PrepTest 114, Section 4, Question 22
In humans, ingested protein is broken down into(76 more words not shown)
Which one of the following(8 more words not shown)
- AElevation of mood(13 more words not shown)
- BFailure to consume(12 more words not shown)
- CSerotonin can be(10 more words not shown)
- DIncreasing the level(11 more words not shown)
- EThe consumption of(10 more words not shown)
Reading the argument
What does more serotonin have to do with feeling better? We've followed a story about chemicals entering the brain, but the conclusion is about a person's mood. That connection hasn't been made. We shouldn't supply it just because serotonin sounds familiar.
According to the passage, eating protein supplies amino acids that compete to enter the brain. Eating sugar afterward leads to insulin clearing out the other amino acids, leaving tryptophan able to enter without that competition. The tryptophan then becomes serotonin. We can follow that chain without knowing any biology beyond what we're told. But even if every step happens, why would the resulting increase in serotonin help someone feel relaxed and free of anxiety?
What we’re looking for
The necessary assumption should fill that final gap. My prediction is that increasing serotonin promotes the mood improvement the author is claiming.
Working the answers
- A
This makes increased serotonin required for mood improvement. The argument only needs it to help produce that improvement through the route described. Someone might also relax through another route. A rule saying no one can experience the benefit without an increase in serotonin is stronger than the argument needs.
- B
Failing to get a possible benefit isn't the same as suffering harm. Even if sugar can help someone feel better, not eating sugar-rich foods needn't cause anxiety or lower that person's mood. B describes a negative consequence the author doesn't need to assume.
- C
The passage gives a route from tryptophan to serotonin. The argument doesn't need that route to be the only natural way serotonin can be produced. Other ways of producing it could exist while the described route still works. C also leaves our central question unanswered: how does the increase affect mood?
- DCorrect
This connects the chemical change to the benefit. The evidence ends with increased serotonin; the conclusion credits sugar with helping people feel relaxed and free of anxiety. D says the increase promotes those effects.
Without that connection, all the details about competition, insulin, and tryptophan would tell us about a change in the brain without giving us a reason to expect the mood improvement. D supplies the link this explanation relies on.
- E
We aren't told that eating protein causes anxiety or lowers mood. Competition among amino acids doesn't establish that negative result. The argument is trying to explain a possible benefit from sugar through increased serotonin, not establish that protein-rich foods harm a person's mood.
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