Example 1
Body temperature increases after exercise. Explain why sweating is negative feedback.
The initial change is a temperature rise. Evaporation increases energy transfer away from the skin, opposing that rise.
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Year 9
Temperature regulation and negative feedback
Apply a feedback-loop model to sweating, shivering and skin blood flow.
Method and worked examples
Homeostasis maintains internal conditions within a suitable range despite external changes. Temperature regulation involves receptors, a coordinating centre and effectors. If body temperature rises, responses include sweating and increased blood flow near the skin. Evaporation of sweat transfers energy away; increased skin blood flow can increase heat transfer when surroundings are cooler. These responses reduce the initial temperature rise.
If body temperature falls, shivering increases muscle activity and energy release, while reduced skin blood flow limits heat loss. The hypothalamus helps coordinate these responses. Negative feedback regulates around a range, so small fluctuations do not mean the system has failed. Read temperature graphs by checking the direction of the deviation and whether the response tends to bring temperature back, rather than expecting a perfectly horizontal line.
Example 1
Example 2
A graph rises from 37.0 to 37.6∘C and then returns to 37.1∘C. What pattern suggests regulation?
The temperature returns towards its starting range after a deviation. It need not return to exactly 37.0∘C to show regulation.
Watch out: Homeostatic variables fluctuate within ranges; feedback limits departures rather than preventing every fluctuation.