Research Question:
__________________________________________________________________________________
How does an increase in sucrose concentration added to 5ml of 30% yeast affect the amount of CO2
produced in yeast as measured by the height of froth of CO2 after 6 mins?
Raw Data
Height of froth after 6 mins
Sucrose
conc (%)
trial 1 (mm)
± 1mm
trial 2 (mm)
± 1mm
trial 3 (mm)
± 1mm
trial 4 (mm)
± 1mm
trial 5 (mm)
± 1mm
Standand
Deviation
0
6
4
7
9
15
4.2071367
5
21
21
19
25
24
2.44948974
10
23
21
25
22
22
1.51657509
15
25
20
26
26
30
3.57770876
20
40
36
22
30
31
6.79705819
Processed data
Sucrose conc (%)
Average Height of froth after 6 mins (mm) ±
1mm
0
8.2
5
22
10
22.6
15
25.4
20
31.8
Pearson Coefficient calculated by Excel (r): 0.92629881 → indicates a strong correlation
Critical value for this experiment: 0.878
As r > 0.878 the results are statistically significant.
As seen by the graph, the height of the yeast and sucrose concentration has a strong positive
correlation. The Pearson coefficient for the data is 0.92629881, and the critical value for this
experiment is 0.878 meaning it is statistically significant. Thus we can be more than 95%
confident that the results of the experiment are not due to chance, and that if the experiment
was repeated, similar results would be collected. Most of the data points are near the trendline
with the exception of the 5% sucrose concentration. These data point seems to be the furthest
away from the line. This is because there isn’t a large difference between the height of the froth
measured at 5 and 10 % sucrose concentration. However, all the data points follow the trend
since, as the sucrose concentration increase so do the heights of the froth. The error bars were
calculated to show 1SD on either side of the mean. For some data points, the error bars are
quite small like for 10 and 5 % sucrose concentrations, whereas the rest are quite large, the
largest being 20% sucrose concentration. This means that for some of the variations there was a
large spread of data whereas for some others there is a small spread of data. This suggests that
some data collected for some variations were more reliable than others. This can be due to
many reasons which will be talked about in the evaluation. In addition, there is quite a bit of
overlap between the error bars, especially the last 4 data points. This suggests that data points
collected for the different sucrose concentrations were similar for certain trials, which may be
due to the limitations in the ‘evaluation’
In conclusion, as the sucrose concentration increases, so does the amount of CO2 produced by
the yeast. Sucrose is utilized by the yeast through the process of respiration. In respiration,
sucrose is broken down into glucose and fructose and glucose is used as a sugar source to
produce carbon dioxide and water in the presence of oxygen. This process is called aerobic
respiration and is given by the equation glucose + oxygen . The carbon dioxide produced in the
yeat is seen in froth, hence increase in sucrose solution will produce a larger amount of glucose,
which is used as a substrate for respiration. Therefore the rate of respiration increases, which
increases the amount of carbon dioxide produced. This data supports the conclusion, as each
data point follows this trend. For example, for sucrose concentrations 0, 5, 10, 15, 20, 25 % the
heights of the froth are 8.2, 22, 22.6, 24.5, and 31.8 mm respectively. Additionally, most of the
data points or at least their error bars interact with the trendline, with the exception of the 5%
sucrose concentration.
Strengths
Significance: How it supported the methodology of the
investigation
Maintaining
constant
temperature
Temperature was maintained at 40 degrees celsius using a water bath, and
putting the samples in to acclimate. As this temperature in the optimal
temperature for yeast. This is important as it allowed the reaction to occur
quickly enough for the results to be collected, and made sure that the maltase
in yeast did not denature, therefore the experiment could be carried out
successfully. The fact that this was standardised for all samples in also
important as it meant that temperature wasn’t affecting the rate of respiration,
and the independent variable; sucrose concentration, was the only variable
having an affect on the rate, thus making the results valid.
Amount of trials per 5 trials were performed for each sucrose trial. Every experiment has some level
sucrose
of error. When an experiment is performed several times, various mistakes
concentration
tend to 'balance out,' and the outcome is statistically more accurate. Thus
doing 5 trials per sucrose concentration is likely to have improved the accuracy
of the final data.
Limitation of the How significantly could this have
method
impacted on your results and why
Improvement
Carbon dioxide
escaping
As the test tubes were open and air was being
allowed to escape, some carbon dioxide
produced from the reaction may have
escaped, whilst some got trapped in the
solution. This would have resulted in a small
height of froth recorded as the froth in the
direct result of CO2 being trapped in the
solution. This would have hindered the
accuracy of the results, as the values
recorded would have been lower than the
actual amount of CO2 that would have been
produced. This may also be the reason why
the averages for 5% and 10% sucrose were
so close, as CO2 may have escaped and
caused a lower value for 10% sucrose to be
measured.
Although this would be a difficult
limitation to improve, as the
problem lies in the methodology
of the experiment, a balloon can
be places of the test tube so that
CO2 doesnt not escape the the
test tube. However, some CO2
may still escape from the solution
and enter balloon, thus
qualitative observations of the
size of the balloon after 6
minutes a long with the
measurement of froth can be use
together to come to a final
conclusion.
Using sucrose
Although sucrose can be used as a substrate
in this experiment, it needs to first be broken
down into fructose and glucose, and then only
the glucose is used in respiration. This means
that there is an unknown amount of time that it
takes for the sucrose the break down into it’s
monosaccharides. Thus it is difficult to know
whether the time given to the samples to
respire is long enough for the results to be
accurate.
Use varying concentrations of
glucose solutions so that the
sucrose doesn’t need to break
down into glucose.
Putting in and
taking out the
samples before
measuring
Before putting in the sample, the yeast was
pipetted into the test tube with the sucrose.
This was dones with 5 test tubes with the
same concentration of sucrose. There was an
inevitable delay caused by human error that
resulted in some yeast being in contact with
sucrose longer than others. Thus there was a
slight difference between the amount of time
each sample was undergoing respiration for. A
similar circumstance occurred when they were
being taken out of the water bath, as some
samples froth was measured before some
others. This added even more to the time
difference and may have affected the results.
This may have been the reason for the large
error bars, as samples with the same
concentration of sucrose showed a lot of
variance.
With more time, each trial can be
performed one by one to limit the
amount of time.
Alternatively, a marking system
can be used to mark the order in
which the yeast was added to
the test tubes, and the test tubes
should be taken out of the water
bath in the same order to all
samples are reacting for
approximately the same time.
Extension:
Further exploration can be done into how varying temperatures affect the rate of respiration of
yeast, whilst controlling the sucrose concentration. The temperature could be easily
manipulated using the water bath and setting the temperature at different intervals to explore
its affects on respiration.