Matthew Billowes, of Nayland College, asks :-
We learn that respiration supplies energy to keep warm blooded animals warm. So why doesn't respiration do the same for cold blooded animals?
David Bolton, a physiologist at the Otago University Medical School, responded.
"Cold-blooded" animals aren't necessarily cold; but they haven't developed the extremely expensive habit of keeping their bodies warm all the time. They are more correctly poikilotherms i.e. animals varying in temperature. At rest they can conserve energy by allowing their bodies to cool and thereby save a great deal of fuel.
Using the term "respiration" to mean the consumption of oxygen and breaking down of food, theirs produces as much heat, per ml of oxygen used, as in mammals, but they can get away with much less of it. You can measure the oxygen consumption of a mouse quite easily, but the same weight of earthworms or lizards uses up oxygen so slowly that it is difficult to detect.
In the cold a mouse will increase its respiration reflexly, generating more heat and staying warm, whereas lizards will themselves cool, and their respiration will passively slow down. Our bodies don't work at all well if we are cooled down, so we have to continue a high rate of respiration at rest, and use all sorts of mechanisms to keep our "core" temperatures within very narrow limits.