Cell death: cell death reasons in multi-cellular organisms are apoptosis and necrosis. One is natural cell death process that is apoptosis and other is because of accidental harms, named as necrosis: apoptosis is a natural process that is called as programmed cell death. It is normal part of multi-cellular organisms and occurs because of the biochemical changes. Apoptosis helps to eliminate unnecessary cells from body. Figure 18. 1:apoptosis phenomenon: apoptotic bodies are smaller sized sealed membrane vesicles produces when cells undergo programmed cell death. Apoptotic antibodies help to prevent the inflammations by saving the discharge of toxic cellular contents of dyeing cells during apoptosis: cell necrosis is the death of cells by accidents and unexpected accidents. Necrosis can be result of radiation exposure, heat, trauma or decrease of oxygen in arteries because of blood flow obstruction. Figure 18. 2: a close look of apoptosis and necrosis. Intracellular proteolysis is breakdown of protein molecules into smaller amino acids.