2012: Advent Biology: Too cold in here?

by on December 8, 2012

Wonderful as the crisp winter days are, my fingers are creaking with cold as I type. I am however, maintaining an internal temperature with no input from my conscious mind, all the time (even if I am currently applying blankets externally to hoard my warmth!). Everything living will gain heat from and lose heat to their surroundings, as well as generating some heat as by product from metabolism at cellular level. It’s important that internal temperature is right for everything to keep working, as processes at all levels from inside cells to organs and muscles operate with a range of temperatures smaller than the ones the organism will experience. How organisms manage their temperature has been used to categorize them though as with all such attempts, there are different ways to do so.

One possible set of classes is the constant vs. the changing, ‘homeotherms’ and ‘poikilotherms’. For homeotherms, as the temperature of the environment they are in increases so their body temperature remains about constant. Poikilotherms on the other hand are subject to change, and their body temperature will be dependent upon their environment. The issue with this classification is that homeotherms too can go through periods of reduced body temperature.

The alternative description of ‘ectotherm’ and ‘endotherm’ describes the divide better. Organisms which rely on external sources of heat to raise their body temperature are ectothermic, such as reptiles and plants: endotherms are the group who can generate heat internally for the express purpose of raising their temperature. This group consists of mammals and birds, so we’re among the few creatures that aren’t ultimately reliant upon the external environment for our temperature control.  This is much more expensive for the organism, and the further away from the ideal temperature or range of temperatures for the ectotherm, the more energy it expends maintaining that core temperature. The advantage is the high level of control over body temperature, whereas ectotherms are reliant upon adaptations such as behavioural mechanisms to exert any control over theirs. For ectotherms, those mechanisms used to control heat loss and gain will cost them still, but their advantage is a much less intensive energy requirement, and adaptations for extreme temperatures are found aplenty in both groups.

[Image from Futurity.org]

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