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Investigating Osmosis.

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Introduction

Investigating Osmosis Aim Our aim is to investigate what the effect is of 7 different concentrations of sucrose solutions on the potato cylinders. Background information Osmosis is the passage of a solvent (e.g. water) through a semi permeable membrane (one that acts like a sieve) from a less concentrated (weaker) solution to a more concentrated (stronger) one. Osmosis occurs whenever solutions of different strengths are separated by a semi permeable membrane and continues until the solutions are of equal strength unless the movement of solvent is opposed by applying pressure to stronger solution. The pressure needed to stop all such movement is called osmotic pressure.(is basically the measure of whether it is likely to lose or gain water molecules to another solution) Semi permeable membranes are widespread in the body - they surround all cells. These membranes allow water, salts, simple sugars (such as glucose), and amino acids (but not proteins) to pass through. Consequently, osmosis plays an important part in regulating the distribution of water and other substances. Osmosis involves water molecules only. The factors which affect osmosis are the concentration of the water molecules, the distance over which osmosis has to occur and lastly the temperature of the solution. ...read more.

Middle

Test tube no. 1 2 3 4 5 6 7 Sucrose solution % 10 5 1 0.5 0.1 0.01 0 ..Then you place a single potato cylinder into each of the 7 test-tubes, insuring that the solution covers the cylinder. ..You then leave the test-tubes overnight ..Next day, you remove the potato cylinders from their tubes and blot them dry ..Then you measure the new length(c) and the new mass (d) of each potato cylinder again. ..You then calculate the change in length(e) by finding the difference between the lengths (a) and (c) for each potato cylinder (would have been a gain or loss in length) ..Also you calculate the change in mass by finding the difference between mass (b) and (d) for each potato cylinder. ..Finally you note what each cylinder feels like. (is it firm=turgid or limp=flaccid) Fair test In order to make this a complete fair test, we measures out the required sizes of potato cylinder and volumes of sucrose solutions accurately. Also to make it fair we washed out each of the measuring cylinders each time we added a different sucrose solution. ...read more.

Conclusion

Lastly we could of increased the range of sucrose concentration so that it would give us a longer range of results so it would be easier to spot any mistakes or where I went wrong.(0.02, 0.03, 0.75 etc ) The accuracy of my results was pretty accurate as it showed me plenty of patterns and trends. The only unusual result I found was the change in mass for 0.1% concentration of sucrose. The change was -0.2 and it seemed wrong as I would of thought that it would of gained some mass and also the change in mass of 0.01% was higher than 0 which seemed unusual as I would expect 0 to have gained more mass. This could have been because washing out the measuring cylinder may of left some in the measuring cylinder and this would change the concentration leading to different results. I would extend the experiment by doing it over about 3 times more to see if all the results are near enough the same so I would know that my conclusion was right and also I would this time definitely use a electronic pipette washing our probably changed results. Finally increasing the range of glucose solution would help as it would show if this pattern carries on or not and therefore it can back up the conclusion. ...read more.

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