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Investigation Of Water Potential

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Introduction

Planning Title: Investigating the water potential of root vegetables. Aim: The aim of the experiment is to find the water potential of potato tuber cells. Background: This investigation is based largely on water potential. Plant cells behave in certain ways when subjected to certain conditions. If a plant cell is immersed in a solution with the same water potential as the plant cell the mass will remain the same. If the plant cell is immersed in a solution with a higher water potential than the cell then the mass will increase. Finally in the plant cell is immersed in a solution with a water potential lower than that of the cell it will decrease in mass. This is due to the rule of water potential. Water will diffuse through a partially permeable membrane down its concentration gradient from a region of high water potential to a region of low water potential. Thus we can find out the approximate water potential of potato tuber cells using this method and getting a more accurate reading from the graph. I found this diagram on a website. Identified in the references section. Prediction: Based on my background information I predict that at a low concentration of sucrose the potato tuber cells will increase in mass. In potato tuber samples immersed in a solution with high concentration of sucrose will decrease in mass. I believe this because in solutions of low sucrose concentration there is a high water potential. This means water will move from the solution to the potato tuber cells. In solutions of high sucrose concentration the water potential is low, therefore the water will move from the potato tuber cell to the sucrose solution. Meaning it will decrease in mass in solutions of high sucrose concentration. Preliminary Experiment: Introduction: In this experiment the lengths of potato tuber cells will be examined after being immersed in sucrose solutions of different concentrations. ...read more.

Middle

Results: Results Table Showing Concentration, Mass at the start and end, Average masses at the start and end. Sucrose Concentration/ (M) Mass at Start (g) Average Mass at Start (g) Mass at End (g) Average Mass at End (g) 0.00 2.60 2.69 0.00 2.60 2.57 2.70 2.73 0.00 2.50 2.80 0.10 2.40 2.53 0.10 2.70 2.53 2.70 2.65 0.10 2.50 2.72 0.20 2.50 2.48 0.20 2.40 2.43 2.51 2.48 0.20 2.40 2.45 0.30 2.70 2.53 0.30 2.30 2.46 2.51 2.46 0.30 2.40 2.40 0.40 2.38 2.38 0.40 2.41 2.43 2.35 2.41 0.40 2.35 2.41 0.50 2.38 2.28 0.50 2.32 2.35 2.22 2.23 0.50 2.20 2.19 0.60 2.20 2.05 0.60 2.20 2.27 2.13 2.11 0.60 2.40 2.15 Fig. 6 Results: To be able to plot these points accurately on a graph the results must be used to calculate the change in mass per gram. Change in mass per gram = Change in mass/ Mass at Start The average mass at the beginning and end of the experiment will be used to calculate the change in mass per gram. Also this will produce only one result allowing the graph to be produced using one point. After calculating the average change in mass per gram the percentage change in mass per gram can be calculated. Change in mass per gram X 100 = Percentage change in mass per gram Table Showing Calculations and Change in mass per gram for each Sucrose concentration and the Percentage Change in mass per gram for each sucrose concentration Fig. 7 Sucrose Concentration (M) Calculation (g) Change in mass per gram (g) Percentage change in mass per gram (%) 0 (2.73 - 2.57) / 2.57 0.06 6 0.1 (2.65 - 2.53) / 2.53 0.04 4 0.2 (2.48 - 2.43) / 2.43 0.02 2 0.3 (2.46 - 2.46) / 2.46 0 0 0.4 (2.38 - 2.43) / 2.43 -0.02 -2 0.5 (2.23 - 2.35) ...read more.

Conclusion

Improvements: Table showing possible Improvements in the Experiment Limitation Improvement How improvement increases reliability? Identifying particular potato cell (3 potato cylinders per boiling tube) Use 2 different colour water proof pens Each potato tuber cell can be identified when in solution removing chance of misleading inaccurate results Inaccurate concentration made by using sucrose and water to create an approximate concentration Making solutions using sucrose powder More accurate technique means results more likely to be a true representation of that concentration Removing excess water Leave cells out of solution for a set time before weighing Allows all cells to lose the same amount of water Reliability of Evidence: The reliability of the evidence is very good. The results show that the net movement of water molecules are from a region of high water potential to a region of low water potential. This is the same conclusions made by other published studies, for example the Biology 1 book. Published by the press syndicate of the university of Cambridge and endorsed by OCR. Validity of Conclusions: My conclusion states: After analysing the experiment I conclude that it was a success. The tables show no particularly anomalous results. Also the results followed the basic principles of osmosis. When the concentration of sucrose was low the results showed an increase in mass of the potato tuber cells, they then levelled off at a medium concentration. Finally when the concentration of sucrose was high the results showed a decrease in mass of the potato tuber cells. Although the limitations may have affected results I believe this would have been very slight. Even the main source of error being the ability to remove excess water would have had little significance on the overall results. I believe this because precautions and improvements were made after the preliminary stage to make results more accurate. Making the limitations less relevant. The results coincide with other published studies and predictions made. For these reasons I believe the conclusions are valid and the investigation was a success. ...read more.

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