PrepTest 109, Section 3, Question 20
Galanin is a protein found in the brain.(56 more words not shown)
Which one of the following,(6 more words not shown)
- AThe craving for(15 more words not shown)
- BThe brains of(26 more words not shown)
- CThe chemical components(11 more words not shown)
- DThe rats that(18 more words not shown)
- ERats that metabolize(15 more words not shown)
Reading the argument
Which came first: the galanin or the fatty diet?
The rats that choose fatty foods have more galanin in their brains. That association fits the author's explanation: perhaps the protein causes the craving. But it also fits another possibility. Eating the fatty foods might cause the rats to produce or accumulate more galanin. We would then be looking at a result of their eating habits rather than the cause of those habits.
What we’re looking for
For a strengthener, I'd want evidence favoring the author's direction. A fact showing that the fatty diet didn't create the higher galanin concentration would help answer our objection. So could an explanation of how galanin produces the craving. We need more than the association we already have.
Working the answers
- A
This separates craving from choosing: a rat can crave fatty food and still select lean food. That doesn't show that galanin creates the craving. If anything, it gives us a reason to be careful about using the rats' food choices as a direct measure of what they crave. It doesn't establish that any craving is weak, just that craving doesn't invariably determine the choice.
- B
The comparison is about fat in the brain, not galanin in the brain. Equal amounts of brain fat wouldn't tell us why the galanin concentrations differ or whether galanin causes the preference. We would need an additional connection between brain fat and the protein for B to resolve our concern.
- C
Finding the components in both food types doesn't establish that the rats produce equal amounts of galanin from them. Nor does it show that eating fatty food couldn't lead to a higher concentration. The amounts, processing and accumulation could differ. C leaves the causal direction unresolved.
- DCorrect
The higher galanin concentration was already present before the fatty foods were offered. Choosing and eating those foods in the experiment cannot explain a difference that was present beforehand.
That addresses our concern about the order: perhaps the diet produced the galanin rather than galanin producing the preference. D places the measured difference before the food choice, making the author's explanation more convincing.
It doesn't prove galanin caused the craving or eliminate every possible earlier dietary difference or third cause. This is a strengthening question. Undercutting the immediate reverse explanation is enough to add support.
- E
This links high galanin concentrations with inefficient fat metabolism. We aren't told whether those rats prefer fatty food or whether their galanin causes a craving. A fact about processing fat doesn't by itself establish the proposed cause of wanting to eat it.
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