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How does concentration affect osmosis?

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How does concentration affect osmosis? Rajwinder Mandair April 07 Introduction Osmosis is the diffusion of water molecules that occurs only when there is a movement of water molecules from a region of higher concentration to a region of lower concentration through a partially permeable membrane. The process ends only when the two concentrations are equal or the cell is unable to take any more water because the cell is turgid. For osmosis to take place a partially permeable membrane is required to allow water movement to take place and to prevent such a transfer between other molecules. If a cell is in contact with a solution of lower water concentration than its own contents, then water leaves the cell by osmosis, through the cell membrane. The living contents of the cell contracts and eventually pulls away from the cell wall and shrinks, this is known as plasmolysis. If you put a plant cell in water, water enters by Osmosis, and then swells up. However, the cell will not burst. This is due to the fact that the cell walls are made from cellulose, which is extremely strong. Eventually, the cell stops swelling, and when this point is reached, we say the cell is turgid. Plan for Pilot experiment Apparatus: 300cm3 1 Molar sucrose solution Distilled water A potato - White potato preferred No. ...read more.


Results - For Pilot experiment Concentration of sucrose solution / M Length of potato cylinders / cm Percentage difference in length / % 1st reading 2nd reading 3rd reading 0.0 0.2 0.4 0.6 0.8 1.0 1.8 1.6 1.5 1.3 1.4 1.2 1.6 1.6 1.5 1.4 1.2 1.2 1.6 1.6 1.6 1.4 1.3 1.3 20.00 6.67 6.67 -8.89 -11.11 -17.78 The highlighted data in the table are anomalies because these cylinders had one face covered with potato peel. The potato peel affected the amount of osmosis that took place in the 23 hours because the potato peel is not partially permeable membrane therefore osmosis cannot take place in those regions with the potato peel still in place. Potato cylinder Length 1.5 cm The total surface area of potato cylinder = 6.283185307 cm2 Surface area of potato peel = 0.785398163 cm2 Percentage of potato peel = 12.5% The fact that 12.5% of the potato's surface area was inactive in the process of osmosis can be demonstrated by comparing the results for the potato cylinders with peel and those without peel. For example: For the distilled water the length of the potato without peel was 1.8cm whereas with peel it was 1.6cm. Percentage difference for 1.8cm potato cylinder (without potato peel) ...read more.


Whereas the rods placed in high concentrations of sucrose were very bendy and were rather wilted. The reason for the change in structure was probably caused by the movement of the water particles from the sucrose solution and the potato. Results - For experiment Analysis Looking at the graph which I have produced to demonstrate how the concentration affects osmosis the line of best fit is negative. This shows that the potato cells increase in length in solutions with a higher water potential and decrease in size in solutions with a low water potential. This was not surprising as in earlier experimens and from past knowledge I am aware that osmosis occurs down the gradient. Osmosis with low sucrose concentration Osmosis with high sucrose concentration However, I believe that there is a limit to how much water can be lost after a higher concentration of sucrose due to the fact that the cells has been completely plasmolysed. Evaluation During this investigation it was very difficult for a person to be accurate. For example, cutting the potato cylinders accurately to 1.5 centimetres was demanding task and even then accuracy wasn't assured because the rules used could only measure to the nearest millimetre. In addition to this measuring the change in length was hindered by measuring with a rule since many rods happened to be bendy not straight. The handling of the ...read more.

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