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June 2007 - Sec 2 - LR - Q14

Video Transcript:

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question fourteen: A cup of raw milk, after being heated in the microwave oven to
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50 degrees Celsius, contains half its initial concentration of a particular enzyme,
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lysozyme. If, however the milk reaches that temperature through exposure to a
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conventional heat source of 50 degrees Celsius, it will contain nearly all of
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its initial concentration of the enzyme. Therefore, what destroys the enzyme
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is not heat but
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microwaves, which generate heat. So, first step argument or facts? Clearly an argument structural
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indicator of 'therefore'. The conclusion being that what destroys the enzyme is not heat
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but microwaves which generate heat. And how do we know that? Well, we have a cup of
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raw milk that was heated in a microwave oven to 50 degrees Celsius, contain half
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of its initial concentration of a particular enzyme Lysozyme. However, when I used
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a conventional heat source of 50 degrees we had nearly all the lysozyme present. So, based on
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that and then those are our premises the author concludes that it's not heat but
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microwaves that are destroying this enzyme lysozyme. So if you notice this is a
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cause and effect argument. And if you notice, what is the observed effect that we are trying to
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explain here? It is the missing enzyme lysozyme. And what is this author's proposed cause for this
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observed effect. Well it's not heat but
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microwaves which generate heat. So now that we have a clear understanding of this
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argument it is a cause and effect argument let's procedure the questions stem which says:
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Which of the following, if true, most seriously weekens the argument? So this is clearly a
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weaken question. So, we were trying to weaken this argument that what is
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destroying this enzyme lysozyme is not heat but microwaves. So let's take a
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look here at (A). Heating raw milk in a microwave oven to temperature of 100
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degrees Celsius destroyes nearly all of the lysozyme initially present in that milk.
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And you notice if anything
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(A) seems to strengthen this argument by showing where we get even hotter in a
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microwave even more lysozyme disappears. It definitely does not weaken so (A) is out. (B)
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Enzymes in raw milk that are destroyed through excessive heating can be replaced by
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adding enzymes that have been extracted from other sources. And (B) is
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completely irrelevant. Ahat difference does it make me to our argument if these
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enzymes that are being destroyed can later be replaced. Its not what this argument
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is about so (B) does not follow. Moving to (C): A liquid exposed to a conventional heat
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source of exactly 50 degrees Celsius will reach that temperature more slowly
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than it would if it were exposed to a conventional heat source hotter than 50 degrees Celsius.
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And obviously thats groundbreaking. If you're exposed to a lower temperature you will reach that temperature
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more slowly than if you were exposed to a higher temperature. I mean great, but again
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this is not about being hotter than 50 degrees its about 50 degrees. (C) is completely irrelevant so
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(C) is out. Moving to (D): Milk that has been heated in a microwave oven does not taste
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noticeably different from milk that has been briefly heated by exposure to a
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conventional heat source. Again completely irrelevant this is not about
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how the milk tastes. So (D) is out, which brings as process of elimination to (E): Heating
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any liquid by microwave creates small zones within it that are much hotter
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than the overall temperature in the liquid will ultimately reach. And you
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notice that (E)
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does weaken this argument that it's not the heat but rather the microwaves by
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showing that when you use a microwave even though it's only 50 degrees
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Celsius small zones are created that are much hotter than the overall temperature
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that the liquid will reach. So, while this milk ultimately reached 50 degrees Celsius
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these small zones that were created within it due to the microwave are much hotter.
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So it proposes as an alternate cause to our observed effect that it's not actually the
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microwaves but it is the heat. Particularly the heat from these small zones. So, (E) again weakens the
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argument by pointing out a possible alternate cause to the observed effect of the
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missing enzyme lysozyme.