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Finding out the affect of different concentrations of sucrose solution on the mass of potato chips.

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Biology Coursework Finding out the affect of different concentrations of sucrose solution on the mass of potato chips Introduction The aim of this investigation is to see when osmosis occurs in potato cells and whether anything happens to them when they are put in different concentrations of sucrose solution. I have to apply my background knowledge to devise an experiment which will tell me whether if different concentrations of water molecules in a solution will affect the mass of plant cell when they are put into it. Background knowledge Osmosis is like diffusion but only of water molecules and it only happens when there are different concentrations of water molecules on either side of a selectively permeable membrane. The selectively permeable membrane "gaps" are only small enough to let water molecules pass through and not big molecules such as sucrose molecules. Water molecules from each side of the membrane always pass to the other side. When one side of the selectively permeable membrane has a higher concentration of water molecules than the other, more water molecules from the side containing a higher concentration of water molecules will pass through to the side with a lower concentration of water molecules. Less water molecules from the side with a lower water molecule concentration will pass to the other side because there are less of them. If the concentration of water molecules on either side of the selectively membrane is the same then the net flow of water in either direction will be the same. This results in no net flow of water-osmosis. An example of osmosis happening in a plant cell is when a potato chip is put into distilled water. The cell membrane of the potato cells is the selectively permeable membrane between the concentration of water molecules inside the potato cells and the distilled water that is outside of the potato cells. As the concentration of water molecules is of a higher concentration in the distilled water than inside the potato, there are ...read more.


* Forceps * Paper towel Method Using a cork borer I will cut out 5 potato cylinders. To make sure they are of the same length and diameter I will line them up and use a scalpel to cut the ends so they are of 4.5 mm in length. I then have to blot them dry with a paper towel to remove surface water. I will then weigh each one on the top pan balance and record the mass (grams to 2.d.p.) in a table below. I will fill each specimen tube with one of the different concentrations of sucrose solution so that one specimen tube has 25cm3 of distilled water and another has 25cm3 of 5% sucrose solution etc. I will put one potato cylinder in each of the filled specimen tubes and put the bung on. I will leave the potato cylinders in the specimen tubes for 21 hours. After the potato cylinders have been left in the solutions for 21 hours, I will take the potato cylinders out of the specimen tubes with forceps. I will put the wet potato cylinder on a paper towel and blot them dry. I will put them on the top pan balance and record the mass in the table shown below. % concentration of sucrose solution Start mass (g) Mass after 21 hours (g) Change in mass. Percentage change in mass Turgid/flaccid Distilled water 0% 5% 10% 15% 20% 25% I will then calculate the mass change and the percentage change. Also note down the state the potato cylinder is in-is it flaccid or turgid. (changes in mass have to be recorded to 2.d.p) Use these calculations for the changes in mass: The change mass=mass after 21 hours - start mass Percentage change in mass=change in mass/start mass x 100. (Note that the signs before the values are to show whether they have lost mass (-) ...read more.


To this in a future experiment that requires a weigh, I could use one that will give more accurate masses e.g. gives masses to the nearest 0.0001g instead of the normal 0.01g. Even though the results were fairly close to 'line of best fit' on my graph, there was one that was not as close to the line of best fit than the others. I think this result is a slight anomalous result as the mass is slightly lower than of the expected mass shown by the line of best fit. I think this was probably caused when I blotted excess water off with a paper towel, I took off too much water and therefore took off some of the mass too but the result still supported my conclusion as it followed the overall trend of the data. In order to make sure this does not happen again, I need to have a system or way of taking the same amount excess water off all the potato chips. Maybe next time I could roll each potato chip down the paper towel once and blot the ends of them two times on the paper towel. To prove that my prediction is correct in any osmosis experiment, I could do another experiment, which shows osmosis happening and why it happens-different concentrations between a selectively permeable membrane. The experiment is shown below: Apparatus * 20cm in length visking tubing. * 20cm3 water * 10cm3 plastic syringe * testing tube Method Tie a knot at the end of 20cm length visking tube that has been soaked in water. Put 3cm3 of strong sugar solution in the plastic syringe and use that to partly fill the visking tube-it should be floppy. Place the visking tubing into a test tube containing water 20cm3 . Leave the visking tubing in the test tube for about 30-45 minutes. You should record your observations of the visking tubing before it was put into the test tube of water and after it had been left in the water. Look for any changes in how it looks and feels. ...read more.

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