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The effect of osmosis on potatoes

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Introduction

Liv Gell Osmosis Introduction Osmosis is the movement of water molecules, across a partially permeable membrane, from a high concentration of water to a lower concentration of water molecules. This process allows plants to take in water through their roots, as well as being used in kidney dialysis machines to filter the blood. When pieces of potato are placed in different concentrations of sugar solution, as a result of osmosis it is likely that the potato will increase in mass and length. This is due to the fact that potatoes contain a far less concentration of water molecules than water itself; therefore molecules in the water will travel through the potatoes membrane, hence increasing the concentration of water in the potato as well as its measurement lengthwise and weight. The aim of our investigation is to identify the effect of varying concentration of a certain sugar solution on the amount of osmotic activity between the solution and a potato chip of a given size. For this particular investigation I think that the lower the concentration of the sugar solution in the plastic cup the larger the mass of the potato will be. This is because the water molecules pass from a high concentration, i.e. in the water itself, to a low concentration, i.e. in the potato chip. Therefore, the chips in higher water concentrations will have a larger mass than in higher sugar concentrations. www.scienceaid.co.uk/.../plants/images/osmosis.png Liv Gell Preliminary work Test one Method: Using a knife, scalpel and a cork borer I extracted three cylinder shape portions out of a potato. Using a ruler, I (as precisely as possible) measured and recorded the length of each of the three pieces of potato, trying to ensure they were all of a similar length; 3 chips were used to create an average which gave me a better set of results and more accurate graphs. ...read more.

Middle

and dry- this is to stop any kind of contamination and to make sure that I do not pass on any extra water onto the potato. Method * Bore cylinders from a potato using a size 6 bore. * Measure the cylinders of potato with a ruler and cut them to approximately 3cm in length, using a scalpel. * Measure and record the mass of the cylinders, using a set of electronic scales. * Pour 30ml of a concentration of sucrose solution into 3 plastic cups. * Swiftly add a cylinder of potato to each cup and leave for 20 minutes, using a stop watch for time-keeping, allowing a sufficient amount of time for osmosis to proceed. * After the 20 minutes is up, remove each cylinder of potato and gently roll on a paper towel to eliminate excess solution. * Weigh and record the final mass of each cylinder. * Repeat the experiment with different concentrations of sucrose solution (ranging from 0m to 1m) and perform the test 3 times for each concentration, to ensure the results are reliable. * Plot the recorded results on a graph. Range of results The concentrations of sucrose solution I am going to use are as follows; 0m, 0.2m, 0.4m, 0.6m, 0.8m and 1m. I will repeat each test 3 times, however if I come across an outlying result I will perform that experiment again- in order to obtain a reliable and accurate set of results. Factors that could affect the experiment To create a fair test certain aspects of the experiment will have to be kept the same whilst one key variable is changed. I have chosen to vary the concentration of the sugar solution. ...read more.

Conclusion

I think I took enough results for the amount of concentrations that I was using and the duration of the experiment was enough time to allow sufficient osmosis to occur. However if I was to repeat the experiment I might well increase the time to allow more osmosis to happen and possibly find out the saturation point of the cylinders of potato. 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, 1.15m, 1.20m, and so on. The cutting of the potatoes was the most difficult part of the experiment (despite using a borer) 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 of 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. If the experiment was repeated I would find a way in which to eliminate all possible ways in which I could, physically, affect the investigation. However with all this said I think that the experiment was successful and I was very pleased with the complete comparison of my results with my initial prediction. ...read more.

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