Determination of the Solute Potential of Cell Sap

Determination of the solute potential of  cell sap

Introduction

Incipient plasmolysis is the point at which the plant cell contents are just about to lose contact with the cell wall as water is lost from the cell by osmosis. At the point of incipient plasmolysis, the pressure potential is 0 therefore, from the general equation cell=s If plant cells are immersed in a graded osmotic, then examined microscopically, it is likely that signs of plasmolysis will be seen in cells immersed in 1of these solutions. Cells in other solutions will either be turgid or fully plasmolysed. In practice, the point of incipient plasmolysis is taken to be when half the number of cells observed show signs of plasmolysis.

Method 1. Label small dishes appropriately and add sucrose solutions separately to each- 0 mol dm³, 0.2 mol dm³, 0.4 mol dm³, 0.6 mol dm³, 0.8 mol dm³. 2. Carefully peel the pigmented epidermis from a rhubarb petiole and, using scissors, cut into squares with side approximately 5 mm. 3. Immediately place 1 square of tissue into each of the osmotic. 4. Leave the tissue in these solutions for 10 minutes. 5. After 10 minutes, remove each strip 1 at a time using a mounted needle and mount on a microscope slide in adrop of  the same solution in which it had been immersed.

6. Apply a coverslip and examine using a microscope with medium power. 7. Count all the cells which are visible within the field of view, then count all the cells which show signs of plasmolysis. Include all cells in which it is possible to see separation of the cell contents from the cell wall, no matter how slight this may be. 8. For each preparation use 2 epidermal peels.

Observations

Sucrose concentra tion/ mol dm³ 0

0.2 0.4 0.6 0.8

Epidermal peel 1 Tot  Plasmol al ysed 10 32 3 18 64 9 14 67 5 13 101 2 17 162 3

Epidermal   Average % peel 2 Plasmol Tot  Plasmol Tot  Plasmol ysis al ysed al ysed 18 54 14 43 29.5 9 6 13 45 16 55 34.2 2 1 17 64 16 66 41.3 4 0 16 124 15 113 75.3 8 0 15 143 16 153 93.3 4 4

100 90

% plasmolysis

80 70 60 50 40 30 20 10 0 0

0.2

0.4

0.6

0.8

Sucrose conc./ mol dm³

Conclusion 0.45 mol dm³ is the solute potential of the rhubarb cells. It is the sucrose concentration that plasmolysed half the rhubarb cells so we assume it is the solute potential of the cell sap of  rhubarb cells.