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Osmosis experiment

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Introduction

Osmosis experiment Osmosis is the passage of water molecules, which have moved from a high concentration to where there is a low concentration through a semi - permeable membrane. Aim: We have been asked to investigate the effect of osmosis on potato chips, and therefore the effect of osmosis in plant cells. My main aim is to determine whether osmosis occurs in a potato and how it affects the potato in different molar solutions of sucrose and distilled water. I shall be experimenting with a baking potato, and will be using a range of different concentrations of sucrose, and distilled water. By measuring the change in mass and length of the potato cylinders I should also be able to find the isotonic point. An isotonic point is a point where the mass does not increase or decrease from its original mass. I must also experiment with at least 5 types of concentrations, to have sufficient results ,and to see if my prediction is correct I am going to use 6. The diffusion theory of Osmosis: (from 'GCSE BIOLOGY' by D.G. Mackean.Page 36.) Partially permeable sugar molecules pass Membrane through pores more slowly Fewer water molecules more water molecules go in this direction going in this direction Hydrated sugar molecule. Variables: We could: * Look at the type of temperature. * Compare a potato with a parsnip for example. * See if the potato changes with different solutions * I have actually chosen to investigate different molar concentrations of sucrose - by measuring the mass and length of the cylinders. Fair test: To create a fair test certain aspects of the experiment have to be kept the same whilst one key variable is changed. I have chosen to vary the concentration of the sugar solution. This will give me a varied set of results from which I hope to make a decent conclusion. If any of the non-variables are not kept constant it would mean that the test was not fair. ...read more.

Middle

(No.2.7 from a worksheet about plant cells) Cell surface membrane Concentrated solution Less concentrated solution Water diffuses out of the first the cell shrinks slightly, and Cytoplasm and vacuole becomes flaccid; then the cell t through a partially membrane pulls away from the Ppermeable cell membrane cell wall, and the cell is plasmolysed. Osmosis takes place Appearance: Over 24 hours I think the colour of the potato chip will get lighter and fade in the distilled water and possibly 0.1M solution. E.g. if the potato chip was at first a golden yellow colour I think that after 24 hours it would change to a pale white colour. This is because the cell in the potato has become turgid, and water has entered the cell by osmosis. I also predict the chips in 0.2M - 0.5M solution should be dark in colour, and bendy and brittle in texture. This is because the cell has become flaccid. The cell will become flaccid when plasmolysis has occurred. The cell will become flaccid when plasmolysis has occurred. Plasmolysis is when the cell membrane peels away from the cell wall. A flaccid cell is the complete opposite of a turgid cell. Results: This is a table to show the change in mass in the potato chips. Solution used Original Mass (g) Final mass (g) Change in mass (g) Average change (g) % change in mass Average % change 1.73 1.9 0.17 9.83 Distilled water 1.66 1.82 0.06 0.1 3.16 15.3 1.6 1.69 0.09 5.63 1.67 1.76 0.09 5.39 0.1M sucrose 1.68 1.74 0.06 0.06 3.57 8.19 1.77 1.82 0.05 2.82 1.65 1.7 0.05 3.03 0.2M sucrose 1.69 1.75 0.06 0.04 3.55 7.13 1.83 1.83 0.03 1.64 1.8 1.71 -0.09 -5 0.3M sucrose 1.82 1.67 -0.32 -0.19 -16.6 -25 1.66 1.49 -0.17 -10.2 1.76 1.49 -0.27 -15.3 0.4M sucrose 1.74 1.51 -0.23 -0.29 -13.2 -41.5 1.79 1.44 -0.39 -21.8 1.86 1.5 -0.36 -19.4 0.5M sucrose 1.92 1.52 -0.4 -0.37 -20.8 -46.8 1.85 1.46 -0.36 -19.5 % change in mass = change 100 anomalous result. ...read more.

Conclusion

E.g. 0.000g not 0.00g. I was also very surprised as I only had two small anomalous results which means my results were probably fairly reliable. To observe these results look at my graphs or results table. An anomalous result is a result which does not follow the pattern of the other results and so is abnormal or irregular. If I was to carry out this investigation again I could use different varieties of potato or different plant tissues e.g. carrot instead of potato. This way I would be able to compare the results and see what differences and similarities were between the two types of plant tissue. The range of concentrations was adequate but I would possibly create more concentrations if I repeated the experiment so that I would have more varied results, i.e. 0.10M, 0.50M, 1.0M, and so on. This way would have allowed me to also find out the isotonic point far more accurately as the one that I estimated is very approximate. Three repetitions of each concentration are sufficient but unfortunately there were anomalous results (circled on graph). This part of the investigation may need to be repeated, as it did not seem accurate. I think I took just enough results but if I were to do this investigation again I would certainly take more so that I would have a greater chance of obtaining more reliable ones. There were no out of the ordinary results, but some were not as close to the lines as others. This may have been caused by human. When the potato chips were removed from the flat bottomed tubes and dried i may well have dried some more thoroughly than others and so some would have more excess water, which would add mass. If the experiment was repeated I could find another way to dry the potatoes which would ensure that all were dried in the same way for the same amount of time. Although I could not draw a firm conclusion I could see a trend and I was very satisfied with the complete comparison of my results with my initial prediction. ...read more.

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