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Experiment to show that the concentrations ofliquids can affect osmosis

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Introduction

EXPERIMENT TO SHOW THAT THE CONCENTRATIONS OF LIQUIDS CAN AFFECT OSMOSIS ==> PRE-EXPERIMENT Background Information Osmosis is, by definition, the diffusion of water from a weaker, or more dilute concentration, to a stronger solution (i.e. down a concentration gradient) through a semi-permeable membrane, and it is this pinciple which I want to study. In order to observe any results, and draw a conclusion from them, I need to thoroughly research osmosis, and it's effect on plant and animal cells. This will allow me to design some preliminary experiments, and finally the main experiment, which may or may not prove that the concentrations of liquids have an affect on osmosis. Osmosis can occur in both plant and animal cells, and allows processes such as transpiration to occur. It also can change the structure of a cell, to a point where the cell can no longer function. Osmosis is the only way that water can diffuse in and out of a cell. When the solutions on either side of the semi-permeable membrane are equal, or isotonic, the net movement of water is zero. As there is no difference between the two solutions, no water needs to be moved in order to dilute, and osmosis does not occur. In plant cells, osmosis can occur because the cell membrane acts as the semi-permeable membrane, and water from dilute solutions outside the cell enters through the membrane into the strong solution of the vacuole, and keeps the cell turgid. This process allows for the transport of water through a plant, as each successive cell becomes more dilute than its neighbour. Turgidity is achieved when the cell membrane is pushed against the cell wall due to turgor pressure. The cell does not burst, however high the turgor pressure is. This is due to the cell wall, unique to plant cells, which holds the cell together. Turgidity is the reason that plants stay upright, using the cell wall and the interior pressure to hold it's shape, much like a blown-up balloon. ...read more.

Middle

the time for which the potatoes are left in the solutions, and finally, the number of potato pieces in each test tube. * Temperature will be kept constant at the average room temperature of 21?C. * Volume of the solutions will be measured and kept constant across all 5 solutions. * The potatoes will be left in their solutions for 24 hours, staggered so as to allow time for each solution to be completed and then emptied at the end of the experiment. * There will be 3 potato pieces in each solution, meaning that there will be 3 results for each solution. These results will be averaged for each solution, so the effect of any anomalous result on my results would be reduced. * The potatoes will all have to be underneath the surface, so as to ensure that the full surface area of the potato is in contact with the solution. Prediction In this experiment, I would expect the different concentrations to show fairly noticeable effects on the lengths and masses of the potatoes, with the water diffusing into the potatoes at a high rate in the pure water solution, and therefore making their size bigger than at the start. As the solutions become stronger, I expect the rate of osmosis to decrease (and, as a result, make the potatoes themselves comparatively smaller at the end). Also, the potatoes will be quite turgid at the start of the experiment, there will be already some water inside, and because of this I expect, in the stronger solutions, for there to be a decrease in the mass and length of the potato, due to a reversal in the effect of osmosis. I know that water can pass in both directions, thanks to my preliminary experiments, and that direction depends on the relative concentrations inside and outside the potato. Using this information, I can create a predictive graph of results, which shows the basic pattern that I would expect. ...read more.

Conclusion

This anomalous result could have been the result of human error, or may have been due to the potato surfacing in the solution (meaning that the upper part was not submerged in the solution). However, there are many factors that could have been improved upon. Firstly, my measurements could have been more accurate; I might have used a micrometer instead of a ruler, and more accurate electric scales to weigh the potato pieces. I could also have measured the width of the potato, adding an extra dimension to my results and therefore more accuracy in my findings. Using the extra information I could then calculate the volume of the potatoes, using the formula l?r2, the formula for cylinders. This would give a completely accurate result, which would justify for any change in size, be it in any direction. Therefore, if one potato increased in width but not length, and another increased in length but not width, both changes would be accounted for. The potatoes could also have been cut with a scalpel instead of a knife, making the original measurements even more accurate. I could also have changed the structure of the experiment to ensure more accuracy. I could have tested more solutions, which would have given me a more accurate picture of how the concentrations effect osmosis. I could also have used more samples to test each solution, which would iron out any anomalous results even more efficiently, and produce a more accurate result for each solution. Finally, the experiment could have taken place over a longer period of time, to accentuate my results, as osmosis would continue until the solutions were all of equal concentration, and the effects of the original solutions would be highly visible. I did not change my plan during the experiment, as I used my preliminary experiment to iron out possibilities for the experiment to falter, which fortunately it only did once. The fact that it did however must be taken into account; so more caution must be used for future experiments. ?? ?? ?? ?? Graham Pether GCSE Practical Assessment: SC2 ...read more.

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