Describe the sequence of events that causes blood to be pumped out of the heart during one heartbeat, starting from when the atria contract.

WJEC GCSE Biology (Wales) — 1.4.2 The heart · Describe · 4 marks · View as Markdown

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

Model answer (4 marks)

1. The atria contract, pushing blood into the ventricles through the atrioventricular valves.
2. The atrioventricular valves close to prevent backflow as the ventricles begin to contract.
3. The ventricles contract, raising pressure inside them.
4. Blood is forced out into the arteries (aorta and pulmonary artery) and the semilunar valves open to allow flow.

Examiner tips

  • Use the correct valve names (atrioventricular and semilunar).
  • Show the sequence in order, using bullet points or numbered steps.
  • Mention the direction of blood flow (atria → ventricles → arteries).

Common mistakes

  • Mixing up the order of valve closure and ventricular contraction.
  • Forgetting to name the valves or the arteries.
  • Using vague terms like "pushes blood" without specifying the valves involved.

Mark scheme (4 marks)

  1. The atria contract, pushing blood into the ventricles (through the atrioventricular valves).
  2. The atrioventricular valves close (preventing backflow into the atria) as the ventricles begin to contract.
  3. The ventricles contract, increasing pressure inside them.
  4. Blood is forced out of the ventricles into the arteries (aorta / pulmonary artery), and the semilunar valves open to allow this.

Key terms in this question

atria · contract

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