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What factors affect the rate of osmosis?

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Introduction

What factors affect the rate of osmosis? Osmosis Osmosis is the movement of H2O molecules from a high concentration to a low concentration through a semi permeable membrane. The cellular membrane in this picture is permeable to the small water molecules but impermeable to larger molecules or ions. If you put an animal or plant cell into a liquid containing water, one of these three things will happen. 1. If the liquid surrounding the cell has a higher water concentration than the cell, 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 overall result is that the water enters the cell. The cell is likely to swell up. 2. If the liquid has exactly the same water concentration as the cell, there will be no overall 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 liquid has a lower concentration of water than the cell, 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. ...read more.

Middle

I will take 5 different measurements and then have 3 pieces of potato for each. This means I will be able to take an average. This will make my results more accurate and reliable. Safety Whilst doing this experiment there will be some precautions I need to take to ensure safety. Firstly I will have to take care when cutting the potato to make sure I don't cut myself and the scalpel will be sharp. Also there are a few things I need to watch out for during this experiment. I need to make sure I have clean and dry hands each time I handle the potato. This will stop any extra water entering the potato and affecting the osmosis rate. Prediction I predict that the mass of the potato will increase as the concentration of the water in the glucose solution grows in strength. Then as the solution becomes more concentrated the increased mass will start to decrease until it is almost back to it's original mass. Therefore, the more concentrated the solution is, the smaller the mass gain should be. The reason for my prediction is that when the concentration of the solution is weak, the water, which is in the solution, is greater than that in the potato cells. Therefore osmosis occurs and the potato cells take in water from the solution. ...read more.

Conclusion

This would allow me to see whether size affected the rate of osmosis. I would keep the concentration of glucose the same so that there are not too many different factors. In each petri dish I would have 3 cylinders of potato. I would have masses of 1g, 2g & 3g. I would leave the potato in the glucose concentrations for 30 minutes. This is because I got a good set of results in my last experiment when I left the cells in for 30 minutes. Once I have done this once a recorded the results, I would do it twice more so that I have got three sets of results and am able to take an average. This may be time consuming, but it would hopefully give me accurate results. Fair Test To ensure the experiment is a fair test, I will keep some factors the same throughout. I will keep the temperature of the room, the concentration of glucose, the time each potato is in the solution and the volume of the solution the same so that all of the cells have the same conditions. Also I will keep the top pan balance the same in case one is slightly different to another. Prediction I predict that as the mass of the potato increases, the rate of osmosis will increase. This is because the bigger the potato is, the larger the surface area is. This means that there is more room for osmosis to happen. ...read more.

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