Support 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. Support 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, Conclusion what destroys the enzyme is not heat but microwaves, which generate heat.
The author hypothesizes that microwaves destroy an enzyme in milk. This is based on an observed difference in enzyme concentration between milk heated in a microwave and milk heated through a conventional source: much more of the enzyme is destroyed in the former case.
The author assumes that the two methods of heating—microwaves and conventional heat sources—are comparable in all ways other than their source. This means that the author doesn’t believe that some other difference in the heating methods accounts for the difference in enzyme concentration.
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.
The author's hypothesis only concerns milk heated to 50 degrees Celsius. Whether heat can destroy this enzyme at higher temperatures isn't relevant to the effect of microwaves.
Answer is attractive because it seems to (but doesn't actually) contradict the premises or conclusion.
Enzymes in raw milk that are destroyed through excessive heating can be replaced by adding enzymes that have been extracted from other sources.
This is irrelevant. We’re not interested in how the enzymes in milk can be replenished, only how they're destroyed in the first place.
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.
The stimulus talks about a heat source of 50 degrees Celsius. The effects of conventional heat sources at higher temperatures are irrelevant, especially when there's no connection to enzyme concentration.
Weaken Qs: Answers that try to introduce an alternate explanation, but fall short, or try to explain a different phenomenon.
Strengthen Qs: Answers that try to eliminate an alternate explanation, but fall short, or try to eliminate an explanation for a different phenomenon.
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.
Taste is irrelevant. We’re talking about enzymes, and we have no reason to believe that enzyme concentration has any relationship to taste.
Heating any liquid by microwave creates small zones within it that are much hotter than the overall temperature that the liquid will ultimately reach.
This means that when heating milk in the microwave, some zones reach very high temperatures—perhaps hot enough to destroy enzymes. This provides another possible explanation for the observed difference, thus weakening.
Weaken: Introduce or suggest an alternate explanation for the target phenomenon.
Strengthen: Helps to eliminate an alternate explanation for the target phenomenon.
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