Resistance of organisms to extreme influences in relation to some exobiological problems

The conditions to which organisms have not been able to adapt in the process of evolution are called extreme influences or extreme conditions. The experiments show that organisms and cells have a potential for resistance; among animals, there are forms that are able to stand extremely low temperatures (from -80 to -269 degrees) when the water content of their tissues is large enough. Some species of protozoa can tolerate ionizing radiation in doses (500-1800 kr) of many orders exceeding those existing on the Earth and out in space. There are different ways of obtaining "protection" against ultraviolet (UV) shortwave sun radiation detained by the ozone layers of the Earth's atmosphere (photoreactivation, biological screens non-permeable for UV light, etc.). Many insects, especially alpine species, do not require as much oxygen as is contained in lower layers of the Earth's atmosphere. Hence, earth organisms possess some "margins of safety", enabling us to suggest the existence of similar biological systems in conditions different from the Earth's. The resistance to the action of extreme factors is probably connected with the resistance of biopolymers, protein complexes of cells and also with the capability of the organism to recover from damage.