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To find out the net movement of water when potato chips are put in different concentrations of sucrose solution.

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Main Experiment Investigating the effect of osmosis in potatoes when put in sucrose solution Aim To find out the net movement of water when potato chips are put in different concentrations of sucrose solution. Scientific Knowledge Osmosis is the process by which water molecules pass through a partially permeable membrane from an area of high concentration of water to an area of lower concentration of water (e.g. from distilled water to concentrated sucrose solution). The reason for this is because of the natural tendency of water to spread from regions of high concentration to regions of low. This spreading process is called osmosis. Several examples of osmosis can be seen in nature that can give a better idea of what is happening during osmosis. E.g. if water is withheld from a flowering plant then the plant will wilt. If bacterial cells are placed in concentrated salt-water solution, they collapse and die. Human blood cells placed in fresh water expand and burst. The reason for these events is because of the partially permeable membrane present, in the plasma membrane. Water molecules are very small (one oxygen atom and two hydrogen atoms) while sugar molecules are many times larger. The membrane has very small holes or pores in it, that allows water molecules to pass through them because they are small enough, but do not allow sugar molecules to pass through because they are too big. Therefore when the water molecules are diffusing through the membrane, the side of the membrane, which is gaining water, will expand and increase in mass and volume, as the other side, from which the water molecules came from, decreases in mass and volume by losing the water molecules. Thus osmosis is the movement of water molecules only across a membrane. The water molecules will continue to diffuse across the membrane until equilibrium between concentrations is established. Below is a diagram showing osmosis and the net movement of the water molecules as described on the above: - OSMOSIS diagram (The Scientific knowledge, are extracts from Biology 1, OCR; Revise AS Biology, Fosbery, Gregory & Stevens and from the website: www.web.ukonline.co.uk/webwise) ...read more.


Leave the 24 test tubes, containing the chips for 24 hours. 10. Pour out the liquid. 11. Using paper towels, carefully remove any excess liquid from the potato chips, to ensure that when you record the final mass, the excess water won't cause any of the weight. 12. Place each chip on the balance, weighing its final mass. 13. Do this for all of the chips, and record the results. Safety For safety, you should tie back your hair, and ensure that you handle the scalpel with care when cutting the potato chips. In general this is a fairly low risk experiment. Sucrose is purely a sugar solution, therefore it is not an irritant or explosive. So there's no reason to wear safety goggles. A lab coat would be advisable to protect ones clothing from spillages. A lot of equipment is made from glass; therefore care must be taken to prevent these from falling and smashing. If such an accident were to happen simply use a dustpan and brush to clean up (not hands). Keep stools under tables when not in use and clear up any spillages quickly particularly those on the floor. Fair Test Make sure that there's exactly 10 cm� of solution in each test tube, containing the potato chip. Also repeat the experiment for each concentration at least three times, and use the average measurement. Result Tube No. Concentration (M) Length (cm) Average Length (cm) Mass (g) Average Mass (g) Change in mass (g) Before After Before After 1 0.00 1.00 1.00 1.00 0.51 0.53 0.52 -0.02 2 0.00 1.00 1.00 1.00 0.49 0.61 0.55 -0.12 3 0.00 1.00 1.00 1.00 0.50 0.61 0.56 -0.11 4 0.00 1.00 1.00 1.00 0.54 0.60 0.57 -0.06 5 0.20 1.00 1.00 1.00 0.53 0.65 0.59 -0.12 6 0.20 1.00 1.00 1.00 0.61 0.58 0.60 0.03 7 0.20 1.00 1.00 1.00 0.63 0.79 0.71 -0.16 8 0.20 1.00 1.00 1.00 0.69 0.81 0.75 -0.12 9 0.40 1.00 0.90 0.95 0.64 0.55 0.60 0.09 10 0.40 ...read more.


If the potato chips are from different potatoes, this could also affect the overall results. As each potato is planted from a different place, one of them could have more water molecules inside of it, than another. One could be `older' than another potato, thus it wouldn't be very effective to use such a potato, these are all factor affecting the result and outcome of this experiment. The experiment could have been extended, to a more exact level by looking at the potato cylinders under a microscope, and then one would be able to see the cells in greater detail and draw some more observational results. If another chance were given, to repeat the experiment the method itself wouldn't be changed, to find the sucrose concentration of the potato since this seems like a practicable method. However, in extension to the task, the mass of the potatoes could have been recorded at equally measured intervals throughout the duration of the osmosis process. This would be done, so more fairly mass values could be used to plot the graphs, thus making the graphs outcome more reliable. The use of a best line of fit could also be avoided in future, as it isn't as reliable as one would want it to. Its like an average, and averages are only as accurate as they can be, they aren't a 100 % correct. This could also be said for all the other averages taken such as the average changing mass, and average mass. When drying off the excess water on the potato cylinders after the experiment and before weighed, a paper towel was used. This might have either taken some water out of the potato or it might of left some excess water on the potato. This part of the experiment is difficult to come up with an accurate and fair method, as other ways would also lead to some slight mistakes. Other improvements to the procedure of the experiment could be to keep all of the test tubes refrigerated, this is to help the preservation of moisture (water molecules). ...read more.

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