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Investigation Into How Osmosis In Potatoes Is Affected By Solution Concentration.

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Introduction

Emily Grant 2003 Investigation Into How Osmosis In Potatoes Is Affected By Solution Concentration PLAN Aim To investigate how the concentration of a salt and water solution affects the rate of osmosis in a potato. Osmosis Osmosis is the passage of water from an area of high water concentration to an area of lower water concentration, through a partially permeable membrane (a membrane which allows small molecules like oxygen, carbon dioxide, water, ammonia, glucose etc to pass through, but does not allow larger molecules such as sucrose, starch, protein etc). Cell membranes are partially permeable, which allows water to pass from one cell to another within the organism, and also, as I will be exploring in this investigation, from outside to inside, or vice versa. Osmosis occurs when the area of liquid outside the cell contains more water particles than the area of liquid inside the cell. In the solution, the particles are moving all the time. In a solution in which the concentration of water is high, there are more water particles per cm3 than in a dilute solution, and therefore a higher rate of movement, causing more particles to come into contact with the membrane. In a more dilute solution in which there are less water particles per cm3, less movement occurs and therefore less particles will pass through the membrane. Also, in the solution with low water concentration, there are more particles of sugar or in this case salt, which form a weak attraction with the water particles, inhibiting movement. Therefore, there will be more water moving from the area of high water concentration. This diagram shows how osmosis occurs. The diagram shows an area of high water concentration (on the left) and one of low water concentration. The dashed line at the centre represents a partially permeable membrane, while the large red circles symbolize the salt particles and the smaller blue ones, the water. ...read more.

Middle

1. Select an average-sized potato and feel it to make sure it is ripe and firm. Use an apple corer to cut out a cylinder of potato, making sure it is at least 3 cm long. 2. Using a calliper, measure the potato cylinder and, using a sharp knife, cut it to 3 cm long. 3. Use a paper towel to dry the potato cylinder and leave it on the towel. 4. Repeat with 2 more cylinders from the same potato. 5. Measure the mass of each potato cylinder using top-pan balance and record it. 6. Impale the potato pieces on a small length of wire. 7. Using a measuring cylinder, accurately measure out 60 ml of distilled water and put it in a beaker. 8. Measure out 40 ml of 1M salt solution and add it to the beaker. 9. Measure out 35ml of this solution and put it into a boiling tube. 10. Use a thermometer to measure the temperature of the solution in the boiling tube. Record the temperature. 11. Add the potato cylinders to the solution and put a bung in the boiling tube. 12. Put the boiling tube into a test tube rack. 13. Record the time at which the potato cylinders were added to the solution. 14. One hour from this time, unstop the boiling tube and pour the contents into a beaker. 15. Remove the potato cylinders from the beaker and dry each one with a paper towel. 16. Measure the mass of each cylinder using top-pan balance and record it. 17. Measure the length of each cylinder using the callipers and record it. 18. Repeat with solutions of 0M, 0.2M, 0.6M, 0.8M and 1M. Equipment List Potatoes Apple corer Calliper Sharp knife Paper towels Top-pan balance Measuring cylinder Beaker 6 boiling tubes + bungs Thermometer Test-tube rack Distilled water 1M salt solution Diagram Fair Test There are a number of variables which could affect the rate of osmosis in a piece of potato submerged in a salt solution. ...read more.

Conclusion

I think this can only be because of mistakes made with the measuring either before or after; if I were to do this experiment again, I would make sure that that could not happen. If I were to do the experiment again, I think I would do it using smaller pieces of potato and larger amounts of solution. Also, I would perform the repeat readings in separate boiling tubes as opposed to all in the same one. I would do this because I think it would enable more osmosis to occur, thus giving me a better idea of how the concentration of the solution affects osmosis. In this investigation, the mass of the potato only changed very slightly, and the differences in the changes of mass were also small. I think if I performed the investigation with more solution per potato piece, and left it for longer, it would enable more osmosis to occur and would be a better portrayal of how the molarity of a solution affects the rate of osmosis. Further Investigations There are a number of further investigations that could be performed to do with osmosis. One could investigate the effect that surface area of a potato has on the rate of osmosis; this would be done in the same way as the investigation which I carried out, except that the molarity of the solutions would stay the same, and it would be necessary to change the surface area of the piece of potato by increasing the length and/or width. I think that this investigation would show that more osmosis occurs in a piece of potato with a larger surface area, because there is more partially permeable membrane for the water particles to go through. One could also investigate osmosis in different types of potato, or in different types of fruit or vegetable altogether. For something completely different, you could investigate osmosis in animal cells, specifically red blood cells, in which osmosis occurs when placed into water (this is called endosmosis-the opposite of this is called exosmosis). You could investigate how the concentration of a salt solution affects this. ...read more.

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