Lysis (Greek λύσις, lusis from luein = to separate) refers to the death of a cell by breaking of the cellular membrane, often by viral or osmotic mechanisms that compromise its integrity. A solution containing the contents of lysed cells is called a "lysate".
Cell lysis is used mostly in western blotting to analyse the composition of specific proteins, lipids and nucleic acids individually or as complexes. Depending upon the detergent that is used either all membranes are lysed or certain membranes are lysed, leaving other membranes intact. For example if the cell membrane only is lysed then gradient centrifugation can be used to collect certain organelles - nuclei, mitochondria, lysosomes, chloroplasts and endoplasmic reticulum. The isolated organelles can then be analysed by electron microscopy or western blotting.
Cytolysis is the lysis of cells in a hypotonic environment. Cytolysis is caused by excessive osmosis, or movement of water, towards the inside of a cell (hyperhydration). The cell membrane cannot withstand the osmotic pressure of the water inside, and so it explodes. Osmosis occurs from a region of high water potential to a region of low water potential passing through a semipermeable membrane, so these bursting cells are located in hypotonic environments.
Cytolysis does not occur under normal conditions in plant cells because plant cells have a strong cell wall that contains the osmotic pressure, or turgor pressure, that would otherwise cause cytolysis to occur.
Plasmolysis is the contraction of cells within plants due to the loss of water through osmosis. In a hypertonic environment, the cell membrane peels off of the cell wall and the vacuole collapses. These cells will eventually wilt and die unless the flow of water caused by osmosis can stop the contraction of the cell membrane.