Cytolysis

Cytolysis, or osmotic lysis, occurs when a cell bursts due to an osmotic imbalance that has caused excess water to move into the cell. It occurs in a hypotonic environment, where water diffuses into the cell and causes its volume to increase. If the volume of water exceeds the cell membrane's capacity then the cell will burst. The cell will only burst if the cell is an animal cell and it will only expand if it is a plant cell.

In Plants
Cytolysis does not occur in plant cells because plant cells have a strong bond and that the cell wall lacks in the animal cell and can result to the bursting of the cell cell wall that contains the osmotic pressure, or turgor pressure, which would cause cytolysis not to occur. Contrary to organisms without a cell wall, plant cells must be in a hypotonic environment in order to have this turgor pressure, which provides the cells more structural support, preventing the plant from wilting. In a hypertonic environment, plasmolysis occurs, which is nearly the complete opposite of cytolysis: Instead of expanding, the cytoplasm of the plant cell retracts from the cell wall, causing the plant to wilt.

In Mammals
Osmotic lysis is often one result of a stroke, because improper nutrient perfusion and waste removal alter cell metabolism. Such malfunction results in an inflow of extracellular fluid into the cells.

In Bacteria
Osmotic lysis would be expected to occur when bacterial cells are treated with a hypotonic solution with added lysozyme.

Prevention
Different cells and organisms have adapted different ways of preventing cytolysis from occurring. For example, the paramecium uses a contractile vacuole, which rapidly pumps out excessive water to prevent the build-up of water and the otherwise subsequent lysis.

Other organisms pump solutes out of their cytosol, which brings the solute concentration closer to that of their environment and slows down the process of water's diffusion into the cell, preventing cytolysis. If the cell can pump out enough solutes so that an isotonic environment can be achieved, there will be no net movement of water.