Adrenaline is a hormone released during the 'fight-or-flight' response. Explain how adrenaline prepares the body to respond to a threat, including reference to where it is produced and how it reaches its target organs.

WJEC A-Level Biology (Wales) — 4.3 Variation and evolution · Explain · 5 marks · View as Markdown

Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).

Model answer (5 marks)

Adrenaline is produced and released by the adrenal glands.
It is carried in the bloodstream to target organs.
It increases heart rate and breathing rate, raising oxygen and blood flow to muscles.
It stimulates the conversion of glycogen into glucose in the liver and cells.
The rise in blood glucose supplies glucose for cellular respiration, providing energy for the threat response.

Examiner tips

  • Use the exact phrase "adrenal glands" and "bloodstream". Show the sequence: production → transport → action on heart, lungs, liver. Mention both heart rate and breathing rate as key effects. Include the glycogen‑to‑glucose step and the resulting energy supply.

Common mistakes

  • Confusing adrenal cortex with adrenal medulla. Forgetting to mention the bloodstream as the transport medium. Omitting the glycogen conversion or the energy release step.

Mark scheme (5 marks)

  1. Adrenaline is produced / released by the adrenal gland
  2. Adrenaline travels in the blood(stream) to target organs
  3. Adrenaline increases heart rate (and/or breathing rate), increasing oxygen / blood flow to muscles
  4. Glycogen is converted into glucose (in cells / the liver)
  5. This raises blood glucose levels so that glucose is available for respiration (to release energy)

Key terms in this question

adrenaline · hormone · fight-or-flight · target organ

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