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Investigation to Calculate the Water Potential of Potato Tissue.

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Introduction

Investigation to Calculate the Water Potential of Potato Tissue As part of the investigation to determine the water potential of potato tissue in varying concentrations of sucrose a simple procedure was followed. Firstly, 25cm� of sucrose solution was placed in each boiling tube. In each of the five boiling tubes, there were different concentrations of the sucrose solution containing either from the following of molar solutions: 0, 0.25, 0.5, 0.75, and 1.0M. Each boiling tube was labelled with its particular concentration of sucrose. Then the same cork borer was used to prepare 5 cylinders of potato, which had been cut to the same length of 4cm to minimise the difference in mass between the potato chips for greatest accuracy and fairness. In turn, each cylinder was weighed and placed into the boiling tube and to make sure which potato tissue went in what boiling tube we recorded the masses of the cylinders next to which boiling tube they were placed in. The potato cylinders were placed one by one for an hour at three minute intervals. After this period, the cylinders were removed from the boiling tubes and excess liquid was removed by blotting them lightly. They were then weighed and then the results were recorded. After the implementing of the experiment, I got these results. Table 1: Mass difference of potato tissue in varying concentration of Sucrose solution. ...read more.

Middle

they will collide with the plasmamembrane of the cell and travel out of it. The solutions in testubes 2-5: 0.25-1M sucrose had less water molecules per volume than pure water; they had lower water potentials than pure water; and had negative water potentials. Referring to graph 1, I found this out as the potato tissue in 1M sucrose had lost the most mass. The 1M sucrose concentration had the most negative water potential than the rest of the solutions in the testubes. It had the least molecules of water per volume. To reach its equilibrium, osmotic movement occurred. The solution was of more negative water potential than in the potato cells and furthermore there was movement of water molecules from inside the potato tissue into the solution. Therefore, the potato tissue in 1M sucrose lost mass. Water potential is represented by the equation: ? = ?S + ?P Water potential = Solute potential + Pressure potential "The water potentials of the cytoplasm inside a cell and the solution bathing the cell will determine whether water diffuses into or out of the cell" Advanced Biology. So, depending on what the concentration of sucrose the potato cells are placed in, will decide how much osmotic uptake or loss of water molecules. This you will notice when referring to my graph. In other words the solute potential (sucrose concentration) and the pressure potential (the inflow of water opposed by the plasmamembrane), added together will contribute to whatever the water potential is. ...read more.

Conclusion

However there was one anomalous result that I obtained and that was at 0.5M sucrose concentration. This may be due to many reasons. In my experiment the sucrose solutions were just poured into the boiling tubes according to how much was required. This meant that the distribution of the sucrose molecules may have been uneven particularly in that boiling tube containing the sucrose solution with molarity of 0.5M. Uneven distribution may have caused some degree of inaccuracy. In future methods to be used perhaps, the solutions could be stirred to even out the dispersion of the sucrose molecules. In the method, that we used the temperature was an uncontrolled variable. The experiment was carried out at room temperature, which does vary. The effect that temperature has on water potential is that it increases the free energy of the molecules in the solution and furthermore increasing the movement of molecules from one area to another. In my experiment, an increase in temperature may have occurred which may have caused more movement of molecules from one region to the other. However, an increase in temperature would have affected all of the samples and not just the sample containing a potato cylinder at concentration of sucrose at 0.5M. But in future for maximum accuracy, the experiment could be carried out at a constant temperature of 20 �C rather than at room temperature. To improve the investigation followed in future more replicates of the experiment could be carried out. In that way, any anomalous result would not affect the final results as much and would not cause as much inaccuracy. ...read more.

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3 star(s)

This is a well written report that covers the necessary information for this investigation.
1. The report needs to have subheadings to organize the starting sections.
2. The starting sections should not be written in the past tense and should not have running commentaries.
3. The conclusion is the strongest section but the sources of information need to be referenced.
4. The evaluation includes some good suggestions.
***

Marked by teacher Luke Smithen 23/07/2013

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