Every living organism has a range of conditions over which it is able to undergo normal activity, and when it is pushed to its limits, it struggles to survive. Some species that survive in extreme environments are true extremophiles and do not seem to find the conditions harsh at all. But in most cases, living things develop elegant tolerance mechanisms that help them adapt to their surroundings.
Animals seem to have developed three basic tolerance strategies. The first involves slowing down and sitting it out: animals often reduce their metabolism and sometimes enter into hibernation. Others may find a more favourable environment, like animals that migrate to avoid seasonal extremes. Living things sometimes also launch a counterattack, like wood frogs that produce antifreeze proteins to prevent ice crystals forming in their cells in the extreme cold.
However, these tactics usually only work for occasional exposure and to flourish, major adaptations are required at the biochemical level. For the most part, micro-organisms, like bacteria, archaea and fungi, have achieved these more complex adaptations.