Learning focus
Use precise biological vocabulary, trace control pathways, explain cause-and-effect mechanisms, interpret diagrams and apply ideas to unfamiliar contexts.
When body temperature rises
The hypothalamus activates sweating and vasodilation. Sweat evaporates, removing latent heat from the skin. Increased blood flow through surface capillaries raises heat transfer by radiation and convection. Hair erector muscles relax, so hairs lie flat and trap less air.
When body temperature falls
Vasoconstriction reduces blood flow near the surface. Sweating decreases. Hair erector muscles contract, raising hairs, and skeletal muscles may shiver. Shivering consists of rapid contractions that increase respiration and release heat.
Balancing heat gain and loss
Body temperature depends on the balance between metabolic heat production and heat transfer to the environment. Exercise increases heat production. Wind increases convection and evaporation, while high humidity reduces sweat evaporation. The body’s responses therefore interact with environmental conditions.
Limits of regulation
In severe heat, dehydration can reduce sweating and core temperature may rise dangerously. In severe cold, heat loss may exceed production. Homeostatic systems have limits, so behaviour such as seeking shade, drinking water or wearing clothing is also important.
Practical or data skill
Analyse data for skin temperature, core temperature and sweat rate during exercise and recovery. Distinguish between a response that changes heat production and one that changes heat loss.
Examination tip
Vasodilation does not mean that the blood vessels move closer to the skin; the arterioles widen.
Review questions and suggested answers
Question 1
How does shivering warm the body?
Suggested answer
Muscle contractions increase respiration and heat release.
Question 2
Why is sweating less effective in humid air?
Suggested answer
Evaporation is slower when the air already contains much water vapour.
Question 3
Name one response that reduces heat loss.
Suggested answer
Vasoconstriction, reduced sweating or raised hairs.
