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Determine the osmotic properties of a potato and how osmosis within the potato is affected in different concentrations of sucrose and water [molar solutions].

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Introduction

Osmosis : Coursework Aim: The aim of my investigation is to determine the osmotic properties of a potato and how osmosis within the potato is affected in different concentrations of sucrose and water [molar solutions]. How does the mass of the potato correlate with the concentration of the solution? Is there an isotonic point in this experiment? What's the 'isotonic point'?: If the concentration of the molar solution is equal on both sides, the water will move back and forth but it won't have any result on the overall amount of water on either side. This point in osmosis is known as the isotonic point as "iso" means "the same". How can we determine when this equilibrium has been reached? What is osmosis?: Osmosis is a form of diffusion. It is the movement of water from an area of high concentration to an area of low concentration through a semi permeable membrane. The below diagram (which I have drawn) is a good example of how diffusion in water works. The water molecules are shown in blue, the semi permeable membrane as a dotted line and the pink circles with 3 blue circles surrounding represent hydrated sugar molecules. There are more free water molecules on the left, so more will diffuse from left to right than in the other direction. Sugar molecules will diffuse more slowly from right to left. Prediction: I predict that the higher concentration of sucrose in the solution, the less the potato will weigh (less mass). ...read more.

Middle

5. Leave the petri dishes for approximately 24 hours. 6. After 24 hours has passed, remove the cylinders from their dishes using tongs, wiping off any excess solution using a paper towel (and being careful not to squeeze or damage the cylinders). 7. Now statistics can be collected in order to draw a conclusion. Weigh each cylinder and determine the weight gain or weight loss. From these statistics one can determine percentage increases/decreases and use averages to draw conclusions about the correlation of their results etc. The Formula, Explained: Here is an example as to how the formula could be used when preparing different molarities of sugar/water solution. Total vol.= 40 cm�? 0.2M = Concentration Required from 1.0M = Stock solvent V1 = 0.2 X 40 cm� 1.0M = 8 cm�? of sucrose solution = 32 cm�? of water to dilute 0M = 40 cm �? of water 0.2M = 8 cm �? of water / 32cm �? of sucrose solution 0.4M = 16 cm �? of water / 24cm �? of sucrose solution 0.6M = 24 cm �? of water / 16cm �? of sucrose solution 0.8M = 32 cm �? of water / 8cm �? of sucrose solution 1.0M = 40cm �?of sucrose solution Fair test: In this experiment there should only be two changing variables: 1: Different molarities of sugar solution. 2: Changing weight of the potato samples. To keep these two variables the only variables in the experiment I must: 1: Keep the potato samples the same length (2cm). ...read more.

Conclusion

2 It was hard deciding how much solution could fit into each petri dish, along with the cylinders. Spillage caused me to repeat the experiment several times to ensure accuracy. In the end I ended up cutting each cylinder in half so the lid and the solution could all fit properly with minimum spillage. 3 Mass was more important than weight in this experiment, although I had cut all the cylinders to the same length, they varied in mass. Slicing the potato cylinders more in order to ensure they were around the 1.22g margin was extremely time consuming. One could say this procedure was a little ushered, as we had time restrictions which lead to the results not being as accurate as they could be. 4 If I could do this experiment again I think I would use molarities with gaps of 0.1M, e.g 0.0M,0.1M,0.2M,0.3M etc. I would also be more inclined to use larger petri dishes to avoid spillage. I would also investigate which parts of the potato had the highest water potential and see if a conclusion could be drawn as to how this may have effected my initial results. 5 My results proved to be accurate and showed a strong correlation though I do think that they could be more accurate. I feel that the main factors that would have effected my end results would have been human error as a result of lack of time and resources. 6 If I were to extend this investigation further I would use other types of plant cells, such as leaves or other vegetables. I could then extend my results to further validate my conclusion. ...read more.

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