PT103.S4.P3.Q17 > Analytics

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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)

17.

Which one of the following ████ ██████████ █████████ ███ ████████████ ██ ███ ████ ██████████

One explanation is ██████████ ███ █ █████████ ███████████ ██ █████████

This is an accurate low-res summary of P4. The author first criticizes the researchers’ explanation for why the dolphins died and then presents an alternative explanation.

71%

An argument is ████████ ███ ████ ███████ ██ █████ ██ ██ ████████ █████████

This describes the organization of the passage, not of P4. In P4, the only argument advanced is the author’s preferred hypothesis for why the dolphins died (the synthetic pollutant theory), and that hypothesis is never refuted. Meanwhile, the argument that does get refuted in P4 (the researchers’ brevetoxin theory) isn’t advanced in P4—it was advanced back in P3.

Objections against a ██████████ ███ █████████ ███ ██████████ ██ █████████ ████ ██████ ███ ████ ███ ██████████ ███ █████████

Only the first part is correct. Objections against the researchers’ hypothesis are advanced, but immediately after that, the author turns to presenting an alternative hypothesis. The researchers’ hypothesis is never explained more fully in P4, and the author’s objections to the researchers’ hypothesis are never rejected.

New evidence in █████ ██ █ ██████ ██ ██████████ ███ ████ ███ ██████ ██ ███████████

No theory is reaffirmed. The researchers’ theory (which the author never affirms) is critiqued, and then an alternative theory is presented for the first time.

Discrepancies between two ████████████ ███ ██████ ███ █ █████ ███████████ ██ █████████

There’s no third explanation. The only explanations discussed in P4 (or anywhere in the passage) are the researchers’ brevetoxin hypothesis and the author’s synthetic pollutant hypothesis.

11%

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PrepTest 103 - Section 4 - Passage 3 - Question 17

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