Explain how the hormone adrenaline prepares the body for a 'fight or flight' response during a stressful situation.

Edexcel A-Level Biology A: Salters-Nuffield (9BN0) — 4.5 Hormonal coordination · Explain · 5 marks · View as Markdown

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

A student is about to sit an important exam. As they wait outside the exam hall, they notice their heart is beating faster and they feel more alert than usual.

Model answer (5 marks)

Adrenaline is released from the adrenal glands into the bloodstream. It binds to β‑adrenergic receptors on the heart, increasing heart rate and the force of contraction. The increased cardiac output delivers more blood, oxygen and glucose to skeletal muscles. Adrenaline also stimulates glycogenolysis in liver and muscle, raising blood glucose concentration. The extra glucose and oxygen supply provide more energy and enable faster muscle respiration, preparing the body for a rapid fight‑or‑flight response.

Examiner tips

  • Mention adrenal glands as source, β‑adrenergic action on heart, glycogenolysis, and energy provision
  • Use precise terms: heart rate, cardiac output, glycogenolysis, blood glucose
  • Show causal links between each step

Common mistakes

  • Confusing adrenaline with cortisol or omitting glycogenolysis
  • Failing to specify the source of adrenaline or the receptor type
  • Using vague language such as "more energy" without explaining the mechanism

Mark scheme (5 marks)

  1. Adrenaline is released from the adrenal glands
  2. Adrenaline increases heart rate / causes the heart to beat faster
  3. More blood / oxygen / glucose is delivered to muscles
  4. Adrenaline increases blood glucose concentration / causes glycogen to be converted to glucose
  5. This provides more energy / enables faster respiration in muscles so the body is prepared to respond quickly (fight or flee)

Key terms in this question

adrenaline · fight or flight

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