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Water Potential Changes In A Germinating Potato.

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Introduction

Water Potential Changes In A Germinating Potato. Introduction: In order to carry out this investigation, I firstly need to define the terms of the objectives so that there is an understanding in my mind so a clear process can be carried out. What is Water potential? The net direction of water movement in a cell depends on the water potential of the cell and whether it is more negative or positive than the water potential of the surrounding solution. The water potential of a solution is the term given to the tendency for water molecules to enter or leave a solution by osmosis. Pure water obviously has the highest water potential set at zero. Dissolving any solute into pure waters lowers the water potential. The water molecules are immediately less likely to diffuse. Therefore the effect of dissolving a solute in water is to lower it's water potential. Consequently solutions at atmospheric pressure have a negative value of water potential, and the more concentrated the solution the more negative the water potential. Water potential is determined by the components: the solute potential, and the pressure potential this is expressed as a simple equation: Cell = s + p Water potential is really a measure of the free kinetic energy of the water molecules. If a plant cell is in equilibrium with an external solution, there is no loss or gain of water, then the solute potential of the external solution will be equal to the water potential of the cell or Solution = Cell. The use of this information can be made to find the water potential of a plant tissue, such as potato, by immersing pieces of potato in a range of solutions and determining the changes in the mass of tissue. Hypothesis: The aim of the investigation is to explore the changes in water potential of a germinating potato. So to do this I am going to take samples along the potato at different positions towards the sprouting. ...read more.

Middle

These results have been plotted on a scatter graph, which is shown on the following page: Main Experiment Aim: To find the change in water potential in a germinating potato Apparatus: Electronic weight balance*1; Filter paper*10; Cork hole-borer (1cm Diameter)*1; Graded Pipettes*5 and Filler*1; Labels*20; Large Potato with sprouting*1; Ruler*1; 150cm� of each of the following Graded Sucrose Solutions: 0.2mol dm� �, 0.4mol dm� �, 0.6mol dm� �, 0.8mol dm� �, Petri dishes*4; 150cm� of Tap Water; Boiling tubes*5; Bungs to fit Boiling Tubes*5; Stop Clock*1; Razor Blade*1; White tile*1; Safety mat*1; test tube rack*1. Why I've changed/added some apparatus: Graded Pipette and Filler this gives a much more accurate measure for the sucrose solution that is being used. Bungs to fit Boiling Tubes lowers the amount of evaporation taking place. Razor Blade gives a neater cut on the potato and is easier to use for something so thin. White tile to cut the potato on so nothing on the workbench contaminates the potato that is being used. Diagram: Method: My method is the same as in the preliminary experiment however I have changed some things that improves the experiment overall. What I have changed or added I have highlighted in red. Now pour the 10ml of sucrose solution needed into each of the boiling tubes using the Graded pipette and filler. Once the sucrose solution is in the each of the boiling tubes seal the top up using a bung this is to prevent any evaporation of the sucrose liquid solution. Every time you use a different sucrose solution make sure that a clean graded pipette is used. This will ensure no mixing of solutions takes place. Slice off the end exposed to the air of the potato sample to ensure the cylinder that is to be used is fresh. Take a ruler and measure accurately 1mm and cut using the razor blade and repeat this five times. ...read more.

Conclusion

Then decreases again for 0.8mol dm� �. However in some cases the decrease in percentage change in mass does not change that much for example in position 1 of the potato there is a 0.50 percent difference between 0.6mol and 0.8mol. Unlike position 4 on the potato is a difference of 41.00 percent difference these results may be due to the small difference in weight of the cylinder of potato. I explained in my fair test that this would affect the results, which this looks like this has proved. From completing this experiment I have learnt that the water potential is much lower nearer the sprouting on the germinating potato. This has proved the hypothesis that I made I at the beginning of the experiment that the closer you are to the sprouting on the potato the lower the water potential, because as the sucrose solute goes up the water potential goes down as it becomes more negative. Evaluating: I feel that the experiment went well, there was one result that stands out this is position 4 on the potato. This anomalous result shows that there is not much of decrease between Tap water and 0.2mol. The decrease is only 1.42 percent decrease. I think that this may have been due numerous errors, for example the balance may not have been very precise; water from previous potato cylinders may have been on the balance. Also it may have been down to human error of not measuring and cutting the potato precisely this could have affected the amount of water gained or lost. The precision of measuring the concentration of the solution may also have changed for this result. Finally, I could extend the experiment to a more exact level by looking at the potato cylinders under a microscope, and then I would be able to see the cells in greater detail and draw more observational results. Rebecca Moor 12T - 1 - ...read more.

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