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    I need help on this question please.

    For the evaluation, I don't understand why the mark scheme said the optimum could be between pH6 and pH8. Only one value between pH6 and pH 8 is tested. The shape of data implies optimum pH less than 7.
    Improvement: I also don't understand why the mark scheme says more pH values between 6 and 8 should be tested.

    For the evaluation I thought that as the difference between ph6 and pH7 is 4%, more tests should be carried out to see which one is optimum. I wrote for the improvement that the procedure should be repeated more times and wider range of pHs should be used.
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    Hey nice question!

    Ok to answer the first one: Why is the optimum pH between 6 and 8?
    Plotting a graph of activity against pH, you'll find that its a 'bell-shaped' curve, i.e. as pH increases activity will increase, peak and decrease. The peak is the optimum pH. Looking at their results, activity is increasing through from pH 4, 5, 6 and 7, then starts decreasing at 8 and 9. Obviously the optimum cannot be between 4-5 or 5-6 because after the peak the activity can only decrease with further deviation. It is between 6-8 because from 6-7 it could peak at e.g. 6.5 (with an activity of say 105) then decrease to 100 at pH 7, 50 and pH 8 etc. However, it could have peaked at pH between 7-8 e.g. 7.5 as it would also have the same trend of increasing then decreasing afterwards.

    For the second one:
    I've done a billion of questions before and the typical answer is that for the evaluation you would say:
    'insufficient evidence to conclude the optimal pH is 7.0 because it is anywhere with the range of pH 6-8'
    and for the improvement:
    'Take more readings within range of pH 6-8 in order to determine accurate optimal pH. In order to determine optimal pH was indeed 7.0 would be to take readings of pH 6.9 and 7.1 and have an increasing then decreasing trend to provide sufficient evidence to conclude optimal pH is 7.0 to 1.d.p.

    The 4% thing you said is quite interesting (no idea about the new spec) but percentage errors/differences I really have never used in biology (although I have in physics!) so I'm not sure if you'd get credit for that. Also, perhaps saying wider range of pH's is a bit ambiguous because there's really no need to test any other pH besides those within the range of 6-8.

    Anyway, sorry for this 'book'-like response! I'm also doing my A levels so please take what I write with a pinch of salt
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    Sorry I didn't get a notification about your reply. Thank you so much for the help
 
 
 
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