During exercise, the breathing rate of a student increases. Explain how this helps to maintain efficient gas exchange in the lungs.

Edexcel GCSE Biology (1BI0) — 8.1 Gas exchange · Explain · 4 marks · View as Markdown

Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).

A student begins a vigorous exercise session. Their breathing rate increases from 15 breaths per minute to 40 breaths per minute.

Model answer (4 marks)

During exercise the breathing rate rises, bringing more fresh air into the alveoli and expelling more CO₂. This keeps a steep concentration gradient for O₂ and CO₂ between the alveolar air and the capillary blood. A steeper gradient increases the diffusion rate of O₂ into the blood and CO₂ out of the blood. Consequently, enough O₂ reaches the working cells and CO₂ is removed efficiently to meet the higher metabolic demand.

Examiner tips

  • Use the word ‘steep’ or ‘large’ for the concentration gradient
  • Show the link between increased rate and diffusion rate
  • Mention both O₂ uptake and CO₂ removal
  • Keep the answer concise and use exam terminology

Common mistakes

  • Confusing ventilation with perfusion
  • Failing to mention the concentration gradient
  • Using vague terms like ‘more oxygen’ without explaining diffusion

Mark scheme (4 marks)

  1. Increased breathing rate brings more fresh air (oxygen) into the alveoli / removes carbon dioxide from the alveoli more quickly
  2. This maintains a steep / large concentration gradient (for oxygen and/or carbon dioxide) between the alveoli and the blood
  3. A steeper concentration gradient increases the rate of diffusion (of oxygen into the blood / carbon dioxide out of the blood)
  4. This ensures sufficient oxygen is delivered to (respiring) cells / carbon dioxide (a waste product of respiration) is removed efficiently during increased exercise demand

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