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Investigate the water potential of celeriac.

Extracts from this document...

Introduction

Aim Investigate the water potential of celeriac. Apparatus Celeriac - this is the specimen that we will be finding the water potential of. 1.00 mol dm-3 sucrose solution - this will be placed in the test tube in which the experiment will take place. We will dilute the solution to produce a range of concentrations. 10.0ml Graduated Pipettes (x2) - I had a choice of 5.0ml, 10.0ml and 20.0ml graduated pipettes. I chose this size pipette because it is time efficient and accurate at the same time. It is an accurate piece of equipment because as opposed to standard pipettes, this graduated pipette has 0.1ml graduations to ensure the utmost accuracy. One pipette will be used for water and one will be used for sucrose solution. 250ml Beakers (x2) - these will be used to hold water and the 1.00 mol dm-3 sucrose solution in a safe environment. Cork Borer - this will be used to cut the precise shape of the celeriac. This will also ensure that the surface area to volume ratio is constant throughout the experiment. Razor - this will be used to cut the pieces of celeriac to a precise length. Ruler - this will be used to measure the length of celeriac that will be used in the experiment. Scales - they will be used to measure the mass of celeriac before and after the experiment with accuracy. Therefore, the mass increase/decrease can be calculated after the experiment. These scales give a digital measurement to 2 decimal places; therefore they are more accurate than conventional scales. Paper towels (x5) - they will be used to absorb any excess solution from the celeriac when it is removed from the appropriate test tube. Stopwatch - this will be used to time the experiment. It is accurate to 2 decimal places. Test tubes (x5) - this is where the experiment will take place. The test tube will be used to provide a safe environment for the experiment to take place in. ...read more.

Middle

If the volume was to differ in each test tube, more/less osmosis may occur. For example, if test tube E has a larger volume of solution than test tube F and assuming everything else was constant, then at the end of the experiment, test tube E would have the greater percentage increase/decrease in mass than test tube F. This would be because test tube E had more solution molecules in it than test tube F, thus there was a greater number of molecules to diffuse in/out of the celeriac. Another factor that will be kept constant will be the size and shape of the celeriac we will use. We will ensure constant surface area to volume ratio by using a cork borer, to determine the shape of the celeriac. Then we will cut each celeriac to 5cm in length. This will guarantee surface area to volume ratio is consistent. If the surface area was to differ between test tubes, then this factor would affect the percentage increase/decrease. For example, if test tube G contained a celeriac of length 5cm and test tube H had one of 10cm, while assuming everything else was constant, then at the end of the experiment, test tube H would have the greater percentage increase/decrease in mass than test tube G. This would be because test tube H had more surface area exposed to the solution molecules than test tube G, thus there were many more channels for the solution molecules to diffuse in/out of the celeriac. The final factor that will be kept constant will be the celeriac that is used. Cells from different celeriac plants may have a different water potential to each other. So, I will only use one celeriac plant throughout the experiment. If I were to use a range of celeriac plants during the experiment, I cannot guarantee valid results. For example, if test tube J contained a celeriac that was different to that in test tube K, while assuming everything else was constant, the water potential may be different for each celeriac. ...read more.

Conclusion

This would eliminate the delay that would normally occur between each test tube and therefore, each celeriac disc would have equal amount of time in the solution. This would allow us to see a true representation of the percentage change in mass of the celeriac discs at different concentrations, which in turn will also increase the reliability. Another improvement would be to find a more suitable way of blotting of the discs to absorb excess solution. The range of results for 0.0 mol dm-3 sucrose solution has the greatest range of results. This means that it is the least accurate and reliable sets of results that we have recorded. The range is consistent, around 21.0% for 3 concentration of sucrose. The lowest range is that of concentration 0.6 mol dm-3 sucrose solution. This meant that this set of results was the most reliable and accurate. These large differences in range lead me to believe the main error factor influencing the results would be the blotting of the discs. If this source of error was to be eradicated, I believe the range would be consistent and reduced to at least 20.0%. When considering the large range, my results do not feel very reliable. The range bar for 0.4 mol dm-3 sucrose solution overlaps the range bar for 0.2 mol dm-3 sucrose solution. This is because the highest percentage change of 0.2 mol dm-3 sucrose solution is 24.3% and the highest percentage of 0.4 mol dm-3 sucrose solution is greater than that of 0.2 mol dm-3 sucrose solution, 25.9%. This leads me to believe that when group 3 blotted their celeriac discs for 0.4 mol dm-3 sucrose solution, they did not apply enough pressure and therefore they left some excess solution on their discs. This means that the discs weighed more than there true mass and it therefore affected the results. Regardless of this, I am confident that my other results are adequate. When finally assessing all the evidence, I still believe that conclusions I drew are true, but they may not be based on reliable evidence. ?? ?? ?? ?? Adhal Mahmood ...read more.

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This is a thoroughly and carefully written up account of the investigation. The author has a clear understanding of water potential theory and uses A level biological terminology accurately and appropriately throughout. There is a high level of attention to detail.

Marked by teacher Adam Roberts 05/09/2013

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