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Investigating the Water Potential of Root Vegetables.

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Introduction

Investigating the Water Potential of Root Vegetables. Introduction For my experiment I will be investigating the water potential of root vegetables. The vegetable I am going to use is turnip. I am going to use turnip because it is a uniform vegetable. This investigation is about osmosis. "Osmosis is the net movement of water molecules from an area of high water potential to an area of low water potential. This takes place through a partially permeable membrane." Water potential is the potential energy of the water molecules on either side of the partially permeable membrane to move. Where the water molecules are more concentrated the potential energy of the water molecules is higher. If a solution has a high water potential it has a higher concentration of water molecules and a lower concentration of solute molecules. The solution is said to be hypotonic. Low water potential is the opposite of this; the solution would have a low concentration of water molecules and a higher concentration of solute molecules, and is referred to as hypertonic. If a plant cell is placed in a solution that has lower water potential than the cell (hypertonic solution) it becomes turgid. When a cell becomes turgid it swells, water enters the vacuole by osmosis, its protoplast expands and its turgidity increases. The cell does not burst because of its cellulose wall, when the cell wall is fully stretched it resists any further expansion of the cell. ...read more.

Middle

From my results, I gathered that the tube that had been cut into smaller discs had a greater rate of osmosis because it had gained more weight. I want to complete the experiment in one lesson so I am going to use the method of cutting the tubes into discs, so the experiment happens faster. I put the swede in to the 2-test tube containing 20cm of 1mol dm-3 sucrose solution. When I reached this point of the experiment I felt that my method was working very well. After 20 minutes I emptied the test tubes and wiped the surface water of the swede. I then weighed the tube and then all the discs at once. These were my results... Original weight (g) Weight after (g) Weight diff. (g) % Change Tube Discs Tube Discs Tube Discs 2.73 2.84 2.87 0.11 0.14 4% 5% There was some weight change but it wasn't great. So in my experiment I am going to increase the time that the turnip is in the solutions, to see if there is more of a change. After I finished this preliminary experiment I wanted to do another 3 experiments using all the concentrations to make sure that I wouldn't get any anomalous results. At the end of the 3rd experiment I wanted to find the average weight and then the % change. The results can be seen on the results table. ...read more.

Conclusion

towel, I could have pressed harder on the other samples and absorbed some of the water making them all lighter than these disks or I may have just missed them out by accident, having the excess water could make them heavier. Apart from my single anomalous result I would say that my results are very reliable, they show a trend that I predicted to see; the lower concentration gaining more weight than the higher concentration. I did my experiment three times; the preliminary experiments all had close results. I could improve the reliability of my results by using more concentrations, so that I would have a wider range to view, although I don't think that there would be much of a difference in what I have already seen but using a greater range of molarities over smaller increments would show more accurate results. I don't need to repeat my experiment because I carried out preliminary experiments so I know that my results weren't gained through chance or influenced by outside influences. I took the samples of tissue for one experiment from the same turnip, even though I tried not to cut through the xylem/phloem there would probably still be differences in texture between the different sample which could have influenced the results so ideally all samples would come from the same part of the turnip. The last improvement would be that during the experiment handle the turnip tubes with tongs or forceps to allow minimum contact with cell surface membranes. ...read more.

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