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Water potential of a potato

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Introduction

Biology Coursework For this coursework I am going to be investigating the water potential of a potato. I will now go over the relevant scientific processes which are going to take place during this investigation. Firstly, Osmosis is the passage of water from a region of high water concentration through a semi-permeable membrane to a region of low water concentration. The movement of water in plant cells is controlled by this process. fig.cox.miami.edu The factor determining how much water will move from the potato is decided by the water pressure of the solution. Water potential is measured in KPA - Kilo Pascal's of pressure. Pure water has a water potential of 0. Here is a diagram of a potato cell. The starch grains found in the cytoplasm allows water potential to stay higher because starch is insoluble and want mix to make a solution. The middle of the cell contains the cell sap. http://www.uq.edu.au/_School_Science_Lessons/2.0CellPotato.GIF There are two terms used toward the structure of a plant cell. They can become either Turgid or Flaccid. Flaccid occurs during plasmolysis where there is a low water content and minimal outward pressure on the cell wall. ...read more.

Middle

+ ( 22x11) (11x16) = 342 so therefore is 342g of sucrose in 1000cm3 of water. From sucrose I would need to work out the how many grams in 1000cm3. Of course this is to high to work with so by dividing both the Sucrose weight and cm3 of water by 5 I received and more workable amounts of 68.4 g of sucrose is 1 mole in 200cm3 of water. The apparatus I used to for included: * Sucrose * Test Tubes * Beaker * Distilled water * Potato's * Electronic balance 0 Mol 0.5 Mol 1Mol Cells: 40 40 31 Plasmolysised: 0 5 19 % Polymolysised 0 % 12.5 % 61 % Using the information I have gathered here it would appear that the equilibrium is somewhere between 0.5 Mole's and 1 Mol. I do not believe it is entirely accurate to measure the plasmolysis this way so I have left the opened the next investigation from 0.25 - 0.75. I have also decided that I am going to measure mass change rather than count plasmolysised cells as I believe this will be more accurate. ...read more.

Conclusion

into the potato cell due to osmosis making the potatoes cells to become turgid and causing and increase in potato mass Here is the diagram I used before. Here it shows what happens when the sucrose solution concentration is above the 0.27Mol of the potato cell chip and vise versa if the solution is lower. Here is the other diagram from before this is now relevant in that it show that at the point of equilibrium (0.25Mol) in this case. There is equal movement of water between the cell tissue and solution as there is nothing to be balanced out . As you can see from the graph showing the kPa of the different sucrose concentrations 0.27 Mol dm-3 equals 720 kPa This means that the potato chip has water potetinal 720kpa. The potato chip could potentials have a higher water potential but it contains starch molecules within the cells. This starch molecules are insoluble, if they were soluble they would mix with the water and the water potential would be increased and the cells could burst from the increased in turgor pressure within the potato cell The starch molecules can be identified in this diagram I used before ...read more.

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