Explain why the human circulatory system is described as a double circulatory system.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Model answer (4 marks)
The human circulatory system is double because blood passes through the heart twice for each complete circuit of the body. One circuit is the pulmonary circulation, carrying blood from the heart to the lungs and back. The other is the systemic circulation, carrying blood from the heart to the rest of the body and back. This arrangement keeps oxygenated and deoxygenated blood separate and allows the heart to maintain high pressure in the systemic circuit.
Examiner tips
- Use the terms ‘pulmonary’ and ‘systemic’ circulation explicitly
- Explain the two passes through the heart
- Mention separation of oxygenated/deoxygenated blood and pressure maintenance
Common mistakes
- Failing to name both circulations
- Confusing the direction of blood flow
- Omitting the reason for separation of blood types
Mark scheme (4 marks)
- Blood passes through the heart twice for each complete circuit of the body
- One circuit carries blood from the heart to the lungs and back (pulmonary circulation)
- The other circuit carries blood from the heart to the rest of the body and back (systemic circulation)
- This ensures oxygenated and deoxygenated blood are kept separate / maintains high pressure to the body
Key terms in this question
Related
- All WJEC GCSE Biology (Wales) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →