Table 1:
Error and Uncertainties: Temperature was measured using data logging software that could measure to the
nearest ±0.1 C
̊ . Mass was measured using a digital scale that was able to measure to the nearest ±0.01 g. Since
the total mass change was calculated by subtracting the Total Final Mass from the Total Initial Mass, the
uncertainties were added together as well to produce a total uncertainty of ±0.02 g.
Qualitative Observations: When placed into the various sucrose solutions, the groups of potatoes in the 0.0M
and 0.2M solutions sank to the bottom of the container, while the groups in higher sucrose concentrations
(0.4M-1.0M) all were able to float in the solution.
Once the potatoes were removed from the solutions after the given time periods, it was noted that the
potatoes in the 1.0M sucrose solution was the most pliable, while the potatoes placed in the solution with no
sucrose was the most crisp and unbendable.
Table 2:
*Red values indicate highest and lowest percentages for each solution.
Table 3:
Table 4:
*In order to eliminate outliers, the highest and lowest values from the group data for each solution were
removed and the data was processed again for comparison.
Standard deviation was calculated using Microsoft Excel. It can be hand calculated by the equation:
http://ellemedit1234.wordpress.com/2013/05/05/the-maths-of-biology/
Standard Error of Mean (S.E.M.) was used in order to determine how well the group data would represent the
actual water potential of the potatoes in a given solution. The smaller the S.E.M., the closer the data would be
to the true mean. This was calculated by taking the standard deviation and dividing by the square root of the
population sample size.
Figure 1:
Group Mean % Mass Change of Solanum tuberosum in
Varying Sucrose Solutions
15.00%
Mean % mass change
10.00%
Percent (%) Msss Change of Potatoes
% Mass Change excluding Highest
and lowest values
y = -0.2127x + 0.0757
R² = 0.9582
5.00%
Isotonic Solution =
0.36 moles dm-3
% Mass Change including outliers
Linear (% Mass Change excluding
Highest and lowest values)
0.00%
0.0
0.2
0.4
0.6
Isotonic Solution=
0.35 moles dm-3
-5.00%
y = -0.2117x + 0.0734
R² = 0.9607
-10.00%
-15.00%
Sucrose Solution/Moles dm-3
0.8
1.0
Figure 2:
Individual Data for Water Potential of Solanum tuberosum
in Varying Sucrose Solutions
10.00
8.00
% Mass Change of Potatoes
6.00
y = -18.657x + 6.0352
R² = 0.9139
4.00
Isotonic Solution=
0.32 moles dm-3
2.00
0.00
0.0
0.2
0.4
0.6
-2.00
0.8
1.0
% Mass Change
Linear (% Mass Change)
-4.00
-6.00
-8.00
-10.00
-12.00
Sucrose Solution/ moles dm-3
*Isotonic solution point for each line was determined by calculating the x-intercept from the equation
given for each trend line in figures 1 and 2.
Conclusion and Evaluation:
Osmosis is a process in which water will move from an area of low solute concentration to an area
of higher solute concentration. This investigation allowed us to be able to estimate an average solute
concentration within the Solanum tuberosum. By varying the solute concentration of sucrose dissolved
in distilled water, we were able to measure the mass change of S. tuberosum and determine the net
movement of water either into or out of the potato. Looking at tables three and four, we can see that
the mass of S. tuberosum increased when placed in 0.0 and 0.2 molar sucrose solutions, which
indicated that the potatoes have a higher concentration of solutes than the solutions they were placed
in. For the samples placed in 0.4M to 1.0M sucrose solutions, the mass tended to decrease; most
dramatically in the 1.0M sucrose solution. However, the potatoes in the 0.4M solution showed the
least mass change between -3.14% and -3.20% which suggests that S. tuberosum has a solute
concentration a little less than 0.4M , which is consistent with the isotonic solution calculations shown
in figures 1 and 2 that are between 0.32 and 0.36M. All three trend lines show a relatively high r2 value
above .90 which suggests a strong correlation between increasing solute concentration and mass
change. The strongest correlation was .9607 which was seen in the data where the outliers had been
eliminated.
In processing the data, it was noticed that there were several sets of data that seemed as outliers
when compared to the other groups’ data. In order to see how these values may have altered the
sample, standard deviation and standard error of mean was calculated with the outliers and without.
Evaluating the calculations there was a small difference between the two. The data including the
outliers saw an increase in the percent mass change for each of the groups typically when compared to
the data without the highest and lowest values. It can also be seen that the S.E.M. also decreases
significantly with the highest and lowest values removed making the data less variable and more
representative of the mean mass change for S. tuberosum in various solute concentrations.
There was a lot of variation within the sets of data for each solution used which can be contributed
to several different factors. Each group was required to cut their own S. tuberosum pieces for each
testing solution. This can provide a lot of variation for each sample group which might possibly affect
the outcome. Since a percent mass change was used, the significance of the different potato slices may
have been minimized. Another factor that may have affected the outcome was the environment
temperature. Each sample was placed in a separate container at room temperature. As one can see,
the temperature did not stay constant for each of the samples. This may have altered the speed of
which water was able to move in or out of the potato slices since molecules will speed up or slowdown
in response to change in temperature. In order to keep temperature constant, it may have been better
to place each sample in a warm water bath after they were placed in each solution. Lastly, it is known
that each sample of S. tuberosum may not have had the same water potential. In nature there is
always variation between individuals and even within individuals. In preparations, potato slices were
pre made and the individual disks were cut to size. In order to help minimize the variability of the
tissue, each group could use their own potato and cut their pieces themselves. This would make sure
that the tissue pieces would be as uniform as possible.