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Investigate the effects of varying concentration of certain solutions on the amount of osmosis in a potato chip of a given size.

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Introduction

Osmosis in Plant Cells Plan: Aim To investigate the effects of varying concentration of certain solutions on the amount of osmosis in a potato chip of a given size. Prediction A definition of osmosis is: 'the movement of water molecules from an area of high water concentration to a low water concentration across a semi-permeable membrane' (Oxford dictionary 2000). In a high concentration of water the amount of solute (e.g. sugar) is low. These solutions are usually known as a dilute or weak solution. But in a low concentration of water the amount of solute (e.g. sugar) is high. These solutions are usually known as concentrated or strong solutions. When a weak solution and a strong solution are separated by a partially permeable membrane, the water will move from the area of high concentration to the area of low until both sides are equal. This is osmosis, and is shown in the diagram below. An Example of Osmosis Examples of osmosis can also be seen in living cells. Root hairs on plants take in water from the soil via osmosis. Water continuously moves along the cells of the root and up the xylem to the leaf. Water is moving to areas of lower water concentration all the time. This is shown in the diagram below. Example of Osmosis in a Root Hair Cell When a cell is placed in distilled water which is high water concentration water will move across the semi- permeable membrane into the cell which has lower water concentration by osmosis, making the cell swell in size. The cell is now known as turgid. If a potato cell was placed in the same circumstances the cells would increase in length, volume and mass because of the osmotic effects. If the same potato cells were placed in a solution with a low water concentration, then the effects would be the opposite - water would move out of the cell into the area of lower concentration, the water. ...read more.

Middle

I took three average sized ground potatoes and checked that they were both hard and not damaged. 2. Using a potato borer, I carefully cut out 15 cylinders of potato. The borer ensured that all my cylinders were the same shape and diameter. 3. Using a scalpel and ruler I cut the potato's into chips so they were all equal length. I had to be very careful whilst cutting the potato's as the scalpel is exceptionally sharp. I then had 15 chips and I placed them side by side, in groups of three, on a smooth white tile. 4. I took a test tube rack and placed 5 test tubes in each one and then labeled them 0.1 molar, 0.2 molar, 0.3 molar, 0.4 molar and 0.5 molar. 5. Using a measuring cylinder I measured out different amounts of sucrose solution and distilled water, so I could make my chosen concentrations. Which I then poured into the test tubes, putting one of each concentration in each test tube rack. I then had, three test tubes containing 25ml of each concentration. This will allow me to make an average of each sucrose concentration. 6. I then weighed every potato chip on an electronic scale and recorded the weights. 7. I quickly, but carefully, put 1 potato chip into each test tube. 3 chips were used for each concentration to create an average which gave me a better set of results and more accurate graphs. 8. I then tightly covered the top of each test tube with a small piece of cling film, to prevent any evaporation, which cold ruin my results. 9. I then placed my three test tube racks, (containing my test tubes) on a table, away from direct sunlight. 9. After 2hours minutes I drained out the solutions one at a time, in the sink and placed the chip on the blotting paper in the order I had put them in the test tubes as to not confuse myself as to which chip came from which solution. ...read more.

Conclusion

0.05m, 0.15m, 0.25m, etc. This will enable me to find out the isotonic point far more accurately as the one that I estimated is approximate. I measured the concentrations using a measuring cylinder; in the future the concentrations could be made more accurately using titration. Further more, I used a scalpel to cut the potato's, it was very difficult to do and un-precise cutting, could well have affected the surface area and so the overall rate of osmosis, in further experiments I could possibly find a machine to cut the potato chips as it would make sure that all the potato chips would have exactly the same dimensions. I could also weigh each chip on a more accurate scale, to improve accuracy further. E.g. not to 0.00g but 0.000g. 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 get a more accurate result. Finally, I could extend the experiment to a more exact level by looking at the potato cylinders under a microscope, and then I would be able to see the cells in greater detail and draw some more observational results. Further investigations that I could carry out in the future are, using a different variety of potato, for example, a 'king Edward' rather than a 'maris piper'. Also I could use a different plant tissue, for example, a carrot or an apple. Then I could find out whether osmosis occurs with the same patterns and trends with any vegetable. Conclusion However despite this, I think that the experiment I carried out, (given the apparatus I was given to carry out the test) was successful, my results were consistent, and I was pleased with the comparison of my results with my previous prediction. I followed the method plan correctly; I believe I gained accurate and sufficient enough results to conclude the experiment, and to prove my initial prediction. ...read more.

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