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Experiment to Investigate Osmosis in Potatoes

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Introduction

Experiment to Investigate Osmosis in Potatoes The aim of this experiment is to investigate the movement of water in and out of plant cells. The cells chosen for study will be taken from potato tubers. Firstly I will explain what osmosis is. Osmosis is the passage of water from a region of high water concentration through a semi permeable membrane to a region of low water concentration. This definition contains three important statements: a) It is the passage of water through a semi permeable membrane b) It is the passage of water from a region of high water concentration c) It is the passage of water to a region of low water concentration. All the above statements are included in the definition, but define certain aspects of it. Semi-permeable membranes are very thin layers of material which allow some things to pass through, but prevent others. A cell membrane is semi permeable. They allow small molecules like oxygen, water, amino acids etc. to pass through but will not allow larger molecules like sucrose, starch, protein etc. through. A region of high concentration of water is either a very dilute solution of something like sucrose or pure water. In each case there is a lot of water: a high concentration of water. A region of low water concentration is the opposite of the above, i.e. a very high concentration of sucrose solution: a low water concentration. The water content of plants varies depending on environmental conditions. In Land plants this water plays a vital role in the support of tissues and the transport of materials around the organism. Lack of water leads to wilting and eventually death. ...read more.

Middle

All the lengths will be cut to 25mm. The solutions will be altered according to the molarity required and cm^3 of each solution placed in each test tube. Each molarity will occupy three test tubes. The chips will then be put into each test tube and left over night. They will then be taken out of their test tubes, dried lightly with a paper towel and the new mass and lengths recorded. Once the results have been collected, they will be tabulated and analysed. A graph will be drawn and any trends noticed explained. Prior to the experiment we carried out a short pilot test, using potato chips and solutions of strength 0.0, 1.0 and 2.0 molar solutions. The chips were 25mm in length each, and each chip was placed in 5 cm^3 of either distilled water/1.0 molar / 2.0 molar sugar solutions and left for 30 minutes. The potato chips were then measured and the results recorded. They are shown below: Chip Solution 1 Water 2 1.0 molar 3 2.0 molar Chip number Original length Resultant length 1 25mm 29mm 2 25mm 24mm 3 25mm 20mm These results show that a potato chip placed in water will gain in length, a weak sugar solution will lose length and a strong sugar solution will lose length also. The results from this test will allow me to choose an appropriate range of moralities in order to find out what the concentration is inside the cell vacuole. I am going to investigate 0.0, 0.2, 0.4, 0.6, 0.8 and 1.0 molar sugar solutions. I have chosen these concentrations to try and accurately find when there is no net movement of water, hence the concentration of the cell vacuole. ...read more.

Conclusion

The mass was more accurate to measure for many different reasons. Length does not take into account the change in diameter of the chips, and you can not measure fractions of millimetres on a ruler, but the electric balance will record change from 2 decimal places, e.g. mass: 1sb43 � 1sb34 length: 25 � 23 whilst length can only be measured to the nearest millimetre. For the mass, we had to be careful that all the potato chips were dried in the same way as this may have altered the reading. This may have been what caused the anomalous results, as it was lighter that the best fit line i.e. some water may have been lost through harder drying, or squeezing during the drying process. If some of the water evaporated overnight, it would have incresed the molarity of the solutions, thus making the results innaccurate. This could be combatted by putting a bung in the top of the test tubes to stop the evaporation and keeping the sugar slution concentrations the same. To improve the accuracy of the results I would include more concentrations to find the point of plasmolysis as in my experiment, I did not get to the point of plasmolysis in my experiment, so if I was to extend this experiment, I would investigte a wider rage of concentrations to investigate furthur and increase accuracy. I would also increase the repetitions to 5 per molarity and increase the molarity to try and find the point of plasmolysis. I could also decrease the range between each molarity (every 0.05 for example) to try and find the exact concentration of the potato cells where there is not net gain. This investigation was succesful but could still be made more accurate by some of the above ways. ...read more.

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