Osmosis
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Method
In this practical the objective is to determine the water potential of tissue from the same potato in different molarities of sucrose solution by submerging the samples of tissue cut into disks, in the varying solutions for an hour, weighing their mass before and after the samples had been submerged. (As instructed in appendix A)
Results
Molarities
Original Mass
Final Mass
Change In Mass
% Change In Mass
12.5g
12.98g
0.48g
3.84%
12.65g
12.99g
0.34g
2.69%
12.33g
12.36g
0.03g
0.24%
12.73g
11.66g
1.07g
8.41%
12.34g
10.56g
1.78g
14.42%
12.63g
10.60g
2.03g
16.07%
Calculations
0.0 M
12.98g – 12.5g = 0.48g X 100 = +3.84%
12.5g
0.1 M
12.99g -12.65g = 0.34g X 100 = +2.69%
12.65g
0.25 M
12.36g – 12.33g = 0.03g X 100 = +0.24%
12.33g
0.5 M
12.73g – 11.66g = 1.07g X 100 = -8.41%
12.73g
0.75 M
12.34g – 10.56g = 1.78g X 100 = -14.42%
12.34g
12.63g – 10.60g = 2.03g X 100 = -16.07%
12.63g
Observations
In this practical the following observations were made.
The samples in water appeared to become more translucent and became turgid in touch and appearance. This is due to the vacuole gaining water as the membrane expands to the cell wall causing it to swell. These changes became less obvious in the tissue samples as the sucrose molarity increased as the amount of water needed for equilibrium would be less.
The samples in the higher ranged sucrose molarities appeared to be weak and flaccid compared to the samples in weaker sucrose solution. This indicates dehydration in plant cells. There was also some minor discolouration, which was brown in appearance. I believe this would be an example of plasmolysis. As the cell is in a hypertonic solution the vacuole will loose water and the plasma membrane in the cell will recede to the centre of the cell thus making the cells themselves smaller in appearance and as some of the cells die they will cause discolouration.
Discussion
Erroneous Variables
Size of samples e.g. the thickness of the cuttings could have been kept at a consistent amount, obviously the thicker the samples the more solution would have been needed to fully immerse the samples so the solution can access the core of the root samples and the time would also have to be adjusted to compensate for this as the solution would take longer to permeate the core of the sample itself.
Mixing the solutions. As the solutions were mixed as part of the practical this could lead to errors if they were slightly incorrectly mixed. I believe this was the case for the result for 0.25 M