Plan And Method
To improve the accuracy of the results for each concentration of sucrose solution I will be looking at the effect on three cores. I have chosen the range of sucrose solutions from five percent to twenty percent as this is a reasonable range which will give me a total of five readings, (including water) and should produce a good graph.
I will then use my results to make a graph of the percentage differences of the cores.
I will use the same method each time I carry out a part of the experiment, which ensures fairness of the experiment.
Diagrams Of Apparatus:
List Of Apparatus:
5 flat-bottomed test tubes
1 beaker of water
1 beaker of 5% sucrose solution
1 beaker of 10% sucrose solution
1 beaker of 15% sucrose solution
1 beaker of 20% sucrose solution
1 test tube rack
1 razor blade
1 safety mat
1 pincer
1 weighing machine
1 safety goggles
1 potato borer
1 potato
1 napkin
Method:
1. I will put on my safety goggles.
2. I use the potato borer to obtain around 15 potato cores.
3. I cut the cores till each core is roughly the same length and so it will be easier to make sure they are the correct weight.
4. I weigh the cores in sets of three and then dry the weighing machine and reset it back to 0.00g.
5. I put one set of cores in a flat-bottomed test tube of water, another set in 5% sucrose solution and so on with each solution.
6. I labelled each test tube according to its solution.
7. I put a lid on each tube.
8. I leave each core for twenty-four hours.
9. Dry each core after twenty-four hours.
10. Weigh each core after twenty-four hours.
11. Feel each core and test its turgidity.
Results
The experiment was repeated twice. This was to improve accuracy and also to show that the results were reproducible. The weakness of this was that I did not use the same potato core for both experiments. It would have been better if I had, as this would have reduced variability between experiment 1 and experiment 2. Also I changed the mass of the cores in experiment 2 to see if there was any noticeable effect.
Experiment 1
Here are my results for the first set of cores.
BEFORE AFTER
Here is a graph to show the change in mass of the potato cores before and after they were placed in different solutions
Series 1 is the mass of each set of cores before they were placed into different solutions. Series 2 is the mass of each set of cores after they had been placed in different solutions.
Experiment 2
For this set of results I changed the mass of the cores to 4 grams to see if there was any noticeable difference.
AFTER
BEFORE
Here is a graph to show the change in mass of the potato cores before and after they were placed in different solutions.
Series 1 is the mass of each set of cores before they were placed into different solutions. Series 2 is the mass of each set of cores after they had been placed in different solutions.
With both of the experiments I found that the cores that were placed in the less concentrated solutions were more turgid than the ones that were placed in the more concentrated solutions.
Above is a table showing the percentage difference in each set of cores.
Graph to show the percentage difference in the mass of five sets of potato cores after twenty-four hours of submersion in different concentrations of solutions.
Conclusion:
I found that changing the mass from 6.30g to 4g had no noticeable effect on the rate of osmosis although the graph showing the change in mass for experiment 2 is a lot steeper than the one for experiment one. So maybe if I was to do this again I might use a larger range. I would do one at 5g and one at 10g or 15g. But I do think that the rate of osmosis did increase with a smaller mass because if you look at the percentage difference graph’s the line for experiment 2 goes a lot further down than the line for experiment one. From the results I noticed that the potato cores lose mass when put in sugar solutions and also their stiffness changes. The graph line for experiment 1 showing the change in mass, the mass of the potato cores decreases consistently when the concentration of sucrose is increased. This is because of osmosis. If there is a very high concentration of sucrose then the concentration of water is very low. Therefore lots of water from the cells in the potato core diffuses across the partially permeable membrane and into the sucrose solution (high water concentration to low water concentration). This makes the potato core shrink slightly and is left flaccid.
You will also notice from this graph that the potato cores that were left in water for twenty-four hours increases in mass. This is because there is a higher water concentration outside the potato core therefore the water diffuses into the core and makes it turgid. In this experiment I think that I must have put the wrong kind of sucrose in the tube or I put too little for there is an anomalous result for one of the 15 % sucrose concentration readings, which does not follow the pattern. Which one, I am not sure because the other readings are all parallel but not at this reading. As mentioned above there appears to be some experimental error as the line of the graph is not quite as predicted. When I found the cores the day after the experiment the top parts of the three cores was not submerged and therefore the surface area available for osmosis would have been reduced. Therefore less water would have been able to leave the cores and enter the sucrose solution in the duration of the experiment. The line graphs of the two experiments showing percentage change are parallel to each other rather than superimposed. This is probably because I changed the mass of the potato in each experiment.
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Evaluation:
This procedure is pretty easily accomplished for it does not need particularly intricate tools. Therefore measurements are easily taken and on the whole they are reliable. The mass was easily obtained I think because once one had dried the core, the weighing machine and reset it, the results were pretty accurate.
I am very happy with the reliability of the experiment and therefore think that the evidence is sufficient to support a firm conclusion that osmosis occurs more when there is a larger difference in concentration of water either side of a partially permeable membrane. However I don’t think that the investigation was fair due to the reasons I will explain below.
There could have been lots of problems in this experiment because of small mistakes, which could have made big differences in my results. When measuring the solution I used a syringe but I didn’t use the same syringe for the whole investigation it changed. Also when measuring the solution I could easily made a mistake as I was measuring out four lots of five millilitres of solution each time. There could have also been contamination as I used the same syringe for measuring each type of solution. To improve on these errors I would probably use a different syringe for each solution and try to use the same one everyday. I would also try to measure as carefully as possible the amount of solution I used each time. However even if I did employ these techniques into my investigation I would still have loots of other sources of error. For example I would have to try and keep the same potato. I did do this where I could and I did use the same type of potato but could not use the exactly the same potato. I didn’t use the same weighing machine each time either so there could have been unnoticed errors in my results. Drying the potatoes was a huge source of error. If I had time I would make sure that each core was dried as much as the next one. The temperature of the room was not under my control and as temperature increases the rate of osmosis I would have to make sure that the temperature stayed the same if I had time. The concentrations may not have been exactly the right concentration and may have changed slightly from day to day.
If I had more time I would also attempt to look at different types of potato or go past the 20% concentration level and look at plasmolysis. Or I would investigate the things I didn’t change like different surface areas (therefore smaller and larger sites for osmosis) or different temperatures or variable light intensity or even smaller changes in the concentration of sucrose
