PrepTest 123, Section 2, Question 14
A cup of raw milk, after being heated(61 more words not shown)
Which one of the following,(7 more words not shown)
- AHeating raw milk(22 more words not shown)
- BEnzymes in raw(20 more words not shown)
- CA liquid exposed(33 more words not shown)
- DMilk that has(25 more words not shown)
- EHeating any liquid(21 more words not shown)
Reading the argument
Has a microwave ever left one part of your food burning hot and another part barely warm? That's what I want to check here. Milk ending up at 50 degrees doesn't necessarily mean every part stayed at or below 50 degrees while it was heating.
The results are facts we should accept. Microwave the milk to 50 degrees and it loses half its initial concentration of lysozyme. Bring it to that temperature with a conventional 50-degree heat source and it keeps nearly all the enzyme. Something about the methods makes a difference.
But have we really ruled out heat? Maybe part of the microwaved milk briefly gets much hotter, and that heat destroys the enzyme in that part. Once the temperature evens out, the milk could be at 50 degrees even though some of it had been hotter. That would let heat explain the loss after all.
What we’re looking for
We're asked to weaken the claim that microwaves themselves, rather than heat, destroy the enzyme. I'd look for support for that uneven-heating possibility. The comparison only rules out a heat explanation if the relevant exposure to heat was comparable. The same final temperature doesn't establish that.
Working the answers
- A
At 100 degrees, nearly all the enzyme disappears—but this milk is still heated in a microwave. Is the extra loss caused by more heat or by the microwave exposure? A doesn't separate those possibilities. It gives us another result the proposed explanation could accommodate, rather than a reason to reject that explanation.
- B
Replacing destroyed enzymes doesn't tell us what destroyed them. We could add enzymes afterward whether the original loss came from heat or from microwaves directly. This doesn't address the cause we're trying to test.
- C
This compares a conventional heat source at 50 degrees with a hotter conventional heat source. Fine: one gets the liquid to the target temperature faster. But what happened inside the microwaved milk? C gives us no reason to think it reached a damaging temperature or that the different heating rates explain the loss. We'd have to add that missing connection ourselves.
- D
Taste isn't the result we're explaining. Two cups could taste the same while having different enzyme concentrations. Nothing here tells us whether heat or microwaves caused the enzyme to disappear.
- ECorrect
The microwaved liquid develops small regions that are hotter than its eventual overall temperature. That is exactly the problem with treating “50 degrees at the end” as “never exposed to more than 50 degrees.”
Imagine some of the milk gets hot enough to destroy the enzyme before the temperature evens out. The milk can end at 50 degrees and still have lost enzyme because of heat. The conventional 50-degree source doesn't supply that same higher-temperature explanation.
We don't have to prove that this is what happened. E gives a concrete reason heat could still account for the result, so the argument hasn't successfully ruled heat out.
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