Negative Feedback and Control Systems

This lesson draws together the concept of negative feedback and applies it across the homeostatic control systems you have studied, as required by the AQA GCSE Combined Science Trilogy specification (8464). It also provides exam-style practice and revision of key ideas from the entire Homeostasis and Response topic.

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What Is Negative Feedback?

Negative feedback is a control mechanism in which a change in a condition triggers a response that counteracts (reverses) that change, returning the condition to its normal (set) level.

The word "negative" refers to the fact that the response is in the opposite direction to the original change — not that something bad is happening.

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The General Negative Feedback Loop

All negative feedback systems follow the same general pattern:

flowchart TD
    A["Normal / Set Level"] --> B{"Deviation detected\n(change from normal)"}
    B -->|"Level INCREASES"| C["Receptor detects increase"]
    C --> D["Coordination centre processes information"]
    D --> E["Effector acts to DECREASE the level"]
    E --> A
    B -->|"Level DECREASES"| F["Receptor detects decrease"]
    F --> G["Coordination centre processes information"]
    G --> H["Effector acts to INCREASE the level"]
    H --> A