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# Investigating osmosis in potato cells

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Introduction

Investigating the Isotonic Point Of Potato Cells - Preliminary Work Osmosis Osmosis is a process where water molecules move across a semi-permeable membrane from areas of high water concentration to areas of low water concentration. Movement of water in and out of plant cells through the cell membrane is an example of osmosis. Isotonic Point If a piece of potato is placed in a glucose solution it will either gain or lose water due to osmosis as water moves across the cell walls of the potato. The concentration where there is an equal flow of water moving in and out of the cell through the cell membrane defines the isotonic point. Independent variable The concentration of glucose solution will be varied. Dependant variable The change in mass of the potato cylinder (in grams) from beginning to the end of the experiment will be observed and measured. Fair Test To ensure that the experiment is kept fair, the size and shape of the potato cylinder will be kept the same, the amount of time the potato is immersed in the water will be kept the same and to ensure that any excess glucose solution is not weighed, after the experiment the potato cylinders will be dabbed on filter paper. ...read more.

Middle

After ten minutes the potato pieces were withdrawn from the test tubes and dabbed on filter paper to minimalize any excess glucose solution. Finally the potato cylinders were weighed; the results recorded and change in mass worked out. Results Glucose concentration (M) Initial Mass Final Mass Change (g) Change (%) 0 3.9 4.528 0.628 16.1 0.2 3.852 4.063 0.211 5.5 0.4 3.916 3.669 -0.247 -6.3 0.6 3.889 3.531 -0.358 -9.2 0.8 3.915 3.434 -0.481 -12.3 1 3.888 3.46 -0.428 -11.0 The results above suggest that the isotonic point is between 0.2M and 0.4M as the change in mass between these two point changes from an increase to a decrease. The isotonic point where there is no increase or decrease in mass must therefore be in this range. Investigating the Isotonic Point Of Potato Cells - Final Experiment Independent variable The concentration of glucose solution will be varied. Dependant variable The change in mass of the potato cylinder (in grams) from beginning to the end of the experiment will be observed and measured. Fair Test To ensure that the experiment is kept fair, the size and shape of the potato cylinder will be kept the same, the amount of time the potato is immersed ...read more.

Conclusion

This graph shows the potato cells tested had an isotonic point of 0.245M. The results above and the attached graph prove that my earlier prediction was correct. At 0 or low concentration levels the potatoes gained mass as water enters the cell. As the concentration levels were increased the potatoes increased in mass less until crossing the isotonic point. After crossing the isotonic point the potatoes actually lost mass as concentration of glucose solution was increased. Evaluation Due to running out of time and errors in work in the laboratory advice was given to complete the experiment on computer software (Focus Educational Software was actually used). The attached graph of the results shows that there were no obvious anomalies as the curve on the graph is smooth. Possibly this is because an average was taken of three individual experiments for each of the glucose concentration levels so a more accurate or reliable result was given. To improve on the experiment: larger pieces of potato could be used, the experiment could be set for a longer amount of time, more individual tests could be done and the experiments could be more focused around the isotonic point e.g. - 0.15M, 0.2M, 0.25M, 0.3M and 0.35M. ?? ?? ?? ?? ...read more.

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