Quick questions on Thermoregulation in endotherms and ectotherms (QCE Biology Unit 2)

Endotherms. Generate most of their body heat internally through high-rate metabolism. Maintain a roughly constant body temperature (around 37 degrees Celsius in mammals, 40 in birds) regardless of ambient temperature. - Examples: all mammals, all birds. - Cost: high food and oxygen requirement; small mammals can need 10 to 20 percent of their body mass in food per day.

Heat moves by four mechanisms. - Radiation. Electromagnetic energy to or from any object. A basking lizard absorbs solar radiation; a warm body radiates heat to a cooler environment. - Conduction. Direct contact between objects of different temperatures.

The hypothalamus heat-loss centre is activated. - Sweating (or panting). Evaporative cooling. Sweat across most of the human body; panting in dogs (small surface area lacking sweat glands) and many birds. - Vasodilation of skin arterioles. Skin flushes red.

The hypothalamus heat-promoting centre is activated. - Vasoconstriction of skin arterioles. Skin pales. Less blood reaches the surface; heat is retained in the core. - Shivering. Rapid involuntary skeletal muscle contractions generate heat as a by-product of ATP hydrolysis.

Ectotherms rely mostly on behavioural responses. - Basking. Position on warm rocks or in sun to absorb radiative heat. - Sheltering. Move to shade or burrows to avoid overheating. - Body orientation. A lizard turning broadside to the sun maximises heat gain; turning end-on minimises it.

Generate most of their body heat internally through high-rate metabolism. Maintain a roughly constant body temperature (around 37 degrees Celsius in mammals, 40 in birds) regardless of ambient temperature. - Examples: all mammals, all birds.

Body temperature is set largely by the environment. Heat from metabolism is small; ectotherms rely on external heat sources. - Examples: reptiles, amphibians, fish, invertebrates.

"Warm-blooded" is informal and inaccurate. A basking lizard can be warmer than a small mammal in shade; the difference is the source of heat (internal vs external), not the temperature itself.

They are ectothermic. A lizard in the sun can be warmer than a human.

Choice of clothing and shade is part of the answer.

Cold: vasoconstrict (skin pale, conserve heat). Hot: vasodilate (skin flush, dump heat).

Piloerection, non-shivering thermogenesis, behavioural responses and hormonal changes are also examinable.