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    OK, I need some help.

    Could someone please tell me why the rate of fermentation of yeast varies with the sugar used.

    By this I mean why does yeast ferment faster with glucose than it does with - for example - sucrose.

    Any help would be appreciated and I'll rep anyone who helps (even though my rep is worth almost nothing).




    Please . . .
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    OMG dude. The title of your thread led me to believe this thread was about something totally different.
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    I remember doing this coursework, and I remember my teacher saying how there's no set answer to this, and how you have to work out why this happens.

    However, are you comparing monosaccharides and disaccharides (e.g. glucose and sucrose), or are you comparing different monosaccharides (e.g. glucose and fructose), because these 2 have different reasons.

    If you're talking about comparing a monosaccharide (glucose) and a disaccharide (sucrose), then I simple said:

    Monosaccharides, such as glucose or fructose, can be transported into the yeast cell straight away, whereas disaccharides have to be broken down first. Therefore this means that it takes less time for the monosaccharide molecules to be transported into the yeast cell. Therefore more respiration can occur in the yeast cell in a given time.
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    (Original post by junners)
    I remember doing this coursework, and I remember my teacher saying how there's no set answer to this, and how you have to work out why this happens.

    However, are you comparing monosaccharides and disaccharides (e.g. glucose and sucrose), or are you comparing different monosaccharides (e.g. glucose and fructose), because these 2 have different reasons.

    If you're talking about comparing a monosaccharide (glucose) and a disaccharide (sucrose), then I simple said:

    Monosaccharides, such as glucose or fructose, can be transported into the yeast cell straight away, whereas disaccharides have to be broken down first. Therefore this means that it takes less time for the monosaccharide molecules to be transported into the yeast cell. Therefore more respiration can occur in the yeast cell in a given time.


    Thanks. I think I sort of remember doing this, but I can't find any of my notes, and I've only been given a few hours to do this in.

    I'm actually comparing a range of sugars: Maltose, sucrose, glucose, lactose and fructose.
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    If you're comparing 2 monosaccharides, then I had 3 possible reasons as to why the rate of respiration was different:


    • There is one carrier molecule for all hexose molecules (such as fructose and glucose), and glucose is able to fit into the carrier protein better than fructose. Therefore the glucose molecules are transferred more efficiently.



    • There is a carrier molecule for fructose molecules and a carrier protein for glucose molecules in the cell surface membrane of the yeast cell. The efficiency of the glucose carrier proteins is greater than the fructose carrier molecules.



    • There is a separate carrier protein for glucose and sucrose, but there are more glucose carrier proteins in comparison to fructose carrier proteins.
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    It depends totally on the strain of yeast you are using.

    What are you 'working' with? S.cerevisiae?
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    (Original post by Fluffy)
    It depends totally on the strain of yeast you are using.

    What are you 'working' with? S.cerevisiae?

    The handout thing I've got says 'saccharomyces'.
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    (Original post by Robber's ghost)
    The handout thing I've got says 'saccharomyces'.
    That is not specific to a type of yeast though. Does it say anything else like cervisae or vibrio anywhere?
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    (Original post by Golden Maverick)
    That is not specific to a type of yeast though. Does it say anything else like cervisae or vibrio anywhere?
    'Saccharomyces' is all I've got. I think in the practical we'll be using ordinary dry baker's yeast.
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    (Original post by Fluffy)
    It depends totally on the strain of yeast you are using.
    At this level, we weren't supposed to investigate into the exact reason as to why the rate of respiration was different; merely to hypothesise based on our A-level knowledge so far. (At least that's what our assessor said ...)
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    (Original post by junners)
    At this level, we weren't supposed to investigate into the exact reason as to why the rate of respiration was different; merely to hypothesise based on our A-level knowledge so far. (At least that's what our assessor said ...)
    Really? Because when I did A-Level biology (granted it was a while ago), we were expected to know that different strains/genus of yeast had different metabolistic enzymes, and not all strains can metabolise all sugars, simply because they do not have the required enzyme...

    I can't imagine A-Levels have gotten that much more easy
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    If the yeast cells were not able to metabolise a particular sugar, then the rate of respiration would been have zero/close to zero. But in the practicals I performed, there was a reasonable rate of respiration when I tested each type of sugar as the respiratory substrate.

    Either way, at this level, I'm pretty sure we're not supposed to know the structure of individual yeast cells in relation to whether they're able to metabolise certain sugars.

    We are, however, supposed to know how yeast cells metabolise sugars using extracellular digestion, and how the products are absorbed, based on the distinguishing characteristic of each kingdom. (AQA: Syllabus A, Module 5).

    Maybe the fact that I got 100% on this coursework represents the ever-declining standards, huh? ""
 
 
 
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