Self-study
P1
For nearly a century after the discovery in the 1880s that a bacterium, . ██████ █████████ ██████ ████████ ██████████ ████████ ████ ██ ████████ ██ ███ ██████████ ███████ ████ ███ █████ █████ ███ ████ █████████ █████████ ████████ ████ ███ ████████ ██████ ███████ ██████████████ ██ █████ ██████ ██ ████ ███ █████████████ █████ █████████ ███
Scientists' belief ·
Vibrio cholerae (VC), which causes cholara, travels only by human hosts
VC epidemics occur when bacteria spreads through human waste.
Puzzling phenomenon ·
VC pops up in places we thought it had been eliminated
And, where does it go in between epidemics?
P2
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Colwell's discovery ·
Found VC in Chesapeake Bay
Others were skeptical because they thought VC couldn't survive without a human host, and there were no cholera epidemics since 1911.
Colwell's hypothesis ·
VC can survive in seawater, and can't always be detected by traditional methods
Traditional methods involved growing bacteria in a petri dish. Perhaps we can't do this with VC.
Testing Colwell's hypothesis ·
New detection method finds VC in water
Used this method near New Orleans and in Asia. Method involves an antibody that produces light if VC is present.
P3
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Additional findings ·
VC can become dormant and stop reproducing
That's why it sometimes can't be cultured. In this dormant state, VC can survive away from humans. We don't know what awakens VC from a dormant state, but it might be changes in seawater temperature or salinity (saltiness).
Passage Style
Phenomenon-hypothesis (RC)
Single position
18.
Which one of the following ██ ████ ████████ █████████ ██ ███ ████████
a
V. cholerae bacteria ██ ███ ███ ██ ██████ ███ ████ ██████ ██ ██ ██████████ ██ ███████████ ███████ ███████ ████ ███████████ ████████████ █████ ███ ██ ████████ ██████
b
When the salinity ██ ████████ ██ ███ ███ ██ ██████ ██████████ ██ ████████ ████████ ███ ██████ ██ █████████ █████ ███ █████ ███████ ██████████
Although the author suggests that salinity might be related to awakening V. cholerae, we don’t know whether salinity needs to increase or decrease to awaken the bacteria. It’s also too strong to say that the bacteria is “likely” to awaken and cause cholera outbreaks from a change in salinity. It might become more likely, but we don’t know that this rises to the level of likelihood (over 50%).
c
Although V. cholerae ███ ███████ ██ █████████ ██ █████ ████████ █████ █████ ██ █████ ██ ██████ █████ █ █████████
Anti-supported, because Colwell found V. cholerae in water from the Chesapeake, even though there were no recent cholera epidemics. The passage supports the idea that V. cholerae can survive in seawater even without infecting a human host.
d
Bacteria that are █████ ████ █ █████ ████ ███ ██████ ██ ██████ █████ ███████████ ███████ ███████ ████ ███ ████████ █████ ████ █████████
Not supported. Although Colwell’s antibody test was more likely to detect V. cholerae than traditional cultured methods, there’s no suggestion that those cultured methods involved bacteria taken from a human host. In fact, the tests were conducted on water samples.
e
Antibodies are less ██████ ██ ████ ██ ███ ████ ████████ ██ ██ ████████ ████ ███ █████████ ██ ██ █ ███████ ██████
Not supported, because the dormant state of V. cholerae isn’t connected to the likelihood of antibody bonding. In fact, the passage suggests that