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Factors affecting Osmosis in living tissue.

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Introduction

Emily Hatton MB July 2001 Factors affecting Osmosis in living tissue. Plan Plants need water to photosynthesise: Light Energy Carbon Dioxide + Water ( = Glucose + Oxygen Chlorophyll They take up water through their roots as these have a larger surface area. Water enters the roots from the soil by osmosis. Osmosis is the movement of water molecules through a partially permeable membrane. The water molecules move from a high concentration of water molecules (A weak solution) to a low concentration of water molecules (A strong solution). The water molecules enter the cells through the cell membrane (which controls what enters and exits the cell). In osmosis the cell membrane acts as the partially permeable membrane. Once the water molecules have entered the cell they make the cell wall swell up. They push against the cell wall until it reaches the cell's maximum capacity. Because the cell wall is so strong it stops the cell from bursting, we say it is turgid. Plant cells mostly become turgid in a weak solution because there is a higher concentration of water molecules outside the cell so the molecules move in to the cell. ...read more.

Middle

and finally plasmolysed. Although I only expect the highest M sucrose solutions (1 molar) to contain plasmolysed cells as this is where there is the largest concentration gradient (there is no water molecules outside the cell) therefore all the water molecules would diffuse from the cell eventually leading to the cytoplasm peeling away from the cell wall leaving the cell plasmolysed. I would only expect one sample to retain an unchanged mass, the 0.5M solution. As this means that there is an equal amount of sucrose (sugar) solution and water inside and outside the cells therefore no concentration gradient, although osmosis does occur but equally in both directions. However I do not expect any of my results to show this as I am only investigating 0M, 0.2M, 0.4M, 0.6M, 0.8M and 1M solutions. Trial Run I carried out my trial run investigating only the extremes of M solutions (0M and 1M). I also investigated whether using carrots or potatoes would give me the clearest examples of osmosis. Although in my trial run I only left the samples in for 20 minutes whereas my plan states 30 minutes. ...read more.

Conclusion

I would have concluded the 0.8M solution as flaccid and the 1M solution as plasmolysed. Overall the experimental method I used worked very well and if I had followed as accurately as possible and had had more time to re do odd results then the results would have concluded the prediction perfectly. However my results obtained from the experiment are reliable as they support the background evidence and prediction and when comparing the three readings of the same solution they are very similar and any odd results can be explained. But if I was to do it again I would take more than three readings to ensure a more accurate conclusion and I would use a better method to dry the potatoes as some may have been slightly drier than others. I feel that the results are good enough for me to make a firm conclusion. They match my prediction and follow a pattern of results as the concentration. However by including 0.1M, 0.3M, 0.5M (where we could see no change in mass - no concentration gradient), 0.7M, 0.9M would improve the look of the graph by giving a more accurate line of best fit. ...read more.

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