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What effect does the concentration of salt solution have on the amount of osmotic activity in a potato chip?

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Introduction

What effect does the concentration of salt solution have on the amount of osmotic activity in a potato chip? Skill Area P - Planning Experimental Procedures The aim of this experiment is to investigate the movement of water into and out of potato cells by osmosis, and what effect the concentration of salt in that water has on the rate of osmosis. Variables: To ensure that the experiment is fair, certain aspects of it will have to be kept constant, whilst one key variable is changed. I have chosen to vary the concentration of the salt solution because this will give me a varied set of results from which I hope to make a decent conclusion. This means that in order to get accurate results I must keep all of the other non-variables the same. If any of the non-variables below were not kept constant, it would mean it would not be a fair test. * I shall ensure that all the potato chips are the same length and that all the ends are cut to 90 degrees. If one of the potato chips was longer than the rest, the surface area of the chip would be larger and there would therefore be more space for osmosis to occur. * I shall carry out all of my experiments at room temperature, because different temperatures would cause osmosis to be carried out at different rates. * I shall keep the water potential of the potato initially the same by using the same variety of potato, which have been treated in the same way, e.g. ...read more.

Middle

When a cell is like this it is said to be plasmolysed. If the water potential of the potato cells' cytoplasm is less than that of the solution it is in (hypotonic solution), then water molecules will diffuse from the solution into the potato cells. This increase in the volume of the cells' cytoplasm causes the cells to swell and become turgid. This means that the cell has become swollen and hard and the potato cylinder will increase in size and become stiff and rigid. This is because the hydrostatic pressure inside the potato cells rises, the cells swell, but they have a strong cell wall around them, which prevents them from bursting. This means that there is a limit to how much water can be absorbed, and it will not just absorb water until the water potentials are equal. If the concentration of water molecules is exactly the same in both the potato cells and the solution, then no water will diffuse in either direction because there will be no concentration gradient. In this case the solution is known as isotonic. Prediction: I predict that in the distilled water the potato will gain water and become turgid because the concentration of water in the potato must be lower than distilled water. As the concentration of salt in the solution increases, I predict that the potato cylinder will become smaller because the cells will become more and more plasmolysed due to more water leaving the cells. ...read more.

Conclusion

The cutting of the potatoes was one of the most difficult parts of the experiment as although I was recording my results by mass, it could well have affected the surface area and so therefore the overall rate of osmosis. If I were to repeat the experiment I would have possibly found a machine like a guillotine to cut the potato as it would ensure that all potatoes would be the same weight and dimensions. As well as the potato I could have found a more accurate way to measure out the solutions and to determine the molar concentrations. Perhaps I could have used a pipette or burette. This would ensure that I have an accurate amount of fluid in each test tube. I could also weigh each chip on a more accurate scale, e.g. not to 0.00g but to 0.0000g. There were 2 anomalous results on my graph at 8 and 12 ml. This may have been caused by human error, such as adding too much water or too little salt to the solution, or cutting them differently from the others. When the potato chips were removed from the test tubes and dried, I might have dried some of the chips more thoroughly than others, and so some would have excess water on them, which would add to the mass. If the experiment was repeated I could find another way to dry the potatoes that would ensure that all were dried in the same way for the same time. However with all this said I think that the experiment was truly successful and I was very pleased with the outcome. ...read more.

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