Laboratory work 3: observing plasmolysis and deplasmolysis in a plant cell
Cell sap contains many water-soluble substances. If a cell is placed in a salt solution more concentrated than its own sap, water leaves the cell by osmosis, the vacuole shrinks and the living part (protoplast) pulls away from the cell wall: this is plasmolysis. If the cell is then moved to pure water, water re-enters and the protoplast presses against the wall and becomes firm again: this is deplasmolysis; it requires that the cell is alive and its membrane semi-permeable. In the experiment a salt solution prepared by the teacher (about 6 g of table salt in 100 mL of water) is dropped on one side and water is drawn off from the other side with filter paper; after 5–7 minutes plasmolysis is visible. Then the salt is replaced with pure water and deplasmolysis is observed. Only the teacher works with sharp tools (knife, scalpel); students take a ready preparation or a small piece of an Elodea leaf with tweezers.
“Salt solution calculator”. A group calculates the mass of salt needed to prepare different volumes of solution (at 6 g per 100 mL). The teacher prepares it in practice.