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Investigation on Osmosis.

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Carly Mckenzie 19TH April 2002 Investigation on Osmosis Aim We are trying to discover how changing a certain variable would affect the rate of osmosis of skinless potatoes. Variables There are several factors which affect the rate of osmosis such as the potato (in this case) must not have any peel on it as the peel of a potato is impermeable and therefore would prevent the movement of the water. Here are the possible variables (listed below): - * The width and length give different surface areas which change the amount of osmosis performed by the plant (bigger surface area = more osmosis and vice versa) * Different vegetables have different concentrations of solution inside * Temperature-high temperatures give a faster rate of osmosis * The volume of the solution-the potato must be entirely covered for complete osmosis * Light intensity-strong light gives heat. (Heat as said above) * The type of solution e.g. sugar solution * Must use the same potato as different potatoes may have different concentrations inside * Must have a bung to prevent evaporation of the solution We are changing the concentration of the solution. We are going to be changing it to 0.0M, 0.2M, 0.4M, 0.6M and 0.8M. Prediction Osmosis is the movement of water from a dilute solution (lots of H20) to a concentrated solution (little H20) through a semi-permeable membrane. The experiment we are performing determines how different concentrations of solutes (e.g. salt) affect the rate of osmosis. Below shows a diagram of osmosis From the pilot experiment we could see that when the potatoes were placed a dilute solution (where there is more water and less solute) ...read more.


At this point there is no Osmosis taking place. We know this as the weight of the potato hasn't changed when the line crosses the X-axis and so no water has had to move to balance the concentrations. The point at which it crosses the X-axis is the concentration inside the potato. The average concentrations of my potatoes are 0.41 M. From my graph (above) you can see that when the concentration of the solution is below 0.41 M the potato gains weight especially when the concentration is exceptionally low such as when the concentration is 0.0 M (the lowest) the potato is at its heaviest (0.33g). This is because water moves into the potato due to there being less water inside the potato than outside of it, so water moves in due to osmosis and causes it to put on weight and become turgid. A potato placed in a solution of 0.0 M will gain the most weight in this case because the most water has to move in to balance the concentrations both inside and out. So compared to a potato placed in a solution of 0.4 M the potato will not gain a lot of water to balance up the concentrations because they have similar concentrations both inside and out. The same applies for the highest concentration which is 0.8 M as the most water moves out and so the most weight is lost. I.e. The lower the concentration the heavier the potato From my graph you can see that when the concentration is higher than 0.41 M the potato looses weight, particularly when the concentration was at its highest in this case 0.8 M when the potato lost an average of 0.34g. ...read more.


They can be placed in a straight line and sliced together and so will all have the same length and thusly the same surface area. 5. Be a lot more careful when removing the potato from the solution, and ensure that not too much pressure is put on it whilst transferring it from the solution to the scales. 6. Blot the potatoes. Make sure that each potato has been blotted an equal amount of times to make sure that the test remains fair. 7. Place the potatoes in an incubator to ensure a constant heat. There are many different experiments that can be carried out to see how osmosis ranges and to expand on the experiment that we have already performed such as: - * We can use a different root vegetable to see how osmosis ranges in this type of vegetable. * We can use a different range of concentrations. We used the even concentrations and so to get a broader idea of osmosis in potatoes we could use the odd ones such as 0.1 M, 0.3 M, 0.5 M, 0.7 M, and 0.9 M. * To find out the actual concentration inside the potato we could use some more precise measurements of the concentrations around the point at which the line crossed the X axis on my graph. This point was 0.41 M and so we could use concentrations of 0.38 M, 0.39 M, 0.40 M, 0.41 M, and 0.42 M. * We could repeat the experiment around our anomalous result to find out for sure what it was meant to be. * We could carry out the experiment in different temperatures to how this affects osmosis. In conclusion, the osmosis of a skinless potato is affected when placed in solutions with concentrations less than 0.41 M and solutions with concentrations higher than 0.41 M. ...read more.

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