Experiment Aim: To investigate the effects of placing onion epidermal cells in different solutions.

Observation:

Table showing the A & B dimensions of five onion cells in both 0.6 moldm-3 and 1.0 moldm-3 solution of sucrose and extent of plasmolysis.

Discussion: Osmosis is the movement of water molecules down their diffusion gradient, through a partially permeable membrane. When placed in solution water molecules will enter or leave a plant cell through osmosis depending on water potential. The water potential is the tendency for water to a solution. It diffuses out a dilute solution (a lot of water- high water potential) and into concentrated solution ( a lot of solute- low water potential). When a plant cell is placed into a dilute solution which has a greater water potential than it, water enter the cell by osmosis. The cell wall of the plant cell does not directly affect this movement, because it is fully permeable to water and to most of the solute in it. As water enters the cell it swells but does not burst because as it swells it has to push out against the strong cell wall. The cell was resists expansion exerting a force called pressure potential. The cell became full and still, a sate called turgid. If a plant cell is placed in a solution that is more concentrate than the cell content meaning that it is being placed in a solution which has a lower water potential than it water will move down the water potential gradient. Water would therefore leave the cell. As water leaves, the volume of the contents shrink and the pressure exerted by the cell wall on the contents decreases. As the contents of the cell shrinks steadily, the cell membrane begins to pull away from the cell wall and plasmolysis take place. Using the measurements of the dimensions A and B the extent of plasmolysis by each concentration was obtained. This showed how far the contents of the cell moved from the cell wall.

 A greater extent of plasmolysis occurred in the 1.0 moldm-3 solution than the 0.6 moldm-3 whcich meant it has a greater  water potential. More water therefore left the cell in the 1.0 moldm-3 solution than the 0.6 moldm-3. The procedure could have been extended by observing more cells and also by keeping the tissue in longer in the concentrated solution.

Conclusion: It can be concluded that the cells in the 1.0 moldm-3 sucrose solution lost more water and therefore became more plasmolysed than the cells in the 0.6 moldm-3 solution. Hence the higher the concentration the greater the extent of plasmolysis in the cells.