Explain how the respiratory system and the cardiovascular system are integrated to maintain gas exchange during physical exercise.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Model answer (4 marks)
Increased muscle activity during exercise raises CO₂ and lowers O₂ in the blood.
Chemoreceptors detect the change in CO₂/pH and send impulses to the medulla oblongata, which increases breathing rate and depth.
The higher ventilation brings more O₂ into the alveoli and removes CO₂, steepening the diffusion gradient for gas exchange across the alveolar‑capillary membrane.
The heart rate rises via sympathetic stimulation/adrenaline, delivering oxygenated blood to the muscles more rapidly and returning CO₂‑laden blood to the lungs more quickly.
Chemoreceptors detect the change in CO₂/pH and send impulses to the medulla oblongata, which increases breathing rate and depth.
The higher ventilation brings more O₂ into the alveoli and removes CO₂, steepening the diffusion gradient for gas exchange across the alveolar‑capillary membrane.
The heart rate rises via sympathetic stimulation/adrenaline, delivering oxygenated blood to the muscles more rapidly and returning CO₂‑laden blood to the lungs more quickly.
Examiner tips
- Use the exact terms ‘ventilation’, ‘diffusion gradient’, ‘sympathetic stimulation’
- Show the causal chain from muscle activity to chemoreceptors to medulla to breathing and heart rate
- Include both increased O₂ uptake and CO₂ removal
Common mistakes
- Confusing ventilation with heart rate as the primary response
- Omitting the role of chemoreceptors or the medulla oblongata
- Using vague terms like ‘more breathing’ instead of ‘increased breathing rate and depth’
Mark scheme (4 marks)
- Increased muscle activity during exercise raises carbon dioxide levels / lowers oxygen levels in the blood.
- Chemoreceptors detect the change in blood CO₂ / pH and send nerve impulses to the medulla oblongata, which increases breathing rate and depth.
- Increased ventilation brings more O₂ into the alveoli and removes CO₂, steepening the diffusion gradient for gas exchange across the alveolar capillary membrane.
- The heart rate increases (via sympathetic nervous stimulation / adrenaline) so that oxygenated blood is delivered to respiring muscles more rapidly and CO₂-laden blood is returned to the lungs more quickly.
Related
- All IB DP Biology Standard Level (2023 syllabus) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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