A2 Biology - Rate of Respiration in YEAST

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Sahir
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Fairly simple question but no idea what the answer is.. it's for my coursework.

Basically with different respiratory substrates (e.g: fructose, maltose, glucose, sucrose blah blah blah) the TIME TAKEN FOR THE RATE OF RESPIRATION TO BECOME CONSTANT was different. This was in my preliminary work by the way..

But the question is WHY?!

As far as i know it has nothing to do with a "switch" or anything from aerobic to anaerobic because thats controlled by presence of O2, right?

Why else would the rate of change of mass lost suddenly decrease - less CO2 being produced obviously but why?


Thankya very much!
Look forward to a reply.
SAHIR
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madmazda86
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Not really sure what you want answered - different respiratory substrates have different respiratory quotients (i.e. the amount of oxygen consumed/CO2 released though you wouldn't have to worry about the former in anaerobic respiration.)

In terms of *why* the rates of respiration are different for the different substrates - it's down to enzymes. If you do Chemistry it helps because structural isomerism is involved.

If you look at the chemical structures of fructose and glucose you'll see that they have the same number of carbon, hydrogen and oxygen atoms etc - but the groups are arranged differently around the 6-carbon backbone. So fructose is a structural isomer of glucose. Yeast uses enzymes (coenzymes - Krebs cycle an' all that) for respiration that act on these substrates to release their energy. Enzymes have a specific shape of active site due to their unique tertiary structure. This will work for ONE isomer only - so an enzyme that works on glucose wouldn't work for fructose because fructose is a different atomic shape. These enzymes (I think) are present in different concentrations. So the lower the concentration of enzymes specific to a particular substrate e.g. lactose or whatever, the lower the rate of respiration using that substrate.

Ach, it's 00.11am - bed calls. Hope this makes sense - I'm a bit tired.
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Sahir
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Cheers for the reply, which definately helps..

But what really what i was getting at was.. in fermentation why was the rate of respiration high (found by the mass of the reaction mixture that was lost) at first, and then decreased to a relatively constant rate.

The time taken for this to happen was different with different substrates - i understand about the isomers but what exactly would you look for in the structural formula? What substrate is best for yeast? glucose? I hope so because glucose seems to take longer to reduce to that constant rate than others.. so it produces more CO2 and ATP in this period. Therefore more efficient. correct?

Note: conditions not necessarily anaerobic because the evironment for yeast was NOT anoxic.
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madmazda86
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(Original post by Sahir)
Cheers for the reply, which definately helps..

But what really what i was getting at was.. in fermentation why was the rate of respiration high (found by the mass of the reaction mixture that was lost) at first, and then decreased to a relatively constant rate.

The time taken for this to happen was different with different substrates - i understand about the isomers but what exactly would you look for in the structural formula? What substrate is best for yeast? glucose? I hope so because glucose seems to take longer to reduce to that constant rate than others.. so it produces more CO2 and ATP in this period. Therefore more efficient. correct?

Note: conditions not necessarily anaerobic because the evironment for yeast was NOT anoxic.
That is a seriously odd way of measuring the rate of respiration - I wouldn't honestly know... unless it was caused by the yeast running out of oxygen and switching to anaerobic respiration? *frowns* If that were the case then glucose would not be the best respiratory substrate because it took longer to switch to anaerobic respiration, therefore was using up the oxygen more slowly... confuzzling! Sorry, I don't really know the answer to that.

In terms of the isomers - Here's glucose and here's fructose (see attachment). The only difference between the two is that glucose has an aldehyde group (its C=O is at the end of the carbon chain) and fructose has a ketone group (its C=O is not at the end of the chain - it's in the 2nd carbon position)

Edit: Dah, I forgot to put the picture up! :rolleyes:
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Sahir
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(Original post by madmazda86)
That is a seriously odd way of measuring the rate of respiration - I wouldn't honestly know... unless it was caused by the yeast running out of oxygen and switching to anaerobic respiration? *frowns* If that were the case then glucose would not be the best respiratory substrate because it took longer to switch to anaerobic respiration, therefore was using up the oxygen more slowly... confuzzling! Sorry, I don't really know the answer to that.

In terms of the isomers - Here's glucose and here's fructose (see attachment). The only difference between the two is that glucose has an aldehyde group (its C=O is at the end of the carbon chain) and fructose has a ketone group (its C=O is not at the end of the chain - it's in the 2nd carbon position)

Edit: Dah, I forgot to put the picture up! :rolleyes:
Cheers that's really useful.. thanks a lot.

Anybody else with any ideas? What i was asking again was this:
In fermentation why was the rate of respiration high (found by the mass of the reaction mixture that was lost) at first, and then decreased to a relatively constant rate.

Other than a switch from aerobic to anaerobic respiration which is not possible because O2 was present all the time, the only thing that i can think of is that yeast takes time to accommodate or something? Not very scientific though.

Eek! Please, any help will be something. Cheers.
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jacie
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I have got that coursework for my human biology A2...i am confused over why the fermentation rates were equal for glucose and sucrose even though sucrose is a disaccharide so you would think it would be slower then glucose (monosaccharide)...?

Anyway...your question isn't that...erm...maybe the respiration rates decreased over time because the sugar was being broken down (digested) over time...so as time progressed there would be less substrate for the yeast enzymes to act on and so rate decreased therefore reducing respiration and therefore CO2 production?!
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Sahir
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(Original post by jacie)
I have got that coursework for my human biology A2...i am confused over why the fermentation rates were equal for glucose and sucrose even though sucrose is a disaccharide so you would think it would be slower then glucose (monosaccharide)...?

Anyway...your question isn't that...erm...maybe the respiration rates decreased over time because the sugar was being broken down (digested) over time...so as time progressed there would be less substrate for the yeast enzymes to act on and so rate decreased therefore reducing respiration and therefore CO2 production?!
Cheers Jacie,

It's possible yea..

Anybody have any other ideas why yeast would take time to reach a constant rate of respiration??

Cheers, SAHIR
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jacie
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Oh another thing i thought of is that yeast have to synthesize enymes to break down the sugars, that means they'll follow the traditional lag, log, stationary, decline mechanism of growth/respiration. The reason they take time to reach their constant is because they are in their 'lag' phase, so it takes time to synthesize the necessary enzymes??
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Sahir
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(Original post by jacie)
Oh another thing i thought of is that yeast have to synthesize enymes to break down the sugars, that means they'll follow the traditional lag, log, stationary, decline mechanism of growth/respiration. The reason they take time to reach their constant is because they are in their 'lag' phase, so it takes time to synthesize the necessary enzymes??
But then why would they be losing ANY mass before reaching a constant rate? I agree it must have something to do with this but as all substrates lost mass due to CO2 produced from respiration (even sucrose and maltose) before reaching a constant rate it doesn't entirely make sense.

Also the rates were abnormally high (but not constant), and then they reached a LOWER constant rate. So somehow the yeast was respiring fast to begin with and then sort of accommodated to the substrate and reached a constant rate of respiration.

ARGH! Weird weird subject.
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Ralfskini
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(Original post by Sahir)
But then why would they be losing ANY mass before reaching a constant rate? I agree it must have something to do with this but as all substrates lost mass due to CO2 produced from respiration (even sucrose and maltose) before reaching a constant rate it doesn't entirely make sense.

Also the rates were abnormally high (but not constant), and then they reached a LOWER constant rate. So somehow the yeast was respiring fast to begin with and then sort of accommodated to the substrate and reached a constant rate of respiration.

ARGH! Weird weird subject.


What school do you go to????
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madmazda86
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(Original post by Sahir)
But then why would they be losing ANY mass before reaching a constant rate? I agree it must have something to do with this but as all substrates lost mass due to CO2 produced from respiration (even sucrose and maltose) before reaching a constant rate it doesn't entirely make sense.

Also the rates were abnormally high (but not constant), and then they reached a LOWER constant rate. So somehow the yeast was respiring fast to begin with and then sort of accommodated to the substrate and reached a constant rate of respiration.

ARGH! Weird weird subject.
Just had a thought... did you leave the yeast solutions to equilibriate in the water bath? If not then the fluctuations in respiration rate may be due to the yeast adjusting their respiration in response to the temperature
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Sahir
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(Original post by madmazda86)
Just had a thought... did you leave the yeast solutions to equilibriate in the water bath? If not then the fluctuations in respiration rate may be due to the yeast adjusting their respiration in response to the temperature
Yeah i've got a feeling that you're right. Cant really be anything else can it..? There's nothing else to accommodate to..

Except that the yeast suspension was made up in solution with the substrate from DRIED yeast.. so is it respiring in this form? I guess not.. Maybe that's why it then accommodates to the substrate?

What do you reckon?

Cheers for all the help guys n gals..

SAHIR
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happydadtoo
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(Original post by Sahir)
Cheers that's really useful.. thanks a lot.

Anybody else with any ideas? What i was asking again was this:
In fermentation why was the rate of respiration high (found by the mass of the reaction mixture that was lost) at first, and then decreased to a relatively constant rate.

Other than a switch from aerobic to anaerobic respiration which is not possible because O2 was present all the time, the only thing that i can think of is that yeast takes time to accommodate or something? Not very scientific though.

Eek! Please, any help will be something. Cheers.
You missed the point - it's aerobic to anaerobic. The oxygen has to dissolve in the solution before it is available to the yeaast. If the yeast is respiring rapidly, it soon uses up the O2 in the solution and switches to (largely) anaerobic. Unless you have an aquarium pump running into the solution pumping pure O2 in, then the dissolved O2 concentration will be pitifully low very quickly.
That's how beer, wine etc is made!
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Sahir
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(Original post by happydadtoo)
You missed the point - it's aerobic to anaerobic. The oxygen has to dissolve in the solution before it is available to the yeaast. If the yeast is respiring rapidly, it soon uses up the O2 in the solution and switches to (largely) anaerobic. Unless you have an aquarium pump running into the solution pumping pure O2 in, then the dissolved O2 concentration will be pitifully low very quickly.
That's how beer, wine etc is made!
Are you sure?? Because you see this is effectively the reasoning i gave for my hypothesis in the first place, except i didn't explain explicitly that oxygen had to dissolve in solution.. The planning section is marked first and I was told that there can't be a 'switch' from aerobic to anaerobic because that is solely dependent on amount of O2 present.

Now you have made this point I have to say that this makes most sense of all explanations that I have come up with..

So you expect that different substrates would consequently take different lengths of time to use up the O2 in solution with aerobic respiration and then switch to anaerobic?? Which would you say would switch first? Monosaccharides or disaccharides??

I can always ahhhhmm.. engineer my results i guess.. I'm already contemplating saying that I used a layer of mineral oil on top of the yeast solution in the conical flasks.. soo.. yea.

Cheers for your input! v. useful..

SAHIR
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happydadtoo
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The fastest substarte will always be glucose, but note that the others depend on what substrate the yeast was growing on BEFORE. If the substarte is changed, then 'induction' must first occur. This means the yeast has to synthesise new enzymes to allow the uptake and utilisation of the substrate, BEFORE using it in respiration.
Lactose cannot be fermented; all other disaccharides are broadly similar in speed, though maltose is quickest, since once split, two identical mols. of glcose are produced, thus only one pathway needs to be followed.
Any oil on top works!
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