1. This site uses cookies. By continuing to use this site, you are agreeing to our use of cookies. Learn More.
  2. Hi Guest, welcome to the TES Community!

    Connect with like-minded professionals and have your say on the issues that matter to you.

    Don't forget to look at the how to guide.

    Dismiss Notice

how does yeast respire?

Discussion in 'Science' started by 98wilsden, Apr 25, 2007.

  1. This may sound like a stupid question but I cant find a straight answer on t'internet!

    I know its aerobically or anaerobically....how does it occur in bread-making? Is it aerobically? Hence no alcohol production?

    Cheers

    emma
     
  2. This may sound like a stupid question but I cant find a straight answer on t'internet!

    I know its aerobically or anaerobically....how does it occur in bread-making? Is it aerobically? Hence no alcohol production?

    Cheers

    emma
     
  3. nomad

    nomad Star commenter

    Yeast can respire in both ways. Yeast gets more energy from aerobic respiration, but when it runs out of oxygen it does not die. It can continue to respire anaerobically, but it does not get so much energy from the sugar. Yeast produces ethanol when it respires anaerobically but if any was produced in bread-making, it would evaporate away fully in the baking process.

    It is worth noting that humans (and some other animals) can respire in both ways too. When undertaking physical exercise we may not get enough oxygen into our blood, so our muscles start to respire anaerobically. Unlike yeast we produce lactic acid, which causes cramp.

    If I were able to produce ethanol anaerobic respiration I might exercise more often!
     
    ZwaneGM likes this.
  4. thanks nomad

     
  5. nomad

    nomad Star commenter

    The two word equations for years are:

    Glucose + Oxygen = Carbon Dioxide + Water + Energy

    Glucose = Carbon Dioxide + Ethanol + Energy

    According to this site: http://www.le.ac.uk/education/centres/sci/selfstudy/eco7.... respiration in bread-making is anaerobic, rather than aerobic. But I suspect that a bit of both goes on..

    "Bread-making uses the carbon dioxide produced by anaerobic respiration, not the ethanol. Starch in the dough breaks down to sugar, which feeds the yeast. The carbon dioxide bubbles make the dough rise before it is baked into bread."
     
  6. the ethanol made in bread production evaporates during baking. part of the reason it smells so good i suspect!
     
  7. pcsimon

    pcsimon New commenter

    Agree with all posts, but as a chemist I really don't like seeing equations with Energy written as a product - it causes huge problems with students putting Heat, Energy and all sorts of things into equations. Suggest you say:

    Glucose + Oxygen = Carbon Dioxide + Water (with a large amount of energy given off)

    Glucose = Carbon Dioxide + Ethanol (with a small amount of energy given off)

    or in humans...

    Glucose = Lactic Acid (with a small amount of energy given off)
     
    ZwaneGM likes this.
  8. nomad

    nomad Star commenter

    Pcsimon,

    I take your point, but a physicist wouldn't agree. After all, energy = mass (E = mc2), so energy could be regarded as being as much of a product as lactic acid or alcohol.


    WitchKing,

    A garee. However, "As drunk as a baker" doesn't feature amongst the occupational or behavioural similies of which I am aware.
     
  9. pcsimon

    pcsimon New commenter

    Nomad - you're right - but we don't teach E=mc2 at KS3, so when it comes to SATs and they have to fill in the boxes for a reaction they get very confused and complain there's no space. Of course because they've learned the respiration equation they put 'Carbon Dioxide' in every reaction so it's not much of an improvement.
     
  10. ZwaneGM

    ZwaneGM New commenter

    Thanks to you all for sharing such an insight... #enriching.my.mind
     
    frnc likes this.

Share This Page