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To investigate how the concentration of water in a sucrose solution affects a potato using different concentrations of sucrose solution and measuring the effects.

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Introduction

Aim: To investigate how the concentration of water in a sucrose solution affects a potato using different concentrations of sucrose solution and measuring the effects. Hypothesis: Osmosis is the net movement of water molecules across a selectively permeable membrane from an area of high concentration to low concentration. The selectively permeable membrane. A selectively permeable membrane is a type of barrier that will only allow certain molecules through it. It acts like a sieve in which microscopic holes only let small molecules through it and keep out larger molecules, therefore 'selecting' smaller molecules. An example of the usage of a selectively permeable membrane is in a dialysis machine. Used as an artificial kidney, a dialysis machine allows urea through its membrane but does not allow protein to escape. This is because protein molecules are larger than urea molecules. Urea is mainly made up of water molecules, H2O, which are possibly the smallest compound atoms as hydrogen consists of only one electron, proton and neutron. In the same way, water would have smaller molecules than sugar, which means that out of the two main ingredients for a sucrose solution, (water and sugar), water molecules would be more able to pass through a selectively permeable membrane than sugar molecules. Potato cells are surrounded by their own type of selectively permeable membrane. Inside the potato cells they contain a concentrated solution of sugars, proteins and other substances in water. As protein, sugars and other substances other than water have large molecules, they are unlikely to be able to pass through the selectively permeable membrane. However, water could. The water concentration Pure water has a maximum water potential of 100%. The more water molecules there are in one area the more pressure there is and energy to move the water particles around, called water potential. This means they collide and tumble around each other quite freely. When water and sugar molecules are dissolved together (sucrose solution), this creates a smaller concentration of water molecules as the sugar molecules combine with some of the water molecules which makes them too big to penetrate the membrane. ...read more.

Middle

I used the same amount of sucrose (100ml) for each set of potatoes. I used the same potato borer to get the same size of potato, and measured each piece to be 3cm long. I left the pieces in the solution for 45 minutes and stopped them all at the same time. I did the experiment in the same room the whole time. Apparatus Potato borer with an 8mm diameter - to remove the potato pieces Two potatoes Knife - to cut the pieces into 3cm length White tile Tweezers 5 beakers (one for each solution) Stopwatch - to make sure they are all left in at the same time Ruler - to measure the results 5 different strengths of sucrose solution - to compare the affects of osmosis on the potato: 0.0M - distilled water 0.5M 1.0M 1.5M 2.0M Method: * Use the potato core to take 15 pieces out of the potatoes * Peel the skin off the edges of the potato pieces using the knife (as this barrier is not selectively permeable) and cut the pieces so that they are all 3cm in length. Thanks to the potato borer, each piece should have the same diameter of approximately 8mm. * Pour the 5 different strengths of sucrose solution into the 5 beakers. * Put three pieces of potato in each beaker. Due to lack of equipment, we were only able to use 5 beakers for each solution. However, after some discussion, we decided that this would still be a fair test if each beaker had the same amount of potatoes. This is because each solution would still have the same amount of comparative water potential, as the same amount of potato is added to each one. * Leave for 45 minutes and then take out. * Measure each potato piece and record the results. Due to the amount of time we had, we were not able to repeat the experiment 3 times. ...read more.

Conclusion

It was not difficult to keep most of these factors the same except for temperature, which we did not measure, as it only required using the same type of materials or making set measurements However, the problems above could have been avoided by: * Using one jar of solution per piece of potato * Finding a more accurate measuring equipment to measure the potato pieces. My results are probably not the best example to use to prove osmosis because of the problems that we faced making them inaccurate and difficult to depict. However, with the problems solved the results may have shown a better idea of osmosis. I do not completely trust my results. They do not show the pattern that I had predicted, or any scientifically proven pattern associated with osmosis. Repeating the experiment would probably show a different set of results each and every time, which is why I used an average, as I knew it would change. However even this didn't fit the pattern I had expected, and it was only through making a line of best fit that I was able to come to my conclusions as I did. To further this enquiry I would solve the problems I had above and repeat the experiment to see if the pattern actually occurs (although I strongly predict it will). I would also experiment with leaving the potatoes in for about a 5 hours in order to find a larger size difference between each sucrose solution. Another idea that might be worth investigating is to try out 0.625M on a potato piece to see if the potato changes size or not, to coincide with my result from my graph that showed 0.625M to be the amount of molars which wouldn't alter the potato's size. If this doesn't work, perhaps finding out what the actual strength is would be useful. ?? ?? ?? ?? Jing Ting Lau Osmosis Investigation 10MP ...read more.

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