Results
Discussion
My results showed that as the molarity of the solution increased, the weight loss in the potato’s also increased. This is due to the process known as osmosis and water potential within the different substance strengths.
The discs in the weaker substances gain weight because the water potential outside the cells is greater than that inside the cells, meaning that the water molecules move from the region of high potential (outside the cells) to regions of lower water potential (inside the cells) i.e. down-gradient. This also applies with the strong substances where the discs lost weight. This is because water was diffusing out of the cells into the strong solution in order to try and make the water potential of the cells and the solution the same, as water diffuses out of the cells, the discs lose weight. Osmosis also happens within the cells of the potatoes. This is where water molecules pass through a semi permeable membrane until the two solutions become equal in concentration. Both osmosis and water potential differences explain the results of my experiment.
The water potential of the potato tuber cells can be easily worked out using my graph. Take the point on the x-axis where the percentage change in mass is equal to zero. Using my line of best fit, the solution molarity where no mass is gained or lost is 0.18. Using a conversion table, I can see that the water potential of the potato cells is around –500 kPa. At this water potential the potato’s don’t gain or lose mass, this is because the potentials are equal so the water into the cells equals the water out of the cells.
In my experiment I incurred anomalous results. This could be due to inaccuracies in the experiment. Some of the inaccuracies that could have happened are, inaccurate cutting of the potato discs, as changing the shape, and surface area of the potato chips could make it easier for osmosis to take place and for molecules to diffuse along the down-gradient. Also another inaccuracy that could have occurred is that the excess water may still have been present on the potatoes when they were weighed. This would increase the overall mass of the potato discs because the water will add mass which hasn’t been gained from water potential.
If I was to repeat this experiment again, there would be changes I would make to increase to overall accuracy of the experiment, this is because as the experiment is there is limitations which include the range of results, and the inaccuracy of the potato cuttings and measurement.
If I was to repeat it the changes I would make would be: -
I would use calipers to measure the size of the potato; this would make it accurate to millimeters depending on the accuracy of them. This more accurate measuring equipment would make a more accurate mass calculation so then the percentage change would be more accurate, meaning the results would be more accurate. Use more accurate cutting equipment to ensure the faces of all the potato discs are the same meaning that no change in surface shape could result in quicker diffusion. I would also perform the experiment in a temperature and light intensity controlled room, this would prevent changes in both of these. These changes could cause the cell work rate to rise or drop also it could cause the water and sucrose molecules to speed up movement which could effect the rate at which osmosis takes. I would also leave the chips in the solutions for a longer. I would perform the experiment using a wider range of solution strengths, including 0.05’s. This would give the experiment more validity and would also give a wider spread of results, thus meaning the experiment would show more clearly how the mass changes as the strength increases. Also I would accurately measure the solutions as adding more solution into one test tube than into another would increase the amount of sucrose molecules to water molecules. So if all the solutions were the same, the ratios would be similar, where as just guessing means that it is inaccurate and the ratios could be different.
Conclusion
In my hypothesis I predicted that the potatoes in the solutions with the highest sucrose molarity would shrink and lose weight and that the potatoes in the weakest solutions will gain weight and increase in size. The ones in the solution where the sucrose and water content is the same as the potatoes sucrose and water content will not increase or decrease in size and will not increase or decrease in weight. As you can see for my results and graph where 0 is distilled water to 0.5 which is the solution with the highest sucrose molarity, my prediction was proved right. I predicted this because I knew that the different water potentials would lead to the movement of water from the cells into the solution or vice versa meaning weight would be either lost or gained. Also I knew that osmosis would take place, osmosis is when water molecules diffuse from a dilute solution into a concentrate solution through a semi permeable membrane. So with solution O the water from outside the potato, diffused through the PPM to dilute the high concentration of sucrose in the cells of the potato. This gave the appearance that the potato chip had grown and increased in weight, this is because of the excess water in the cells. Where as in solution 0.5 the potato lost weight and decreased in size. This is because the water from inside the cells diffused out through the PPM into the high concentrate sucrose solution to try and dilute it and make it equal to the cells sugar concentration.
