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An investigation into the effects of osmosis on potato tissue.

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Biology SC1 PLANNING Title An investigation into the effects of osmosis on potato tissue Aim To see how the concentration of a sucrose solution surrounding some samples of potato tissue will affect the percentage change in mass of the potato after a set length of time. Brief explanation of diffusion and osmosis Diffusion-is the net movement of particles from an area of higher concentration to an area of lower concentration. The process is purely physical and doesn't require energy from respiration. Cells take up oxygen and get rid of carbon dioxide by diffusion. Osmosis-a special case of diffusion where water passes in and out of cells from an area of higher concentration to an area of lower concentration through a partially permeable cell membrane. The mass of various objects in a water based solution will vary according the amount of water it has gained or lost due to osmosis. Variables * Change in mass of potato * Change in volume of potato * Change in length of potato * Concentration of sucrose solution * Temperature of the solution * Volume of the solution * Type and size of potato * Time in solution I have created a table to make it easier to see the best variables to select for the investigation: Variable Easy to Change in Lab Easy to Measure I can get at least five results I can explain the science Change in mass Yes Yes Yes Yes Change in volume Yes ...read more.


* Alter time to 15 minutes to allow osmosis to take place fully Prediction Background Science of Osmosis Osmosis is a special case of diffusion. Biochemical processes in living cells always take place in a solution. The solvent (dissolving fluid) and solute (particles dissolved in the solvent) are the two parts of a solution. In living organisms: the solvent is water and the solution is called an aqueous solution. Living cells are separated from their surroundings by the partially permeable cell surface membrane. The contents of the cell, the cytoplasm, is one aqueous solution and the surroundings of the cell (e.g. pond water) are also an aqueous solution. If the two solutions do not have identical concentrations of various substances then the molecules may move from one solution to the other by diffusion, if the cell membrane is partially permeable. Here is my prediction of what I think will happen: Concentration of Sucrose Solution (M) Prediction 0.0 Potato will absorb water and increase in size. 0.5 Water in potato is of a higher concentration than the solution, water in potato passes into solution. Potato loses mass. 1.0 Water in potato is of an even higher concentration; therefore potato loses even more mass. 1.5 As the amount of sucrose increases, the loss in mass increases 2.0 " " In the first solution which is entirely distilled water; the potato will gain mass. ...read more.


I constructed the table below to try and discover why the gradient does this. Average % Change in mass Difference between the changes +3.62% -------------------------------------------------- -1.46% -5.08 -6.44% (bigger change) -4.98 (smaller change) -8.50% (bigger change) -2.06 (smaller change) -10.40% (bigger change) -1.09 (smaller change) Although the mass decreases by a larger percentage as the concentration of sucrose is raised, the difference between these average changes in mass becomes smaller. This is shown in the table above. This is the reason the gradient slows down at the end of the graph. General conclusion This experiment has worked smoothly and efficiently. As the concentration of sucrose solution surrounding a sample of potato tissue increases, the percentage loss in mass increases. Although as the percentage loss in mass increases, the difference between them decreases. This is why the graph is in an "S" shape. Evaluation My method was suitable and I have no alterations to make towards it. However, I have some ideas on how to improve the method. * A small guillotine mechanism would be more accurate at making equally sized potato samples * A dryer would do a better job at removing surface moisture than the paper towels. Although it would have to be a blow-dryer and at a cool temperature to avoid drying out the potato completely * I could extend the time limit beyond 15 minutes to make sure that osmosis has taken place fully, although this could allow enough time for the temperature to change Jack Cullen 4set3 ...read more.

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