Also, safety is important, when cutting with the scalpel and the cork borer a tile was used to cut on so damage to the bench or fingers is less likely.
Prediction
I predict that the graph will show a small slope at the top and at the bottom because at the top there would be the cell stopping taking water at the top because no more can get in (turgidity) and at the bottom the cells have lost all the water they can and so no more can be lost (plasmolysis).
Diagram
Method of Obtaining Evidence
Points of Accuracy
- Use the same cork borer
- Put in the same area to soak the potato (so it is under the same conditions)
- Same volume of solution
- Roughly the same surface area
- In the solution for the same amount of time
- The solution was made in bulk to make the concentration more accurate.
- Used the same potato so that the potato pieces will have the same properties as each other (same concentration of water in the cells).
Method
- Conduct a test run to see what are the needed concentrations to get good results in the proper test.
- Use a cork borer to get some pieces of a potato (same potato) and cut them to the same length (3.5 cm).
- Weigh the pieces to the same weight (I did it to 0.9 grams) with electronic scales to two decimal places, cutting the potato as necessary to adjust.
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Put the pieces of potato in the different molar solutions in boiling tubes (0.1 - 0.9 molar solutions of sucrose) in equal amounts (25 cm3.
- Put three pieces in each strength molar solution so that you can compare the results later so that you are less likely to get anomalous results from your experiment.
- Leave the pieces in the solutions for the same amount of time (until the next lesson was what I did).
- Take the pieces of potato out of the solution and work out the change in the weight of the potato pieces using the electronic scales, then use the results to find out the change in the percentage of the weight in the potato cells which would show the rough amount of water absorbed.
Results
The results of the first test went missing so I do not have them to show
Analysis
In the experiment osmosis took place, the fact that the weight of the potato changed (due to change in the amount of water in the piece of potato) proves this since there was nothing apart from water and a small amount of sucrose in the boiling tube.
The potato took on more water at all concentrations of sucrose. This is abnormal because the potato would at some point start losing water through osmosis before it reached the osmotic balance (when the water leaving the potato is equal to the water entering the potato because the concentration of water in the cells and outside the cells are the same), this did not happen and the net movement of water seemed to be always into the potato.
The cells do appear to come close to plasmolysis (the cells losing so much water that they cannot be restored because the cytoplasm pulls away from the cell wall) near the end of the results so the predicted graph is right in the way it tapers off near the end but plasmolysis seems to be occurring while there is still more water taken on by the potato than lost, the point of plasmolysis should happen at a point when the potato has lost water.
The results cannot be relied on, because the results do not comply with a logical prediction of what would happen (or with other groups results).
I can’t get a conclusion from the results because there are too few results done and those appear wrong anyway so any conclusion drawn would have precious little evidence to back it up.
The graph does, though, show that a change in the purity of the water does affect osmosis taking place in potato cells.
Evaluation
There is a lot of room for error in the results, this is partly shown by the anomalous results.
Points of inaccuracy
Cutting the bored potato, 0.4 cm
First weighing, 0.004 g
The measuring of the solutions concentration
Measuring out the solution, 0.4 cm3
In the solution for different amounts of time, 1 min
Final weighing 0.004 g
Fair Test points used
- Use the same cork borer
- Put in the same area to soak the potato (so it is under the same conditions)
- Same volume of solution
- Roughly the same surface area
- In the solution for the same amount of time
- The solution was made in bulk to make the concentration more accurate.
- Used the same potato so that the potato pieces will have the same properties as each other (same concentration of water in the cells).
Points To Improve On
- I included only 4 solutions in the experiment, this range is far too few because I have to use a curved line to fill in a predicted curve instead of actual results.
- The tested solutions should have been from a more narrow range (narrowed by the tests) so that the guess work was not needed.
- I had to put the results in order as the results or the pieces of potato seem to have got switched at least once at some point.
- I only had one piece of potato per solution in the end so anomalies were more likely to occur.
- Potato held in the hand or left in the air may have dried before they were weighed a bit, this would affect the results.
Conclusion
If I did the experiment again I would; use each of the solution concentrations to get an accurate graph and put three pieces per solution to avoid inaccuracies as badly.
Two points that may have affected the results.
- The pieces were starting to smell badly afterwards, bacterial activity could have affected the cell structure and so the rate of osmosis
- The beginning weights could somehow be wrong, I don’t know how this could have happened but it would explain why the line is mostly the right shape but isn’t in the right place.