Prediction:
If the solution is:
- Isotonic – the potato will stay the same length and weight.
- Hypotonic – the potato will get larger, heavier, longer and become turgid.
- Hypertonic – the potato will get smaller, lighter, and shorter and become flaccid.
Results Table:
Graph:
Conclusion:
In this experiment we were trying to find out the concentration of cell sap. This is why we were putting the potato in different solutions to see if they absorbed the water, or gave out water. From this we should be able to tell the concentration of cell sap. From my results , I have drawn a graph of the percentages that I have calculated. It is obvious to me that two of my results are clearly wrong, and I have circled them on the graph. I have tried to draw a line of best fit from the results, and as you can see from the weight results, the concentration of cell sap should be 0.57m. From the length results, the concentration of cell sap should be 0.41m. The average of these is 0.485m, so this should be the concentration of the cell sap in a potato.
As I said in my prediction, if the solution is isotonic, the potatoes weight and length should stay the same, and this nearly happened, as for the 0.6m solution, the length of the potato did not change, but the weight did by only 0.2g. This could have been partly to me weighing them wrong, or not leaving them in long enough, but this solution was nearly isotonic. If the solution was Hypotonic, the potatoes length and weight should have gone up. For the solutions 0.2m and 0m, this happened, as they were hypotonic solutions. The Hypertonic solutions, 1m and 0.8m should have lost weight and gone down in length, as they did.
The reason that the solutions that were Hypotonic and Hypertonic changed in weight is because of the process called osmosis. Osmosis is the movement of water across a semi-permeable membrane from a region of high water content to a region of low water content. When the solution is Hypotonic, this means that it has a higher concentration of water than the potato that is in it. This means that the water will flow from an area of high water concentration to an area of low water concentration thus making the potato longer, and heavier, as the water has entered it by osmosis. When the solution is Hypertonic, it has a low water concentration, and so the water from the potato will move into the solution to balance out the amount of water, thus losing weight and length. When the solution is isotonic, it has the same water content as the potato, so there is no movement of water, and the potato should not lose weight or length.
The results that I got for this experiment were not very accurate at all, and not very reliable, I think that this is due to me not leaving the pieces of potato in the solutions for long enough, so my results were not that good. Saying this, the graph that I got, although not the best, I was able to get a pretty good line of best fit, and get a reasonable answer for the concentration of cell sap in the potato.
Evaluation:
In this experiment I had many errors, and these errors reflect in the results that I got. Firstly, I do not think that I was accurate as I should have been at measuring the length of the potato pieces, and also with the weighing of the pieces. The amounts of the solutions I thought were quite accurate, but when you put the boiling tubes next to each other, you could tell that some solutions had slightly more in than the next. This could also have affected my results. Not only this, but I do not think that I left the potatoes in the solutions for long enough for them to conduct osmosis to a reasonable degree of accuracy. I think that this was my biggest error that affected my results the most, and this is why the information that I got was not as good as it potentially could have been.
If I were to do this experiment again, this time I would make sure that I am more accurate with all my measuring and weighing, and that I leave the potatoes in the solutions for over 15 minutes, so that they have time to conduct osmosis. This should make my results reliable and accurate, and let me get a better graph. This should also mean that I get a more accurate result for the concentration of cell sap.
References:
1. Notes from class
