A child is born with a condition called anaemia, in which their blood contains fewer red blood cells than normal. Explain how this condition affects the transport of oxygen around the body, referring to the roles of the heart and blood vessels in the double circulatory system.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Anaemia is a condition in which a person has fewer red blood cells than normal. Doctors find that the child's tissues are not receiving enough oxygen, even though the heart is beating normally.
Model answer (5 marks)
Red blood cells (RBCs) carry oxygen from the lungs to tissues. In anaemia there are fewer RBCs, so the amount of oxygen transported in the blood is reduced.
The heart pumps oxygenated blood from the lungs into the aorta and arteries, delivering it to the body. The arteries carry blood away from the heart under high pressure.
In the double‑circulatory system blood passes through the heart twice: once to the lungs (pulmonary circuit) and once to the body (systemic circuit). With fewer RBCs, less oxygen is picked up in the lungs and consequently less oxygen is delivered to tissues, producing the symptoms of anaemia.
The heart pumps oxygenated blood from the lungs into the aorta and arteries, delivering it to the body. The arteries carry blood away from the heart under high pressure.
In the double‑circulatory system blood passes through the heart twice: once to the lungs (pulmonary circuit) and once to the body (systemic circuit). With fewer RBCs, less oxygen is picked up in the lungs and consequently less oxygen is delivered to tissues, producing the symptoms of anaemia.
Examiner tips
- Use the term ‘red blood cells’ and ‘oxygenated blood’. Explain the role of the heart and arteries. Mention the double‑circulatory system. Show the link between fewer RBCs and reduced oxygen delivery.
Common mistakes
- Confusing the heart’s pumping action with oxygen transport. Forgetting to mention the double‑circulatory system. Using vague terms like ‘blood’ instead of ‘red blood cells’ or ‘oxygenated blood’.
Mark scheme (5 marks)
- Red blood cells carry oxygen around the body
- Fewer red blood cells means less oxygen is transported to the body's tissues
- The heart pumps oxygenated blood from the lungs to the body via the aorta / arteries carry blood away from the heart under high pressure
- In the double circulatory system, blood passes through the heart twice in one full circuit — once to the lungs and once to the body
- Because there are fewer red blood cells, less oxygen is collected at the lungs and so less oxygen is delivered to tissues, causing symptoms of anaemia
Key terms in this question
red blood cells · double circulatory system
Related
- All OCR A-Level Biology B — Advancing Biology (H422) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
More Cardiovascular system questions
- A patient is diagnosed with a faulty valve in their heart. Explain how the doubl…
- A marathon runner's heart adapts over years of training, becoming larger and abl…
- A diver surfaces too quickly from a deep-sea dive. Paramedics suspect the diver'…
- A person is rushed to hospital after collapsing. Doctors find that a blockage in…