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To investigate a factor which might effect the movement of water into and out of potato cells. And test this factor by recording the change in mass of the potatoes.

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Introduction

Biology AT1 Osmosis in Potato Cells The problem To investigate a factor which might effect the movement of water into and out of potato cells. And test this factor by recording the change in mass of the potatoes. Background knowledge Water is diffused during the osmosis process, water molecules diffuse from a high water concentration to a lower water concentration. I have done a similar experiment before using visking tubing instead of potatoes. I used two test tubes; test tube A had salt solution in the visking tubing and water in the surrounding test tube, where as test tube B had salt solution surrounding the visking tubing in the test tube and water in the visking tubing. Osmosis occurred in both test tubes, but the tubing in test tube A increased in mass, where as the tubing in B decreased in mass. This proves that the osmosis process took place because the water molecules diffused from a high concentration of water in the test tube to a low concentration of water in the salt solution/visking tubing. 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. The content of the potato cells shrinks and pulls away from the cell wall. These cells are said to be plasmolysed. Key factors Factors which might affect results are temperature, the size of the potato, concentration of the salt solution and what kind of vegetable is used. ...read more.

Middle

To make the experiment as accurate as possible I will take an average out of the three results. The temperature may affect the reliability of the results, for example if it is too high it may speed up the process. To prevent this I will keep all test tubes in the same places where there is a controlled temperature. 1. Set up test tubes, three for each molarity %, making sure that they are labelled. 2. Prepare solutions for each molarity 0% to 100%. 3. Prepare potato samples, cut out cylinders of potato using the same cork borer then cut to 2cm long using a scalpel. 4. Immediately weigh each sample, record the results and then place into the solution. 5. Set the stop clock and leave for 30 minutes. 6. Remove samples, put onto paper towels to wipe off excess water. 7. Re-weigh samples and record results, then work out the change in mass. Apparatus List 3 medium sized potatoes 1 size 6 cork borer 3 test tube racks 1 scalpel Distilled water 2 paper towels 1 measuring cylinder 1 molar strength salt solution 11 test tubes (large) x3 Results I have taken three sets of results so that I can find an average, as replicates enable me to be more accurate with my results and give me more evidence to prove my prediction from. When obtaining my results, I reset the balance, so that it would read zero. ...read more.

Conclusion

I followed the safety instructions throughout my experiment so I know it was performed safely. My results agree with my prediction, which was when you increase the molarity of the salt solution, the mass of the potato decreases. This is due to osmosis; the movement of water molecules through a partially permeable membrane, from a region of high water concentration to an area of lower water molecule concentration. This meant that water molecules left the cell sap and went through the potato cells partially permeable membrane and into the surrounding salt solution. When the potato chips were removed from the test tubes and dried I may well have dried some potatoes more thoroughly than others and so some would have more excess water, 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. If I was to repeat the experiment I might well increase the time of the experiment, leaving each set for a longer period of time, this would probably lead me to better results, because the osmosis action would reach its maximum capability, and therefore tell me how much water could be transferred for each solution. I could extend my enquiry by testing the percentage change in mass with morality using a different substance. By this I mean using a different vegetable, perhaps celery. Then I could find out whether osmosis occurs with the same patterns and trends with any vegetable. ...read more.

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