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Investigation to Determine the Water Potential of Potato Tuber Cells .

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Introduction

Investigation to Determine the Water Potential of Potato Tuber Cells . AS Biology Coursework Aim: Investigate and determine the water potential of potato tuber cells. Water potential is a measure of the tendency of water molecules to pass from one place to another. The principle in this experiment is to discover a solution of known water potential, in which the tissue being examined neither gains nor loses water. Samples of the tissue are allowed to come to equilibrium in a range of solutions of different concentrations and the solution which induces neither an increase nor a decrease in mass or volume of the tissue has the same water potential as the tissue. The method is described below. Materials * Fresh potato tuber * Distilled water * 1 mol dm-3 sucrose * 6 test tubes * Test tube rack * Labels or wax pencil * 2 * 10 cm3 or 25 cm3 graduated pipettes * Tile * Scalpel or knife * 2 * 100 cm3 beaker Method 1. I was provided with a solution of 1 mol dm-3 sucrose. ...read more.

Middle

At 0.4 sucrose solution the graph shows a 0.5 mm change in length. This length remains unchanged throughout until 0.6 sucrose solution. This can be an experimental error. At 0.8 sucrose solution the change in length is 0.0 mm. This is were the curve cuts the axis. This means that the external water potential and the internal water potential and the internal water potential was equal as there was no water molecule movement. At the final sucrose solution (1.0) the change in length was -1 mm. The size of the potato strips decreased. All these changes were due to the process called osmosis. Osmosis is the passage of water molecules from a region of higher water potential to a region of lower water potential through a partially permeable membrane. It is best regarded as a form of diffusion in which only water molecules move. The tendency of water molecules to move from one place to another is measured as the water potential, represented by the symbol ?. Water always moves from a region of higher water potential to a region of lower water potential. Solute molecules reduce water potential. ...read more.

Conclusion

Using the morality table the solute potential of the potato strips at 0.8 sucrose solution can be worked out. At 0.8 sucrose solution the table shows that the solute potential is -2580. From this we can work out water potential of the potato strips. ? = ?s, therefore ? = 2580 => 2580 = Water potential inside potato. Evaluation I think that the experiment went very well. There were no odd results and they produced a good graph. Even though the results came out fairly good but still there was room for improvement. During the experiment, some minor errors may have been encountered. These errors are as follows:- Two different potatoes were used for the experiment. The results could have been affected by this because the internal of the two potatoes may have been different. When I got rid of the solutions from the tube in order to carry the potatoes strips, I might have either taken some water out of the strips or I might of left some excess water in the potato. This part of the experiment is difficult to come up with an accurate and fair method, as other ways would also lead to some slight inaccuracy. ...read more.

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