TEMPERATURE AND LIFE

Changes in temperature have profound effects on biological processes. In general, the rate at which life processes (such as metabolism, respiration and growth) proceed declines as the temperature decreases and elevates as it increases. This is because high temperatures supply more kinetic energy to reactions than do low temperatures, allowing the reacting molecules to come into contact and to interact more frequently. If the temperature continues to increase, however, it starts to have destructive effects on organisms. The rate of metabolism, and other life processes, declines again. There is thus an optimum temperature at which metabolism is at its greatest rate and, if the temperature decreases or increases from this optimum, the metabolic rate declines (see Figure 1.1). As was pointed out in Chapter 1, the decline in metabolic rate at low temperatures (below the optimum) is due to very different causes from those producing a decline at high temperatures (above the optimum). The rate declines at low temperatures mainly because there is less kinetic energy driving the metabolic reactions, but the effect is largely reversible (unless freezing or some other event occurs which the organism cannot survive; see Chapter 5). The decline in metabolic rate at high temperatures is, however, due to destructive effects on the proteins, and the other components, of the organism. Some of these destructive effects may be reversible if the temperatures are not too high. At higher temperatures, irreversible changes occur or there is too much damage to repair and the organism will die.