Multiple choice

Forced deep breathing for a few minutes by a person sitting at rest may be followed by the temporary cessation of breathing. This is due to

  1. too much oxygen in the blood

  2. too much CO2 in the blood

  3. very little CO2 in the blood

  4. both too much O2 and very little CO2 in the blood
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Forced breathing (hyperventilation) lowers the partial pressure of CO2 in the blood. Since CO2 is the primary chemical stimulus for the respiratory center, its reduction leads to a temporary cessation of breathing (apnea) until levels rise again.

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