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Investigation of water potential in plant cells.

Extracts from this document...

Introduction

Biology coursework - Investigation of water potential in plant cells The aim of my experiment: The aim of this experiment is to investigate the water potential of plant cells. I am going to achieve this by first, researching about water potential and then conducting a pilot study. I will conduct a pilot study to identify the vegetables I am going to use, and to learn how to conduct the actual experiment. Once I have completed this task, I am going to conduct my actual experiment. I will repeat my experiment 3 times to gain both accurate and reliable results. Hypothesis: I expect the sweet vegetables to have a lower water potential than the less sweet ones, since concentrated solutions have a lower water potential than less concentrated solutions. The sweeter vegetables should contain more sucrose than the less sweet vegetables, meaning that there is a higher concentration of sucrose in the sweeter vegetables; therefore, they should have a lower water potential. Introduction: Background information: Osmosis is defined as 'the movement of water from an area of high water potential to an area of low water potential, through a semi-permeable membrane'. It is a special case of diffusion. Water potential is the tendency for water to move from one place to another. Water potential is represented by the Greek Letter ???Pure water has the greatest water potential, concentrated solutions have the least water potential. Water potential is decreased by the addition of a solute (creating a more concentrated solution) and is increased by the application of pressure. (Reference:http://www.bbc.co.uk/education/asguru/biology/01cellbiology/05pathways/10osmosis/index.shtml) Semi-permeable membranes: these are very thin layers of material (cell membrane's are semi-permeable) which allow small particles to pass through them but prevent larger ones from passing through. Cell membranes will allow small molecules like Oxygen, Water, Carbon Dioxide, Ammonia, Glucose, amino acids, etc. to pass through. Cell membranes will not allow larger molecules like Sucrose, Starch, protein, etc. ...read more.

Middle

* The type of vegetable I use will also be a controlled variable. I have decided to use a carrots and turnips, as they give me the biggest change in mass. I therefore think that they will give me the most reliable results. * The sucrose solution: The solution in which the vegetables are placed in must be made precisely and accurately, for every experiment. If too much sucrose, or too much water were placed in a solution, anomalous results could be produced, as the solution could be more concentrated or more dilute, therefore, I would not be measuring the mass of the vegetable at the mass I thought I was. The concentration of the sucrose solution is a dependent variable, as it is a variable that I control in the experiment. * The mass of the vegetable: The mass of the vegetable is the dependent variable. It is the variable that will change depending on what solution it is placed it. I must ensure that I have weighed the correct mass before I put either the carrot or turnips into each of the solutions. I must also ensure that I have dried off all vegetables before weighing them again after they have been removed from the solution. Method for actual experiment: 1. Use the 1 mol solution of sucrose to create of each of the following concentrations in 2 separate test tubes: 0.0 mol, 0.2 mols, 0.4 mols, 0.6 mols, 0.8 mols and 1 mol Place the test tubes in the test tube rack. All of the solutions should be 10cm3 in total. There should be 10 test tubes in all, one test tube for each vegetable containing the solutions stated above. Below is a table that shows how to create each of the solutions: Sucrose solution concentration made /moldm-3 Distilled water added (cm3) 1moldm-3 sucrose added (cm3) 0.2 0.8 0.3 0.4 0.6 0.4 0.6 0.4 0.6 0.8 0.2 0.8 1.0 0 10 2. ...read more.

Conclusion

For my 1 mol solution of sucrose, and my pure water solution (0 mols of sucrose), I used the pipette only once. For my 0.2 mol, 0.4 mol, 0.6 mol and 0.8 mol solutions, I used the pipette twice. Therefore, for my 1 mol solution of sucrose and for my solution of pure water, the pipetting error can be calculated as following: 0.05 x 100 = 0.5% 10 For my other solutions of sucrose, since I used the pipette twice, the pipetting error can be calculated as followed: (2 x 0.05) x 100 = 1% 10 Of all my limitations, I think that the fact I used different vegetables on different days had the most adverse effect on my experiment, as it would mean that the concentration of sucrose in each of the vegetables would be different, it would therefore affect the rate of osmosis in a huge way. Improvements If I were to carry out this investigation again, I would make the following improvements to try to eliminate any sources of error: * I would conduct the experiment using the vegetables that were grown and produced in the same field 3 times, one after another. I think that this would make a fair improvement to my results, as it would mean that all results came from the same vegetables that were all similar to each other. * I would conduct all experiments in the same laboratory to avoid change in temperature affecting my experiment. * All vegetable cylinders would be cut to the exact same size, to ensure that the surface area for all cylinders was exactly the same. * I would try to use the same part of every vegetable. * I would measure the each amount exactly, ensuring that the meniscus of the solution in the pipette was touching the exact amount I wanted to measure. Although there were many limitations to my experiment, I feel as though I have gained accurate and reliable results and I can disregard these limitations, as I have gained a strong pattern of results. ...read more.

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