Temperature

Temperature or degree of hotness and coldness is an essential and variable factor in any environment. It influences all forms of life by affecting many vital activities of organisms like metabolism, behaviour, reproduction, development and even death in the Biosphere. The minimum and maximum temperature of an environment regulates the survival of a cell. Van’t Hoff’s rule Van’t Hoff proposed that, with the increase of every 10ºC, the rate of metabolic activity doubles or the reaction rate is halved with the decrease of 10ºC.

This rule is referred as the Van’t Hoff’s rule. The effect of temperature on the rate of reaction is expressed in terms of temperature coefficient or Q value. The Q values are estimated taking the ratio between the rate of reaction at XºC and rate of reaction at (X-10ºC). In the living system the Q value is about .

. If the Q value is . , it means 10ºC increase and the rate of metabolism doubles. The metabolism of organisms is regulated by enzymes which are temperature sensitive.

In many organisms, determination of sex and sex ratio, maturation of gonads, gametogenesis and reproduction is influenced by temperature. In certain environments, the size and colouration of animals are influenced by temperature. Birds and mammals attain greater body size in colder regions than warmer regions ( Bergmann’s rule ). Warm blooded animals, living in colder climates, tend to have shorter limbs, ears and other appendages when compared to the members of the same species in warmer climates ( Allen’s rule ).

In some aquatic environments, an inverse relationship between water temperature and fish meristic characters is observed - lower the temperature, more the vertebrae ( Jordon’s rule ). Bergman's rule Bergman's rule is an eco geographic principle that states that within broadly distributed taxoncmic clade, populations and species of larger size are found in colder and of smaller size are in warmer regions.