Yeast Investigation


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Yeast Investigation

Introduction

In this investigation I am going to try and find the optimum
temperature at which the new strain of yeast respires using trial and
improvement. I will test from 20°c to 70°c as this is the most
suitable. This means that little heating will be needed to get the
maximum respiration in the yeast and therefore the most efficient
alcohol production. Yeast respires glucose an aerobically producing
carbon dioxide and ethanol as waste products. The carbon dioxide is
given off as bubbles and the number given off in a certain amount of
time can be used to estimate the rate of reaction. I will be using
this method in my experiment.

Method

To do this investigation I will test the yeast in a water bath (beaker
filled with water of a certain temperature) so I can adjust the
temperature and mix the yeast with water using a syringe and some
tubing. I will be using 250ml of water, 25g of sucrose (sugar) and 2g
of dried yeast. I will also use tin foil wrapped round the beaker to
keep the temperature from changing.

Fair Test

I will make this experiment a fair test by using the same water bath
syringe and tubing each time and by measuring the water sucrose and
yeast very carefully.

Prediction

I predict that the optimum temperature will be around 20°c as yeast
respires glucose an aerobically and a higher temperature will speed up
the reaction but if the temperature is too high then the reaction will
be slowed down.

Apparatus

Preliminary work

I did a preliminary test in order to help me plan my experiment out
more carefully and so I can get an idea of what's going to happen. I
tested the yeast in temperatures of 20°c and 70°c (the range that I
will be testing in in my final experiment).

Preliminary Results

Temperature tested

Bubbles counted

20°c

15

70°c

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80

These results show that the set up of the experiment is good as the
preliminary experiment went smoothly and well.

Final Experiment Results - Test 1

Temperature

Bubbles counted

20°c

17

30°c

12

40°c

41

50°c

73

60°c

99

70°c

75

[IMAGE]

Final Experiment Results - Test 2

Temperature

Bubbles counted

20°c

31

30°c

42

40°c

62

50°c

118

60°c

132

70°c

109

[IMAGE]

Final Experiment Results - Test 3

Temperature

Bubbles counted

20°c

5

30°c

30

40°c

48

50°c

67

60°c

80

70°c

59

[IMAGE]

Analysis

I have found that the optimum temperature at which yeast respires is
at 60°c. This is because the at 60°c the temperature is high enough to
speed up the cell reproduction of the yeast but not too high to slow
down the reproduction and kill cells.

Evaluation

I think the experiment went quite well apart from a few anomalies such
as at 20°c in test 1 of the final experiment. This was maybe due to an
inaccurate measure in the temperature of the water or in the amount of
yeast. To make the results more reliable I would increase the level of
accuracy in the measuring of yeast and the temperature of water and
also more results would make a more accurate average of results. If I
were to do the experiment again then I would do 5 tests instead of 3
in the final experiment. This would make a more accurate average at
the end.


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