To determine at what pH all the amylase becomes denatured, we need to consider the typical working pH range for amylase. Amylase, an enzyme that breaks down starch into sugars, generally has an optimal working pH around 6.7 to 7.0 and can become denatured in more acidic (below pH 5.0) or more basic (above pH 8.0) conditions.
From your options, we want to find values that might cause denaturation. Here’s the analysis:
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Option A: 6.0 and 7.5 - 6.0 is on the lower end of the optimal pH for amylase, so it might still function but could begin to become inactive in a less effective manner. At 7.5, it's getting towards a pH that might begin to denature it, but it wouldn't be complete denaturation for amylase.
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Option B: 5.5 and 7.5 - At 5.5, amylase would be more likely to start denaturing, and at 7.5, it may not be completely denatured but could start showing some effects.
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Option C: 5.5 and 8.5 - 5.5 is definitely acidic and could denature the enzyme. 8.5 is quite basic and would certainly denature all of the amylase.
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Option D: 6.5 and 7.5 - 6.5 is within the functional range, and 7.5 might start to show effects but not be complete denaturation.
Given this consideration, the most appropriate choice indicating that amylase would become denatured at both pH levels would be C) 5.5 and 8.5. At these pH levels, we are confident that all of the amylase would be denatured.