Reading comp PrepTest 103 · Section 4 · Question 18

Topic: Science

Paragraph 1

• Paragraph note
  • Victims of the massive bottlenose dolphin die-off between June 1987 and May 1988 showed evidence of opportunistic bacterial infection.
• Views, minor Meta-Structures, and the author's attitude
  • Phenomenon: between June 1987 and May 1988, up to 50% of the coastal population of Atlantic bottlenose dolphins died (first-second sentences)
    • This scale of die-off was unprecedented (third sentence)
    • Physical characteristics of victims: skin lesions, internal lesions in liver, lung, pancreas, heart; these signs indicated opportunistic bacterial infection (fourth sentence)
  • Author’s attitude: “overall disaster” (second sentence); “presumably worse” (second sentence); “never before been observed” (third sentence); “startling range” (third sentence); “massive opportunistic bacterial infection” (fourth sentence); “already weakened animals” (fourth sentence)

Paragraph 2

• Paragraph note
  • Toxicology revealed that brevetoxin was present in almost half the dolphins tested and polychlorinated biphenyls (PCBs) were present in almost all dolphins tested.
• Views, minor Meta-Structures, and the author's attitude
  • Brevetoxin is produced by an algae bloom of Ptychodiscus brevis ( brevis) (second sentence)
  • Author’s attitude: “stricken dolphins” (first sentence); “almost all animals” (second sentence)

Paragraph 3

• Paragraph note
  • Research team concluded that brevetoxin poisoning was probably the cause of the dolphins’ weakened state, which in turn led to opportunistic bacterial infection.
• Views, minor Meta-Structures, and the author's attitude
  • Explanation 1: research team thought that brevetoxin poisoning began the cascade of illness and stress that eventually killed the dolphins (first sentence)
  • A red tide, or bloom of the algae in question, occurred along the Atlantic coast in October 1987 (second sentence)
    • Researchers believe brevetoxin accumulated in the bodies of fish and was ingested by dolphins (third sentence)
  • Dolphins were metabolizing their blubber reserves, which means the synthetic pollutants like PCBs that were stored in those reserves were affecting them (fourth sentence)
    • buoyancy and insulation also affected (fourth sentence)
  • Combination of brevetoxin, metabolism of blubber reserves, and synthetic pollutants released from blubber made dolphins vulnerable to opportunistic bacterial infection (fifth sentence)
  • Author’s attitude: “ordinarily not found” (second sentence); “these researchers believe” (third sentence); “further exacerbated” (fourth sentence); “combined impact” (fifth sentence)

Paragraph 4

• Paragraph note
  • An increase in exposure to synthetic pollutants, not brevetoxin, was a more plausible cause of the dolphin die-off.
• Views, minor Meta-Structures, and the author's attitude
  • Brevetoxin poisoning not the likeliest cause of the cascade of illnesses (first sentence)
    • Bottlenose dolphins live in Gulf of Mexico and so does brevis, yet, no dolphin die-off of the same size has ever occurred there (second sentence)
    • Die-off began in June, but red tide didn’t begin until October, many miles south of where first dolphins died (third sentence)
    • Specific effects of brevetoxin poisoning on dolphins are unknown (fourth sentence)
  • Explanation 2: Sharp increase in exposure to synthetic pollutants like PCBs actually precipitated the die-off (fifth-sixth sentences)
    • PCB poisoning known to cause the symptoms observed in the dead dolphins: impair functioning of immune system, liver, and cause skin lesions (fourth sentence)
    • Perhaps this increase came from offshore dumping (fifth sentence)
    • Increase in synthetic pollutant exposure triggered a cascade of disorders because dolphins were already full of pollutants (fifth sentence)
  • Author’s attitude: “not entirely plausible” (first sentence); “hundreds of miles north of and some months earlier than” (third sentence); “PCB poisoning is known” (fourth sentence); “all of these problems were observed” (fourth sentence); “alternative hypothesis” (fifth sentence); “accounts for these facts” (fifth sentence); “sudden influx of pollutants” (fifth sentence); “triggered a cascade” (fifth sentence); “heavily laden with pollutants” (fifth sentence); “actually precipitated the die-off” (sixth sentence)

Main Point: While a team of researchers concluded that exposure to brevetoxin caused a massive Atlantic bottlenose dolphin die-off between June 1987 and May 1988, the evidence suggests that it was more likely to have been a dramatic increase in the dolphins’ exposure to synthetic pollutants that caused the die-off.

Paragraph 1, Sentence 1 (P1 S1) - Phenomenon

P3 S1 - Explanation 1 (mistaken explanation)

P4 S5-6 - Explanation 2 (author’s explanation)

Phenomenon/Explanation: This passage uses a Phenomenon/Explanation Meta-Structure. The author first introduces the phenomenon to be explained: a massive and unprecedented dolphin die-off in the late 1980s, then introduces the evidence from which a research team concluded that brevetoxin had been the precipitating factor in the die-off. This is Explanation 1. Then, the author casts doubt on this explanation by pointing out that it is inconsistent with certain other evidence. The author then asserts that it was a dramatic increase in exposure to synthetic pollutants that caused the die-off rather than brevetoxin. This is Explanation 2, and the one the author favors.

The author does not merely criticize the views of others, but introduces their own hypothesis, so it is not a Criticizing a Viewpoint passage. It doesn’t answer an explicit question, so it is not a Question/Answer passage, and it doesn’t counter a misunderstanding, so it is not a Correcting the Record passage. The cause of the die-off is not presented as an ongoing debate, either, so it is not a Resolving a Debate passage. And it is not a Proposing a Hypothesis passage because there is already an explanation that has been proposed.

The author’s perspective on the phenomenon to be explained is not made clear until the fourth paragraph, when they cast doubt on the explanation put forward by the team of researchers and introduce some additional evidence that supports an alternative hypothesis. Thus, the author’s thesis statement is actually found in the last two sentences of the passage, but it is important to take note of how those sentences affect your understanding of the rest of the information presented.

This passage takes a definite stand on the cause of an ecological disaster, making its point at the very end. This is different from most passages, which let you know in the first paragraph where the author’s argument is heading. In this case, it is important to keep track of where the author’s evidence for their thesis is located in the passage, because it is somewhat scattered, and some of the information that is presented as supporting Explanation 1 is also used to support Explanation 2. For example, the team of researchers uses the fact that almost all dolphins tested had PCBs in their tissues to argue that PCBs were a contributing but not decisive factor in the die-off and the author uses this fact to argue that PCBs were the precipitating factor in the die-off (P1 S3, P2 S4, P4 S4-6).