- Test-tube A: 0% (i.e. distilled water)
- Test-tube B: 5% sugar solution
- Test-tube C: 15% sugar solution
- Test-tube D: 20% sugar solution
- Test-tube E: 30% sugar solution
6. Leave each potato chip in the test tube for 30 minutes.
7. Remove the potato chips.
8. Dry the chips with the tissues and re-measure the potato chip weights, record the weights in a table.
9. Re-measure the potato chips to the nearest millimetre and record in a table.
10. Empty and clean the test-tubes
11. Repeat this method three times.
To make the sugar solutions you dissolve the percentage of sugar you want in 100cm³ of water. For example, to make a concentration of 30% you would dissolve 30grams of sugar in 100cm³ of water. To make this accurate you should use a measuring cylinder to measure the water that goes into the beaker.
Explanation of Method:
I came up with this method from a previous experiment done in class. I am going to use potato chips as it is easier to cut potato chips from the potato rather than using a potato itself as it is hard to find five potatoes all the same size. Potato chips are also easier to measure than potatoes.
In my preliminary work done in class we only tested three different concentrations, 0% concentration (i.e. distilled water), 2% concentration and a 10% concentration. Then we pooled our results as a class and averaged them. This was a mistake, as we never started off with the same length so our results were inaccurate after averaging them. This told me that all my potato chips should all be the same length and have the same amount of solution covering them in order to make my experiment accurate.
I decided to use five solutions as this way I can have a control, a low, a high and two medium concentrations. This is basically expanding on the preliminary experiment we did in class. I chose to cut my potato chips to 30mm as this is a shorter length I chose in my previous experiment (approx. 45mm). I chose 20cm³ of solution to cover the chip because I felt it was necessary to cover the entire potato chip and provide it with excess, I felt that 20cm³ of solution satisfied this demand.
I chose to weigh my chips before and after to actually see how much water is absorbed during osmosis. I felt it necessary to dry them after removing the potato chips from the solutions so as to absorbed the solution remaining on the outside of the potato chip. It is essential to record my results accurately in a clear table so that it is easy to draw a conclusion. I chose to record my change in length in millimetres because this is what the original length is measured in.
Fair Testing:
To create a fair test certain aspects of the experiment will have to be kept the same whilst one key variable is changed. In this experiment I have chosen to vary the concentrations of the sugar solution. This should give me a varied set of results from which I can draw conclusions.
To make sure this is a fair test we should have a control (this is the potato chip in the distilled water). It is also important to measure the weights of the potato chip accurately before and after the experiment to make sure the results are reliable.
Safety:
In order to make this experiment safe I must make sure all the glassware is away from the edge of the work surface to avoid knocking them off and smashing the glass. I should be wearing a lab coat and safety spectacles to protect my clothes and eyes from potential spillages and broken glassware. When I am using the scalpel I should be careful to avoid cutting myself.
Reliability:
I have tried to make my experiment as reliable as possible by using distilled water to eliminate any variation in the water. I am going to measure the amount of solution needed by using a measuring cylinder because it gives me more accurate readings than for example a beaker. I will wash and clean the measuring cylinder between experiments so as not to contaminate the next solution. I will use a measuring cylinder that is close to 20cm³ (my required amount) so I can measure the solution out accurately. I am also going to use the same type of potato etc. (see fair testing). To make my results more reliable I am going to repeat the test three times and take averages.
Other Sources:
As well as my class work and the previous experiment we attempted I also used biology textbooks (Biology for You – by Gareth Williams and GCSE Science the complete revision & practice). I also used the BBC bite size website. These also state that osmosis occurs where there are varying concentrations either side of a selectively permeable membrane and then water will pass from a higher to a lower water potential. Therefore backing up my prediction and reasoning behind it.
Skill Area O: Obtaining Evidence
Preliminary Work
For my preliminary work I used a 30mm potato chip. Preliminary work is important to do so that you can foresee if any complications could arise whilst doing your experiment. Complications that may occur are; the potato chip getting wedged in the test-tube, if the solution would overflow when the potato chip was added, that osmosis might not occur in the allowed time etc.
My original plan was that the potato chips would be left in their solutions for thirty minutes and then removed. This however proved to be too short a time for osmosis to occur in any huge amount. This can be seen in the table below.
This table shows me that in thirty minutes the results produced are too minute to conclude my prediction.
Modifications
As a direct result of the preliminary experiment I have learnt to increase the time needed for osmosis. This is because the results I obtained from my preliminary work did not show a clear trend, this could be because osmosis was still occurring. Therefore I felt it appropriate to increase the time limit that the chips are in their solutions in my plan. Other than this I did not need to change any other part of my plan.
Modified Method:
- Core five potatoes chips using the potato corer.
- Using the scalpel and the ruler on the tile cut the potato chips to exactly the same size (30mm in length).
- Taking the test tubes label them A – E so as to get accurate results.
- Weigh each potato chip and record their weights in a table.
- Place each potato chip in a test-tube each containing 20cm³ (this should be measured with a measuring cylinder) of a different sugar solution.
- Test-tube A: 0% (i.e. distilled water)
- Test-tube B: 5% sugar solution
- Test-tube C: 15% sugar solution
- Test-tube D: 20% sugar solution
- Test-tube E: 30% sugar solution
- Leave each potato chip in the test tube for 12 hours.
N.B. to ensure a sensible time for collecting data this experiment either needs to be set up early in the morning or late at night.
7. Remove the potato chips.
8. Dry the chips with the tissues and re-measure the potato chip weights, record the weights in a table.
9. Re-measure the potato chips to the nearest millimetre and record in a table.
10. Empty and clean the test-tubes
11. Repeat this method three times.
To make the sugar solutions you dissolve the percentage of sugar you want in 100cm³ of water. For example, to make a concentration of 30% you would dissolve 30grams of sugar in 100cm³ of water. To make this accurate you should use a measuring cylinder to measure the water that goes into the beaker.
Accuracy
The way I have ensured maximum accuracy is to use 20cm³ is to measure this using measuring cylinders. I used separate measuring cylinders so as not to contaminate the solutions, which may of affected the experiment. Also, and most crucially, I am repeating the experiment three times so as to obtain maximum accuracy and then I am taking an average figure to plot on a graph.
Recording Evidence
I think that a clear and concise way of recording my data would be to put the data I have obtained in a table. The original table I produced can be seen overleaf, but I have also separated the data into other tables, which can also be seen overleaf.
Table to show all of my data collected
Table to show how osmosis affects the length of a potato chip
Table to show how osmosis affects the weight of a potato chip
Observations
When I placed the potato chips in their solutions they were all firm and waxy cream in colour. I noticed that the potato chips (this means on every test) in the 20% and 30% solutions where floating. The potato chips (again, on every test) in the 10% solutions were “half floating”. This is because the water is getting denser with the amount of sugar in it, whereas the potato chip’s density remains the same.
When the potato chips were removed from their solutions all of the potato chips had sunk to the bottom of their test tubes.
When chips in the 20% and 30% solutions were removed they were floppy, therefore their cells were flaccid. The potato chips removed from 0% and 5% solutions were firm therefore their cells were turgid. The chips in the 10% solutions were neither.
Anomalies
From my table I can see that the three cells highlighted in red are possibly anomalies.
The reason behind 33† being a potential anomaly is that the other two results I obtained from the chips in the 20% solutions decreased in length to 24mm. The same situation applies with 33†† as the other two tests produced results of 23mm and 22mm. 1.69††† also seems like anomaly because the weight produced from the other two tests in the 20% solutions gave lower results of 1.62g and 1.63g, which are much lower than 1.69g.
Skill Area A: Analysis Evidence
Analysis
I had initially predicted (on pages 2-3) that as the concentration of the sugar solution around the potato chip decreases, the size of the potato chip would increase. Also, the weight of the potato chip will increase as the concentration of the sugar solution decreases.
There are various ways of presenting the data I have achieved and each have individual qualities. The first way I have presented my data is in a table format, this is very useful for obtaining exact numerical values for calculations and so forth. But from the table it isn’t easy to identify any trends, so I plotted the data I felt would produce trends on graphs therefore making it easier to read. To these graphs I added trendlines to see if my data was within the predicted ratios. These graphs can be seen overleaf.
I was able to identify certain trends from the evidence. The graph entitled “Average Change in Mass Against Concentration” shows quite clearly the relationship of how increasing the concentration of the sucrose solution forces the potato chip to lose more mass. This trend can be summarised as: If you increase the concentration of the sucrose solution, the mass of the potato chip will decrease. The trendline is not a straight line therefore indicating to me that the graph shows no direct proportional or indirect proportional link. This could be that my points are slightly wrong and I have made an error.
From the graph entitled “Average Change in Length Against Concentration” shows me, again, clearly how as the concentration of the sucrose solution increases, the length of the potato chip decreases. The average change in length against the concentration could be summarised as: If you increase the concentration of the sucrose solution, the length of the potato chip will decrease. Once again, the trend line is not straight therefore indicating that there isn’t a direct or indirect proportional link between the two.
Looking at the chart entitled “Comparison of Length against Mass” there appears to be a proportional difference between length and mass at the 0% and 10% concentrations. At 5% the difference is greater this could be caused by an error on my part. At 20% the mass increases in steepness whilst the length remains more of a gentle curve. At 30% the length and mass are identical.
I added trendlines to the “Comparison of Length against Mass” graph, but I found it too difficult to read so I have excluded it from my conclusion but it can be found on page 21.
Conclusion
From my investigation I can conclude that it was reasonably accurate, due to the graphs as the points on the graphs follow the shape of the trendline. My conclusion is that as the concentration increases the length decreases and so does the potato chips’ mass. This statement can be backed up by my results. All of this evidence backs up my initial prediction (which can be found on pages 2-3 and referred to on page 16).
I noticed from the first two graphs that the points for the 20% concentration and the 30% concentration are relatively close together, therefore making the trendline start to trail off towards the end of the graph. I feel this was due to the fact that the cell walls were unable to expand or contract anymore, so therefore the potato chip cells put up more resistance and prevented the shape from being altered further.
I would be interested to continue with the concentrations to see if nearer the extremities i.e. the higher concentrations, whether the results would show a continuation of the trend that is beginning to appear in my experiment, which is nearer the end of my graph the trendline begins to trail off. I would expect to see a straight line where even higher concentrations are used. I expect to see this because there must become a point where osmosis cannot occur, because the cells become too flaccid and cannot contract anymore.
Skill Area E: Evaluating Evidence
Evaluation
I do believe that my results were accurate enough to support my prediction. I am of the opinion that the procedure I used for my experiment was applicable, as I was trying to discover whether the concentration of the surrounding solution had an affect on osmosis in potato tissue.
The proof for this can be found in the graphs and tables that I have produced. The graphs were produced using averages from three experiments. The experiments produced results that were all convincingly similar with one or two anomalies. I have accounted for these anomalies in my analysis. My results show that I was consistently accurate with my experiments as there is little chance that I could have completed every experiment incorrectly.
My experiment was suitable because it provided me with the information I needed to confirm my initial predication (which can be found on pages 2-3). There are however places and ways that errors could have occurred. First starting with the concentration. It is possible that when I made-up my sucrose solutions they were not accurate. They might not have been accurate because I could have used the wrong amount of distilled water – which should have been equal to 100cm³ or I might have measured the amount of sugar incorrectly. Also a major factor was the cutting of the potato chips. I could have easily left a larger surface area on one and not on the others. Therefore one potato chip would be at an advantage as a larger surface area induces more osmosis to occur. One way to avoid this would be to use complicated machinery to weigh and cut the potato; although this would have been beneficial, this wasn’t practical. So by just taking extra time and care with the cutting would make the experiment more accurate.
Logically I could have done more work. I could have repeated the experiment more times to gain a more accurate average. Also, if I had tested a wider range of concentrations it may have made my results more accurate. Also I could experiment with exposing the same weight pieces, but with different surface areas. This would be helpful to do, as it would show if surface area greatly affects osmosis.
If I were to repeat the experiment again I would go to a higher range of concentrations as explained in my conclusion on page 22. I would also use concentrations with smaller differences so I could plot a more accurate graph.