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death

Cessation of all life functions, so that the molecules and structures associated with living things become disorganized and indistinguishable from similar molecules found in nonliving things. In medicine, a person is pronounced dead when the brain ceases to control the vital functions, even if breathing and heartbeat are maintained artificially.

Medical definition

Death used to be pronounced with the permanent cessation of heartbeat, but the advent of life-support equipment has made this point sometimes difficult to determine. For removal of vital organs in transplant surgery, the World Health Organization in 1968 set out that a potential donor should exhibit no brain-body connection, muscular activity, blood pressure, or ability to breathe spontaneously.

Religious belief

In religious belief, death may be seen as the prelude to rebirth (as in Hinduism and Buddhism); under Islam and Christianity, there is the concept of a day of judgement and consignment to heaven or hell; Judaism concentrates not on an afterlife but on survival through descendants who honour tradition.

Cell death Living organisms expend large amounts of energy preventing their complex molecules from breaking up; cellular repair and replacement are vital processes in multicellular organisms. At death this energy is no longer available, and the processes of disorganization become inevitable.

Individual cells can die in two ways. Necrosis is the result of an accident, when as a result of poisoning, heat or a lack of oxygen, a cell swells up, loses its integrity and dies. Aptosis is a biologically controlled process, when a cell shrinks and its components are digested by neighbouring cells; for example, when a tadpole loses its tail.

Biological purpose Biologists have a problem in explaining the phenomenon of death. If proteins, other complex molecules, and whole cells can be repaired or replaced, why cannot a multicellular organism be immortal? The most favoured explanation is an evolutionary one. Organisms must die in order to make way for new ones, which, by virtue of sexual reproduction, may vary slightly in relation to the previous generation. Most environments change constantly, if slowly; without this variation organisms would be unable to adapt to the changes.

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