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Science GCSE coursework: osmosis

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Introduction

Science GCSE coursework Investigating the factors that affect water uptake by potatoes Plan Osmosis is the movement of water from a region of a high concentration to a low concentration of water through a selectively permeable membrane. Aim To find the concentration of the solution in the vacuole of the potato. Prediction I predict that when the potato chip is placed into the water solution, its mass will increase because that water moves from a high concentration to a low concentration. When the potato chip is placed in 100% salt solution, I predict its mass will decrease. Variables * Concentration of the salt * Size of the potato chip * Time of incubation * Variety of potato * Skin on potato chip * Temperature * Volume of water Scientific Explanation I think that when the potato chip is placed in water its mass will increase because water moves from a high concentration to a low concentration. This process is called osmosis which is the movement of water from a high concentration to a low concentration through a selectively permeable membrane. ...read more.

Middle

I will keep the type of potato the same so that it does not interfere with the results. I will keep the temperature the same by using a thermometer and checking the temperature of the water regularly. I will use a stop clock to keep the time of incubation the same. To keep the size of the potato chip same I will be accurate and use a measuring ruler and a sharp knife. Trial Run * Cut the potato chip to the size 35mm * Measure its mass and record it * Place potato chip in salt solution * Leave it in the solution for two minutes * Remove from the salt solution and record its mass * Place back in solution and leave for two minutes again * Repeat this process until you have done this for at least 20 minutes. I have chosen to leave the chip to incubate for 20 minutes because it has the biggest change of mass. Concentration of salt (m) Final mass (g) Initial mass (g) % change in mass Average % change in mass 1 2 3 1 2 3 1 2 3 0 2.33 2.40 2.47 ...read more.

Conclusion

In the experiment, the chips vacuole was the high concentration and the solution was the low concentration. When the water in the chips vacuole is removed, the mass of the chip decreases. The water potential of the solution inside the vacuole was 0.32m. Evaluation The accuracy of the results were as good as they could have been considering the circumstances and conditions of the experiment. The results were not very reliable because we did not have the time to re-do the experiment more than 3 times. The individual % changes are not very close together, but the average percent change and median percent change are close. An example is the fifth line of results (0.8m). The median is 15.38 and the average is 15.28. Generally, the results did not fit on the line of best fit. The anomalous result (2m) was a freak result. Possible sources of error for it may have been a miss calculation of the mass of the chip. If I were to redo the experiment I would make sure there were more boiling tubes and stop clocks so I could the same concentration more than 3 times. This would have made my results more accurate. ?? ?? ?? ?? David Hall 11s 1 ...read more.

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Here's what a teacher thought of this essay

4 star(s)

****
The planning and experimental method described are very good. A clear understanding of the principles of osmosis is shown. The analysis is a little weaker.

Marked by teacher Adam Roberts 26/04/2013

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