11. 01 Osmosis Investigation
To investigate the effects of changing the sucrose concentration on osmosis in plant cells.
Water passes into cells through a special type of diffusion called osmosis. Water molecules diffuse through the membrane from a weak solution into a strong solution until the concentration is the same on both sides. A membrane that allows only certain molecules to pass through is called a semi-permeable membrane. In a plant, water passes from a weak cell sap solution to an adjoining cell with a stronger solution, as water passes in, the volume of the sap vacuole increases. When a full sap vacuole presses against the cell wall, it is said to be turgid. If water that is lost is not replaced the sap vacuole shrinks and pulls on the cell wall, the cell becomes flaccid; this is known as plasmolysis.
In the cells shown below, water molecules will diffuse from the turgid cell into the flaccid cell, until the cells contain equal concentrations of cell sap.
I intend to use potatoes for my investigation because these are sufficiently large, to enable all cores to be taken from the same potato, which will assist in ensuring a fair test.
The concentration of sap in the sap vacuole of a potato cell is approximately
10% - 15%. I intend to place a predefined weight of potato cells (0.15g) in varying concentrations of sucrose solution (0%, 20%, 40%, 60%, 80%), to see the effects of osmosis in the cells of a potato in varying levels of sucrose solution. The potato cores will be prepared, weighed and then placed in the solution and left for a certain amount of time, they will then be removed, re-weighed and the difference in weights calculated and plotted, and a conclusion reached.
I have done some preliminary work into osmosis in potato cells. I weighed six potato cores, and then put three into sucrose solution and three into distilled water...