Logical reasoning PrepTest 131 · Section 1 · Question 22

Incorrect. While this answer connects plankton and domoic acid, it doesn't explain why a drop in plankton would lead to a drop in toxic levels of domoic acid in anchovies. The stimulus notes that this is just one of many common types of plankton in the region, and so there's no reason to believe that a drop in this plankton would cause a drop in domoic acid levels in anchovies.

Correct. Argument or Facts:
Facts

Question Type:
Paradox

Stimulus Summary:
A city recommended against eating anchovies because they had a neurotoxin (we can think of another reason to avoid anchovies . . . ). But plankton levels are back to normal, so the city says it's safe to eat anchovies again.

Answer Anticipation:
The reason that the anchovies faced a warning was that they were tainted with a certain neurotoxin. The city gave the all-clear not when they tested the anchovies and saw the neurotoxin wasn't present, but rather when they saw the level of some plankton go back to normal levels. Therefore, that plankton must have something to do with neurotoxin levels in anchovies.

Either the plankton itself is responsible for the presence of neurotoxin in the anchovies, or the plankton is a good measurement for the presence of that neurotoxin (e.g., the neurotoxin promotes fertility in this plankton, so when population goes down, that suggests a drop in neurotoxin, as well).

In short, any answer that connects plankton to the neurotoxin should be considered. And the answer should also connect the plankton to the anchovies—the stimulus never does (e.g., it doesn't state they eat the plankton).

Answer Explanation:
This answer connects the P. australis plankton to domoic acid and establishes that anchovies become toxic when and only when the population level of them is extraordinarily high. That "extraordinarily high" matches with the stimulus—if a "dramatic drop" led to levels getting back to "normal," then the levels at the time of the toxic anchovy period must have been extraordinarily high.

Key Takeaway:
Be very careful with the connections drawn in a Paradox question. Here, it'd be easy to believe that the anchovies and plankton were already connected, but the stimulus never actually established that the anchovies at the plankton or were exposed to substances from the plankton in any way.

Incorrect. This answer establishes that the plankton have domoic acid, but it doesn't connect the abnormally high population levels to the warning, and a drop to "normal" with things being in the clear. In fact, this answer doesn't even establish that the anchovies eat the plankton, and neither does the stimulus.

Incorrect. This answer connects the populations of the two organisms in question, but it doesn't tie that into domoic acid levels.

Incorrect. This answer connects the plankton to domoic acid levels, but the stimulus discusses the plankton population levels as being abnormally high before going back to normal—both of those population levels could be "large" (e.g., it could have gone from "unbelievably and abnormally large" to "large"). So this answer doesn't establish any certain change in the domoic acid levels in the water.