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Potato and Osmosis Investigation.

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Introduction

Biology Coursework: Potato and Osmosis Investigation. PLANNING: (P) Some background Information: Water Potential and Living Plant Cells Plant Cells in Pure Water: If plant cells are placed in pure water (a hypotonic solution) water will initially move into the cells. After a period of time the cells will become turgid. Turgor pressure is the pressure exerted against the cell wall by contents of the cell. At first most water movement is into the cell. As the turgor pressure increases water will begin to diffuse out of the cell at a greater rate, eventually equilibrium will be reached and water will enter and leave the cell at the same rate. Free Energy and Water Potential: Free energy can be simply defined as the energy available (without temperature change) to do work. Chemical potential of a substance is the free energy per mole of that substance. Water potential is the chemical potential of water and is a measure of the energy available for reaction or movement (Bidwell 1974:59). Water potential is important when studying osmosis because it measures the ability of water to move, water always moves from areas of high potential to areas of low water potential. The formula for calculating water potential is: Water Potential = Osmotic Potential + Pressure Potential Water Potential in Plant Cells: Water will move by osmosis into and out of cells due to differences in water potential between the cell and its surroundings. Remember that water always moves from areas of high potential to areas of low water potential. Some Basic Principles: * Water always moves from high water potential to low water potential. * Water potential is a measure of the tendency of water to move from high free energy to lower free energy. * Distilled water in an open beaker has a water potential of 0(zero). * The addition of solute decreases water potential. * The addition of pressure increases water potential. * In cells, water moves by osmosis to areas where water potential is lower. ...read more.

Middle

We must also be careful when using the scalpel, when we cut our chips so we don't accidentally cut ourselves and also wear goggles when our solutions are being stirred by the 'electronic heat stirring' machine. We will use five different sucrose solutions, the table below show the precise measurements of sugar to use, plus the molar mass we will use. Molar concentration Mass of Sugar (g) 0.5 Molar 17.1 0.4 Molar 13.68 0.3 Molar 10.944 0.2 Molar 8.7552 0.1 Molar 4.3776 Apparatus: Below is a list of the apparatus we will use when conducting our main experiment: * Potato * Core borer (diameter of 10mm) * Scalpel * Sugar ( at 5 differently weighed measurements) * Water (5 x 100ml of water) * 5 beakers * Weighing machines * Electronic heat stirring machine * Goggles * Paper towels Method: Below is a bullet point format of our investigation will be set out. * Collecting our beakers, filling each one with the volume of 100cm� of distilled water. * Next we will be collecting our sugar, measured to the most accurate measurements to the nearest 0.01g, we can get in relation to be required, and this ensures a fair experiment. * After weighing our sugar we will cut our potatoes using a core borer, we have to ensure that all our potato chips have precisely the right length and diameter this should enable us to have a fair experiment. * Next, we will be able to add our sucrose to the water and with an electronic heat stirring machine place our beakers with the sucrose solution in it and stir it up so we can dissolve the sucrose to create a n equilibrium in the solution (if this didn't happen the sugar would just dissolve to the bottom of the beaker and there would be a greater water potential at the top and not at the bottom). ...read more.

Conclusion

Especially with the different concentration levels, time can have an effect because it does take time for net movement to pass through a semi-permeable membrane and it would be useful to conduct a test in the future to see what the affects would be if we increased or decreased the time period. I think what would be interesting would be one test that was 24 hours long and one that was 72 hours long. I think our test overall was fair and accurate. EVALUATION: The effect of anomaly results means that some areas of my test may be unreliable as regards to how the change in mass was affected by different concentration levels. For example the mass of potato chip left in a molar concentration of 0.5 is vastly different from one that was left in 0.4 M, why though? I thought when the experiment was complete I would be able to draw a graph that had an angle of 45? however there is a much steeper drop between 0.4 M and 0.5M on my graph. I think I'd have to say 0.5M would be one point I would rule out for the next experiment. I think overall my prediction did work well because from my prediction and test I was able to match my ideas and theories with the experiment, so that part was a success, I did obtain anomalies as mentioned above and some improvements which could be made are more accurate measurements with weight and length of chips, make some changes with concentration levels of our sucrose solution, this has been mention previously on pages 9 and 10 and more time and care taken to improve on drying our potato chips; this my reduce the weight of our chips and give more accurate weight measurements when we do our final weigh in. I think was experiment was a good for obtaining evidence and therefore had no need to do a re-test of our potato chips, on a photocopied sheet of my graph I have circled my anomaly results (sucrose concentration level of 0.5M) ...read more.

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