A student sprints 400 metres and then rests. During the sprint, the student's muscles respire anaerobically as well as aerobically. Explain why anaerobic respiration occurs during the sprint and describe what happens in the student's body during the recovery period after the sprint.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
During intense exercise, the body cannot always supply muscles with oxygen fast enough to meet energy demands.
Model answer (5 marks)
During sprinting the muscles demand ATP faster than oxygen can be delivered, so oxygen supply is insufficient.
Because of this oxygen deficit, the muscles use anaerobic respiration, which can produce ATP without oxygen and therefore keeps the energy supply going.
Anaerobic respiration in muscle cells produces lactic acid.
After the sprint the student’s breathing becomes faster and deeper to take in more oxygen – the oxygen debt must be repaid.
The extra oxygen is used to oxidise the accumulated lactic acid, converting it into carbon dioxide and water, which are then expelled.
Because of this oxygen deficit, the muscles use anaerobic respiration, which can produce ATP without oxygen and therefore keeps the energy supply going.
Anaerobic respiration in muscle cells produces lactic acid.
After the sprint the student’s breathing becomes faster and deeper to take in more oxygen – the oxygen debt must be repaid.
The extra oxygen is used to oxidise the accumulated lactic acid, converting it into carbon dioxide and water, which are then expelled.
Examiner tips
- Use the phrase ‘oxygen supply is insufficient’ to show understanding of the cause.
- Show the two pathways (anaerobic and aerobic) and link lactic acid to the recovery process.
- Mention the breathing change and the oxidation of lactic acid explicitly.
Common mistakes
- Confusing aerobic respiration with anaerobic respiration as the main energy source during sprint.
- Failing to mention the breathing change or the oxidation of lactic acid during recovery.
- Using ‘glycolysis’ instead of ‘anaerobic respiration’ or omitting the oxygen debt concept.
Mark scheme (5 marks)
- During sprinting, oxygen cannot be delivered to the muscles fast enough / muscles do not receive sufficient oxygen to meet the energy demand
- Anaerobic respiration produces energy (ATP) without oxygen / allows energy release to continue when oxygen is limited
- Anaerobic respiration in muscles produces lactic acid
- During recovery, the student breathes faster/deeper to take in extra oxygen / oxygen debt must be repaid
- The extra oxygen is used to oxidise / break down lactic acid (into carbon dioxide and water)
Key terms in this question
anaerobic respiration · aerobic respiration · recovery period
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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