If the potato strip is placed in a highly concentrated sugar solution (e.g. 0.15M) then water molecules will diffuse from the cells in the potato strip into the sugar solution. The sugar solution contains many sugar molecules and so therefore there are few free water molecules. This gives a low water potential. The solution in the vacuole of each potato cell contains fewer sugar molecules so there are many free water molecules giving a high water potential. The definition of osmosis says that water molecules will always move from a higher water potential to a lower water potential. Based on this theory, predict that water will diffuse out from the cell vacuole and into the surrounding sugar solution. The cells will become flaccid (The cells may eventually become plasmalysed ). The potato strips will decrease in mass.
Results
The first set of results for each quantity of sucrose solution is the preliminary experiment and the second is the actual experiment.
Results of both preliminary and final experiments in average form:
Conclusion
Based on my results I can reach a conclusion to this experiment. There is a definite link between the concentrations of sugar solutions and the effect on potato tissue.
As the sugar solution concentration increases, the mass of potato chips decreases
As the sugar solution concentration decreases, the mass of potato chips increases
This is due to the Osmosis theory
Osmosis is the movement of water molecules from a high water potential to a low water potential across a semi-permeable membrane
Diagram of Osmosis
Sugar molecules pass through pores
Partially permeable membrane
Water molecules
Fewer water molecules go
in this direction
More free water molecules go in this direction Hydrated sugar molecule High concentration of free water molecules Low concentration of free water molecules
Turgor Pressure in Plant Cell
Movement of
Water surrounding cell water
High water potential cell wall
Cytoplasm Cell
membrane
Vacuole Low
When a potato chip is placed in water, the mass of the chip will increase. There is a high water potential in the water, (low sugar concentration) and a low water potential in the cell vacuole (high sugar concentration) of the potato. Water will move from the higher water potential to the lower water potential, and therefore enter the cell vacuole. The cells will become turgid.
Plasmolysis in a plant cell
Movement
Sugar solution surrounding of water Cell wall
Cell. Low water potential
Cytoplasm Cell
Cell membrane
Vacuole
When a potato chip is placed in concentrated sugar solution, the mass of the chip will decrease. There is a low water potential in the sugar solution, (high sugar concentration) and a high water potential in the cell vacuole (low sugar concentration) of the potato. Water will move from the higher water potential to the lower water potential, and therefore water will exit the cell and enter the sugar solution. The cells will become plasmolysed.
In general, my results did support my original prediction. My prediction and results both say that:
As the concentration of sugar solution increases, the mass of potato strips will decrease
As the concentration of sugar solution decreases, the mass of potato strips will increase
In my prediction, I stated that I thought the results would give a straight line on a graph. After obtaining my results, and drawing the suitable graph of sugar solution concentration versus mass change, I can say that the graph gave a straight-line. This shows that the results are proportional. In my prediction, I mentioned that I thought that if the concentration of sugar solution were doubled, then the percentage mass loss would double. This was not the case.
In my hypothesis, I gave quite precise predictions of results by using my preliminary results. Here is a table that compares my predicted values to that of the actual results obtained.
It shows that the quantitative predictions were fairly accurate.
Table Comparing Prediction and Results
Evaluation
I will now evaluate all of the work that I have carried out. I will begin by commenting on the accuracy of my results. I think that my results obtained were as accurate as possible, but inaccuracy may have arisen from various possibilities:
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The mass measurement equipment was not very accurate. Even though the mass scales gave readings to a hundredth of a gram, the mass of each potato chip would constantly change slightly on the scales. Movements of air caused the masses to alter.
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Excess water on the potato chips may have caused inaccuracy in the mass. The excess water/sugar solution left on the potato chips after being submerged in the solutions may have increased their final masses, and so disrupting the experiments. I did ‘dab’ the chips gently with a paper towel before recording their final mass, although I am not certain that the entire surplus was removed successfully.
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The potato chips may not have been exactly 50mm in length. I tried to measure the potato chips with immense accuracy, although one can never be sure that they were all cut exactly 50mm. I used an accurate ruler and a sharp scalpel and took away any errors of judgement, but this is still an area where inaccuracy would have appeared.
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Some chips came from different potatoes. I think that this point is quite minor. The different potatoes used may have had an influence giving inaccurate results. This problem could not have been avoided because only a limited number of potato chips can be cut from a single potato. One potato may have had a disease causing bizarre results to be taken. I do not think that this happened though.
When I studied my graph, I noticed that the result for 1.0M might be anomalous. This unexpected result could have occurred due to many reasons, all of which are stated above. Some of the individual results shown on the tables on the third page were slightly anomalous but these were made normal by creating an average result. This means that my results were reliable – I did each experiment three times and then made an average.
I did not record any measurements that were not following the theory of the concentration of sugar versus the mass change of the potato chips i.e. whenever the concentration of sugar solution was increasing, the mass percentage loss was always increasing. Whenever the concentration of sugar solution was decreasing, the mass percentage loss was always decreasing. There were no anomalous results in that sense. I cannot find any other points to comment on with unexpected results.
If given time I would like to investigate how the period of time the chip were submerged in the sugar solutions effect the potato cells. Osmosis may have continued further in the cells after the 30 minutes that I left the chips for. This would be interesting to investigate.
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