Practice question

A lizard basking on a sun-warmed rock changes its location and posture to control heat exchange, an example of behavioural thermoregulation. Solar radiation and conduction from the rock raise body temperature, increasing enzyme activity, nerve conduction, muscle performance, digestion, and escape speed toward an optimal range. Once sufficiently warm, the lizard may move into shade, flatten or elevate its body, orient differently to the sun, or retreat into a burrow to avoid overheating. Most lizards are ectothermic: environmental sources provide the majority of their heat. This differs from endothermy, in which metabolic processes generate most regulatory heat, and from homeothermy, which refers to maintaining relatively constant temperature. Allen’s rule describes evolved geographic variation in appendage proportions, not an immediate behavioural response. Behaviour allows an ectotherm to maintain body temperature more precisely than ambient temperature alone would suggest, so “cold-blooded” does not mean passive thermal conformity. The effectiveness of basking depends on wind, substrate, colour, body size, predation risk, and access to thermal microhabitats, illustrating how physiology and habitat structure interact.