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Osmosis. An experiment to find the concentrations of salt solution which is the same as the concentration of cell sap in a potato.

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Introduction

An experiment to find the concentrations of salt solution which is the same as the concentration of cell sap in a potato. Concentration of salt in solution/ % Mass of potato core at start/ g Mass of potato core at end/ g Change in mass/ % % change in mass/ % 10 2.03 1.99 - 0.04 - 1.97 8 2.13 2.05 - 0.08 - 3.75 6 2.14 2.12 - 0.02 - 0.93 4 1.95 1.93 - 0.02 - 1.02 2 2.16 2.11 - 0.05 - 2.31 0 2.17 2.15 - 0.02 - 0.92 Investigation > To find out about osmosis in potato cells. > To find the concentration of salt solution which is the same as the concentration of cell sap in the potato. Prediction > The higher the concentrations of salt solution, will make the potato go flaccid. > However, the lower concentrations of salt solution will make the potato go turgid, increasing the length and mass. Biological knowledge which supports prediction > Osmosis- diffusion of water molecules from a dilute solution to a concentrated solution across a semi-permeable membrane. > Potatoes don't have a very salty taste so there is a probably a more dilute solution of salt solution in the cell sap. ...read more.

Middle

1-6) and record its number in the table, as when you have finished the experiment it would be easier to compare the core to its original weight. 7. Place each potato core in of the test tubes, and leave for 30 minutes. - Remember to time on the stop watch! 8. After 30 minutes, removed each core, and dry them carefully with a paper towel. Now, weigh each core, and record. 9. Compare with previous weight. 10. The one which weighs the same as it weighed before being put into the solution is the one with the same concentration of salt in the cell sap of potato, as the salt solution. Because my results were unreliable, and inaccurate, the teacher provided the class with an accurate set of results, where the experiment had take place for 5 hours. Because of this, the changes in mass for potato cores depending on the amount of salt concentration were more precise. Table of results, from accurate + reliable experiment: Concentration of salt solution/ % % change in mass Mean % change in mass 10 -3.62 1.89 -1.36 -1.03 8 -1.81 -0.63 -0.34 -0.93 6 -1.38 -1.18 0.66 -0.63 4 -0.9 -1.23 2.62 0.16 2 0 1.85 1 0.95 0 3.2 2.53 1.37 2.37 Analysis The shape of the graph was a smooth curve sloping downwards. ...read more.

Conclusion

The ranges of concentrations were adequate but I would extend the range of concentrations so that there would be more varied results, i.e. 1, 2, 3, 4, and so on. Another way of improving the results would have been to leave the experiment running longer, this would have enabled me to find the saturation point (when the potato can no longer take in any more water) and dehydration point (when the potato cannot lose any more water) and therefore attain more accurate results. The cutting of the potatoes was the most difficult part of the experiment as although I was recording my results by mass, it could have affected the surface area and so the overall rate of osmosis. If I were to repeat the experiment I would have found a machine to cut the potato, as it would ensure that all potato cores would be the same weight and dimensions. Finally, I would have achieved more precise results through measuring out the solutions more accurately. This could be done using a pipette. In conclusion, I have been able to draw up a final theory which has proved my prediction to be correct: As the concentration of salt increases, the mass of the potato decreases. ?? ?? ?? ?? Melissa Patel - 11th October 08 ...read more.

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