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What affects osmosis

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Introduction

Elena Uteva Investigating the factors that affect osmosis in a model potato cell Introduction In the following investigation, I shall explore and come to a conclusion on the effect of varying the concentration of the surrounding sucrose solution on a model potato cell. Osmosis is defined as the passage of water molecules through a selectively permeable membrane from a region of high water concentration to a region of low water concentration until a state of equilibrium is reached. The selectively permeable membrane is permeable to the solvent and not to the solute and therefore results in a pressure gradient across the membrane. My hypothesis regarding this investigation is that an increase in the concentration of the sucrose solution will decrease the mass of the potato chip. This is because a higher solute concentration will result in lower water concentration, since by increasing the solute concentration there would be more solute molecules in a given volume and hence a lower amount of water molecules. Therefore by placing the model potato cell into a hypertonic solution, the water concentration will be higher in the cell in relation to the solution (www.tvdsb.on.ca/westmin/science/sbi3a1/Cells/ Osmosis.htm) and consequently will result in the water molecules diffusing out of the cell and the cell loosing mass. Conversely, by decreasing the concentration of the surrounding sucrose solution on a model potato cell, the mass of the cell would increase. This is because by placing the model potato into a hypotonic solution, the water concentration is lower in the cell in relation to the solution and will result in the cell gaining turgor pressure and mass. ...read more.

Middle

Results Table showing the loss and gain of potato weight in solutions of different concentration Concentration of sucrose solution (%) Start weight of potato in grams (g) Weight of potato after a 24 hour period in grams (g) Weight loss/gain in grams (g) Average weight loss/gain excluding anomalies in grams (g) 0 5.21 6.63 +1.42 +1.43 5.20 6.65 +1.45 5.22 6.64 +1.42 5 5.18 5.69 +0.51 +0.50 5.19 5.67 +0.48 5.20 5.71 +0.51 10 5.22 4.81 -0.41 -0.41 5.21 4.80 -0.41 5.19 4.78 -0.41 15 5.20 4.34 -0.86 -0.87 5.19 4.31 -0.88 5.23 4.72 -0.51 20 5.25 3.81 -1.44 -1.47 5.18 3.70 -1.48 5.19 3.69 -1.50 25 5.23 3.29 -1.91 -1.95 5.21 3.27 -1.94 5.22 3.32 -1.99 I shall now use the following table to plot the results on a graph in order to analyse their reliability and the overall outcome of the experiment. Analysis By studying the graph shown above, which shows the line of best fit for the percentage change in the mass, it is evident that the concentration of the sucrose solution and the weight gain of the potato is not directly proportional to the each other because the line of best fit is not straight and does not go through the origin. However, as the concentration of the solution increases, so does the weight loss of the potato and this therefore shows that the weight loss/gain is inversely proportional to the concentration of the sucrose solution. ...read more.

Conclusion

As well as that, some of the water could have evaporated and made the solution more concentrated. To improve the overall accuracy and reliability of my experiment I would alter the method of the investigation. In order to control the surface area, I would have to cut the potato horizontally with a sharp knife or would have to use a machine to cut the potato chips into equal lengths and widths. In order to keep the surrounding temperature constant in my experiment, I would place the solutions and potato chips into the fridge. To make sure that the concentration of the solution remained the same, I would dry all the equipment thoroughly and would cover up the test tubes with cling film in order to prevent evaporation. I would also increase the amounts of different concentrations used so I would have more varied results and a more accurate isotonic point. As well as that, the measurement of the solutions could have been more accurate by using a burette to determine volume. The accuracy of the potato weight could also be improved by using digital scales to several decimal places. In conclusion, the investigation has shown me that by placing the potato into a concentrated solution the mass of the potato decreases, whereas by placing the model potato cell into a dilute solution, the mass of the potato increase. To further extend my investigation, I could test another variable and investigate its affects on osmosis in a model potato cell. For example, I could test the affect of the temperature or length of potato on osmosis 1 ...read more.

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A well planned investigation with excellent results tables and analysis which uses A grade biological terminology.

Marked by teacher Adam Roberts 10/05/2013

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