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Introduction

Investigating the Effect of Concentration on the Rate of Osmosis in Potato Tissue Introduction: Osmosis is the net movement of water molecules from an area of high concentration to an area of low concentration across a selectively permeable membrane. It is only net movement as the molecules will move randomly, and therefore though most will move into the area of low concentration, some molecules will still move against the trend. Factors that affect the rate of osmosis are listed below with an explanation: * Concentration Gradient: If the concentration gradient of water molecules is high, then the rate of osmosis will also be high as there is a greater 'pressure' that will cause the net movement of molecules into the area of low concentration. There is also a greater 'need' for the concentration on both sides of the membrane to be equalled, and so the rate will be high. This can be illustrated with the aid of diagrams. Very high concentration Rate=High Very low concentration High concentration Rate=Lower Low concentration * Temperature: If the temperature is higher, then the molecules all have more energy and therefore move faster. If the molecules move faster, then the time it takes for them to move through the selectively permeable membrane is shortened. This therefore means that the rate of osmosis is higher. On the other hand, if the temperature is lower, then the molecules move slower and the rate of osmosis is lower too. * Pressure: If the pressure is higher, then that means there is less space for the molecules to move in. ...read more.

Middle

It also allows us to compare that potato chunk with other potato chunks fairly. Finally, the percentage change was then converted into a rate (Percentage Change / time) so that we could see the rate of osmosis for each potato chunk and still be able to compare it with the other results. Apparatus: Potato Potato Corer Scalpel 5 Petri Dishes 0M 0.2M 0.4M 0.6M 0.8M 1M Electronic Scales Paper Towels Prediction: I believe that any potato chunks left in a sucrose solution of lower than 0.27M (see secondary source) will gain mass as they will have a lower concentration of water molecules in them than in the solution surrounding them. Therefore, the net movement of water molecules will be into the chunks via osmosis, in an attempt to even up the concentration of the inside and outside of the potato, since sucrose molecules cannot pass through the selectively permeable membrane. On the other hand, I believe that any solutions the potato chunks are immersed in above 0.27M will cause their mass to decrease. This is because the concentration of water molecules is greater inside the potato, thus causing the net movement of water molecules out of the potato and into the solution, causing a decrease in the mass of the pieces. Also, I think that the further the sucrose solution that the potato is immersed in is from 0.27M, the greater the rate of osmosis, whether it be into or out of the chunks. ...read more.

Conclusion

While this may not solve the problem of the amount of water being dried off, it will ensure that all the readings after the initial ones are all relative to each other. We could also make sure that all the potatoes are of sufficient size, thus preventing the issue of tissue nature being a factor. This may, in turn, allow all the chunks to be taken from the same area (e.g. the middle) of the potato, again ensuring the cells are of the same nature. On the issue of size and shape, if such equipment were available to us, we could use much more accurate (or even machines) equipment to measure and cut the pieces. We could also make improvements to the experiment by ensuring that an equal amount of solution is placed into the petri dishes, allowing the entire potato piece to be submersed in it. In order to EXTEND the experiment further, a much larger range of solutions could be used in the investigation in order to explore whether or not there is an actual maximum rate, and what it is. In addition to this, to try and find a more exact value for the molarity of sucrose inside potato cells, we could conduct the investigation, concentrating mainly on the molarities of value 0.2-0.3M. Finally, the experiment could be conducted over a much longer period of time, allowing us to find more results, making it easier to see the trends and to isolate anomalies. Geoffrey Tan The Effect of Concentration on the Rate of Osmosis ...read more.

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