PrepTest 103 - Section 4 - Passage 3 - Question 18

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Between June 1987 and May 1988, the bodies of at least 740 bottlenose dolphins out of a total coastal population of 3,000 to 5,000 washed ashore on the Atlantic coast of the United States. █████ ████ ██ ███ ████ ███████ █████ ██████ ███████ ███ ███████ ████████ ███ ██████████ ██████ ███████ ██ ███████ ██ ███ ██████████ █████ ███

Phenomenon · Almost a thousand dolphins washed ashore dead

Presumably many more died and didn't wash ashore. What caused this?

Phenomenon Details · Skin lesions; internal lesions in the liver, lung, pancreas, and heart

Evidence of massive opportunistic bacterial infection of already weakened animals.

Phenomenon Details · Autopsy found presence of brevetoxin and PCBs (synthetic pollutants)

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Hypothesis · Brevetoxin poisoning

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Causal Mechanism · Alga bloom, toxin, stress, release of synthetic pollutants, bacterial infection

Unusual bloom of P. brevis resulted in toxin accumulation in fish which was then eaten by dolphin. Dolphins then metabolized blubber which reduced their buoyancy and insulation and released synthetic pollutants (PCBs). This provided opportunity for bacterial infection which ultimately caused death.

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Critique · No die-off in Gulf of Mexico; timing and location mismatch; brevetoxin effects unknown

Red tides are common in Gulf of Mexico but no dolphin die-off there; dolphins began dying in the north in June yet red tide bloomed in the south in October; effects of brevetoxin on dolphins are unknown.

Alternative Hypothesis · Exposure to synthetic pollutants

Sudden influx of pollutants triggered a cascade of problems in dolphins already heavily laden with PCB poisoning which is known to include symptoms like impaired immune system, impaired liver function, and skin lesions, all of which were observed.

Passage Style

Critique or debate

Phenomenon-hypothesis (RC)

18.

It can be inferred from ███ ███████ ████ ███ ██████ █████ ████ ████████ █████ ████ █████ ███ ██ ███ █████████ ██████████ █████ ███████████

Question Type

Author’s perspective

Implied

We’re looking for what’s implied about the author’s perspective on brevetoxin. Note that although the researchers think brevetoxin was the cause of the die-off, the author disagrees. She acknowledges that brevetoxin was present in some of the dolphins, but she notes that its effects on dolphins are unknown and argues that it doesn’t explain the die-off.

It may have ████ ███████████ ███ ███ █████████ ████ ███████ ███ █████ ███ ████ ███████████ ██ ███ █████████ ██████████

Unsupported. The author states that the effects of brevetoxin on dolphins are unknown. She doesn’t take any position on what those effects are. She even concedes that brevetoxin may have been a contributing factor, so she doesn’t rule out the possibility that it contributed to a bacterial infection. She just thinks it’s not the root cause of the die-off.

It forms more ██████ ████ ████ ██ ██████ ███ █████████ ██████████ ███ ███████ ██ ███ ███████████ ███████████████

Unsupported. There’s only one brief reference to how brevetoxin is formed: it’s produced by P. brevis. The author notes that synthetic pollutants were also present in the dolphins, but she never suggests that those pollutants ever play a part in forming brevetoxin.

It damages liver ████████ ███ ██████ ██████ █████████ ██ ██████████ ████████ ███ ███ ███ ████ █████████ ████ ██████████ ███████ ████████

Misdirection. According to the author, PCBs are what have this effect. The never takes a position on what effects brevetoxin has. In fact, she states that the effects of brevetoxin on dolphins are unknown.

19%

It is unlikely ██ ██ █████ ███ ███████ ████ ███████████ ██ ███ ███████ ████████

Anti-supported. The author concedes that brevetoxin may have been a contributing factor. She just argues that it wasn’t the root cause.

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Strongly supported from the author’s perspective. She argues against the theory that brevetoxin caused the die-off, and one of the reasons she gives is that the presumed source of brevetoxin, the “red tide,” wasn’t present when the die-off began.

64%

PrepTest 103 - Section 4 - Passage 3 - Question 18

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