Question No. 10
- What distinguishes living organisms from non-living?
- Answered 24 December 2006.
Question author: anonymous.
Asked 18 December 2006.
In contrast to the dead one, the living organism continuously consumes energy from the environment or internal stores. This ordered process of energy consumption, which is regulated by the organism itself, represents the organism's power or metabolic rate. It supports all life processes in the organism and cannot drop below a certain minimum threshold value. This minimum rate of energy consumption, which for human beings is in the vicinity of 100 W (or 2 W/kg) prevents the organism as a whole from disintegration, as well as its organs and cells from getting biochemically disordered. These undesirable outcomes inevitably follow as soon as the metabolic rate is switched off; they cause the organism's death. It should be noted that in his daily activities man can develop a much higher power — for example, a trained long-distance runner exerts up to 1 kW at a 5 km distance, while sprinter and weight lifter — even up to 10 kW. Thus, the difference consists in the fact that a living organism has metabolism, while a non-living has not.
Death is an irreversible loss of orderliness by the living organism. The irreversible character of death, i.e. impossibility of anastasis or resurrection, is conditioned by the ultra high level of orderliness of living organisms in comparison to any objects of the inanimate world, where many processes can be reversed. Information that governs the structure and function of living organisms is written in macromolecules of DNA. A random assemblage of these DNA-based genetic programs is absolutely improbable in any physico-chemical conditions in the whole Universe. Namely the irreversibility of death disorder, a consequence of the ultracomplex organization, distinguishes any living organism from any inanimate object.
Under some unfavorable conditions some organisms are able to get biochemically "conserved" and switch off the life-supporting metabolism. This happens, for example, in dry bacterial spores, in trees and some insects tolerating freezing at very low temperatures, in some air-breathing organisms in anoxic environments. The residual chaotic biochemical reactions occurring in such states have a very low power, which is hundred or thousand of times less than the minimum life-supporting metabolic rate. These chaotic reactions are slowly but steadily destroying the organism's orderliness. When the unfavorable conditions are over, the organism switches on its metabolism and repairs all the accumulated damage. However, if the unfavorable conditions stay for too long, the process of degradation may go too far. The organism then will have irreversibly lost its order, it never revives and, hence, dies. Therefore, one can say that in some (but by far not all) organisms there is a third state apart from life and death. In this state, which is sometimes called anabiosis, the organism does not live, but it is not dead, because it retains its potential ability to live.
See also the following paper about minimum metabolism and order (Makarieva, Gorshkov, Li, Chown 2006).