Antonella Torres
Does temperature change affect the respiration of yeast?
Introduction:
Cell respiration is the process by which cells are able to produce energy in the form of
ATP, thus releasing other waste products. The process of cells respiration can either occur
in the presence or absence of oxygen and this will result different products. The first stage
of cell respiration consists of glycolysis by which carbon is separated into two C3
molecules, named pyruvates and releasing ATP. The effect of temperature in cell
respiration mainly depends on the effect of enzyme activity. As the temperature rises the
rate of cellular respiration ascents, giving the molecules more motion and activity.
However if the temperature is too high, the enzyme will denature and this will decrease
cell respiration. Through out this experiment we will measure the amount of CO2
produced whilst increasing the temperature to see if it affects the respiration of yeast.
Yeast is commonly used in bakery’s to help the bread rise. This happens through
anaerobic respiration of the cells, where carbon dioxide is released as a product helping
the dough become nice and big. Nevertheless, yeast can also respire without oxygen. This
process is known as anaerobic respiration; here glucose (sugar) is transformed into
alcohol, which enables the process of fermentation. This is used when making wine or
beer.
Aerobic respiration:
Glucose + Oxygen  Carbon Dioxide + Water + ENERGY
Anaerobic respiration:
Glucose  Ethanol + Carbon Dioxide + ENERGY
Hypothesis:
The higher the temperature, the more carbon dioxide will be released by yeast, therefore
forming a greater amount of bubbles. This is because when temperature increases, rate of
respiration increases as well because heat speeds up the reactions which means kinetic
energy is higher.
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Variables:
Independent: The changing temperatures of the water bath
Dependent: Amount of Carbon Dioxide released in 1 minute (number of bubbles)
Control:
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Same amounts of yeast (5ml) and glucose (10ml) solution
Same period of time for counting the number of bubbles for each temperature, in
this case 1 minute
Covering each test tube with solution inside, completely with the hot water
Experimental Design:
Delivery
tube
Thermometer
Carbon
dioxide
coming
out as
bubbles
in water
Test tube
fitted with
bung with
glucose
solution and
yeast. It is
important that
the water
covers all
solution
Hot water starting at
60 degrees Celsius
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Stopwatch
Pipettes used to measure 5ml of yeast
and 10ml of glucose
Dried yeast
Test tube rack
Materials and Equipment:
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Water Bath
Dried Yeast (48gm yeast 0.6dm3)
Thermometer
Timer
Test tube rack
Test tubes (one fitted with bung)
Delivery tube
Rubber connection and jet
Glucose solution (5%)
Big beaker (400cm3)
Method:
1. Gather all of the apparatus required to set up a water bath
2. In a 400cm3 beaker pour 200ml of hot water
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3. With a thermometer measure the temperature of water until 60 degrees is
reached and work down wards
4. Using a pipette pour 5ml of yeast and 10ml of 5% glucose solution
5. Avoid mixing or shaking the test tube
6. Deposit the test tube in water bath covering it with a bung and its delivery tube
7. At the other end of the delivery tube, place another 400cm3 beaker with tap water
where the carbon dioxide bubbles will be seen as product.
8. With a timer record the number of bubbles you see every minute
9. Repeat steps 2-8 but with 50, 40, 30 and 20 degrees
10. Record your results
Results and process:
Temperature (Degrees Celsius)
Number of bubbles produced in 1 minute
(CO2 released)
0
0
3
6
30
20
30
40
50
60
Graph:
Does temperature change affect the
respiration rate of yeast?
7
Number of bubbles
6
5
4
Number of bubbles
produced in 1 minute
(CO2 released)
3
2
1
0
-1
0
20
40
Temperature
60
80
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Conclusion:
In conclusion, our hypothesis was supported to some extent because our results clearly
show how the number of bubbles released at 60 degrees was the highest compared to
other lower temperatures. The graph shows a rising slope; where at 20 degrees no
bubbles were emitted in comparison to 60 degrees. The difference is quite staggering and
there is not a periodic increase in number of bubbles, this might be due to errors in the
experiment. The yeast respires rapidly at higher temperatures than at lower and this can
be explained due to the kinetic theory. At higher temperatures more heat energy is
provided to the particles and they would move faster having more collisions in a certain
amount of time (1 minute). Nevertheless 60 degrees is a pretty high temperature for
respiration to occur as enzymes would denature causing them to be unable to bind with
the yeast and glucose particles but in this case we could say that the test tube was just
beginning to heat up with the yeast and so the actual temperature inside was not 60
degrees at all. Therefore, most of the CO2 was released here. Probably the optimum
temperature for respiration of yeast would be between 40-50 degrees.
Evaluation:
Errors:
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We did not repeat our results enough times to get a proper average and
therefore our results are unreliable.
We moved the test tubes around a lot and this biased the results for our
respiration
A proper water bath was not used so the temperature was not controlled
precisely.
30 bubbles produced at 60 degrees could be seen as an anomaly as it is a
lot of bubbles compared to the rest of the results, this was because the
yeast was cold and it was just starting to heat up. This biased our
experiment
Try with yeast at room temperature as the one used was previously left on
the fridge
The yeast and glucose mixture was not the same temperature as of the
water
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Proposed modifications:
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Find an optimum respiration temperature for yeast which could be between 40
and 50 degrees, it would be nice to try the experiment for example at 45 degrees.
Repeat results twice or three times to get mean
Give more time for the respiration to occur. At least more than 1 minute.
To be sure our solutions were not contaminated we could have worked in a much
cleaner space, further away from other experiments
We could have used more precise pipettes to have the correct amounts of
solutions
Next time we could try with a different type of yeast, not only dried yeast