A person goes outside on a very cold day. Explain how their body reduces heat loss and maintains core body temperature. [4]
- vasoconstriction / arterioles (supplying skin capillaries) narrow / constrict; accept blood vessels in the skin narrow; reject 'capillaries constrict' / 'capillaries (or blood vessels) move'(1)
- less blood flows (through capillaries) near the skin surface, so less heat is lost (by radiation); accept conduction / convection(1)
- any two from: shivering / rapid involuntary muscle contractions; (increased) respiration (in muscles) releases heat; less / no sweat produced so less heat lost by evaporation; hairs stand up / erect, trapping an insulating layer of air — first point(1)
- second point from the list above(1)
- Answer: Vasoconstriction (arterioles narrow) so less blood flows near the skin surface and less heat is radiated; plus any two of: shivering, muscle respiration releases heat, less sweating, hairs stand up trapping air.
- Examiner tip: Capillaries cannot move or constrict — it is the arterioles that narrow.