However when the cube of Solanum tuberosum is placed in an isotonic solution, a solution with the same concentration of solute as the cell, water diffuses in and out of the cell as a constant weight resulting in no change of the cells mass. Considering the low amount of sodium found in raw potatoes it is possible to predict that when surrounded by the high concentrations of sodium water that the potato cube will shrivel and decrease in mass. Taking in to consideration the almost equal concentrations of sodium within distilled water and that of the potato it is also plausible that the water will prove an isotonic solution and the potato will not change in weight.
Investigation Variables:
TABLE 1: Practical Investigation Variables
1.2 TABLE 2: Control Treatment of Variables
Control Experiment: The control for this experiment is the distilled water test. This will be used to judge any changes caused by the higher concentrations of sodium in the solutions surrounding the potato samples.
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Experimental Method:
Materials:
Apparatus Required Quantity
25 ml Test Tubes 25
Large potatoes 2
Apple corer 1
Cutting knife 1
50 ml of distilled water 1
50 ml of 10% sodium solution 1
50 ml of 20% sodium solution 1
50 ml of 30% sodium solution 1
50 ml of 40% sodium solution 1
10 ml Measuring cylinder 1
Electronic balance + 0.01 g 1
Ruler (300 mm) + 1 mm 1
Cutting board 1
Test tube rack 1
Paper towel 5
Practical Safety and Risk Assessment
Refer to Appendix A - QAHS STUDENT ACTVITY RISK ASSESSMENT and PRAC ORDER FORM
Method:
- First gather all equipment and place gently on surface.
- Then using the apple corer, remove amounts of potato and using the knife, slice so that the potato pieces are 1 cm long.
- Once 25 pieces of potato have been cut, measure and record the mass of the samples using the electronic balance.
- Next pour 10 mls of distilled water into five of the test tubes and add one cube of potato to each test tube.
- Then repeat this step using the different concentrations of solution. Starting with 10% concentration until five of each of the test tubes are filled with a different concentration.
- Leave the samples for 24 hours.
- Remove each sample from its test tube and record the change in weight.
- Lastly, pack up and remove all equipment.
Diagram 1: Experimental set up
- Data collection and processing
Qualitative Data: Setting up- Some potato pieces where brownish in colour and so were not used in the experiment and replaced with fresher potato pieces.
After testing- The 10% concentration samples seemed to have blackened and the sodium solution had taken on a darker colour.(Appendix C) In all the samples salt crystals had started to form along the rim of the test tubes and the potato samples had shrunk in size.
Quantitative Data: Table 1: Initial Weight + 0.001 grams
Table 2: Final Weight + 0.001 grams
Processing Raw Data:
Presenting Processed Data:
Table 3: Average Weight before and after osmosis + 0.001 grams
Graph 1: Average Weight before and after osmosis + 0.001 grams
This graph demonstrates the relationship between the weight of the potato samples before and after the experiment took place and osmosis occurred. It displays the large decrease in weight in the salt concentrations after osmosis and shows that higher concentration the larger the difference between initial weight and final weight after osmosis. From the graph it is possible to determine that the higher concentration the greater amount of water will diffuse via the permeable membrane into the solution.
- Conclusion and Evaluation
Statement: The aim of this experiment was to ascertain the effect different concentrations of salt solutions have on Solanum tuberosum samples and whether or not the higher the concentration (the highest in this experiment being 40%) the more water would diffuse via the process of osmosis into the solution causing the potato sample to lose weight. The data and graphs from this experiment show that the higher in concentration the larger the loss in weight over 24 hours. This supports the predicted hypothesis however the second claim that distilled water would have the same weight was proven to be incorrect.
Explanation: The original hypothesis was supported in this experiment as the results were reflective of those expected. However the initial belief that distilled water would not undergo a loss in weight as the distilled water was predicted to be an isotonic solution. This suggests that the knowledge of the relationship between the salinity of the Solanum tuberosum and distilled water was under researched and more researched needed to be conducted regarding the salinity of the actually potato in order to determine what liquid would be completely isotonic. From the large decrease in weight of the Solanum tuberosum as osmosis occurred it is plausible to reach the assumption that the distilled water itself also hypertonic solution in comparison to the potato cells.
However the data from this experiment supports the hypothesis that solutions of high concentrations of salt, i.e. 40% salt solution. Though the average weight of the potato samples fluctuate, Table 3, displaying the actual difference between these weights makes it apparent that as the concentration became stronger the difference in weight increased by a number of grams. In the distilled water sample, the difference between the original and final weight was that of merely 0.218 grams + 0.001, however when the concentration was increased to 40% the difference in weight was equal to 0.408 grams + 0.001. This increase in difference is due to the water molecules attempting to balance out the cell by moving through the cells permeable membrane, (Bowen, 2000)
Reliability: This experiment can be considered as reliable due to the large number of test samples used and this reduces the chance of random error affecting the results. However as this experiment involved a large amount of measuring using equipment, it is highly plausible that systematic error could have resulted in the weight recorded being inaccurate or an unsuitable amount of solution being used. This could cause the concentrations to be incorrect or some the data as being regarded irrelevant.
When measuring the pieces of Solanum tuberosum it is possible that the water or mixture contained within the potato leaked out while being measured on the scales and this random error may cause some of the results to be inaccurate thus registering the data as unreliable.
In this report, calculations involving the mean and standard deviation were performed in ordered to produce more useful results to be displayed easily in the form of graphs. This was done through the use of a calculator and therefore can be regarded as quite accurate and reliable. The low standard deviation of some of the results indicates that that this experiment was of high precision and allows the data to be regarded as fairly accurate. However the fairly large standard deviation on the average results of the 30% concentration of salinity suggests that the data was fairly varied and therefore may not be able to be considered reliable enough to support the hypothesis. However considering that all points of data incurred a drastic decrease it weight it is plausible to assume that the data is accurate enough to be used in order to support the suggested hypothesis.
Limitations/Weaknesses: The main possible limitations to this experiment are due to the high likelihood of human error that would have occurred during the experimentation period. One of these could be due to any difficultly measuring liquids and the inaccurate reading on a meniscus, though this could have affected the amount of solution added to the Solanum tuberosum it is quite unlikely that this would have a dramatic effect on the end results of this experiment.
A limitation to this experiment may be the sudden change of equipment from test tubes to measuring beakers as the experiment was originally designed to be tested using small test tubes, this could have altered the amount of solution covering the Solanum tuberosum however as all samples were tested in the same type of equipment the chances of this altering the outcome of the experiment is rather unlikely.
By testing the experiment in only one location with the same temperature and humidity, the results can only be generalised as to the effect of osmosis on Solanum tuberosum in that same location rather than places with other variables such as biotic factors. As the results did include some high standard deviation and the size of the potato pieces was dependant on the experiment conductors accuracy when cutting it is difficult to determine how ecologically valid this experiment it in concern with other situations.
Modifications to the Experiment In order to improve this experiment it is necessary to alter the experiment and test under different conditions in order to be able to generalise the results. It may also be required to repeat this experiment with different solutions and concentrations in order to verify the trend of higher concentration the larger the decrease in weight. This repeat of experiment would allow for a build up on the original hypothesis in order to confirm its reliability. It may be beneficial to determine the actual salinity of the Solanum tuberosum itself and from there be able to create a control solution in order to compare the results with that of the different concentrations.
As there was a fairly large standard deviation for some of the initial and final weight of the Solanum tuberosum samples it is difficult to confirm the precision of this experiment. Considering this, it may be possible to improve this experiment by taking precautions in order to make the initial potato samples are similar in weight and this would make it easier to compare results and verify the trend.
Bibliography:
Bell, Rebekah P., et al, Investigations into Biology 121. Chattanooga: University of Tennessee at Chattanooga , 2004
Bowen, R. "Osmosis." arbl.cvmbs.colostate.edu. N.p., 2 July 2000. Web. 31 Oct. 2010. <http://www.vivo.colostate.edu/hbooks/cmb/cells/pmemb/osmosis.html>.
"Hypertonic - definition from Biology-Online.org." Life Science Reference - Biology Online. Biology Online, 16 Apr. 2009. Web. 30 Oct. 2010. <http://www.biology-online.org/dictionary/Hypertonic>.
Appendix:
APPENDIX A Risk Assessment and Laboratory Order Form
APPENDIX B Diagram set up
APPENDIX C Salt build up on the rim of measuring beakers
