The scientific definition of plasmolysis is stated as the contraction of the protoplasm of cells within plants due to the loss of water through osmosis. It is when the cell membrane peels off of the cell wall and the vacuole collapses when placed in a hypertonic environment.
The process of plasmolysis occurs when water is drawn out of the cell into fluids outside of the cell through the process of osmosis. Osmosis occurs when a cell has a higher concentration of water than its surroundings. The phenomenon of plasmolysis is unlikely to occur naturally, and is typically induced in laboratory environments by immersing a plant cell into a strong saline or sucrose solution.
A common exhibit of plasmolysis is to place the outer tissue of an onion in a solution of calcium nitrate. When immersed, the onion cells rapidly lose water through osmosis, and the protoplasm of the cell shrinks. This occurs because the calcium nitrate solution can easily pass through the cell membrane and cause an imbalance of osmotic pressure with the solution in the large vacuole in the center of the cell. The vacuole loses water and becomes smaller causing the plasma membrane and protoplasm within it to contract. Unless the onion tissue is transferred quickly from the sugar or saline solution, the cell dies.