Crenation

Crenation is the contraction or formation of abnormal notchings around the edges of a cell after exposure to a hypertonic solution, due to the loss of water through osmosis. The word is from the Latin "crenatus" meaning scalloped or notched, and is named for the scalloped-edged shape the cells take on when crenated.

Crenation occurs because in a hypertonic environment, (that is, the cell has a lower concentration of solutes than the surrounding extracellular fluid), osmosis (the diffusion of water) causes a net movement of water out of the cell, causing the cytoplasm to decrease in its volume. As a result the cell shrinks.

The effects of crenation are especially visible in red blood cells, or erythrocytes, as they become distorted in shape rather than maintaining the usual disc-like shape with the dimple that the blood cell normally has. Instead, the red blood cell looks as if it has legs extending from a smaller central area, like a spiked ball.

Plasmolysis is the term which describes plant cells when the cytoplasm shrinks from the cell wall in a hypertonic environment. In plasmolysis, the cell wall stays intact, but the plasma mebrane shrinks and the chloroplasts of the plant cell concentrate in the center of the cell. Cytolysis is the term which describes the bursting of cells without cell walls in a hypotonic environment. If a red blood cell were exposed to pure water with a solute concentration of zero, the diffusion of the water or osmosis would diffuse from a concentration fof high to low. The water would then be considered a hypotonic solution and the water would then enter the red blood cell. But many times too much water enters the red blood cell and results in the bursting of the red blood cell, otherwise known as hemolysis. Hemolysis gets its name from the prefix hemo- which means blood and the suffix -lysis which means destruction or dissolution.

In an isotonic solution, the concentration of the solute in the solution outside of the cell equals the concentration of the solute inside of the cell so there is no movement of solution.