ABSTRACT
This chapter examines membrane adaptations of ectotherms and endotherms that are related to their high level of metabolic activity and then membrane related aspects of the inability of most endotherms to tolerate hypothermia. A. Krogh was the first to suggest that the level of metabolism of endotherms was considerably greater than that of ectotherms. As well as the dramatic increase in metabolic activity, there is also another fundamental difference between endotherms and ectotherms. The reason why non-hibernating endotherms are unable to tolerate hypothermia is not known but almost certainly centres around the cell membrane. One group of endotherms that are able to tolerate low body temperatures are the hibernators, some of which can tolerate body temperatures near freezing during the hibernating season. Membranes appear to be site of important and general differences between the tissues of endotherms and ectotherms, both with respect to high level of metabolism and also the evolutionary loss by endotherms of the ability to tolerate hypothermia.
