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Osmosis is the passage of water molecules from a weaker solution into a stronger solution, through a partially permeable membrane.

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Introduction

Planning Introduction Osmosis is the passage of water molecules from a weaker solution into a stronger solution, through a partially permeable membrane. In this case, the tiny holes in the membrane of the potatoes will allow the water molecules to pass through in and out of the solution and the potato, depending on the concentration gradient of the two substances. So in this case, when the water concentration is lower in the tissue, the water will go inside the tissue of the potato, and the potato will grow in length, and if there is very little difference in the two water concentrations, there shouldn't be such a big change in length. If there is a higher concentration of water in the potato, the water will go out of the potato. Water molecules have random kinetic energy meaning they move around where they want and wherever they want. The potato, cut up into pieces, will need some sort of element to survive, and in this experiment, it would be light and water. With both of these sources, the potato will keep on working, until it dies of either lack of water, too much water. ...read more.

Middle

This would mean that the differences in the lengths would be greater, making the calculation of percentage change even easier and also proving that osmosis to fully complete on the cylinders. Looking at my results and my graph we can make hypotheses for the actual experiment. Hypothesis These hypotheses are for both the experiment, left for 1 hour and 24 hours respectively. In the distilled water, I believe that the water is more concentrated in the potato, and therefore the water should transfer from the water to the potato, making the potato bigger in size, and therefore increase in length. In the 0.2 molar solution of sucrose I believe the length of the potato cylinders will increase still but only by a small amount as the concentration gradient is close to that of the water The 0.4 molar solution of sucrose, compared to the potato, has a very close concentration gradient to the potato. This is why I am predicting that the length of the potato in this experiment should be increased by only a fraction. Around this area (between 0.2 and 0.6 molar sucrose) is where I believe that the line in my graph will cross the positive/negative percentage change in length (this can be backed by evidence from the pilot experiment). ...read more.

Conclusion

We then took the pen and marked the chips with dots to indicate which of the lengths it was (1 dot is cylinder 1 etc). In the first test tube 40cm� of distilled water was measured using the measuring cylinder to create a total volume of 40cm�. In the second, 32cm� of distilled water and 8cm� of 1 molar sucrose were placed in the tube to create a 0.2 molar solution. Then solutions of 24cm� distilled water and 16cm� 1 molar sucrose, 16cm� distilled water and 24cm� 1 molar sucrose, 8cm� distilled water and 32cm� 1 molar sucrose and 40cm� of 1 molar sucrose were placed into the remaining test tubes. After this a chip of each length was placed in each tube and sealed with a bung. After 60 minutes the stop clock was stopped and the test tubes removed from the water bath and placed into a rack. The bungs were removed and the chips measured again using callipers. The results were recorded and the chips placed back into their respective solutions. The tubes were then placed back into the water bath and the stop clock restarted. The next day we revisited the experiments at approximately 10 minutes before they had been started the day before. When the clock read 24 hours we proceeded to again measure the lengths of the chips. The results were recorded again. ...read more.

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