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Investigation to determine the lowest concentration of lead ions that causes cell membranes to lose partial permeability

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Introduction

Investigation to determine the lowest concentration of lead ions that causes cell membranes to lose partial permeability Knowledge Plasmolysis is the separation of plant cell cytoplasm from the cell wall as a result of water loss. As moisture leaves the vacuole the total volume of the cytoplasm decreases while the cell itself, being rigid, hardly changes. Plasmolysis is unlikely to occur in the wild except in severe conditions. Plasmolysis is induced in the laboratory by immersing a plant cell in a strongly saline or sugary solution, so that water is lost by osmosis. If a cell of almost any water plant is soaked in a 15% sugar solution, its cell contents soon separate from the wall and form a mass in the centre of the cell. This occurs because the sugar solution that has passed freely through the cell wall now encounters a selective semi-permeable cell membrane. ...read more.

Middle

In the above picture, the cell on the left is turgid, the cell in the middle is just starting Plasmolysis and the cell on the right has been plasmolysed. Apparatus > Red Onion > Distilled Water > Microscope > 2 Slides > 2 Cover Slips > Pipette > A supply of 1 mol dm�� lead nitrate solution (toxic) > Sucrose Solution > A small Beaker Safety Issues Hazard Precaution Cutting your self on broken glass. Handle all glass with care, and if you see a chip in any piece of glass, put it to one side and use another piece of equipment. Solution splashing into your eyes. Wear eye goggles at all times. Slipping on a liquid. If you spill some solution or water clear it up straight away before you forget about it, or before someone else comes along and slips over on it. ...read more.

Conclusion

5. Place the slide and cover slip to one side; this will be used as a reference so that you can see if Plasmolysis is taking place using different moralities of lead nitrate solution. 6. Dilute the 1 mol dm�� lead nitrate solution to 0.1 of a mol with distilled water in a small beaker. 7. Place another piece of onion on a slide and focus on a group of cells at 100X magnification, like in step 2. 8. Add 3 drops of this solution to the onion, and then firmly place the cover slip on top. 9. Wait for a 5 minutes, then change the magnification to 400X 10. Look to see if Plasmolysis is taking place. 11. If Plasmolysis isn't taking place repeat steps 6-10 but using a lead nitrate solution of 0.1 more morality that the previous test (i.e. 0.2, then 0.3, then 0.4... etc) until you see Plasmolysis taking place Results Morality of dm�� lead nitrate solution Did Plasmolysis occur? 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0. ...read more.

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