animals to ever exist on earth are aquatic animals. The metabolic rate of animals scales with a mathematical principle named quarter-power scaling according to the metabolic theory of ecology. Mass and heat transfer Mass transfer, such as diffusion to smaller objects such as living cells is faster than diffusion to larger objects such as entire animals. Thus, in chemical processes that take place on a surface – rather than in the bulk – finer-divided material is more active. For example, the activity of a heterogeneous catalyst is higher when it is divided into finer particles. Such catalysts typically occur in warmer conditions. Heat production from a chemical process scales with the cube of the linear dimension (height, width) of the vessel, but the vessel surface area scales with only the square of the linear dimension. Consequently, larger vessels are much more difficult to cool. Also, large-scale piping for transferring hot fluids is difficult to simulate in small scale, because heat is transferred faster out from smaller pipes. Failure to take this into account in process design may lead to catastrophic thermal runaway. See also Biomechanics Allometric law On Being the Right Size, an essay by J. B. S. Haldane that considers the changes in shape of animals that would be required by a large change in size Surface-area-to-volume ratio Kleiber's law Bergmann's rule References Area Volume Mathematical principles