When your lungs "answer" before you do
The first time you sprint for a bus, your breathing doesn’t politely ramp up. It jumps. One moment you feel normal, the next you’re taking sharper, louder breaths like your body just remembered an appointment it can’t miss. In IB SEHS, that sudden shift is the story: as exercise intensity rises, your respiratory system adjusts fast to deliver oxygen (O₂) and remove carbon dioxide (CO₂) so muscles can keep producing ATP.
If you can describe what changes, why it changes, and how it supports performance, you’re basically writing the markscheme.
IB SEHS quick checklist: what to say in exam answers
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Breathing rate (frequency) increases with intensity.
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Tidal volume increases (deeper breaths), especially from rest to moderate work.
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Minute ventilation increases because it equals breathing rate x tidal volume.
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At higher intensities, tidal volume may plateau, so ventilation rises mostly via breathing rate.
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Link it to gas exchange: more O₂ in, more CO₂ out, pH stability improved.
For structure, borrow the approach in Exercise Responses Explained for IB Exams.
Breathing rate increases as intensity rises
In IB SEHS, breathing rate is one of the cleanest variables to describe. As soon as exercise begins, CO₂ production increases and blood becomes more acidic (lower pH). Chemoreceptors detect this change and ventilation is driven upward to remove CO₂ more quickly.
