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Aim: To estimate the solute potential of a plant tissue.

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Solute Potential of Cell Sap of Plant Epidermal Cells Aim: To estimate the solute potential of a plant tissue. Results: Molarity of Solution Plasmolysed Cells Percentage of Cells That Were Plasmolysed .3M 1/70 .01% .4M 0/70 0% .5M 5/70 7% .6M 12/70 17% .7M 29/70 41% 1.0M 56/70 80% It must be taken into account, that the experiments procedure was changed. This could have had a great affect on the results. The part of the procedure that was changed was the time. Instead of the epidermal cells being left in the solutions 20 minutes, they were left for a day. Not only, were they left much longer, but the molarity of the solutions could have also changed since they were left uncovered for over 24 hours and some of the water could have been evaporated. ...read more.


The most contracted membranes were found in epidermal cells that were left in the solution with the greatest molarity; in this case it was the cells that were left in the solution with a 1.0 molarity. The graph shows a constant start. It very quickly shoots up, with a huge leap from .6Mto 1.0M. The results for this experiment did not come back exactly the way they should have to prove the point. In the epidermal cells that were placed in the .3M solution .01% of the cells plasmolysed, but in the epidermal cells that were placed in the .4M solution 0% of the cells were plasmolysed. If the experiment had gone exactly as planned, the cells that were placed in the .4M solution would have had more than .01% cells plasmolysed. ...read more.


Another error that could have occurred, and that would explain what happened to the cells that were put in the solution with .4M, is that onion skin dried out before it was placed in the sucrose water. Also, there could have been a variation between the different onion epidermis cells that were used, because not all cells in the same tissue have the same solute potential. Next time, to avoid these errors, the correct time should be used. The pieces of onions should be cut more exactly and each cell that is visible through the microscope should be counted. To evade to possibility of the onion cells drying out they should be immediately placed into the sucrose solution. Also, during the waiting period the solutions that the cells are in should be covered, as to avoid any evaporation that may occur. ...read more.

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Here's what a teacher thought of this essay

**Results and conclusion only.
This piece of work fails in many key aspects that are considered good practice at A level and the data collected cannot be considered to be valid due to problems with the methodology.

To improve:
There is no real attempt to provide a rationale for the choice of investigation in terms of its scope,and its relation to biological principles. The hypothesis should be stated and biological knowledge used to explain a prediction.
Attempts to interpret the data are not linked to any researched information. The candidate needs to include carefully selected reference material to help inform the conclusion.
There is no relevant biological background. The conclusion would be expected to refer to the water potential of the relevant solutions and discuss the movement of water molecules in the solution.
No graph was included and the description of the underlying trends would be helped by the use of technical or scientific language. The solute potential of the cell sap needs to be calculated ( obtained from the graph at 50% plasmolysis) as this was the stated aim of the experiment.
The analysis of the method reveals a catalogue of very poor planning. Detailed suggestions for improvements and extensions would have improved this section.

Marked by teacher Stevie Fleming 22/08/2013

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