These are all examples of apoptotic cell death, or cell suicide. Apoptotic death is different from necrotic death in several ways. Necrotic death of a cell is a response to damage or toxins in the environment. Cells dying a necrotic death due to lack of oxygen, for example, swell and burst, often causing further damage to surrounding cells. Apoptotic cells, on the other hand, do not burst, but rather exhibit shrinking, chromatin condensation, and blebbing.
Apoptotic cells are also rapidly disposed of, engulfed and broken down by neighboring cells.
Because of these characteristic features, it was proposed that there might be an actual program of cell death that is activated within a cell. This was a revolutionary idea initially, and took some time to get accepted. Studies in C. elegans were responsible for transforming the field of cell death by identifying a pathway of genes required for cell death that turned out to have homologies to genes also involved in cell death in mammals. In ced-9 lf mutations, all cells undergo apoptosis during embryogenesis. From its lf phenotype, ced-9 must normally inhibit the death program.