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Investigate the affect of osmosis in potatoes.

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Introduction

Emilie Campbell 11C Mrs Higgenbottom Biology Coursework Osmosis Introduction The aim of the experiment is to investigate the affect of osmosis in potatoes. During this experiment the concentration of sugar solution will be increased to see how it affects the rate of osmosis. Osmosis is the movement of water molecules from an area of high concentration to an area of low concentration through a partially permeable membrane. Preliminary Work In our preliminary work we found out from our results that potato cylinders are good to use when investigating osmosis. Firstly they are easily obtainable and secondly from our preliminary experiment we found that the potato cylinders were affected by osmosis. We found that the length of the cylinders changed. The length of the cylinders was measure before and after the experiment. We found that the length of the potato cylinders in the distilled water increased in the length and the potato cylinders in the sugar solution decreased in length. This happened because of osmosis. The water molecules in the distilled water moved form a high concentration to a lower concentration in the potato cylinders thus making them increase in size. The water molecules in the potato cylinders that decreased in mass went from a high concentration in the potato to a lower concentration in the sugar solution. Results Solution Length before Cm Length After Cm Difference in length Distilled water Sugar solution The results from preliminary experiment have provided me with a good basis for my final experiment and ways in which I can improve it for more accurate results. ...read more.

Middle

Mass of Potato Cylinder After (grams) Difference in mass % difference in mass Distilled water 1.90 2.30 +0.40 +21.1 5% sugar solution 2.28 2.63 +0.35 +15.4 10% Sugar solution 1.90 1.62 -0.28 -28.0 20% sugar solution 2.00 1.39 -0.61 -30.5 30% sugar solution 2.00 1.10 -0.90 -45.0 Finding the percentage change for our results allows us to easily compare the change in mass as all the potatoes originally started with a different mass and finished with a different mass this means making comparisons could have been difficult. Using percentage differences makes the units equal and therefore easier to compare To find a the percentage difference use the following method % difference = Difference in mass x 100 Original value Above are the results of all three experiments we carried out. We carried out three experiments to ensure our results were accurate and reliable. To make are results easy to handle and put in to a graph the number of results has been decreased by finding the average for the changes in percentage of each of the concentrations. For example to find the average of the 5% sugar solution you would do the following: Add together each of the percentage change results from the 3 experiments 1.52 + 14.8 + 15.35 = 7.2 % 3 Averages of Percentage Changes Type of Solution Average Percentage Change Distilled water +20.5 5% +7.2 10% -15.0 20% -27.8 30% -42.0 These above results will be put in to a graph. ...read more.

Conclusion

This shows that at this point there is no change is mass. It is not increasing or decreasing in mass. This is called the isotonic point. No osmosis is taking place because both potato cylinders and solution have the same osmotic strength. The contents of the potato cell shrinks and moves away from the cell wall leaving the cells flaccid. This is why these potato cylinders were soft and floppy. Evaluation This graph shown above gives the line of best fit for the percentage change in mass of the potato chips over the course of the thirty minute experiment. The graph is a curve that slopes downwards and does not go through the origin. Because the line is not straight and does not pass through the origin, it means that the percentage gain and loss in mass and concentration are not directly proportional. However, there is a pattern on my graph, and this is, as the concentration of the solution increases, the percentage change in mass decreases. The graph shows that the percentage gain and loss in inversely proportional to the concentration. The gradient does change in my graph. It gets less steep as X axis gets bigger. This is because the potato chip is becoming as flaccid as it possibly can, and so the change in mass of each molar concentration is becoming closer and closer together. From the line of best fit that has been added in, it can be seen that all of my points were very close to creating a perfectly smooth curve. This shows that my results are fairly reliable. My graph fits in with my prediction of the experiment graph. ...read more.

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