Example 1
Temperature rises and sweating increases heat loss. Is this negative feedback?
Yes. The response opposes the temperature rise, reducing the original disturbance.
Year 12 · SACE Stage 2
Tolerance and negative feedback
Identify stimulus–response components and read tolerance data.
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Method and worked examples
Homeostasis maintains internal conditions within a suitable range, rather than keeping every value perfectly constant. A stimulus is a change detected by a receptor. A control centre processes information and coordinates effectors, which produce a response. In negative feedback, the response reduces the original disturbance. The controlled variable may still fluctuate around its usual range.
Organisms have tolerance limits for temperature, water availability, glucose and other factors. An optimum is the condition with the best measured performance in the supplied context; tolerance limits bound survival or function. Distinguish the independent variable on the horizontal axis from the measured response. A limiting factor can restrict growth even when other requirements are plentiful. These relationships support fixed predictions only within the stated conditions and data range.
Example 1
Example 2
Survival at 5,10,15 and 20∘C is 0%, 70%, 100% and 20%. Which tested temperature is optimal?
15∘C gives the highest measured survival. These points alone do not locate the exact upper and lower tolerance limits.
Watch out: Controlled variables fluctuate within ranges; feedback reduces disturbances.