Explain why the mammalian heart is described as a 'double pump', and explain how this arrangement is advantageous for delivering oxygen to respiring tissues.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
The mammalian circulatory system consists of two circuits: the pulmonary circuit, which carries deoxygenated blood to the lungs, and the systemic circuit, which carries oxygenated blood to the rest of the body. Both circuits are driven by a single organ — the heart.
Model answer (4 marks)
The right side of the heart pumps deoxygenated blood to the lungs via the pulmonary circuit, while the left side pumps oxygenated blood to the body via the systemic circuit – the two sides therefore act as separate pumps.
Blood therefore passes through the heart twice in one complete circuit of the body (double circulation).
Separating the two circuits prevents mixing of oxygenated and deoxygenated blood, so a high oxygen concentration (high PO₂) is maintained in the systemic blood delivered to tissues.
The left ventricle generates a higher pressure than the right, allowing oxygenated blood to be delivered rapidly and at high pressure to distant tissues, sustaining a high rate of oxygen delivery to meet metabolic demand.
Blood therefore passes through the heart twice in one complete circuit of the body (double circulation).
Separating the two circuits prevents mixing of oxygenated and deoxygenated blood, so a high oxygen concentration (high PO₂) is maintained in the systemic blood delivered to tissues.
The left ventricle generates a higher pressure than the right, allowing oxygenated blood to be delivered rapidly and at high pressure to distant tissues, sustaining a high rate of oxygen delivery to meet metabolic demand.
Examiner tips
- Use the term ‘double circulation’ to show understanding of the two circuits.
- Explain that the left ventricle’s higher pressure is essential for systemic perfusion.
- Show the link between separation of circuits and high tissue PO₂.
- Mention the heart’s two sides act as separate pumps.
Common mistakes
- Confusing single and double circulation – forgetting that the heart is a double pump.
- Failing to state that the left ventricle produces higher pressure.
- Not linking the separation of circuits to high oxygen delivery to tissues.
Mark scheme (4 marks)
- The right side of the heart pumps blood to the lungs (pulmonary circuit) and the left side pumps blood to the body (systemic circuit), so the two sides function as separate pumps.
- Blood passes through the heart twice in one complete circuit of the body (double circulation).
- Separating the two circuits prevents mixing of oxygenated and deoxygenated blood, maintaining a high oxygen concentration / high partial pressure of oxygen delivered to tissues.
- The left ventricle generates higher pressure than the right, allowing oxygenated blood to be delivered rapidly / at high pressure to distant systemic tissues, sustaining a high rate of oxygen delivery to meet metabolic demand.
Key terms in this question
Related
- All OCR A-Level Biology A (H420) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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