The effect of different concentration of ethanol solution on
anaerobic respiration of yeast
Why do we choose to conduct this experiment?
Alcoholic fermentation is the basis of brewing and wine making. But
ethanol is toxic to yeast. We conduct this experiment to investigate
the effect of concentration of ethanol on anaerobic respiration of
yeast.
Hypothesis
Since ethanol is toxic to yeast, as the concentration of ethanol
solution increase, the yeast is inhibited to carry our respiration, so we
estimated that the anaerobic respiration rate of yeast will decrease as
the concentration of ethanol solution increase.
Principle
•As yeast will carried out anaerobic respiration in the absence of
oxygen, ethanol is given out which is poisonous to yeast and
respiratory rate of yeast is then slow down. This can be shown by
drops in the increase in air pressure in each syringe the volume of the
syringes are constant.
•As carbon dioxide is produced during anaerobic respiration, air
pressure inside syringe is increase which can be detected by the low
pressure sensor.
Apparatus and Materials needed
•Syringes x 6
•Beakers x 6
•Short rubber tubing x1
•Computer x 1
•Data logger and low pressure sensor x 1
•Electronic balance x 1
•2g of yeast
•10 cm3 of glucose
•Distilled water
•10 cm3 of pure ethanol
Procedure
1. Set up the computer and Science Workshop was got ready.
2. 6 syringes and 6 beakers are prepared and labelled1 to 6.
3. Weigh 0.25g of yeast in electronic balance for each syringe4. Mix
X cm3 pure ethanol and Y cm3 distilled water, 1.25cm3 glucose,
0.25g of yeast into each beaker according to the table below
Syringe
1
2
3
4
5
6
% of ethanol
solution
X cm3 of water
0
1.5
3
6
12
15
18.75
18.45
18.15
17.55
16.35
15.75
Y cm3 of
ethanol
0
0.3
0.6
1.2
2.4
3
Volume of
glucose
solution
3
Total
volume
(cm
)
3
(cm )
1.25
1.25
1.25
1.25
1.25
1.25
20
20
20
20
20
20
•
Take syringe 2 as an example:
The ethanol solution concentration is 1.5%
total volume = 20 cm3
volume of ethanol added: = 20 x 1.5% = 0.3 cm3
•volume of glucose solution added = 1.25cm3•volume of water added
= (20-1.25-0.3)cm3 = 18.45cm3
6. The syringes are filled by the mixture in the beaker through the
nozzle by the plunger.7. A free end of rubber tubing is attached to
the nozzle of the syringe, another end is attached to the low
pressure sensor connected to the data logger.
8. Data is then recorded as a graph.9. The above steps are repeated
in order to obtain result for 6 syringes
10. The slope of the graph of each syringe was taken.The change in
pressure / change in time
= slope = rate of anaerobic respiration11. After all the slopes of
the 6 graphs was taken, a graph was then plotted on rate of
anaerobic respiration of yeast against concentration of ethanol
solution by using Excel.
This is the set-up of our experiment