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GCSE Biology 04 — Coordination and Control

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Topics include Principles of Homeostasis, The Human Nervous System, Synaptic Transmission, Reflex Actions, Practical: Investigating Reaction Time, The Human Brain, Structure of the Eye and Vision, and Eye Reflexes: Pupil & Accommodation.

Biology EN
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Principles of Homeostasis

Homeostasis is the maintenance of a relatively constant internal environment within the body despite external changes, ensuring optimal conditions for cell function.

Key points

  • Definition: Maintenance of a constant internal environment.
  • Key Conditions: Blood glucose, body temperature, and water content must be regulated.
  • Mechanism: Uses negative feedback loops; if a level rises, control systems reduce it, and if it falls, they raise it.
  • Pathway: Stimulus →\rightarrow Receptor →\rightarrow Coordination Centre (CNS) →\rightarrow Effector →\rightarrow Response.
  • Effectors: Muscles (contract) or Glands (secrete chemical substances).

Worked example

Question

Explain how a negative feedback mechanism would respond if body temperature rises above 37°C.

Solution

1. Stimulus: Body temperature rises.
2. Receptor: Thermoreceptors in the skin and hypothalamus detect the change.
3. Coordinator: The thermoregulatory centre (hypothalamus) processes the information.
4. Effectors: Sweat glands produce sweat; arterioles vasodilate.
5. Response: Heat is lost to the surroundings, lowering temperature back to the set point (37°C).

Common pitfalls

  • Confusing 'excretion' (metabolic waste) with 'egestion' (faeces).
  • Thinking homeostasis keeps conditions exactly constant (it actually maintains dynamic equilibrium around a set point).

Prerequisites

  • Enzyme activity requirements (optimum temp/pH)
  • Basic cell structure
Further resources