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Osmosis, My aim for this experiment is to see the results of potato tissue's mass difference, when placed in different concentrations of sugar solutions. Variables involved:

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Introduction

Osmosis Background Information Osmosis is defined as the movement of water molecules from an area of high water concentration to an area of low water concentration, across a semi-permeable membrane. In a high concentration of water the amount of solute (e.g. sugar) is low. This could be called a weak or dilute solution. In a low concentration of water the amount of solute (e.g. sugar) is high. This could be called a strong or concentrated solution. When two such solutions are divided by a semi-permeable membrane the water will move from the area of high concentration to the area of low concentration, until both sides are equal (have reached equilibrium). This can be seen in living cells. The cell membrane in cells is semi-permeable and the vacuole contains a sugar/salt solution. So when a cell is placed in distilled water (high water concentration) water will move across the semi-permeable membrane into the cell (lower water concentration) by osmosis, making the cell swell. This cell is now referred to as turgid. If done with potato cells the cells would increase in length volume and mass because of the extra water. If these potato cells were placed in a solution with a low water concentration, then the opposite would happen. Water would move out of the cell into the solution. In extreme cases the cell membrane breaks away from the cell wall and the cell is referred to as plasmolysed. The potato cells will have decreased in length, volume and mass. ...read more.

Middle

When the concentration gradient is lower in the potato, the water will transfer from the solution into the potato. In the distilled water, I believe that the water is more concentrated in the potato, and therefore the water should transfer from the water to the potato, making the potato bigger in size, and heavier in weight. The potato tissues, being surrounded by a weak solution, will be most likely to swell up and become turgid, taking in all the water it can possibly take in. With the potato in 0.1 molar solutions of sucrose, I don't think there will be much change in the weight of the potato. This is because there isn't much difference between the two substances. I believe that the weight and the size of the potato won't be altered much. The 0.25 molar solutions of sucrose, similar to the 0.5 molar solution of sucrose, compared to the potato, both substances have very close concentration gradients. And that is why I am predicting that the weight of the potato in this experiment should be decreased by only a fraction. The 0.75 molar solution of sucrose, I think, should make a big difference now, noting that it should be a large difference between the two concentration gradients. And therefore the weight should decrease, at least for us to notice with the naked eye. The difference between the water concentration in the potato and the 1 molar solution of sucrose is big, and the water in the potato should be transferred from the potato, through the permeable membrane, to the solution surrounding the potato. ...read more.

Conclusion

Also when the potato was dried to remove surface liquid it was not necessarily done the same on each potato, a more accurate and uniform way of drying would improve the accuracy further. Using more types of molar sucrose solutions would have helped us obtain better results, and more accurate results; so that we can make sure the results are totally correct. Experimenting with one set for a longer period of time, for each set, would lead us to better results, because the osmosis action would reach its maximum capability, and therefore tells us how much water could be transferred for each solution. Also the shape and size could be changed. However this would not affect the results much. This is because the variable would only change the rate of osmosis because of a different weight and size. Temperature could also be changed for example the samples could be placed in different water baths and brought up to different temperatures to see if temperature played its part in the osmosis of potatoes. 5 sets of 3 potato samples could be placed in water baths at 10oC, 20oC, 30oC, 50oC and 60oC. Then leave them for 24 hours making sure all the variables in the first experiment still apply however just using one molar solution. Then after 24 hours re-weigh the samples and record the result. I would expect that at high temperatures the potato samples would osmosis the most. This is because at high temperatures the solutions water molecules would move faster and therefore equal the concentration faster. But overall, given the apparatus that I got to carry out the test, I think this experiment turned out to be very successful, and I'm very please with my results. ...read more.

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