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Investigating the effect of sucrose concentration on osmosis in potato cells

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Introduction

Investigating the effect of sucrose concentration on osmosis in potato cells Osmosis is a vital process that takes place in living organisms. It is the movement of water molecules across a partially permeable membrane and involves the movement of water molecules from a high concentration to a low concentration. It is used in organisms to transport water through the cell membrane into the cells, so it is essential for respiration or take place, as photosynthesis requires water. An important example is in root hair cells in plants, whose purpose is to draw in water and minerals from the soil, therefore osmosis is used to transport water into the plant. Another example in plants is the opening and closing of the stomata. The stomata are tiny holes on the underside of leaves, which allow carbon dioxide required for photosynthesis into the plant for gas exchange to take place. Water moves into guard cells by osmosis, causing their vacuoles to fill the entire cell, so that they are turgid and they close up the stomata. They can also lose water by osmosis, becoming flaccid to open the stomata. In humans, osmosis has an important role as well. It ensures that all cells have the correct amount of water inside them, preventing them from bursting or dying. In the kidneys, it makes urine more concentrated by reabsorbing water into the blood by osmosis. Osmosis is also how the body absorbs water into the bloodstream. So in summary, osmosis is a very useful process in plants and animals, and it would not be possible to survive without it. In this experiment I am going to look at osmosis across the cell membranes of potato cells, using sucrose solutions. I will try to find out exactly how the concentration of this solution affects osmosis. I am going to use circular disks of potato placed in six different concentrations of sucrose solutions, which I will leave to allow osmosis to take place. ...read more.

Middle

I have examined all possible variables, and have looked at the best ways to counter them, so my results should be accurate as well. In summary, I am hoping for a very successful experiment. Results Table showing change in mass of potato cells after being left in sucrose solution of different concentrations (Results in grey are anomalous results that were discounted before averages were formed, results in red are results that are repeats for the anomalous results; all results to 2 decimal places)) Concentration of Sucrose Solution (Mols) Start Mass (g) End Mass (g) Percentage Change in Mass (%) 1 2 3 4 1 2 3 4 1 2 3 4 Average 0.0 4.18 4.6 3.63 n/a 4.47 4.91 3.95 n/a 6.94 6.74 6.94 n/a 6.87 0.2 4.02 3.62 3.85 n/a 4.12 3.75 3.97 n/a 2.49 3.59 3.11 n/a 3.06 0.4 3.54 4.29 4.11 3.44 3.55 4.95 4.10 3.45 0.28 28.48 -0.29 0.29 0.09 0.6 3.94 4.21 3.88 3.50 2.87 4.01 3.64 3.30 -27.16 -4.75 -4.75 -5.71 -5.07 0.8 4.04 3.77 3.18 2.67 3.75 3.64 3.00 2.54 -7.18 -3.44 -5.66 -4.87 -5.90 1.0 3.52 3.16 3.46 3.56 3.16 3.14 3.09 3.32 -10.23 -6.55 -9.11 -8.43 -9.26 This is a selection of my calculations, to show how I worked out the percentage change in mass and average: Result 1 - Concentration 0.2 M Start Mass: 4.02g End Mass: 4.42g Percentage change in mass: 4.12 - 4.02 = 0.1 (0.1 / 4.02) x 100 = 2.49% Result 2 - Concentration 0.2 M Start Mass: 3.62g End Mass: 3.75g Percentage change in mass: 3.75 - 3.62 = 0.13 (0.13 / 3.62) x 100 = 3.59% Result 3 - Concentration 0.2 M Start Mass: 3.85g End Mass: 3.97g Percentage change in mass: 3.97 - 3.85 = 0.12 (0.12 / 3.85) x 100 = 3.11% Average Percentage Change in Mass - Concentration 0.2 M 2.49 + 3.59 + 3.11 = 9.19 9.19 / 3 = 3.06 % Analysis I can conclude from my results that the potatoes gain less, and then lose more mass as the concentration of solution increases. ...read more.

Conclusion

I could have instead looked at the amount of time taken to reach a constant mass, when osmosis has finished in each experiment. Another problem was that, in the more concentrated sucrose solutions, the discs were less dense than the solution, so they floated. This decreased the amount of osmosis that could take place, because it decreased the available surface area of the potato tissue. To counter this, I could have used something like wire mesh to keep them in the middle of the solution, not affecting their surface area as much. If I were to do a further experiment, I think I would look at more closely the concentration inside the cell sap. I know it was around 0.4 M, so if experimented between 0.3 M and 0.5 M sucrose concentration, I could find out more accurately where it was. My experiment would work in the same way as my previous one, except the concentrations would be 0.3 M, 0.35 M, 0.4 M, 0.45 M and 0.5 M, with one in distilled water (0 M) as a control. I would expect to once again find the water potential of the cell sap around 0.4 M. I think that my results are reliable enough to support my conclusion for the substances used, ass there were very few anomalies and I repeated enough times so that I had three valid results for each concentration. However, they cannot support my conclusion for different concentrations of solution, such as stronger concentrations than 1 M. It also cannot support my conclusion for tissue other than potato or solutions other than sucrose. In summary, I have had a successful experiment in which I have managed to conclude that, in potato cells in sucrose solution, potatoes gain mass at solution concentrations lower than 0.405 M and lose mass at higher concentrations through osmosis. 1 For the purpose of these diagrams, I have taken the mols of a solution to be its percentage concentration, so 0.2 M = 20%, 0.4 M = 40%, etc. ?? ?? ?? ?? Page 1 of 10 ...read more.

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Here's what a teacher thought of this essay

4 star(s)

**** A very thorough and well researched report.
Planning The key variables are discussed and are controlled well. A pilot experiment was used to inform the planning of the experiment.
Obtaining Evidence The data has been recorded well and anomalous results repeated. A good range of molarities was used.
Analysing Evidence It would have nice to see the plotted graph. The results were discussed at length and anomalies identified. The relevant scientific background theory was used to interpret the results.
Evaluation A well considered evaluation with some thought given to how the method could be made more valid and the range of the investigation extended to enable the water potential of the potato tissue to be calculated.





Marked by teacher Stevie Fleming 03/01/2013

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