses further studies on V. cholerae, it doesn't explicitly identify future directions for research or describe specific obstacles that researchers need to overcome.

(B)  This option correctly identifies the main purpose of the final paragraph. It acknowledges that the paragraph answers a question raised earlier in the passage regarding the bacterium's survival and introduces new evidence, such as V. cholerae's dormant state, which leads to further questions about the conditions that awaken the bacterium.

(C)  The final paragraph doesn't primarily focus on evaluating the effect of an innovative methodology. While it does mention Colwell's detection method using antibodies, the emphasis is on the findings about V. cholerae's dormant state rather than evaluating the methodology's future impact.

(D)  The paragraph doesn't offer recommendations for future uses of the methodology. Instead, it presents new findings about V. cholerae's dormancy and its implications for survival.

(E)  This option doesn't accurately capture the main purpose of the final paragraph. While the paragraph discusses a biological phenomenon (V. cholerae's dormancy), its main focus is on providing additional insights and raising further questions, rather than enumerating specific effects or describing the limits of current knowledge.

In summary, option (B) is the most accurate as it reflects the dual purpose of answering a question raised earlier and introducing new evidence that generates further questions.

Answer: B

Sajjad1994 · Answer

Explanation

3. It can be inferred from the passage that which one of the following best explains the discrepancy in the findings reported in the last sentence of the second paragraph?

Explanation

The discrepancy in the findings reported in the  last sentence of the second paragraph  is that Colwell’s antibody test detected V. cholerae in 51 of 52 water samples, whereas traditional culture techniques found it in only 7 of the same 52 samples. This suggests that the traditional culture methods are failing to detect the bacteria in many cases where it is actually present.

The passage explains that V. cholerae can enter a dormant,  "viable but nonculturable"  state where it cannot be grown in a petri dish (i.e., cultured) but is still detectable by other methods, such as the antibody test. This is directly stated in  lines 40-49: "Colwell’s further studies revealed that V. cholerae... goes into a dormant, sporelike state... It stops reproducing and therefore cannot be cultured."

Thus, the best explanation for the discrepancy is that V. cholerae cannot always be grown in a petri dish, which is why culture methods miss it while the antibody test (which does not require the bacteria to be culturable) detects it.  Option (A)  directly captures this explanation.

(B)  is not supported; the antibody test works effectively, so bonding is not limited.

(C)  is about what awakens the bacteria, not about detection discrepancies.

(D)  is too absolute and not stated; the passage implies culture methods fail even when samples are from water, not just human sources.

(E)  is misleading; the fluorescing molecule is linked to the antibody, not naturally part of the membrane.

Answer: A

ds2112 · Answer

Old belief: V. cholerae bacterium could spread only through human hosts, so it couldn’t thrive in seawater.
Method used: traditional (old) culture method, which uses a petri dish (this method can detect the bacterium only when it is “active” (means when it can reproduce and spread)
Rita Colwell: V. cholerae bacterium doesn’t need a human host to survive and thrive. She isolated the bacterium (means no human hosts are needed).

For nearly a century after the discovery in the 1880s that a bacterium

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GMAT Reading Comprehension (RC) Questions

For nearly a century after the discovery in the 1880s that a bacterium

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615 to 715 in 15 Days (Ria's Strategies)

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