Explain why the heart rate increases during physical activity.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
During a 400 m race, a student's heart rate rises significantly from its resting value and remains elevated for several minutes after the race ends.
Model answer (4 marks)
During physical activity the working muscles require more ATP, so they respire more rapidly.
Aerobic respiration in the muscles needs oxygen; therefore the body must supply more oxygen to the tissues.
The heart responds by increasing its rate, pumping blood faster through the circulatory system.
A higher cardiac output delivers more oxygen and glucose to the muscles and removes more carbon dioxide, meeting the increased metabolic demand.
Aerobic respiration in the muscles needs oxygen; therefore the body must supply more oxygen to the tissues.
The heart responds by increasing its rate, pumping blood faster through the circulatory system.
A higher cardiac output delivers more oxygen and glucose to the muscles and removes more carbon dioxide, meeting the increased metabolic demand.
Examiner tips
- Use the exact terms: ‘muscles respire more’, ‘aerobic respiration requires oxygen’, ‘faster heart rate’, ‘more oxygen and glucose delivered, CO₂ removed’.
- Show the causal chain: activity → ↑ATP demand → ↑O₂ requirement → ↑heart rate → ↑cardiac output → ↑O₂/glucose delivery & CO₂ removal.
- Keep each point brief – 1 mark each – and avoid extra explanation.
Common mistakes
- Confusing heart rate with heart rate variability; students may write ‘heart rate decreases’ or ‘heart rate stays the same’.
- Using vague phrases like ‘more blood’ instead of ‘more oxygen and glucose delivered, CO₂ removed’.
- Including irrelevant details such as ‘blood pressure rises’ or ‘muscle contraction’ that are not part of the required explanation.
Mark scheme (4 marks)
- Muscles respire (more) during physical activity / muscles need more energy for movement
- Aerobic respiration requires oxygen, so more oxygen must be delivered to the muscles / respiring tissues
- A faster heart rate pumps blood around the body more quickly
- This allows more oxygen (and glucose) to be delivered to / carbon dioxide to be removed from the respiring muscles / tissues
Key terms in this question
Related
- All Cambridge International IGCSE Biology (0610) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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