PrepTest 141, Section 4, Question 20
In a recent study of stroke patients, those(68 more words not shown)
Which one of the following,(6 more words not shown)
- AAny neurotransmitter that(13 more words not shown)
- BStroke patients exhibit(10 more words not shown)
- CGlutamate is the(11 more words not shown)
- DLeakage from damaged(14 more words not shown)
- ENerve cells can(10 more words not shown)
Reading the argument
The patients with continuing brain deterioration also have the most glutamate in their blood. Is the glutamate causing damage, or is the damage producing the glutamate?
That is my first concern about the association. Then the passage supplies something more useful: glutamate leaking from damaged or oxygen-starved nerve cells can kill surrounding nerve cells. Now we have a way the proposed cause could do harm. That makes the causal account more plausible than the correlation alone would.
But where did the glutamate measured in the blood come from? Could there be some other source in the body? The conclusion specifically identifies leakage from those damaged or oxygen-starved nerve cells as a cause of long-term damage. Finding glutamate in the blood doesn't automatically tell us that this particular leakage occurred.
What we’re looking for
For a strengthener, I'd like to close that source gap. If the blood's glutamate could only have come from leaking nerve cells, the study's measurement would more directly connect with the harmful process described. That would improve the argument without requiring us to treat the entire causal story as conclusively proved.
Working the answers
- A
We already know that glutamate can harm surrounding nerve cells if it leaks. Extending that claim to every neurotransmitter doesn't tell us whether the glutamate measured in these patients actually came from the relevant leakage. The additional general rule leaves the source gap in place.
- B
Many abnormal chemical levels would give us more things to investigate, not a specific reason to blame glutamate from damaged nerve cells. The answer doesn't identify which abnormality causes the deterioration or connect the measured glutamate to the proposed source.
- C
This says no other neurotransmitter leaks from these cells. But our question is whether the glutamate in the blood came from these cells at all. Glutamate could be the only substance of that kind leaking from them and still also enter the blood from somewhere else. C doesn't close that gap.
- DCorrect
Now the glutamate in the blood points to the exact process the argument identifies: leakage from damaged or oxygen-starved nerve cells. Coupled with the stated ability of leaked glutamate to kill surrounding cells, that gives the association a stronger connection to the proposed cause of continuing damage. It rules out another source of the measured glutamate.
- E
The leaking cells don't have to survive for their glutamate to damage other cells. Whether the original cells are destroyed or merely damaged doesn't establish where the blood's glutamate came from or strengthen the claimed effect on surrounding cells.
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