Prediction: I predict that the sugar concentration inside a potato cell is 0.25M because this is half way between the two extreme values we are testing. I also predict that anything more concentrated than 0.25 will decrease in mass (with 0.5M decreasing the most) and anything more dilute than 0.25 increasing in mass (0.0M should increase the most). The chips in the 0.0M solution will become turgid and those in 0.5M will be flaccid because they have plasmolysed. I think this will happen because water moves to the area where there is highest sugar concentration.
Measurements: In the experiment I will be taking two set of measurements. I am going to weight the potato chips before the experiment, and after. This should mean that I will be able to calculate the percentage mass change of the potato.
To ensure I have accurate results I will repeat the experiment several times. This makes any anomalous data noticeable so I can exclude them from the study. I am going to do 6 solutions (as previously mentioned) and for each solution I will repeat 3 times. This means that I have enough reliable results to create a good graph.
Apparatus:
18 * flat bottomed tubes
18 * chips
Cork Borer size 4
Measuring cylinder
White Tile
Scalpel
Potato (however many it takes to make 18 chips)
Ruler
Weighing Scales
Sugar concentrations of 0.0M, 0.1M, 0.2M, 0.3M, 0.4M, 0.5M.
Method:
- Collect Apparatus.
- Cut out chips – all same length (3 cm), take off skin
- Pour out 15ml of sugar concentration into three tubes. Label each tube with number and strength of solution.
- Repeat for other chips and tubes.
- Weigh and record mass of each chip.
- Come back in 12 hours and re-weigh.
The pilot run that I conducted at the beginning helped me in two ways. The first was it provided me with the size of cork borer that I need. I also showed me that I would need to do lots of repeats in my final experiment. The results I got from that were useful because they showed me that. In my final experiment I shall repeat results so anomalies are excluded and a trend recognised.
Fair Test: In my final experiment I will need to keep these factors the same; the volume of liquid, the diameter of the potato chip (using the same cork borer throughout will solve this one) the length all the chips are in the solutions and the length of the chips. We are doing three repeats so that any anomalous results can be seen and 6 concentrations will allow us to plot a graph.
Safety: In the experiment, there are a few things I will nee to look out for. Both scalpels and cork borers are very sharp, I should not cut/bore straight onto my hand or the table. Instead, I should use a white tile, this will prevent me from harming myself or the desk. Also, if any glass test tubes should break, I should be very careful and clear up.
-ANALYSIS
Conclusion: The trend of my results is as follows; at low sugar concentration the potato increased in mass, however at high sugar concentration the potato decreased in mass.
For example, at 0.0M the potato cells increased by 28.6% and at 0.5M they potato cells decreased by 16.1%. Due to there being more sugar inside the cell, those cells in sugar concentration of 0.0M have gained water, meaning they have increased in mass. They became turgid and therefore give support to the cell wall. The 0.5M on the other hand, have lost water, due to there being more sugar outside the cell. This leads to the cell plasmolysing and becoming flaccid.
On my graph, there is 0% change in mass at 0.38M, implying that the water balance is the same inside the cell as it is outside. Meaning that the water leaving the cell is equal to the level of water entering the cell, therefore this must be the concentration of the cell.
Prediction: In my prediction, I predicted the concentration inside the potato to be 0.25M. However, after conducting the experiment, I have found that it was in fact 0.38M. However, I did correctly predict that the potato would increase in weight the further you got to 0.0M, and decrease the closer you were to 0.5M.
-EVALUATION
Quality of results and Anomalies: In my research, I came across two anomalies, one in my data and one on my graph. The anomaly in my results was a lot lower than the other results that I had for 0.3M (which was the solution this particular chip was in). It may have decreased because the syringes were contaminated.
The second anomaly was on my graph. This is anomalous due to the fact that this was the % change in mass for 0.3M. The data I have for that may still be incorrect even though I got rid of the anomaly. This is because I was left with only two results, and that does not leave me with accurate results.
Improvements to method: In my experiment, I found that I got anomalous results because my research was not detailed enough. To refine it I can do two things. I could either do more values (0.15M, 0.25M etc.). This would mean that I could see what would happen in-between and not make assumptions. If I had more points from the intermediate stages, I could plot a more detailed graph, and therefore get a better line of best fit.
The second thing I could do would be to do five repeats instead of the three that I did do. By doing this, any anomalies that did occur would be made clearer, and any mistakes that happen due to lack of data would not happen because there would still be four points left to use for calculations.
Reliability of results: On the whole, I do not believe that my results were entirely accurate. The points I recorded in the actual experiment were close together, however it was not easy for me to draw a line of best fit. I do not think that they reliable enough to draw a firm conclusion, instead I was only able to gain a rough trend from the results.
Further Work: If I was to continue this experiment further, I could do this experiment with a carrot instead of potato. This would be investigating to see if other root vegetables have the same sugar concentration as a potato. I could set up the experiment in exactly the same way as my main osmosis experiment.
If I were to do this I would expect to find that the concentration is higher. I can predict this because a carrot tastes sweeter than your average potato.
