Temperature effects on different organization levels in animals.

One of the central concepts in present biology is the recognition of different organization levels and their hierarchical array. Complex multicellular animals are constituted of organ systems, the organs of cells, the cells of organelles, membranes, and molecules. The primary effects of many environmental factors (e.g. light, concentrations of ions and molecules) can be delimited mainly to one level. Temperature, being the macroscopic physical measure of the random motion of smallest material particles, affects directly the animal life at all organization levels. The special physical nature of temperature means also, that during the history of life, organisms have always been subjected to temperature variations. Many different ways to evade the pervasive effects of temperature have been evolved during the course of evolution. The study of the temperature relations of organisms can therefore give models for other branches of environmental biology. The temperature limits and relations of an animal cannot be explained by the temperature relations and limits of its cells without taking into account such interactions between different types of cells, which are found only through the study of the organs. Also, the temperature limits and relations of animal cells cannot be explained just through the study of the constituent molecules. The possible interactions of the molecules (e.g. lipids and proteins in a cell membrane) are so manifold and complex that in order to ascertain the relative importance of them in the temperature relations of the cells we must rely in part on studies done on organelles (e.g. on the plasma membrane). The study of the thermal biology of animal cells thus exemplifies the situation often found in biology: the attainment of a reductive explanation is not always a one-way deduction, but it may involve modifications of the lower level concepts according to the knowledge derivable only from studies of the higher level systems.