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To investigate the different effects of various concentrations of sucrose solution on potato cells.

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Introduction

Aim: to investigate the different effects of various concentrations of sucrose solution on potato cells. Introduction: Osmosis is a special type of diffusion. Osmosis happens when two solutions of different concentrations are separated by a selectively permeable membrane. A selectively permeable membrane has holes in it which are just big enough for water molecules to pass through, but not the much larger sugar molecules. Water moves across the membrane from a weak solution (high concentration of water molecules) to a stronger solution (lower concentration of water molecules). In this case, the two solutions are the cytoplasm inside the potato cells and the sucrose solution that I am placing my potato chip in. The partially permeable membrane is the cell membrane of the potato cells. When potato chips are placed in pure water, the concentration of water molecules surrounding the plant is higher than the concentration of water molecules inside the cytoplasm of the potato's cells. The water will diffuse into the cell and the cytoplasm by osmosis. This means the cytoplasm pushes out against the cell wall as it expands slightly and the cell becomes firm or turgid. The overall effect over time is for each cell to increase slightly in mass and so the whole potato chip shows an increased mass. However, if you put a piece of potato into a sugar solution (where the water concentration around the chip is lower than the water concentration inside the cytoplasm in the potato's cells), then water will move out of the cells of the potato and into the sugar solution. The potato piece will therefore shrink, and become floppy, or flaccid. If a sugar solution has exactly the same water concentration as the potato chip, then it is likely that there will be no overall movement of water in or out of the potato. Therefore, the potato chip will stay the same size. Previously, I carried out a small experiment looking into osmosis in potato cells, to use as preparation for this experiment. ...read more.

Middle

If the cells gain water because they are in a solution where the concentration of water outside the cells is higher then the concentration of water inside the cells, then the cells of the potato chip will gain water until the cytoplasm can expand no more because of the cell wall, making the cell turgid. This means no more water can move in by osmosis. The same applies to the cells losing water by osmosis and becoming flaccid. I have also made some changes to the method that I used for my preliminary experiments, in order to keep the experiment as fair as possible, and hopefully to receive better results. In the previous method that I used, I measured the length of the chips with a ruler before and after placing them in the solution. However, this did not take into account all of the particle movement and cell expansion in width, and it was very easy to measure the chips inaccurately. Therefore, for my new experiment, I intend to measure the change in mass of the potato chips. This is a more accurate way of measuring all the cell expansion or contraction, as it can take into account even very minute changes in the potato's cells and therefore the potato itself, and there is much less room for human error, as the scales are very accurate. It also means that I can ensure that at the beginning of the experiment, all the potato chips are exactly the same size. Ensuring that they are the same size at the beginning of the experiment is very important because it means that they should all have the same surface area and capacity for absorbing or exuding water. They will all initially weigh 1.68 grams. I will use a size 4 cork borer to cut out the potato chips. This is because this method worked well in my preliminaries; using the same cork borer to cut out all the chips ensures that all the chips have the ...read more.

Conclusion

The equation for this would be: Mass at end - Mass at beginning x 100%. Mass at beginning I could not calculate the percentage change in mass for this experiment as I did not record the minute differences between the mass of the potato chips at the start of the experiment, and so if I wanted to calculate the percentage change in mass I would have to record exactly the slight differences in mass between all the potato chips at the beginning of this experiment. I did keep my experiment away from any windows and heaters, but the room the experiment was in probably did warm up or cool slightly in the day. A possible solution to this problem could be to keep the experiment in a water bath or other controlled environment. It would be difficult to find the temperature of the sucrose solution without removing the cling film, however, which would allow some water to evaporate and also affect the experiment. It would also be helpful to have collected more sets of results, as this would allow me to find more accurate averages, and also would help me to spot any anomalous results more easily; with only two results, it can be difficult to tell which result of the two is anomalous. In future, I will try to collect three or four sets of results which should be a great help. It would also be good to have a control experiment where a potato chip is placed in distilled water. This would be useful to get a wider spread of results. I could also try using 0.1, 0.3 0.5, 0.7 and 0.9 mole dm-3, which likewise would give me a wider spread of results to help me draw improved conclusions and graphs. Overall, I think that my results were accurate and useful, and my method was fair, although I could have improved my control of temperature by placing the test tubes in a controlled environment such as a water bath, and I should have taken more results. ...read more.

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