Explain how the respiratory system and the musculoskeletal system are integrated to allow a person to breathe in during inhalation.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Model answer (4 marks)
The nervous system sends motor nerve impulses to the respiratory muscles (diaphragm and/or intercostal muscles), stimulating them to contract.
Contraction of the diaphragm (moves downward / flattens) and/or external intercostal muscles (ribs move up and out) increases the volume of the thoracic cavity.
Increased thoracic volume causes a decrease in air pressure inside the lungs (below atmospheric pressure).
Air flows into the lungs down the pressure gradient (from high atmospheric pressure to lower lung pressure), achieving inhalation.
Contraction of the diaphragm (moves downward / flattens) and/or external intercostal muscles (ribs move up and out) increases the volume of the thoracic cavity.
Increased thoracic volume causes a decrease in air pressure inside the lungs (below atmospheric pressure).
Air flows into the lungs down the pressure gradient (from high atmospheric pressure to lower lung pressure), achieving inhalation.
Examiner tips
- Use the word ‘stimulate’ for nerve impulses, ‘contract’ for muscle action, and ‘increase volume’ for thoracic cavity. Mention the pressure change explicitly. Show the direction of air flow (high to low pressure).
Common mistakes
- Confusing contraction of the diaphragm with relaxation. Forgetting to state the pressure drop inside the lungs. Using ‘push’ instead of ‘pull’ for air movement.”
Mark scheme (4 marks)
- The nervous system sends motor nerve impulses to the respiratory muscles (diaphragm and/or intercostal muscles), stimulating them to contract.
- Contraction of the diaphragm (moves downward / flattens) and/or external intercostal muscles (ribs move up and out) increases the volume of the thoracic cavity.
- Increased thoracic volume causes a decrease in air pressure inside the lungs (below atmospheric pressure).
- Air flows into the lungs down the pressure gradient (from high atmospheric pressure to lower lung pressure), achieving inhalation.
Key terms in this question
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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