During vigorous exercise, muscles require large amounts of energy for contraction. Explain how the body responds to meet the increased energy demands of contracting muscles during vigorous exercise.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
A student runs a 400-metre race at full speed. Within seconds, their breathing rate increases, their heart rate rises, and their muscles begin to fatigue towards the end of the race.
Model answer (5 marks)
Muscles need energy in the form of ATP for contraction.
During vigorous exercise, aerobic respiration in muscle cells produces ATP using glucose and oxygen.
The heart rate increases to deliver more oxygenated blood and glucose to the muscles more quickly.
The breathing rate and depth increase to take in more oxygen and remove carbon dioxide.
When the oxygen supply is insufficient, anaerobic respiration occurs, producing lactic acid, which causes muscle fatigue.
During vigorous exercise, aerobic respiration in muscle cells produces ATP using glucose and oxygen.
The heart rate increases to deliver more oxygenated blood and glucose to the muscles more quickly.
The breathing rate and depth increase to take in more oxygen and remove carbon dioxide.
When the oxygen supply is insufficient, anaerobic respiration occurs, producing lactic acid, which causes muscle fatigue.
Examiner tips
- Use the word ‘aerobic’ and ‘anaerobic’ to show you know the two pathways.
- Mention the role of the heart and lungs explicitly.
- Explain the link between oxygen supply and lactic acid production.
- Keep the answer concise and use the exact terminology from the mark scheme.
Common mistakes
- Confusing ATP with glucose as the energy source.
- Omitting the role of the heart or lungs.
- Failing to mention lactic acid as the cause of fatigue.
Mark scheme (5 marks)
- Muscles need energy in the form of ATP for contraction
- Aerobic respiration in muscle cells produces ATP using glucose and oxygen
- Heart rate increases to deliver more oxygenated blood / glucose to the muscles more quickly
- Breathing rate / depth increases to take in more oxygen and remove carbon dioxide
- When oxygen supply is insufficient, anaerobic respiration occurs producing lactic acid, which causes muscle fatigue
Related
- All Edexcel A-Level Biology A: Salters-Nuffield (9BN0) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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