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factors affecting osmosis
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Osmosis experiment and investigation Aim: We are planning to do an experiment investigating the factors affecting osmosis in a chip. My independent variable is going to be the concentration of the solution-how much sucrose and distilled water in each solution. In my experiment, I plan to find out whether the concentration of sugar in distilled water affects how much water will go into a potato chip. Osmosis: the movement of water molecules from an area of high concentration to an area of low concentration. Cell membranes are completely permeable to water; therefore, the environment the cell is exposed to can have a dramatic effect on the cell. When plant cells are placed in concentrated sugar solutions they lose water by osmosis and they become "flaccid"; this is the exact opposite of "turgid". If you put plant cells into concentrated sugar solutions and look at them under a microscope you would see that the contents of the cells have shrunk and pulled away from the cell wall: they are said to be plasmolysed. When plant cells are placed in a solution which has exactly the same osmotic strength as the cells they are in a state between turgidity and flaccidity. We call this incipient plasmolysis. "Incipient" means "about to be". 1. If the concentration surrounding the cell has a higher water concentration than the cell (a very dilute solution) the cell will gain water by osmosis. Water molecules are free to pass across the cell membrane in both directions, but more water will come into the cell than will leave. The net (overall) result is that water enters the cell. The cell is likely to swell up. 2. If the medium is exactly the same water concentration as the cell there will be no net movement of water across the cell membrane. Water crosses the cell membrane in both directions, but the amount going in is the same as the amount going out, so there is no overall movement of water. The cell will stay the same size. 3. If the medium has a lower concentration of water than the cell (a very concentrated solution) the cell will lose water by osmosis. Again, water crosses the cell membrane in both directions, but this time more water leaves the cell than enters it. Therefore the cell will shrink. This is not continuous. Size:- The size of the cells also varies considerably in different organisms. The variation in size is largely due to specialization of different cell types, according to their functions. The largest cell is the egg of ostrich, which measures about 3 inches or 75 mm in diameter after the shell is removed. Prediction: for the investigation I think that the lower the concentration of sugar in the Petri dish the larger the mass (increase) the potato will be. I predict that the higher percentage of distilled water in the solution the more turgid the chip becomes so the chip will become firm. The higher the percentage of sucrose in the solution the more flaccid the chip will become so the chip will be droopy. This is all to do with osmosis as the water moves from a higher area of concentration to a lower area. Therefore the molecules pass from as high concentration (in the water itself) to a low concentration (in the potato chip). Therefore, the chips in the higher concentrations will have a larger mass than in the higher sugar concentrations. If the chip is in pure water then the increase will be quite a lot, as there are many water molecules in water. To make it a fair test we are going to keep the following things the same: 1. Volume of solution-20ml 2. Same size Petri dishes for each test 3. Same type of potato 4. Temperature-room temperature 5. Same sugar solution 6. Same size potato borer-it is a uniform and reliable way or getting the chips to be the same size (width) 7. Same time left for-24 hours 8. Same size of potato chip Keep the potato samples the same length (25mm): This is because if one potato sample is 1cm long and one is 3cm long then the 3cm long sample will have a larger surface area and will osmosis much more quickly, and will also weigh more. Accurate amount of sugar solution: More sucrose solution may affect the rate of solution. To make the amount of solution placed in the test tube as accurate as possible a syringe will be used to measure out the exact amount needed. Average: To make the experiment as accurate as possible an average will be taken out of the 3 sets of results taken. Also any clearly anomalous results will be ignored. Temperature: The temperature may affect the reliability of the experiment for example at extreme temperatures the cells of the potato may die and at less extreme temperatures the experiment may be speeded up. To keep this from happening, all the beakers will be kept in the same place and at the same time of the 24-hour experiment. Excess Liquid: For a fair test I must dry the potato cores lightly with a paper towel to remove any excess liquid before weighing. Safety procedures: Safety is an important aspect in every experiment, even if the experiment seems to be very harmless. This is why I'll be taking this into consideration. I will be using a very sharp knife, which could injure someone if it's not handled properly. I will also be very careful that the solutions don't get into our bodies internally, just in case, because we are not fully aware of the damage it could do to us. I will also be wearing an apron due to any solutions getting to my clothes.
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