Carrying out the investigation
Equipment:
· Cutting tile – to cut the potato on so no lab surfaces are damaged
· Knife – to cut the potato cleanly, for accurate results
· 5ml Measuring cylinder – to measure the solutions accurately, also to produce more accurate results
· Distilled water – is mixed with the sucrose to produce sucrose solution, as part of the experiment
· Sucrose – is mixed with the water to produce sucrose solution, as part of the experiment
· Potatoes – Osmosis and Plasmolysis will occur due to the presence of the potatoes in this experiment
· Tissue paper – to dry the potatoes before and after Osmosis takes place as not to cause inaccuracies in the results
· Balance – to weigh the potatoes accurately, for accurate results
· Cork borer – to cut out potato cylinders evenly, for fair test reasons
Safety:
Safety is very important in any experiment, even if the experiment seems to be very harmless. And that is why we take this into consideration, no matter what. We will be using a very sharp knife, which could injure someone if it’s not handled properly. And we will also be careful that the solutions don’t get inside our bodies, just in case, because we are not fully aware of the damage it could do to us.
Variables:
In our experiments we chose to use a sucrose concentration variable. We were given pre-measured concentrate of sucrose solutions, measure accurately (to 2d.p.) using a syringe. The range is from a concentration of 0% sucrose to 10% sucrose solution.
Fair Test:
First of all, and most importantly, we will have to get the measurements and the weights of the solutions and the potatoes as exact, and as accurate as possible. We will try and get the measurements of the potatoes as accurate as possible for every single potato by evenly cutting the potato pieces. And we will be using a very sensitive balance so that we can get the best readings possible.
But I believe one of the most important step in the fair testing is to make sure that the potato is dried properly before weighing. This is because if the potato is not dried properly it will give an inaccurate reading on the scale, giving future bad results. The potato must be dried thoroughly using a paper towel. When using the balance, we will make sure that the balance is reading zero before we put the 3 potatoes on it. The balance will also have to be wiped before and after the weighing of each potato. This is so that we don’t get a false reading, with the weight of the potatoes and the previous readings.
Getting and experimenting with the exact measurements of molars and water is vital to this task. If the volume of one solution in a test tube is higher or lower than another, it will affect the pattern of results later on.
We will also make sure that the potato is fully covered by the 6 different kinds of solutions. This is because, is the potato isn’t covered up by the solutions, the effect of osmosis might not occur to the fullest.
Small things such as a dirty test tube, and a slightly cracked measuring cylinder could still affect the results, and therefore we will take these into account as well.
Control:
We will need to have a control experiment in order to assess if we have done the experiment correctly. By comparing our results with other groups we will be able to see if we have made any mistakes in the process of our experiment, and if we have, how we can improve our methods. This goes the same for all the other groups whom we will be sharing our results with.
Measuring Apparatus:
- A ruler was used to accurately measure the length of the potato cylinders to the nearest mm.
- Accurate weighing scales (2d.p.) were used to measure the mass of the potato cylinders both before and after the experiment.
OBTAINING EVIDENCE:
Results
Table of Results: (anomalies are shown in red)
Experiment 1
Experiment 2
ANALYSING EVIDENCE AND DRAWING CONCLUSIONS:
On the next page is a graph showing the change in mass of the potato cylinders for Experiment 1, with a blue comparison line showing roughly what results should have been produced, and anomalies are circled in red.
On the page after is a graph showing results in the same way for Experiment 2.
Conclusion:
After Osmosis:
Experiment 1: As the concentration of sucrose increased (0% - 4%), the % increase in mass decreased, and reached 0 at 5% concentration. From there (6%-10%) the % decrease in mass increased, and reached its peak at around 9%. The anomalies were at concentrations of 2%, 6% and 10%, showing that, overall, this experiment was very inaccurate.
Experiment 2: As the concentration of sucrose increased (0% - 4%), the % increase in mass decreased dramatically, but reached 0 at 5% concentration as well. From there (6% - 10%) the decrease in mass increased dramatically and reached its peak at 8%. These dramatic increases and decreases are all due to anomalies from inaccurate results. The anomalies were at 0%, 8% and 10%.
My predictions were, in general, correct. But due to the large number of anomalies and inaccuracies, it is hard to say how close my prediction was to the actual results of the experiment. This means a true pattern is hard to find. But a rough patter can be drawn from experiment 1: as the % sucrose concentration increases, the % change in mass decreases.
The water has diffused from the potatoes, through the semi-permeable membrane into the sucrose solution, causing it to decrease in mass at a steady rate. The anomalies can only be explained as being due to bad measurements or other variables in the experiment, which have been carried out inaccurately.
Experiment 1 seems to be far more accurate and closer to what the results should have been if the experiment was 100% accurate (this can be seen by comparing the blue and red lines on the previous graphs). Excluding the anomalies, experiment 1 was closest to the accurate results between 2% - 4% and 8% - 10%. The lines crossed once at around 9%, at the value of –8% decrease in mass.
Experiment 2, on the other hand, is completely inaccurate. The anomalies are very large and throw the results line way off course. Even though the lines cross, this is only due to an anomaly dragging the line way off the bottom of the graph’s scale.
EVALUATING EVIDENCE:
Evaluation:
Most of the results obtained were very inaccurate and did not come out as well as was predicted. This may have been for a number of reasons.
Problems may have begun to occur at the very beginning of the experiment when first cutting the potatoes. The potatoes may not have been cut accurately enough or measured to the nearest mm. They may also not have been dried thoroughly enough so they may have already had excess weight, leading to poor quality mass readings. Weighing the potatoes may also have lead to inaccurate results, as water from the potatoes had built up on the weighing scales creating extra weight and more inaccurate readings. The potatoes may also have begun to mould. There may also have been some dead cells already in the potatoes, which obviously would not have been able to carry out Osmosis. All of these errors may also have occurred after Osmosis had taken place when the same things such as weighing and drying had been done.
The only reason I can see for anomalies occurring is poor measurement taking and bad experimentation in general. Many of the things above may have effected the results considerably, and some may have caused anomalies. The precise anomalous results are described in the conclusion, and can be found on the graphs for both experiments.
I would say that if there were an alternative way of carrying out this experiment it may have been better to use it, as the results gathered were of a low quality and inaccurate.
More meaningful results may have been achieved if more care and a lot more time was used for this experiment, this would have meant that more time was taken making sure that all procedures were done thoroughly and correctly. Each step would need to have been taken very slowly and carefully, and each part of the experiment would be checked over for inaccuracies. If any inaccuracies were found at any time in the experiment they should be corrected and changed if need be. This would have produced far more accurate results. From this a proper pattern could have been concluded and graphs would be easier to draw.
I do not believe that the procedure for this experiment was the best one to use, considering the results gathered. The results may be more accurate if the experiment was done several times. Changes to experiment could also be made to provide more meaningful results:
- A larger range (e.g. 0% - 30% sucrose concentration)
- Different potatoes (different type or size may produce more accurate results
But rather than carrying out the same experiment again, with there always being a possibility of more inaccurate results, an alternative experiment could be carried out. This experiment, instead of measuring a change in mass of the potato, a change in length of the potato could instead be measured. This would require a different method and equipment list. Weighing scales would not be required, as the mass is not being measured. Also, the results would be in an entirely different form and the graphs would produce different patterns and curves. Essentially the experiment would be much the same, with the same control, fair tests and safety, but it may produce a more accurate set of results to show the affects of Osmosis, Diffusion and Plasmolysis on a potato.
I am not sure of my results, they are not what I expected to be and I certainly would not bet on them being correct. This is mainly because of the peculiar set of results shown on the second graph.
My results cannot lead to a confident conclusion as they are inaccurate and of a poor quality.
The data was reasonably accurate to some extent, considering that any number of the mistakes mentioned above may have been the cause of anomalies and inaccuracies in the results. The data also shows patterns of some sort, meaning that the experiment was not a complete failure, and that some conclusion can be drawn for this individual experiment, even though a general conclusion for Osmosis in general is impossible to make out from these results alone.
Bibliography:
Biology Exercise Books 1, 2 and 3 (original date 7th September 01)
Encyclopaedia Britannica Deluxe CD2000 (released 00)
The Oxford Popular English Dictionary
Oxford University Press (originally printed 98, reprinted 00)