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Plan and carry out an experiment to investigate Osmosis in Potato tissue

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Introduction

Plan and carry out an experiment to investigate Osmosis in Potato tissue Planning Aim: To investigate osmosis in Potato tissue and find its water potential, using eight different molarities of sucrose Hypothesis Osmosis is defined as the net movement of water or any other solutions molecules from a region in which they are highly concentrated to a region in which they are less concentrated. This movement must take place across a partially permeable membrane such as a cell wall, which lets smaller molecules such as water through but does not allow bigger molecules to pass through. The molecules will continue to diffuse until the area in which the molecules are found reaches a state of equilibrium, meaning that the molecules are randomly distributed throughout an object, with no area having a higher or lower concentration than any other. Apparatus Test tube Label Sucrose solution Potato tissue 8 x test tubes 8 x potato chips 8 different sucrose solutions labels top pan balance test tube rack Method In each test tube, put 30cm� of each solution of sucrose, and label it with the molarity of the sucrose that is in that tube, this is needed because otherwise you would not be able to plot the graph at the end showing how the molarity of the sucrose directly effects osmosis, or if the different molarities become mixed, anomalies will appear in your results. ...read more.

Middle

% change for 1st set of data % change for 2nd set of data average % change 0 6 9.3 7.7 0.0625 5 8.4 6.7 0.125 3 3.5 3.3 0.25 0 0.9 0.5 0.5 -12 -9.1 -10.6 0.75 -17 -12.9 -15 1 -21 -19 -20 1.25 -22 -15.9 -19 Analysing and considering evidence The graph shows the line of best fit for the average percentage change in mass of the potato chip over two experiments, each being forty five minutes in length. 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. Although the last solution being 1.25 molar sucrose, has a higher average than that of the 1 molar sucrose solution. This suggests an anomaly in my results, that either the other chips were not blot-dried to the same extent or that there was water on the chip and that it contaminated the sucrose and diluted the solution making it weaker, or that the chip cell has completely plasmolysed and that there can be no more water loss. ...read more.

Conclusion

The cutting of the potatoes was the most difficult part of the experiment as although I was recording my results by mass, it could well have affected the surface area and so the overall rate of osmosis. If I were to repeat the experiment I would have possibly found a machine to cut the potato as it would ensure that all potatoes would be the same weight and dimensions. As well as the potato I could have found a more accurate way to measure out the solutions and to determine the molar concentrations. Perhaps I could have used a burette. This would ensure that I have an accurate amount of fluid in each test tube. I could also weigh each chip on a more accurate scale, e.g. not to 0.00g but to 0.0000g There were not any out of the ordinary results, but some were not as close to the line as others. This is possible a human error. When the potato chips were removed from the test tubes and dried I may well have dried some potatoes more thoroughly than others and so some would have more excess water, which would add to the mass. If the experiment was repeated I could find another way to dry the potatoes that would ensure that all were dried in the same way for the same time. However with all this said I think that the experiment was truly successful and I was very pleased with the complete comparison of my results with my initial prediction Simon Herbert 8001 ...read more.

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