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Osmosis Investigation. To investigate osmosis I decided to test how the salt concentration of a solution affects osmosis in a potato and where the isotonic point of potato is.

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Introduction

Osmosis investigation By Alasdair Lindsay-Walters Contents Page Scientific explanation................................................................................................3 Introduction.............................................................................................................4 Preliminary test........................................................................................................4 Graph [1]................................................................................................................5 Method...................................................................................................................6 Results table............................................................................................................7 Graph [2]................................................................................................................8 Observations................................................................................................................................9 Conclusions and evaluation.......................................................................................10 What is osmosis? Diffusion is the spontaneous and passive overall movement of substances from high concentration regions to low concentration regions. It is spontaneous and passive because no energy input is required by the cells for this process to work. Despite some particles being able to move back to the high concentration regions (this is because the process is random), the general movement of particles is form a high concentration to a low concentration. Substances such as oxygen, carbon dioxide and dissolved food move in and out of cells by diffusion. Osmosis is the diffusion of water from a dilute solution with a high water concentration to a more concentrated solution with a low water concentration through a semi-permeable membrane. The membrane allows the water molecules through, but no the solute molecules as these are too large: The effect of osmosis is to gradually dilute the concentrated solution. This is what happens at root hair cells, where water moves from the coil into the cell by osmosis, along a concentration gradient. Eventually the level on the more concentrated side of the membrane rises, while the one on the less concentrated side falls. When the concentration is the same on both sides of the membrane, the movement of water molecules will be the same in both directions. At this point, the net exchange of water is zero and there is no further change in the liquid levels. ...read more.

Middle

x 1cm (width) x 1cm (height). Using these sizes enabled me to successfully measure the difference in weight effectively; as if I had used smaller sizes it may have been harder to measure each cutting accurately on the scales. This was also the maximum size I could cut out of the potatoes I was using whilst keeping coherently in line with the parameters I had I chose to use. Following this, I measured out 9 equal sized potato cuttings of 5cmx1cmx1xcm (LxWxH) (I did this by cutting potatoes with a scalpel, measuring them against a ruler). Poured the solutions into the test tubes using the beakers each solution was in before- each concentrated solution into 3 test tubes, and then placed one potato in each test tube. I left them in the solution for 3 hours and measured them again I made up the dilutions for the preliminary test as in the table- I measured these in a burette: Equipment list: * 2x Burettes * 9x Test tubes * 2x Beakers * 2x Funnels * 1x Test tube rack * 2x Clamp stands with bosses * Scientific scales * Scalpel These are the results: Concentration Weight Before (g) Weight After (g) % change Mean % change Range 0 4.08 4.61 12.99 12.46 1.18 4.29 4.83 12.59 4.32 4.83 11.81 1 4.17 2.89 -30.70 -24.09 12.91 4.33 3.3 -23.79 4.33 3.56 -17.78 2 4.32 3.55 -17.82 -17.75 0.14 4.24 3.49 -17.69 4.23 3.48 -17.73 (See graph [1]) ...read more.

Conclusion

However, the scales used to measure the weight were a lot more accurate and gave accuracy to the nearest .0 of a gram, therefore this was more reliable. Furthermore, the burette is read off by eye and it is easy to interpret where the liquid is at wrongly. It was vital for the measurements to be 100% accurate so I therefore made sure that I read the burette accurately in order to ensure that my results wouldn't be affected. There was also the possibility that all of the solutions and potatoes may have been at different temperature which could cause different rates of reaction-e.g. if one solution was at a higher temperature the particles would move faster and therefore there would be a bigger difference between the solution outside the potato and inside the potato resulting in more osmosis in a shorter amount of time. This was easily overcome make sure everything is same temperature (room temperature). To improve the method I would give less time from cutting the potato and placing into the solutions, this is because other factors could have affected the potato while it was about to be put into the solutions-e.g. the potato cuttings could have been left in different places like in sunlight where its temperature would have changed, affecting the rate of osmosis. Judging by my data I would say that the results are fairly reliable as the majority of error bars are small. There are some that I would re-test with more time, as what would seem to be anomalies are in fact in line with the expected trend. ?? ?? ?? ?? 5 ...read more.

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