June 2007 PrepTest, Section 2, Question 14
A cup of raw milk, after being heated in a microwave oven to 50 degrees Celsius, contains half its initial concentration of a particular enzyme, lysozyme. If, however, the milk reaches that temperature through exposure to a conventional heat source of 50 degrees Celsius, it will contain nearly all of its initial concentration of the enzyme. Therefore, what destroys the enzyme is not heat but microwaves, which generate heat.
A cup of raw milk, after being heated in a microwave oven to 50 degrees Celsius, contains half its initial concentration of a particular enzyme, lysozyme. If, however, the milk reaches that temperature through exposure to a conventional heat source of 50 degrees Celsius, it will contain nearly all of its initial concentration of the enzyme. Therefore, what destroys the enzyme is not heat but microwaves, which generate heat.
A cup of raw milk, after being heated in a microwave oven to 50 degrees Celsius, contains half its initial concentration of a particular enzyme, lysozyme. If, however, the milk reaches that temperature through exposure to a conventional heat source of 50 degrees Celsius, it will contain nearly all of its initial concentration of the enzyme. Therefore, what destroys the enzyme is not heat but microwaves, which generate heat.
A cup of raw milk, after being heated in a microwave oven to 50 degrees Celsius, contains half its initial concentration of a particular enzyme, lysozyme. If, however, the milk reaches that temperature through exposure to a conventional heat source of 50 degrees Celsius, it will contain nearly all of its initial concentration of the enzyme. Therefore, what destroys the enzyme is not heat but microwaves, which generate heat.
Which one of the following, if true, most seriously weakens the argument?
Heating raw milk in a microwave oven to a temperature of 100 degrees Celsius destroys nearly all of the lysozyme initially present in that milk.
Enzymes in raw milk that are destroyed through excessive heating can be replaced by adding enzymes that have been extracted from other sources.
A liquid exposed to a conventional heat source of exactly 50 degrees Celsius will reach that temperature more slowly than it would if it were exposed to a conventional heat source hotter than 50 degrees Celsius.
Milk that has been heated in a microwave oven does not taste noticeably different from milk that has been briefly heated by exposure to a conventional heat source.
Heating any liquid by microwave creates small zones within it that are much hotter than the overall temperature that the liquid will ultimately reach.
Explanations
That conclusion sounds really dumb (“it isn’t heat, but something that generates heat”), but I think what it’s saying is that microwaves (not the product—the sciency thing) cause it, not heat.
The reason? Because conventional heat sources don’t cause it when heated to the same temperature. But what if it isn’t being heated to 50º, but the speed at which it is heated to 50º?
This doesn’t help at all. I’m still left wondering if it’s the heat or the microwaves doing it.
But is it heat or microwaves that destroyed the enzyme originally?
This is sort of like my prediction, but not quite. (It’s wrong.) This doesn’t explain the ramifications of being heated slower/faster, so it doesn’t help.
Taste is completely off-topic.
Ah, here it is. This indicates that heat is the cause—microwaves make it super hot, and that heat is probably what causes the enzymes to break down. Remember: Even just 50º in a conventional heat source breaks down some of the enzyme, so you would expect even hotter to break down more enzymes.
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