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Osmosis Investigation

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Prediction I predict that in a high salt solution the potato core will loss mass because water will leave the cells because of osmosis and the net movement through the partially permeable membrane will be from the potatoes to the water. Also if in pure water the potato cores will swell and gain mass because water will enter the cells by osmosis and the net movement through the partially permeable membrane will be from the water to the potatoes. At some point the concentration of the water and the concentration of the potato cores will be the same and there will be a movement of particles through the partially permeable membrane but it will have no net movement e.g. the mass will remain unchanged. Scientific Reason for Prediction Osmosis is the movement of water molecules across a partially permeable membrane from a region of high water concentration to a region of low water concentration. First the definition of osmosis: Partially permeable membranes are very thin layers of material (cell membranes are partially permeable) which allow some things to pass through them but prevent other things from passing through. Cell membranes will allow small molecules like Oxygen, water, Carbon Dioxide, Ammonia, Glucose, amino-acids, etc. to pass through. Cell membranes will not allow larger molecules like Sucrose, Starch, protein, etc. to pass through. A region of high concentration of water is either a very dilute solution of something like sucrose or pure water. ...read more.


+0.17 -0.36 Percentage change in mass +13.9% -30.8% Conclusion By looking at my results I have come to the conclusion that: > I will use potatoes cores that are 3cm long and size 4 diameter. > I will leave the potato cores in the chosen liquid for around hours and 40 minutes to get a good result. > I will place the core in 20mls of liquid so the cores get completely immersed. Variables * My independent variable will be what strength of solution I will use for my potato cores to go in. E.G. 0.0, 0.2, 0.4, 0.6, 0.8 and 1.0 molar solution. * My dependant variable will be the change in mass that the potato cores undergo * My control variables will be how long the potato cores will be (3cms), the volume of the solution (20ml), and the length of time that we leave the potato cores and the diameter of the potato cores (size 4). Apparatus * 2 measuring cylinders (each holding at least 20mls of solution) * Top pan balance (that must be accurate to 2 decimal places.) * Potato cores (3cms in length, size 4 in diameter.) * Test tubes (that must hold the potato cores and the solution) * Knife (that must be able to cut thorough the cores.) * White tile * Clock Safety * Students must wear goggles to protect their eyes for splashes of solution * Students must also be careful when using knife to insure no injury takes place. ...read more.


Although it was a good investigation my results weren't really clear enough on my graph most of the points are in line with the curve of best fit but there are a few anomalies (these were for points 0.2M and 1.0M). The results were clear enough to back up my predication also the graph supports my prediction by clearly showing that if a potato core is placed in a solution with a high salt concentration it will decrease in mass. My experiment was a fair test and I did 3 repeats for each concentration so it was reliable. I carried out my experiment correctly and all results came form the same experiment so this was not the reason for my anomalies. I think that I would have improved the clarity of my results if I was able to measure the lengths of the cores more accurately and if I was able to get all the cores from the same potato. If I had used the same potato e.g. one large one rather that two smaller ones. then the results would have been more accurate because a different potato core could start off with a different salt concentration. I could have also been more accurate if I had insured that each potato core had been in the solution for the same amount of time even though I don't think a matter of a minute or so would have really mattered. I am confident that I did what I set out to do. E.G. prove what happens when osmosis takes place. ?? ?? ?? ?? Biology Coursework By Rachael Cathrew - 1 - ...read more.

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