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How does concentration affect osmosis?

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How does concentration affect osmosis? Osmosis is the movement of water from a high concentration to a low concentration through a partially permeable membrane. This lowers the concentration of the strong solution, and evens out the concentrations on either side. Biological knowledge The water molecules can actually pass through the membrane in two directions, but as there are more molecules on one side than on the other, there is a net flow of water to the side with less water molecules. The sucrose molecules are too large to pass through the partially permeable membrane (also known as a cell surface membrane), so can not pass the other way, and the partially permeable membrane does not allow dissolved substances to pass through. The completely permeable cell wall in plant cells acts as a resistance against the partially permeable cell surface membrane. The cell wall is very strong- strong enough to stop the cell bursting, even when it is full. Even when the cell loses water, the cell wall stays reasonably firm, although the cell becomes a lot less rigid. Pure water has a water potential of zero, so solute makes the water potential lower- or more negative. This means that water moves from a less negative water potential to a more negative water potential. At the end of the experiment, I will look at the net mass difference of the potato cylinders, that is, the overall movement of water which has taken place as a result of osmosis happening. Osmosis is the process by which plant cells become turgid- that is, when the osmotic pressure builds up and the cell swells. Plant cells are not pure water, they are solutions, so they have a lower water potential than pure water. This means that when the cell is placed in pure water, water molecules move into the cell, causing the cell to swell. However, plant cells do have a higher water potential than a strong sugar solution. ...read more.


79 79 79 79 Length after (mm) 79 74 79 77 % difference 0 -6.33 0 -2.53 40 minutes Distilled water 0.3M/dm� 0.7M/dm� 1M/dm� Length before (mm) 79 79 79 79 Length after (mm) 78 75 78 77 % difference -1.24 -5.06 -1.27 -2.53 I found that there was little mass difference in the cylinders that were in the solution for 20 minutes, and looking at my results I can see that I found more percentage difference in the cylinders that were left in the solution for 40 minutes, so 40 minutes would be a more useful time to use than 20 minutes. I also found that I had difficulty getting cylinders 79mm long and I wasted a lot of time trying to get cylinders of this length, so when I next do the experiment I will use smaller cylinders- about 55mm long, which should be a more suitable length. In order to ensure that my results are reliable, I will repeat the experiment 3 times, and then take the average difference of the 3 results for each concentration. By repeating the experiment, any anomalous results will stand out more clearly, so I can then decide whether to repeat that particular cylinder and concentration. Concentration of sucrose solution in Mol/dm� Anomalous result/s 0.0 0.2 0.4 0.6 0.8 1.0 1.0 Set 1 -Cylinder length in mm before 55.0 55.0 55.0 55.0 55.0 55.0 55.0 Set 1-Cylinder length in mm after 56.0 55.1 54.0 53.2 51.4 51.0 52.0 % difference +1.8 +0.2 -1.8 -3.3 -6.6 -7.3 -5.5 Set 2- Cylinder length in mm before 55.0 55.0 55.0 55.0 55.0 55.0 Set 2- Cylinder length in mm after 57.2 56.1 55.3 53.0 53.2 52.0 % difference +4.0 +2 +0.6 -3.6 -3.3 -5.5 Set 3- Cylinder length in mm before 55.0 55.0 55.0 55.0 55.0 55.0 Set 3- Cylinder length in mm after 57.3 57.0 53.0 53.4 52.4 51.1 % difference +4.2 +3.6 -3.6 -4.6 -4.7 -7.1 Average % difference +3.3 +1.9 -1.6 -3.8 -4.9 -6.6 Raw Data ...read more.


However, the average points allowed a line of best fit to be drawn. To extend and go into more detail on this experiment, I would repeat it exactly using one or more other types of vegetable, such as turnip or carrot. To do this I would have to cut exactly the same size cylinders of each vegetable tissue, and make different concentrations of sucrose solutions, as I did in this experiment. I could then use the same timings I used for the potato cylinders (40 minutes), and leave the other vegetable cylinders in for that same amount of time, before taking them out, removing excess solution, and recording the difference in mass. By trying the experiment with other tissues, I could compare the difference the concentration of sucrose makes on the net movement of water molecules in, or out, of the vegetable tissue. Risk Assessment * While the sucrose solution is not corrosive, any spillages will become slippery and potentially hazardous, so they should be wiped up immediately. * To protect clothing, wear laboratory coats, and use goggles to protect eyes. * Also, the sucrose solution is not particularly irritant, but as there is the possible risk of an allergy, it should be wiped off if it comes in contact with skin, and if it comes in contact with the eyes the eyes should be washed out. * Cork borers can be potentially hazardous, so when using to cut potato cylinders, ensure that the hand holding the potato is not covering the exit route of the cork borer. * If any glass is broken, a teacher should be alerted to that fact, and the glass should be cleaned up using a dustpan and brush in a safe manner. Be careful that all the pieces of glass are cleared up. * Be careful with sharp pieces of equipment (such as scalpels), so as not to cut yourself, and when cutting use a tile to protect the surface you are working on. ...read more.

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