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Our aim was to discover the water potential of potatoes cells using different concentrations of sucrose solution

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Introduction

Finding the water potential of potato cells Aim: Our aim was to discover the water potential of potatoes cells using different concentrations of sucrose solution Science: Osmosis is 'the movement of water molecules from a region of higher water potential to a region of lower water potential through a semi-permeable membrane' www.s-cool.co.uk 'Water can move between cells (unligninified) freely as the cell walls are permeable. However its movement is controlled by a number of factors, which are given names; solute potential (), Pressure potential (+ Matrix potential =0 normally)() and water potential (). Solute potential (): this refers to the amount of substance dissolved in the cytoplasm. This effects water movement because water always moves from a less concentrated medium to a more concentrated medium. Pressure potential (): this refers to the pressure exerted by the cell walls. In a plant, the cell will fill with water until the inner membrane is pushing on the outer membrane to the same force as the wall is pushing back; they then are equal forces and cancel out. Therefore there is no more movement of water. Water potential (): this is a figure worked out from the equation; water potential = solute potential + pressure potential (). The figure represents the tendency of a cell to give out water. http://www.restoringearth.co.uk/site/ossmosis.htm Water moving out of cells causes them to lose turgor pressure - cell membrane detaches from cell wall and shrinks (wilting) - plasmolysis Water moving into cells causes them to become turgid, swollen - deplasmolysis http://biomicro.sdstate.edu/Hutchesh/bio101/Graphics/lab4/tsld011.htm The is a dilute solution inside the potato cells due to it's cell sap, this is a 'Dilute fluid found in the large central vacuole of many plant cells. ...read more.

Middle

Transferring the solutions into the McCartney bottles The McCartney bottles are glass and if they topple over the will smash, the shards of glass could cut someone Hold the bottles steady whilst pouring liquid into them, and wear goggles in case of glass shards Using syringes to make the sucrose solutions The sucrose could squirt out of the syringe and could get someone in the eyes Ensure goggles are worn to prevent solutions coming into contact with the eyes Apparatus: * Distilled water * McCartney bottles and lids * Sucrose solution * Potato * Syringes * White tile * Scalpel * Ruler * Balances * Cork borer * Tissues Method: * Find the cork borer with a diameter of 0.8 cm to cut out the potato chips * Put a potato of a white tile to cut the potato- and NOT on your hand as the cork borers are very sharp and will easily cut your hand. * Cut out six cylinders of potato * Ensure there is no skin left on the potato cylinders * Line the six cylinders up and cut the all to 3 cm long. * Weigh each cylinder making sure you know which mass applies to which cylinder and then put the cylinders to the side * Make the sucrose solutions; adding different amounts of 1M sucrose and water can make these. For the 1M sucrose solution measure out 10cm of the sucrose with no water, for the 0.8M measure out 8cm of sucrose and add 2cm of water to make it up to 10 cm. ...read more.

Conclusion

3 cylinders will be needed for each concentration to reduce the risk of anomalous results. 2. Using a scalpel cut all the potato cylinders down to 3 cm and ensures there is no skin left on them, as the skin is less permeable and will affect the movement of water. 3. Weigh each chip and record this on a table, ensure you know which mass goes with which chip so that when they are re-weighed the mass change can be calculated. 4. Make up the sucrose solutions using the method above as guide for the different concentration. 5. Pour the solutions into the McCartney bottles and label immediately to prevent any confusion later. 6. Add the potato cylinders to the solutions, ensuring you know which cylinders are going into which solution, as three cylinders will be going into each McCartney bottle, colour code them so you can tell them apart and know which one weighs what. 7. Replace the lids on the McCartney bottles to prevent the loss of water by evaporation, which would effect the sucrose concentration. 8. After 24 hours, remove the cylinders from the solutions, blot with a tissue and reweigh, do one solution at a time to reduce confusion but don't take too long on each one. Record the results immediately 9. Calculate the average change in mass and plot a graph of mass change against concentration. 10. Find the point where the mass change is 0; find the concentration, which corresponds to this and that is the equivalent water potential. Using the graph of water potential against Sucrose concentration, (ref- see appendix) the concentration for no mass change can be converted into water potential (kPa). This will give you the water potential of potato cells. ...read more.

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