Anaerobic Respiration of Yeast


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Anaerobic Respiration of Yeast

Aim: To investigate the effect of temperature on anaerobic yeast
respiration.

Basic outline plan: I plan to force a solution of yeast and glucose to
anaerobicly respire. I plan to measure the gas collected at allotted
intervals during a set period of time, when the solution is at
different temperatures. I will need equipment to accurately measure
the volume of gas collected, and an indicator to show me that all no
oxygen is present in my solution. I will also need to make a way to
force it to anaerobicly respire by creating an air tight layer over
the top of the substance.

Prediction & Background information:

I predict that a gas will be given off and this gas will be CO2 as we
are anaerobicly respiring yeast.

We know that Anaerobic Respiration In yeast has the following formula.

[IMAGE]Glucose Carbon Dioxide + Ethanol + Energy

[IMAGE]C6H12O6 2CO2 + 2C2H5OH + 210 KJ/Mole.

I predict that the volume of gas expelled will increase with
temperature. I believe this for a few reasons. The first is due to the
'Kinetic theory', this states that the extent of a molecules movement
depends on its state and temperature. As temperature increases, the
particles become more 'exited', and so move around and collide and
react more frequently and rapidly. It is these collisions which cause
the reaction. We also know that heat is a catalyst in all reactions.

I also know that yeast is an enzyme and all enzymes have an optimal
temperature at which they work best, this is around 45º for yeast.
However I predict that if the temperature is raised too much, then the
reaction will not occur at all. I believe this because yeast is an
enzyme, and according to the, 'GCSE revision guide' and the lock and
key theory, enzymes are protein molecules, and each enzyme has a
different shape for a certain reactant to fit into. This is called the
active sight. But protein molecules and the active sight become

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denatured by extreme temperature of pH. When the protein is denatured
this is irreversible and the mechanism no longer works. Most enzymes
become denatured around 45º, but yeast is a little stronger and so
should become denatured around 50º-60º. Therefore I believe that the
amount of gas collected will increase over an allotted time, until the
temperature becomes to high, and then their will be no reaction taking
place at all.

Also I did some preliminary work where we used Hydrogen Carbonate
indicator to detect C02 by turning yellow, and during this experiment
it was made clear that more bubbles were produced in an allotted time,
and the indicator turned yellow quicker with hotter temperatures.

I think it will also be best to use the same yeast for each experiment
before we make it denatured, to ensure that the concentration of
glucose and yeast is constant. This will also be easier as after the
oxygen has been removed for our solution, we will not have to do it
again. However this could be a bad idea, because we know that
anaerobic respiration in yeast produces an alcohol (ethanol) and the
most common reason for which anaerobic respiration is used is to make
consumable alcohol in which the Ethanol eats away at the solution and
kills it. If the solution dies we could believe it became denatured
because of temperature, but in fact it died through the ethanol.

Diagrams to Explain My Prediction:


Why I chose this plan:

In previous experiment I have found that yeast can be a very
uncooperative substance. When Diazine green is placed in it, some
times it can take, 5 seconds to show that there is no oxygen present;
in others it can take ten minuets. This is why I have decided to use
the same yeast each time so that time is not wasted in extracting all
the oxygen.

I have previously done an experiment in which the gas produced is
carried via a delivery tube, through some Hydrogen Carbonate indicator
which detects CO2 by turning yellow. Although it was made obvious to
us that it turned yellow quicker at higher temperature, deciding when
it was yellow, and when it wasn't was up to each individual so the
results would not be accurate enough to plot in a graph. That is why I
have chosen an experiment where to respiration rate is easy to obtain,
and human interaction is minimilised.

I am also choosing a range of temperatures which is not very hot, as I
know that if I picked a range from 60º-100º, then there would be no
results from 60º - 100ºas the yeast would be denatured. Therefore, I
have chosen results which I believe will give me a broad range, but
will but which will show a trend.

Apparatus:

Conical Flask

Delivery Tube and Bung

Gas Syringe

Diazine Green

Glucose and Yeast solution

Thermometer

500ml beaker

Stopwatch

I have chosen equipment which will give me accurate, but easy results
to obtain. For instance, I have chosen the gas syringe opposed to a
solution of Hydrogen peroxide so that I can easily & accurately
measure the volume of gas collected over an allotted time. I have
chosen a stopwatch over a wrist watch as this will measure the time
more accurately, and a conical flask opposed to a beaker because it is
easier to obtain the gas via a bung and delivery tube from a conical
flask.

Method: The big beaker was filled up half way with tap water and using
the thermometer the temperature was measured, the first temperature is
25°C so if it is too cold, hot water from the kettle, or even the hot
tap should be added if it is too hot add ice to cool the water down.
When the temperature is right our pre prepared solution of Glucose and
Yeast should have around 4-5 drops of Diazine green added to it and
sealed with a layer of liquid paraffin. The flask should be corked and
shook, and then the solution should be allowed to settle. The flask
should be placed into the prepared water and allowed to equilibrate to
the temperature for 5 minutes, making sure the temperature of the
water bath is still 25°C, if after 5 minutes the solution hasn't
changed to a pink colour allow it to stand in the water bath until it
does change to a pink colour. This will show you there is no oxygen
present in the yeast solution so anaerobic respiration can take place.
Now the water bath with the flask still in it should be placed near
the gas syringe, ready to place the delivery tube's cork over the top
of the flask. The gas syringe should be set to 0 and the stop watch
reset. The delivery tube should be placed with its cork over the
flasks neck so that all gas will go into the gas syringe and not into
the surrounding air. When the cork is air tight the stop watch should
be started and the results recorded. The experiment should be repeated
three times for this temperature, remembering to set the gas syringe
back to 0 every time, then the other temperatures should be done in
the same way.


Analysing Evidence and Drawing Conclusions

As temperature increased, so did the amount of gas given off in a
certain time up to 50º.

My first graph proves that as predicted, the amount of gas collected
rises with the temperature (1), then after the temperature reaches its
maximum, or optimum temperature (2), it plummets quickly as it has
become denatured (3).

The second graph proves that a constant rate of gas production was
achieved with the equilibrated yeast, despite the different
temperatures, as each one shows a straight line, and the only
difference is the gas produced per minute.

The rise then sudden plummet happened for a few reasons as I will
explain. The first reason is due to the 'Kinetic theory', this states
that the extent of a molecules movement depends on its state and
temperature. As temperature increases, the particles become more
'exited', and so move around and collide and react more frequently and
rapidly. It is these collisions which cause the reaction. We also know
that heat is a catalyst in all reactions.

I also know that yeast is an enzyme and all enzymes have an optimal
temperature at which they work best, this is around 45º for yeast.
However I know that if the temperature is raised too much, then the
reaction will not occur at all. I believe this because yeast is an
enzyme, and according to the, 'GCSE revision guide' and the lock and
key theory, enzymes are protein molecules, and each enzyme has a
different shape for a certain reactant to fit into. This is called the
active sight. But protein molecules and the active sight become
denatured by extreme temperature of pH. When the protein is denatured
this is irreversible and the mechanism no longer works. Most enzymes
become denatured around 45º, but yeast is a little stronger and so
should become denatured around 50º-60º.

I also found that the experiment tied very closely with my prelim., in
my prelim as temperature was raised more bubbles were produced in an
allotted time, and it turned Hydrogen Carbonate indicator yellow
quicker, which in effect is exactly the same as what happened in my
real experiment, except we collected the gas instead of counting the
bubbles for increased accuracy, and we did not feel the need to test
the gas.

I think my conclusion is valid and matches the whole range of
experiments as it seems to follow a trend and the rules, and seems to
fit in n a graph.


Evaluation

I thought the results obtained were very accurate and conclusive. They
seem consistent as the show straight lines on graph two, which means a
constant rate as it should be and a steady rise then a sudden plummet
in graph 1 as it suggests there should be. However, on my repeats
there are some noticeable differences between attempt one and three,
with two, for the volume of gas given off per minute. At 35ºC and 40ºC
the volume of gas collected seems to be consistently higher then the
other two, and even in 40ºC goes above the results for 45ºC, which is
not what I would have expected. The explanation I can offer for this
is that there must have been some change in the temperature, and I
must have not stirred it consistently, which makes that set of data in
accurate. I thought all of my other results generally fitted the
overall trend well however the differences between the gas given off
each minute per temperature seems to be a little random, even if it
does follow the general trend.

I though the experiment allowed the prediction to be tested very well
as it proved the points that I wanted it to, and very concussively as
well. I thought my method allowed the results to be sufficiently
accurate although we did run the risk of killing the yeast by its own
ethanol which could disguise itself as denaturing.

I think my results were reliable enough to support the conclusion
especially due to the fact that there are no obvious abnormalities.
There are a few results hat do not fit the overall trend such as the
cumulative amount of gas expelled as shown on graph 1 does not quite
fit into a curved line but still however shows a general trend.

If I was to test the same variable again I think I would have pre
boiled my glucose and water solution with a paraffin layer already
coating it and then add a yeast tablet, so we would not have to wait
for the oxygen to disperse. And I would also use an electric water
bath to heat the water each time, with an electric thermometer to
achieve more accurate results. If I could make the water bath very
accurate I would test every degree for a 10º period between 40º and
50º to discover exactly when the optimal point for this yeast enzyme
is.


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