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An experiment to show the progress of osmosis in potato tissues.

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Introduction

An experiment to show the progress of osmosis in potato tissues. Aim The aim of this coursework is to investigate the rate of osmosis in different concentrations of sugar solution using potato tissues. Prediction I think that in sugar solutions of high concentration, the mass of the potato will go down. This is due to the rules of Osmosis. Osmosis is the movement of water molecules across a partially permeable membrane, from a region of high water concentration to a region of low water concentration. There are two types of diffusion. These are: * Partially permeable membrane. This allows SOME particles to diffuse through things and not others. Most cell membranes are permeable to water. Diffusion of water through a partially permeable is 'The direction and rate of osmosis which depends on the differences in water concentration between the two sides of the membrane until equilibrium'. Only water molecules are small enough 2 diffuse through a partially permeable membrane. The tendency for water to move through a partially permeable membrane is described as its water potential and is at a maximum in pure water, if sugar is added to the solution, it lowers the water potential. The water potential depends on how much sugar solution is added. In high concentrations of water, the amount of sugar is low and in low concentrations of water, the amount of sugar is high. As the two solutions are divided by a semi-permeable membrane, the water will move from a high concentration to an area of a low concentration, until both have reached equilibrium (this is where both solutions are equal). This happens due to the rules of osmosis. When both concentrations are equal, this is called isotonic. At this point, there is no change in length, volume or mass of potato because the net movement of the particles will be zero, therefore, no osmosis occurs. This movement must take place across a partially permeable membrane such as a cell wall, which lets smaller molecules such as water go through but does not allow bigger molecules (sucrose in this case) ...read more.

Middle

These preliminary results give me an overall impression on the change in mass, gain or loss when placed in varying concentrations of sugar solution. In my preliminary work, it shows when it is just water, the mass of the potato increases and when the potato is in a 1m sugar solution, it decreases in mass. This is because the water molecules in the potato wants to reach equilibrium making the to concentrations equal so water molecules leave the potato tube when the solution is 1m, therefore making the potato decrease in mass. Looking at the results of my preliminary work, I do not think there is enough results so I have decided to use the rang of 0m-1m of sugar solution, I will go up in 0.2m and I will repeat the experiment 3 times. Method. * Set up the apparatus as shown in the diagram. * Cut potato pieces (all the same) by pushing the core borer through the potato, cutting it into long cylinders with a diameter of 9mm. * Remove excess water from potatoes and measure the mass. * Weigh 6 sets of 3 potato cylinders. (I will have 6 sets of potatoes because I have 6 different solutions to test out.) * Make the sugar solution e.g. 1m, 0.8m etc and place them in test tubes. * Add potato tubes into each test tube. * Start stop clock * Leave for approximately 3 hours; take potato tubes out of test tube. * Dry of excess water. * Measure the decrease/increase in mass of each set of potato tubes and record it down, also measure the average reading of the 3 pieces. * Repeat 3 times. Equipment. * Potatoes (to experiment with) * Core borer (to get pieces of potato) * Ruler (to measure the length/width of the potato) * Cutting tile (to cut the potato) * Scalpel (to cut the skin of the potato) ...read more.

Conclusion

The reason for this is because it would be more accurate to put it in 2 minutes different each so we can concentrate on one set of results each time. Another alternative would be to have more people to do the experiment. An advantage of this would be so we can organise the tasks and let each person have a specified job to do. Experimenting with one set for a longer period of time, would lead to better results because the rate of osmosis would reach its maximum capability, and therefore tell us how much water could be transferred for each solution. If I was to repeat the experiment I would increase the time of the results to allow more osmosis to happen and even find the saturation point of the potato tissue. I thought the cutting of the potato was the most important part and most risky part of the experiment because although the potato tissues were cut to the same size, the density and weight of the tissue was varied. As well as the potato, I could have found a more accurate way to measure out the concentrations of the solution. I could have used a burette. This would ensure I had the right amount of liquid in each test tube. I could also weigh each chip on a more accurate scale, e.g. not to 0.00g but to 0.0000g. Looking at the line of best fit on my graphs, there are not any anomalous results, but some were not as close to the line as others. This may have been caused by human. When the potato chips were removed from the test tubes and dried I may have dried some potato tissues more thoroughly than others, so some could have more excess water, which would add to the mass, therefore leading to inaccurate results. If the experiment was repeated I could find another way to dry the potatoes that would ensure that all were dried in the same way for the same time. However, overall I think the experiment was successful and I was pleased with the results I obtained. ...read more.

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