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Investigating Osmosis

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Introduction

Investigating Osmosis Introduction Osmosis is the diffusion of water molecules, down a water potential gradient, across a partially permeable membrane. If the solutions on each side of the partially permeable membrane are equally concentrated then there will be no net movement of water across the membrane. If the solution outside the cell has a low concentration of solute, this causes cells to become turgid as water flows into them, or if the solution outside the cell is of high concentration the cells become plasmolysed as the water flows out. Even if the solute concentration external to the cell is low relative to the vacuole contents, cell will not continue to take in water by osmosis for ever. The cellulose cell wall prevents this. A cell that is full of water is said to be turgid and cannot expand further as the outward pressure on the cell wall is balanced by the inward force of the stretched wall.. At the other extreme, a cell placed in a solution that is high relative to the cell contents will lose water by osmosis. The cytoplasm will cease to exert a pressure on the cellulose cell wall and the cell, described as flaccid, will lack support. Water loss can continue to such an extent that the cytoplasm, and attached cell membrane, contracts and detaches from the cell wall. ...read more.

Middle

-0.89 6.30 5.22 -1.08 0.73 6.23 4.90 -1.33 6.25 4.94 -1.31 6.20 4.92 -1.28 1.46 6.04 4.80 -1.24 6.06 4.83 -1.23 6.10 4.79 -1.31 Table 2 sucrose concentration (moles) average difference (g) percentage change 0 0.94 15.06 0.15 0.75 12 0.29 0.04 0.59 0.37 -0.53 -8.39 0.48 -0.95 -15.27 0.73 -1.31 -20.99 1.46 -1.26 -20.77 Analysing Evidence There are 7 points plotted on chart 1. Numbered from the left hand side . Between points 1 and 2 (high water potential ), there is little indication that the cell is increasing further in size. This is because the cell is fully turgid and no more water can enter. At point 3 the graph suggests that no osmosis ( water movement ) has occurred, suggesting that the concentration of water inside the cell is equal to the solution outside. Between points 6 and 7 (low water potential ), there is no indication that the cell is decreasing further in size. This is because the cell is fully plasmolysed and no more water can leave the cell. This could be explained by the following scientific knowledge . Even if the solute concentration external to the cell is low relative to the vacuole contents, cell will not continue to take in water by osmosis for ever. The cellulose cell wall prevents this. A cell that is full of water is said to be turgid and cannot expand further as the outward pressure on the cell wall is balanced by the inward force of the stretched wall.. ...read more.

Conclusion

I could also find more accurate ways of measuring the mass of the potato. I could also have a more accurate time of leaving the potato in the solution because although 24 hours is sufficient it was not very accurately timed . (I presumed that the pressure and climate conditions were the same although out my experiment . ) I f I had the time and the technology I needed I would have liked to look at the following experiments 1. Leave the test for different lengths of time so that we might of been able to calculate the rate of osmosis in the same conditions . 2. We could have also changed the conditions to see if that would change the rate of osmosis for instance if the temperature was raised a faster the rate of osmosis could be expected. 3. We could have also find out if pressure would effect osmosis in any way if we had suitable apparatus. 4. We could have also seen if there was a difference rate of osmosis in different types of vegetables e.g. root vegetables and vegetables that grow on the ground ( peas) . This would have been interesting because the root vegetable was made by the plant to hold all of the nutrients needed to promote the potato seedling to grow with out sun light . Research Gallagher and Ingram , 1999 , Complete Chemistry , Oxford www.google.com as a search for GCSE osmosis course work Tom Clare 10x Biology Course work ...read more.

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