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Investigate the effect of increasing the concentration of sucrose solution on the rate of osmosis in potato cells, and to investigate the internal concentration of potato cells in terms of sucrose solution.

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Introduction

Plan On Osmosis Experiment Jonathan Anderson Introduction Knowing that osmosis (a diffusion of water) will occur across a semi-permeable membrane whenever there is a difference between the water concentration on the two sides of the membrane. And knowing that when this happens to all they will either become turgid if water flows into them, or plasmolysed if the water flows out of them, and therefore change their volume, we are going to test the hypothesis that: "If the concentration of a solution into which a cylinder of potato cylinders are placed is greater than a certain level the cylinder will contract, and if the concentration is less than that it will expand." Aim 1. To investigate the effect of increasing the concentration of sucrose solution on the rate of osmosis in potato cells. 2. To investigate the internal concentration of potato cells in terms of sucrose solution. Hypothesis For this investigation I think that the lower the concentration of the sugar solution in the test tube 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 allow concentration, i.e. in the potato cylinder. Therefore the cylinders in higher water concentration will have a larger mass than in the higher sugar concentration. Variables 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. This will give me a varied set of results from which I hope to make my conclusion. If any of the non-variables are not kept constant however it would mean that it would not be a fair test. For instance if one of the potato cylinders was 1cm longer than the rest the surface area of the cylinder would be greater and therefore would have more "space" for the osmosis to occur. ...read more.

Middle

I will then have 15 cylinders. * I will then place the cylinders in distilled water until they are ready to be used. * Taking a test tube rack I will pace 5 test tubes and then label them 0 molar, 0.25 molar, 0.50 molar, 0.75 molar and 1 molar. * Using a measuring cylinder I will measure out different amounts of sucrose solution and distilled water which I will then pour into the test tubes in a percentage ratio giving me various molar concentrations. The measuring will be done using a burette. * I will then weigh every potato cylinder on a electronic balance and record the weights, but before doing so," blott" them on a piece of paper towel, and make sure blotting process is exactly the same for each one. * I will then put 2 potato chips into each beaker and start the stop clock, 2 cylinders were used to create an average giving me a better set of results and more accurate graphs. * Whilst waiting I will set new paper towels with which I am going to dry the potato. * After 1 day (approx) I will drain out the solutions in the sink and place all the cylinders on the paper towel in the order that I put them in the test tubes as not to confuse myself as to which chip came from which solution. * After I have dried each chip I will place them on the balance so I can record their mass. * Each potato will be accurately measured using electronic scales. * If there is time after carrying out the first experiment I will redo the experiment under exactly the same conditions and this will give me a secondary set of results and this will enable me to have a more accurate view on the changes. Prediction When basing my prediction on preliminary experiments and my knowledge of osmosis, I think that the concentration of the solution increasing will give a decrease in the percentage change in mass. ...read more.

Conclusion

The range of concentrations was adequate but I may also consider increasing the amount of concentrations as I would get more varied results, i.e. 0.10m, 1.15m, 1.20m, and so on. This way would have allowed me to find out more information. I did not find any part of the experiment particularly difficult but perhaps I would have weighed each chip on a more accurate scale, for example 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, this may have been due to a number of things. 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 overall the experiment was a success and I was pleased with the complete comparison of my results with my initial prediction. I think the results my group and I have gathered show a reasonable level of accuracy. This is because they tie in with what I predicted from my scientific knowledge. To do further research into this topic which is relevant to the investigation, we could: * Measure different potato's sugar contents to see how it compared with the solution strength where no change in length was measured * See how different breeds of potatoes sugar contents differ. * Try different solutes to sugar to see which give the best results. * Look at cells under a microscope in different sugar concentrations, to see their visible differences (see if the cells were plasmolysed). * Try and find a way of measuring turgidity of the cells, perhaps by seeing how 'bendy' the chips are. ...read more.

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