Transcript QEF Datalogger

Biology Project
Effect of
Different
s pH
on Anaerobic
Respiration of Yeast
Aim
To investigate
the effect of different
pH on anaerobic
respiration of yeast.
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Yeast is a type of enzyme. Enzyme, which is made
up of protein, will denature in extreme pH and work
best in its optimum pH, therefore, it should only
work in a certain range of pH. Since enzyme will
loss its biological function once denatured, changes
in the rate of the anaerobic respiration is a very
sensitive measure of denaturation.
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When yeast carries out anaerobic respiration, it will
give out both ethanol and carbon dioxide as
bi-products. By putting yeast in solutions of different
pH value and study the amount of gas (carbon dioxide)
produced, which implies its rate of anaerobic
respiration, we should be able to tell the range
of pH it works best in.
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To measure the amount of carbon dioxide produced，
we can measure the pressure of the gas in a fixed
volume of space， since amount of gas produced
is directly proportional to the pressure it exerted on
the container.
Material
Beaker(250cm3)
×3
Beaker(500cm3)
×3
Buffer solution of pH 4, 7 and 10 × 3cm3 each
Computer
×1
Data logger
×1
Electron balance
×1
Glucose solution
× 450cm3
Ice
Measuring cylinder
×3
Oil
High Pressure Sensor
×3
Thermometer
×3
Yeast
× 1g
Procedure:
1. Computer was set up with data logger and sensors
connected, and the software Science Workshop
was chosen.
2. 100g of glucose solution was weighted using the
Procedure:
electronic balance. Water
was added to it to make
up a solution of 500cm3.
3. Icy water was poured into the 3 500cm3 beakers
to make 3 water baths in order to keep the
temperature of the solutions constant.
4. 150cm3 of glucose solution was poured into 3
250cm3 beakers and 3cm3 of buffer solution of
different pH value was added to each of the
beakers separately.
Procedure:
5. The 3 beakers of solution was then boiled.
After it was boiled, a layer of oil was added to
it and it was then put into the water baths.
Thermometers are put into the beakers of
solution to monitor Procedure:
the temperature.
6. 0.3g of yeast was weighted and grinded into
small particles. It was then poured into the
syringe. The plunger was slowly pushed until
no room was left.
7. After the temperatures of the 3 solutions
became 15oC, the syringe of yeast was
inserted into it to suck 15cm3 of solution up.
Procedure:
8. The syringes were connected to the high pressure
sensors.
9. Recording was Procedure:
started. Pressure in the three
syringes were adjusted by pulling out or pushing
in the plunger until they are of 100kPa.
10. Recording was stopped. Previous records were
deleted.
11. Recording was started again for 600s to plot a
graph of pressure against time.
This is the set up...
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Pressure of gas produced in solution of
pH4， pH7， pH10 against time
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Yeast works best between
neutral to slightly alkaline medium.
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Discussion
From the graphs obtained, we can see that the enzymes in yeast will
denature in acidic medium and work best in neutral and alkaline medium.
When the pH of a solution containing protein is changed, the protonation
state of the amino and carboxylate groups changes, and ionic bonds in the
proteins will be disrupted. This will need to changes in the shape of the
protein molecule that cause it to loss its biological function. The protein is
then said to be denatured.
Discussion
Since yeast is made up of protein, if the protein denature, the yeast can no
longer respire. The pressure of gas produced in fixed volume of space
during anaerobic respiration reveals the ability of anaerobic respiration of
yeast, which in turns reveals the ability of protein to resist denaturation.
From the graphs obtained, we see that the proteins which made up yeast
is capable to work in both neutral and alkaline medium.
Errors
Small amount of oxygen present in the syringe
Increase the volume of the mixture to reduce
the percentage error.
Difference in starting pressure affects the
experimental result.
Increase or decrease the volume of the
syringe so as to split the different.
Errors
Yeast is not totally dissolved
Grind the yeast before mixing it with the
solution to increase its surface area which
enhance better dissolution.
Slight difference in starting temperature
Put all the solutions in one water bath instead of three.
Conclusion
Yeast works
best between neutral to
slightly alkaline condition.
Member List
Sandy Au Yeung (1)
Stephanie Cheung (6)
Winnie Ip (13)
Bernice Law (14)
Amy Wu (28)
6AS
The End