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Chardakov's Banana Experiment

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Becky Saveker Chardakov's Banana Experiment Introduction The ability of water molecules to move is known as their water potential. Water molecules always move down a concentration gradient towards a region of lower water potential, that is, to where there are fewer water molecules, to where the water potential is relatively more negative. As the water potential of one solution decreases, the density of the solution increases and as the water potential of a solution increases the density of this solution decreases. This would mean that if at all mixed, the less dense solution (i.e. the one with the lease negative water potential) would float on top of the denser solution (the one with the most negative water potential). The movement of water molecules down a concentration gradient (from a higher water potential to a lower water potential) through a partially permeable membrane is called Osmosis. Apparatus * 12 test tubes * 1 test tube rack * 1 banana * 1 knife * 2 syringes * 1 square tipped needle * 1M sucrose solution * Methylene Blue (stain) ...read more.


After this, cut up the banana into six pieces so that they are all as near to the same size as possible and small enough to fit into the test tubes. Put one piece of banana into one of the test tubes from each pair and then add one drop of Methylene blue stain to each tube that has a slice of banana in it and then gently shake each of these tubes gently to mix in the stain. Leave the experiment for a minimum of 20 minutes to allow the banana slices to soak. After 20 minutes or so, take the square tipped needle and attach it to a small syringe. Take some of the stained solution from one pair and add one drop to the other test tube of that pair, which has the same concentrated solution. To insert the drop u place the tip of the needle into the middle of the solution and then push out one drop of the stained solution. ...read more.


I can conclude this because the stained 0.4M solution hovered in the other 0.4M solution. This shows that their densities were equal, showing that the water potential of each solution was the same. Therefore, osmosis did not take place between the banana and the first solution, because there was no downward concentration gradient so the water molecules did not favour going to one side of the semi-permeable membrane or the other. The banana can therefore be said to have had a sucrose concentration of 0.4M. Sources of Error * Surface area of banana may have differed * Banana may have been bruised or otherwise damaged * Volumes of solution may have differed * Number of drops of methylene blue stain may have differed * May have dropped more than just one drop of stained solution into the other tube. * May not have injected stained solution directly in the middle of the other solution, therefore affecting whether it hovered/sank/floated. * Different time for each banana slice in the solutions, allowing for more osmosis to take place. * Dilution process may have resulted in mistake of resulting concentration ...read more.

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