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To investigate how different molar concentrations of a salt solution affects osmosis in equal segments of a potato.

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Introduction

Gail Wingham Biology Sc1 - Osmosis Experiment in Potatoes Aim: To investigate how different molar concentrations of a salt solution affects osmosis in equal segments of a potato Background Knowledge: Osmosis is the movement of water molecules from a more dilute solution to a more concentrated solution through a partially permeable membrane. A partially permeable membrane is something that can only let small molecules of substances pass through and not larger ones (for example the wall of the small and large intestine is a partially permeable membrane because it lets smaller molecules such as amino acids and glucose though but does not let the larger chains of molecules through such as starch or fat). In relevance to my experiment, the tiny spacing in between the membrane of a potato will allow the small molecules of water to pass through into the potato tissue but the rate at which it does this depends on the concentration gradient of both substances. When the water concentration in the potato tissue is lower than that of the surrounding solution it will allow for more water molecules to pass through and therefore there will be an increase in mass. Following this; if the concentration in the tissue is higher than that of the surrounding solution then the water molecules inside the potato will diffuse out causing a decrease in mass in the potato. Similarly, if the concentrations of both substances are (almost) equivalent then the change in mass is not very apparent because the movement of diffusion between the two substances is very minimal. Prediction: From my background knowledge I can predict that because the concentration of water molecules in the potato will be constant it means that it is the concentration of the solution it is put in that affects the rate of osmosis. In relation to that it means that the higher the concentration of water molecules in the solution the greater the increase in the mass the segment of potato will have. ...read more.

Middle

and so it is not necessary to have a control because the vary in masses will give a variation of data. Before this I will have measured out accurately, using two 25ml measuring cylinders (one for each liquid so that the ratios between the two are as accurate as possible as this can affect the data), six beakers with six different concentrations of salt solutions (measured in moles). My range of data will be 0mol, 0.2mol, 0.4mol, 0.6mol, 0.8mol and 1mol and I have explained my reasons for this previously in my preliminary test evaluation. For the 0mol I will simply measure out 100ml of distilled water. For the 0.2mol I will measure 20ml or salt solution and 80ml of distilled water. For the 0.4mol I will measure 40ml of salt solution and 60ml of distilled water. For the 0.6mol I will measure 60ml of salt solution and 40ml of distilled water. For the 0.8mol I will measure 80ml of salt solution and 20ml of distilled water. Finally for the 1mol I will simply measure out 100ml of salt solution. After these have been done and the potato pieces have been cut and weighed I will place the potato pieces in the solutions; making sure that they are all properly submerged so the total osmosis is allowed to exist. I will start the stop clock as soon as all pieces are in their beakers and time for twenty minutes. When I put the potatoes in the beakers I will seem aid in order to be able to place each piece at almost exactly the same time so that none of them can have an advantage of time. During the twenty minutes I will not disturb the potatoes at all. Stirring them could provoke a change in the rate of osmosis which would affect the data and moving them around may mean that the atmosphere around them could change (for example the temperature). ...read more.

Conclusion

I cannot seem to think of other factors that could have affected this statistic because the atmosphere in which I performed my experiment was constant throughout; the time that each potato piece was left in the solution was equal and each piece was fully submerged; the ratio of water to salt solution was accurate and the size of the mass of the potato originally was not dissimilar to any of the other pieces. If I could repeat my experiment in order to improve on it I would probably make sure each potato was of identical mass. This means that the amount of water particles in each potato cylinder would be almost exactly the same and so the rate of osmosis in each potato should have a stronger proportional relationship. I would also obtain a larger range of data such as 0mol-1mol with intervals of 0.1mol rather than 0.2mol. This means that my conclusion would be more supported and I could make a more precise estimate of the isotonic point, which although accurate in my previous experiment could be improved. The equipment that I used in my experiment was pretty basic and had no usage of any technical equipment. If I had been able to have access to technology that could possible record the actually concentration on water in both the solution and potato core then this would have given me further evidence to support my prediction and would also be more precise. And although the environment that I perform my experiment in was reasonably controlled it would have been even more appropriate to perform the experiment in a far more controlled environment in which the aspects that could affect my experiment could be both measured and kept constant. This are the factors that I think are most relevant to improving on my investigation other than simply to be more cautious and observant when performing them. ...read more.

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