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Investigating the effects of osmosis on potato cylinders.

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Introduction

Tom Buckland Biology Coursework SC1 Investigating the effects of osmosis on potato cylinders Centre Number 10144 Candidate Number 1913 Background Science Osmosis is the passage of water from a region of high water concentration to a region of low water concentration through a semi-permeable membrane - Oxford English Dictionary Online Figure 1 - Showing the effects of osmosis In a high concentration of water the amount of solute (e.g. salt) is low. This is called a dilute solution. In a low concentration of water the amount of solute (e.g. salt) is high. This is called a concentrated solution. When a semi-permeable membrane the water divides two such solutions will move from the region of high concentration to the region of low concentration, until both sides are equal (have reached equilibrium). Osmosis occurs across a semi-permeable membrane whenever there is a difference between the water concentrations on the two sides of the membrane when this happens, cells will either become turgid if water flows into them, or plasmolysed if water flows out. Figure 2 - Showing Equilibrium This can be seen in living cells. The cell membrane in cells is semi-permeable and the vacuole contains a sugar/salt solution. So when a cell is placed in distilled water (region of high water concentration), water will move across the semi-permeable membrane into the cell (region of lower water concentration), through osmosis, making the cell swell. ...read more.

Middle

* Calliper * Measuring cylinder * Distilled water * Cutting tool * White tile Safety There are many potential hazards in this investigation that must be taken into account. They are outlined in the table below - Hazard Solution Cutting someone with a razor / knife blade Use caution when using the blades. Cut away from yourself and other people. First aid should be available should any incident occur. Breaking any glass objects (Boiling tubes etc) Inform the member off staff then sweep up the glass and place it a broken glass container (if available) or in the bin. Getting any solution in eyes Wear safety goggles at all times during the experiment. Should any solution enter someone's eye, the eye should be washed immediately. Method With the changes from my preliminary experiment outlined in my plan, I shall use the following method in my final investigation - Set Up * Set up six boiling tubes in a boiling tube rack * Label them with the concentration of solution they will contain * In five of the tubes place 35ml of each of the chosen solutions * In the remaining tube place 35ml of distilled water * Select six approximately equal length cylinders of potato * Allocate each cylinder to a concentration of solution * Measure each cylinder individually (noting the length) * Then weigh each of the cylinders (noting the mass) ...read more.

Conclusion

2.92g - 0.95g 47mm 44mm - 3mm 0.5 mol/ dm-3 3.92g 2.75g - 1.17g 45mm 41mm - 4mm 0.6 mol/dm-3 4.18g 2.77g - 1.41g 46mm 39mm - 7mm 0.8 mol/dm-3 3.92g 2.39g - 1.53g 46mm 38mm - 8mm 1 mol/ dm-3 4.22g 2.67g - 1.55g 47mm 39mm - 8mm Experiment 3 Concentration of salt solution Mass before experiment Mass after experiment Change in mass Length before experiment Length after experiment Change in length 0 mol/dm-3 4.27g 4.82g + 0.55g 48mm 52mm + 4mm 0.2 mol/dm-3 4.36g 4.00g - 0.36g 49mm 48mm - 1mm 0.4 mol/dm-3 4.38g 3.37g - 1.01g 49mm 45mm - 4mm 0.5 mol/ dm-3 4.44g 3.19g - 1.25g 50mm 44mm - 6mm 0.6 mol/dm-3 4.19g 2.81g - 1.38g 48mm 41mm - 7mm 0.8 mol/dm-3 4.53g 3.10g - 1.43g 50mm 41mm - 9mm 1 mol/ dm-3 4.44g 2.81g - 1.63g 50mm 40mm - 10mm Appendix C - Glossary Equilibrium Isotonic is when a cell has the osmotic pressure to that of the surrounding medium. Osmosis is the passage of water from a region of high water concentration to a region of low water concentration through a semi-permeable membrane. Plasmolysed is when a cell has suffered from plasmolysis (see below). Plasmolysis is the loss of water by osmosis from a plant cell to the extent that the cytoplasm shrinks away from the cell wall. This happens when the cell is placed in a solution that has a higher solute concentration than that of the cell sap. ...read more.

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