Help with bio coursework results that basically screwed over my hypothesis :P

Hi! I'm an edexcel A level bio student doing my T1 coursework - the effect of different sugars on the rate of respiration of yeast (Saccharomyces cerevisiae) . The sugars that I am working with are glucose, galactose, fructose, maltose, lactose and sucrose.

My hypothesis was that as the disaccharides need to be broken down into monosaccharides before being used for respiration, the rate of respiration for disac. would be lower than for monos. Unfortunately I got some pretty weird results and I'm having some (huge understatement) difficulty in explaining them. I have gone through some other threads on this site regarding yeast but I think I have a pretty unique problem here because I used a very high concentration for the sugar solutions - 1 molar - whereas most of the people here have used 0.4 mol or less. My experimental procedure involved using 100 ml of a 5% yeast solution, 2 gms of activating sugar and 10 ml of a 1 molar sugar solution.

My maltose, glucose and sucrose gave me almost the same rates of respiration (!!!), my fructose was much faster than all the sugars, my lactose was the slowest (which was expected) and my galactose was somewhere in between.

Anyway I did a lot of research on the net to try and explain my results (I ended up having to go through some uni experiments!) and this is what I came up with. I found that if yeast were placed in a solution of glucose, fructose and galactose, it would prefer to take up glucose over the other sugars. I used this to explain why the rate of respiration for sucrose was about the same as that for maltose and glucose. First I said that since the concentration of the sugar solution was so high, when I added the glucose solution, the yeast enzymes would get saturated and thus the yeast would have the highest possible rate of respiration. Then when I used maltose the rate of respiration was about the same as glucose because the high concentration meant that the number of disac. converted to monos. per second would lead to the yeast enzymes being once again saturated and would give the highest rate of respiration possible. This rate would be the same as the rate for glucose because the highest rate of respiration for the yeast would be the same.

Then for sucrose I said that once again the rate of disac. conversion to monos. would lead to a high concentration of glucose and fructose monos. but the yeast would prefer to take up the glucose only and once again the rate of respiration would be the highest possible and thus the same. The problem here is how are the disac. being broken down to monos. so fast (i.e. how is the maltose and sucrose being broken down to glucose and fructose so fast) that the yeast enzymes get saturated. After all they should take at least slightly longer than the glucose to cause the enxymes to get saturated as they are disaccharides and thus need to be broken down before any respiring takes place.

Also I read somewhere that the fructose is actually supposed to give a lower rate of respiration than the glucose and I am really not sure how to explain why my fructose results show that it gives the fastest rate of respiration.

I just want to know if my explanation makes any sense; please tell me if you think it doesn't and if you have an alternate explanation, go ahead. Also I would really appreciate any suggestions as to how I could explain the rest of my readings (fructose).

Also, I want to know if its okay to use information from outside the syllabus because my coursework basically goes 'I used a few basic concepts to form my hypothesis, got weird results, then did a lot more research to try and explain my results'.

Any help at all would be appreciated.

Reply 1

mal3889

I started this thread a long time ago but when the coursework guy posted I kinda lost hope. Anyway I decided to try again. So is there anyone out there who can help me? Pretty please?

Reply 2

martin101

Hmm this has got me interested. I would certainly be suspicious of your experimental design... 1M is a massive concentration. Biologically speaking the glucose should be metabolised faster as it doesnt need to be converted first. but because you have all the pathways totally saturated they are going flat out so you wont really see the differences very well. I suggest you wind back your concentrations to something like 0.1M (even physiologically 0.1M is ultra high - if your blood glucose came out at .1M you would more than likely be dead (its normally around 5mM) I know youre not dealing with humans but you get the idea). Play around with your concentrations- youl find something that works for you!

Reply 3

me_me_mee

CHANGE YOUR RESULTS (Y)

loads of ppl do it dw :wink:

Reply 4

mal3889

Thanks a lot guys. Unfortunately I had already finished carrying out the experiments when I started this thread in February so I can't check what I would get with lower concentrations. Anyway I submitted my coursework yesterday and tried to explain my results as best I could. I spent a lot of time on it - hopefully it'll turn out well.