AS Biology Paper 2

[lonelyboy]

Umm, i think in the question they had already stated that the reaction was taking place at temperature around 30 degrees Celsius. That temperature alone would be sufficient to carry out the reaction between the enzyme and the substrate. And anyway the temperature is meant to be kept constant until the point of increase at 85 degrees Celsius. this suggests that they want to find out the rate of reaction using the concentration of the substrate as the variable, which they did. The temperature must be kept constant to obtain a fair result for each of the concentrations of substrate they used. Therefore the only reason in which why they had increased the temperature was to stop the activity of the enzyme in order to have a definite end point to the reaction as it stated in the passage that the end point in which they were observing was the expected green colour, which is fairly early on and would be obtained with the presence of the smallest amount of reducing sugars.
I agree that you had to heat the Benedict at school but most of the time we were just testing the solution itself for the presence of Reducing sugars. In this circumstance there is an enzyme within the solution as well, which is catalysing the breakdown of the sucrose. therefore if you heat the solution too early then the enzyme would be denatured before the reaction has proceeded and no results would be obtained as there would be no reducing sugars present.

This is just my opinion, don't know if its right or wrong....

Hi, well we won't know the final answer till the MS comes out but a clearer idea can be given only if the chemistry of glucose is understood.

The Benedict's tests positive with glucose only by the reaction of Copper 2+ ions to Copper 1+ ions. What heat does is it isomerizes glucose into an aldehyde, which otherwise is in a ketone form. Ketone is not a good reducing agent, unlike aldehyde which has that C-H bond, if you have done chemistry you would understand that is why aldehyde tests positive with Fehling's, Tollen's as well. Obviously, this chemistry of glucose is really not required at AS-level but the basic idea that a high temperature of 85 degrees would faciliate the precipitation of Copper (II) oxide (responsible for colour change) would be the key to the answer. However as I said, we will not know the final till MS comes out.


Cheers 

[lonelyboy]

Also, if you do want to read up on this,

http://en.wikipedia.org/wiki/Benedict's_solution

 

[kratos009]

Ok, i think we both seem to have different interpretation of the question. I understand what your saying, i do AS Chemistry, but i thought that it would be irrelevant in this particular Biology question because the whole question is about enzymes and concentration of  the substrates. That is why i put an answer concerning enzymes and relating it to the enzymes topic. Well no one knows what the correct answer is going to be....(other than the Cambridge markers ).


All we can do is hope for the best  . No use thinking about it now. I got to concentrate on my Chemistry multi-choice  .

And to all those who are doing the Chemistry multi-choice tomorrow GOOD LUCK.
Ace it and then you can enjoy your holidays after .

[lonelyboy]

Ok, i think we both seem to have different interpretation of the question. I understand what your saying, i do AS Chemistry, but i thought that it would be irrelevant in this particular Biology question because the whole question is about enzymes and concentration of  the substrates. That is why i put an answer concerning enzymes and relating it to the enzymes topic. Well no one knows what the correct answer is going to be....(other than the Cambridge markers ).


All we can do is hope for the best  . No use thinking about it now. I got to concentrate on my Chemistry multi-choice  .

And to all those who are doing the Chemistry multi-choice tomorrow GOOD LUCK.
Ace it and then you can enjoy your holidays after .

Haha you're right mate.
For all we know either of us are out of line on this one OR the MS is flexible enough to accomodate both the answers

Take care, cheers mate.