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Osmosis is defined as 'the movement of water molecules from an area of high water concentration to an area of low water concentration, across a semi-permeable membrane' (Collins, 1999).

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Introduction

Prediction Osmosis is defined as 'the movement of water molecules from an area of high water concentration to an area of low water concentration, across a semi-permeable membrane' (Collins, 1999). If you get information from books put the copied text in brackets and at the end put the authors surname and date the book was published in brackets. Then put the full details of the book at the end of the course work in the 'References' In a high concentration of water the amount of solute (e.g. sugar) is low. This could be called a weak or dilute solution. In a low concentration of water the amount of solute (e.g. sugar) is high. This could be called a strong or concentrated solution. When two such solutions are divided by a semi-permeable membrane the water will move from the area of high concentration to the area of low concentration, until both sides are equal (have reached equilibrium). This can be seen in living cells. The cell membrane in cells is semi-permeable and the vacuole contains a sugar/salt solution. So when a cell is placed in distilled water (high water concentration) water will move across the semi-permeable membrane into the cell (lower water concentration) by osmosis, making the cell swell. This cell is now referred to as turgid. If done with potato cells the cells would increase in length volume and mass because of the extra water. If these potato cells were placed in a solution with a low water concentration, then the opposite would happen. Water would move out of the cell into the solution. In extreme cases the cell membrane breaks away from the cell wall and the cell is referred to as plasmolysed. The potato cells will have decreased in length, volume and mass. The greater the concentration of water in the external solution the greater the amount of water that enters the cell by osmosis. ...read more.

Middle

And this tells us that my experiment was successful. The graphs and the results show that: v Osmosis actually took place in the experiment. v As the molars increased, the percentage of the weight difference decreased. There doesn�t seem to be any results, which undermine my predictions, and our group didn�t find any anomalous results, which means we didn�t have to repeat any of our experiments more than three times. Having the results which backs up my hypothesis, proves that this investigation was fully accomplished, and was an achievement. Solution Weight Weight Weight + or - Percentage change Before(g) After(g) (g) (%) water 5.84 5.87 0.03 0.55 0.2 5.84 5.84 0.00 0.07 0.4 5.76 5.61 -0.15 -3.15 0.6 5.87 5.58 -0.29 -5.89 0.8 5.76 5.41 -0.35 -7.35 1 5.77 5.38 -0.39 -8.18 In the table above, the percentage shows a steady decrease, telling us that the percentage of the difference decreases as the water concentration decreases. This experiment helped me find out that osmosis occurs between 2 liquid substances with a partially impermeable membrane, and that higher the water concentration is, the larger increase in grams. This means that the percentage will also be higher, increasing with the gram. Evaluation We followed the plan correctly, I believe we gained accurate and sufficient enough results to conclude the experiment, and to prove our hypothesis. My final results were very reliable, due to the precautions I took to make this a fair test. To make this experiment better, I believe that we could have done one test at a time, so that we can reduce the time difference, when we have to move the potato from the test tube to the balance. Between this, we have to dry the potatoes just enough, and then put it on the balance. When we are doing this for one set, writing down the results at the same time, while the other 5 sets are on the tissue paper, the water outside the potato tissue is going to vary for all. ...read more.

Conclusion

I obtained accurate results from which I was able to create informative graphs. I think I took enough results for the concentrations that I was using, and the time that I used for the experiment to last was enough to allow sufficient osmosis to occur. However if I was to repeat the experiment I could possibly try to find out the saturation point of the potato. The range of concentrations was adequate but I would possibly create more concentrations if I repeated the experiment so that I would have a larger amount of results to test this idea further. 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 take more care when cutting the potato to ensure that all potatoes would be the same weight and dimensions. I will also use the same balance to weigh my potato chips. This is because the measurements may slightly vary between the top pan balances. I would have liked to repeat this experiment again to obtain a second set of results. This will hopefully produce more accurate results from which I will be able to draw a more accurate conclusion. There were not any out of the ordinary results, but some were not as close to the line as others. This may have been caused 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. Essaybank ...read more.

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