Investigation Of Water Potential

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Planning

Title:

Investigating the water potential of root vegetables.

Aim:

        The aim of the experiment is to find the water potential of potato tuber cells.

Background:

        This investigation is based largely on water potential. Plant cells behave in certain ways when subjected to certain conditions. If a plant cell is immersed in a solution with the same water potential as the plant cell the mass will remain the same. If the plant cell is immersed in a solution with a higher water potential than the cell then the mass will increase. Finally in the plant cell is immersed in a solution with a water potential lower than that of the cell it will decrease in mass. This is due to the rule of water potential. Water will diffuse through a partially permeable membrane down its concentration gradient from a region of high water potential to a region of low water potential. Thus we can find out the approximate water potential of potato tuber cells using this method and getting a more accurate reading from the graph.

I found this diagram on a website. Identified in the references section.

Prediction:

        Based on my background information I predict that at a low concentration of sucrose the potato tuber cells will increase in mass. In potato tuber samples immersed in a solution with high concentration of sucrose will decrease in mass. I believe this because in solutions of low sucrose concentration there is a high water potential. This means water will move from the solution to the potato tuber cells. In solutions of high sucrose concentration the water potential is low, therefore the water will move from the potato tuber cell to the sucrose solution. Meaning it will decrease in mass in solutions of high sucrose concentration.

Preliminary Experiment:

Introduction:

        In this experiment the lengths of potato tuber cells will be examined after being immersed in sucrose solutions of different concentrations.

Equipment:

  • Borer
  • Potatoes
  • Scalpel
  • Ruler
  • Sucrose Solutions (0.1, 0.2, 0.3, 0.4, 0.5, 0.6 molar)
  • Distilled Water
  • Boiling tube
  • Boiling tube rack

Fig.1

Method:

  • The equipment was set up for quick and efficient use (see fig.1)
  • The borer was used to extract 7 cores from the potatoes.
  • These 7 cores were then measured accurately and marked at 30mm in length
  • The cores were then cut accurately with the scalpel to 30mm in length
  • Then 20ml of distilled water was put into one boiling tube
  • Each concentration of sucrose solution was put into a separate boiling tube. 20ml of 0.1 into one boiling tube, 20ml of 0.2 into a different boiling tube…and so on until all concentrations were in a boiling tube up to 0.6
  • Then one potato core was put into each boiling tube.
  • The cores were left for 25 minutes
  • The change in length was measured and the results recorded.

Results:

Table Showing Change in Length of Potato Tuber Cells in the Preliminary Experiment

Fig. 2

Conclusion:

        From the results I conclude that the preliminary results were not particularly accurate. The results do not seem to show any particular pattern or relation to my prediction.

Evaluation:

        There may be a few reasons for this. The length is not a particularly good measurement as it ignores any width expansion. Also the length of time the potato tuber cells were left in the solution was not sufficient for any significant effect to take place. Not only that but the method of measurement not particularly accurate. The potato tuber cells were already small to begin with; therefore a ruler with smallest measurements of 1mm may not be small enough to indicate the true change. I also have to consider possible human error in cutting the potato tuber cells so they may have been slightly different in length. Some of the cores may also have been from different potatoes this could mean that the water potentials may be slightly different due to the different environmental conditions of the potato. Also the actual function and properties of the cell wall are a reason the length is not a good thing to measure. The cell wall provides structure and turgidity to the organism. This means that even when the water is passed into the cell the actual change in length will be so small that it would not provide any significant or workable results. Overall this preliminary experiment wasn’t particularly successful however it has highlighted areas of weakness within the experiment which I can alter for the real experiment.

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Modifications:

        Due to the areas of weakness highlighted by the preliminary experiment I have decided to make a few modifications to make the real experiment more accurate therefore increasing the chances of a successful experiment.

        Firstly I have decided that instead of measuring the change in length of the potato tuber cells, I have decided to measure the mass. This is because it allows for all increases in size of the cells and also the scales can measure to a much more accurate degree than a ruler.

        Secondly I will attempt to take all cores from ...

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