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Biology Coursework-Osmosis

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Introduction

Biology Coursework-Osmosis Aim To find out what effect altering the concentration of sucrose solution would have on the occurrence of osmosis in a potato. Prediction I predict that as the concentration of the sugar solution around the potato decreases, the size of the potato will increase. I have come to this conclusion due to the previous work we have done on osmosis. So, if we put a potato in a 2M concentration of sucrose it would decrease in size, whereas if we were to put it in a 1.5 M concentration it would not decrease as much in size as the one in 2M concentration. Essentially what I am saying is that as the concentration increases, so will the amount of mass lost by the potato. I feel that nearer the extremes of concentration the results will be more closely grouped. Reason Osmosis is a process in which water moves through a partially permeable membrane. It will move from a higher concentration of water to a lower concentration. For example:- if there was one side of a partially permeable solution with 8/10 parts water and the other side was 4/10 parts water, the side with 8/10 would flow from its higher concentration to the lower concentration in an attempt to even out the concentration on both sides. The reason the water molecules are able to pass through and even out the concentration is that they are small enough to fit through the membrane whereas the sucrose molecules are too large to fit through. Below is a diagram to show osmosis across a partially permeable membrane: Due to the water molecules being smaller than the sugar molecules, they are able to fit through into the cell. ...read more.

Middle

Evidence I measured 5 different concentrations of solutions to make sure that I got a meaningful set of results. I feel that taking 5 different concentrations was varied enough to get a fair set of results due to my preliminary work. Also testing it three times allowed me to identify any anomalies that may have occurred and consequently take them in to account. Accuracy The way I have ensured maximum accuracy is to use 25ml measuring cylinders and made sure not to contaminate all the equipment. Also, and most crucially, I am repeating the experiment 3 times so as to obtain maximum accuracy and then taking an average figure. Recording Evidence I think that a clear and concise way would be to put them in a table such as the one shown below:- SEE TABLE ON NEXT PAGE m Volume (ml) Volume of water (ml) Volume of sucrose (ml) Initial mass (g) After mass (g) Change in mass (g) Average change in mass (g) % difference average % difference 2 20 0 20 1.90 0.91 -0.99 -52% 2 20 0 20 1.89 0.82 -1.07 -1.02 -56% -54% 2 20 0 20 1.87 0.865 -1.01 -54% 1.5 20 5 15 1.90 1.13 -0.77 -40% 1.5 20 5 15 1.922 1.11 -0.81 -0.79 -42% -41% 1.5 20 5 15 1.93 1.14 -0.79 -40% 1 20 10 10 1.94 1.58 -0.36 -18% 1 20 10 10 1.87 1.49 -0.38 -0.36 -20% -19% 1 20 10 10 1.90 1.56 -0.34 -18% 0.5 20 15 5 1.94 1.99 0.05 0.02% 0.5 20 15 5 1.87 1.97 0.10 0.08 0.05% 0.04% 0.5 20 15 5 1.90 2.01 0.11 0.05% 0 20 20 0 1.86 2.20 0.34 18% 0 20 20 0 1.88 2.29 0.41 0.36 21% 19% 0 20 ...read more.

Conclusion

One way to avoid this would be to use complicated machinery to weigh and cut the potato; although beneficial, this wasn't practical. So just taking extra time and care with the cutting would make it more accurate. I could have done more work. I could have done the experiment more times to gain a more accurate result . Also I could test more of a range of concentrations - again to obtain a more accurate result. Also I could experiment with exposing the same weight pieces , but with different surface areas. This would be interesting to do. The results were perhaps a bit undetermined here and there. I think this could have been from one, if not more of the above factors. If I was to repeat the experiment again then I would go to a higher concentration to see what happens in relation to the cell wall. And exactly how much osmosis is able to occur and what would happen to the cell and its wall when it reached the limit. The reason I would do this as I think it would be both interesting and beneficial to see what the capabilities of the cell and its cell walls were. Also if I were to do it again I would test more values of concentration. For example I tested 0,0.5,1,1.5,2. Then I would go in to more values like 0,0.25,0.5,0 .75,1, 1.25.....etc. The reason for this is I feel it would provide me with more accurate results to base my graph and theories on. Also I would like to see how the surface area would affect osmosis. This is because I feel that it would be interesting to know what affect it has and to compare it to the other set of results I obtained. ?? ?? ?? ?? ANDREW DUNCAN 10P BIOLOGY MRS HUGHES OSMOSIS COURSEWORK ...read more.

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