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Osmosis Investigation

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Apparatus: 6 specimen tubes Scales (g) Potato Sizes 1 and 2 bores Distilled water 1,2,4,6,8 molar sucrose solutions Filter paper Pipettes Blade Method * Initially I took the potato and cut a strip out of it with my size 2 bore. I carefully pushed it out with my size 1 bore making sure that it landed on the filter paper. I repeated this process 6 times. * I then took the 6 strips of potato and placed them on the cutting board. I called the teacher to supervise me using the blade and then I cut the potato strips so that they were exactly the same size, making sure the two ends of skin were cut off. * I then placed the strips back on their pieces of filter paper and using a very accurate electronic scale, I recorded the weight in a table of results. * I took my boiling tube and placed a strip in it. I then measured out of distilled water and poured it into the boiling tube. I repeated this for 1, 2, 4, 6, and 8 molar sucrose solutions. * I left the potato strips in the tubes for 48 hours. ...read more.


This is why it is called a SELECTIVELY PERMEABLE MEMBRANE. There is a higher concentration of sugar molecules on the right hand side of the membrane than on the left hand side. If the membrane was not there, the sugar molecules would diffuse from the concentrated solution to the dilute one until they were evenly spread out. However they cannot do this because the pores in the membranes are too small for them to get through. There is also a concentration gradient for the water molecules. On the left hand side there is a high concentration of water molecules. On the right hand side there is a lower concentration of water molecules because the sugar molecules are taking up a lot of the space. The molecules are not evenly spread out so the water molecules diffuse through the pores to the right hand side. They can do this because the pores are large enough for them to fit through. As the diagram illustrates, water has diffused from the dilute solution, through the selectively permeable membrane, into the concentrated solution. The concentrated solution will become more dilute, because of the extra water molecules coming into it. This process is called osmosis. ...read more.


If the cells become plasmolysed, the potatoes will shrivel up and become useless, as the cells inside are dead. Link: So if a chip shop owner pre-cuts chips and stores them in water before they are served to the customers. The owner has found that by storing the chips in water, it causes them to taste soggy when cooked. To prevent this he adds salt to the water, however on the other hand he has found that by adding too much salt it will also have an effect on the taste of the chips. I am going to investigate this by placing slices of potato in different concentrated solution and examine the changes to the potato. I am going o try to find the best concentration of solution that least affects the taste of the potato. Prediction: I think that as the chips are placed in distilled water, the mass will increase because the water will diffuse into the cells of the potato. I predict that if the potatoes are placed in a salt solution, the mass will decrease because the water from the cytoplasm will flow out through the selectively permeable membrane along the concentration gradient into the salt solution, in other words the cell will lose water and possibly be plasmolysed. I think that this will vary as the concentration of the solutions change. ...read more.

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