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To determine how the concentration of salt water affects osmosis in potatoes

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Introduction

Investigation - To determine how the concentration of salt water affects osmosis in potatoes Planning Aim - To determine the effect the concentration of water has on osmosis in potatoes Prediction - I think that when the concentration of salt water is higher then there will be a greater loss of weight in the potatoes. This is because the water molecules inside the potato move from an area of high water concentration to low water concentration. When the concentration of salt is higher it will therefore have a lower water concentration meaning that there will be a steeper concentration gradient. The salt molecules will not diffuse into the potato because they cannot pass through the partially permeable membrane. I think that in all the salt solutions above 1% the potato will become plasmolysed. Whilst this doesn't usually happen the potato will be surrounded by solutions of a very high concentration. It will become plasmolysed because a lot of water will have left the cell to the point when the cell wall can no longer shrink and the cell membrane will tear away from the cell wall. This will kill the potato cell. ...read more.

Middle

Original mass (g) New mass (g) % Change 0% 2.95 3.01 2.03 1% 2.97 2.94 -1.01* 2% 2.85 2.63 -7.72 3% 3.09 2.83 -8.41 4% 2.83 2.67 -9.19 5% 3.12 2.86 -8.33 Concentration (%) Original mass (g) New mass (g) % Change 0% 2.82 2.88 2.12 1% 2.98 2.87 -3.69 2% 2.96 2.77 -6.41 3% 3.08 2.87 -6.82 4% 3.02 2.82 -6.82 5% 3.05 2.7 -11.48 Concentration (%) Original mass (g) New mass (g) % Change 0% 3.34 3.41 2.1 1% 3.03 2.99 -4.62 2% 3.22 3.13 -2.8* 3% 3.35 3.22 -3.88* 4% 3.2 3.09 -3.44* 5% 3.33 3.2 -3.9* Concentration (%) Average % Change 0% 2.08 1% -4.16 2% -7.07 3% -7.62 4% -8.01 5% -9.91 * Believed to be an anomalous result and therefore excluded from calculations Analysis Whilst no formula can be determined to summarize the trend, there is a clear trend. The trend is shown clearly by the graph overleaf. When the salt water is more concentrated, above 2% more weight is lost from the potato because the cells become plasmolysed and die. However in tap water there is a small gain in weight, because the cell becomes turgid. ...read more.

Conclusion

I therefore think that the evidence is sufficient. I think that the experiment could have mainly been improved by being more precise generally. Due to time constraints we seemed to choose reliability over accuracy and produced several anomalies in the process. If I could repeat the experiment I would do only 2 sets of results but be as precise as possible. If I then didn't have 2 sets of results close together I would do repeats where necessary. I think that the way we did it meant that our conclusion is not as firm as it could have been. Also we could have dried the potato off more thoroughly because the excess of surface moisture on the potato made it too heavy and adversely affected the results, especially in the 3rd set. I think that using sugar water instead of salt water could extend the enquiry. This could finally prove the conclusion by showing that it works for solutions apart from salt. Or use a different plant apart from potatoes such as apples because at the moment the conclusion only describes potatoes in salt water and is therefore not particularly "concrete". Jonathan Laurence 10.5 ...read more.

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