I have mentioned a number of terms that describe organisms which grow in or survive extreme environmental conditions. Perhaps I'd better explain these terms a bit more before we go any further. There is an imposing terminology that has been developed by scientists working on different types of organisms and different types of environmental stress. Organisms that grow best under extreme conditions (the conditions for their optimal growth is much higher or lower than the average for most organisms) are referred to as being extremophilic. The ending '-philic' means 'loving' (from the Greek 'philia', meaning affection or fondness). Organisms that can survive extreme conditions but whose optimal growth conditions lie within the more normal range are referred to as being 'tolerant'. The extreme conditions result in a reduction in metabolism and a period of dormancy which the organism can survive. Where metabolism ceases altogether, organisms are called cryptobiotic. This means 'hidden life' and is derived from the Greek words for hidden ('kryptos', hide or conceal) and life ('biosis').
Terms which describe the responses to different environmental stress are derived by adding these endings to roots for the particular stress. The roots are: thermo- (heat, from the Greek 'therme'), cryo- or psychro- (cold, from 'kryos' for icy cold and 'psychros' for cold or frigid); anhydro- or xero- (desiccation, from 'anhydros' for waterless and 'xeros' for dry); piezo- or baro- (pressure, from 'piezo' for press and 'baros' for weight); halo- or osmo- (osmotic stress, from 'halos' for salt and 'osmos' for pushing); and acido- or alkali- (low and high pH). A lack of oxygen is referred to as anaerobic (without air) or anoxic (without oxygen). These terms are summarised in Table 1.1.
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