Respiratory, Circulatory and Excretory Systems · Zoology

Which gas is the main stimulus for breathing in humans?

  1. Oxygen
  2. Nitrogen
  3. Carbon dioxide
  4. Carbon monoxide
Show answer and explanation

Correct answer: Carbon dioxide

Elevated carbon dioxide levels stimulate the respiratory center. This increases breathing rate to expel excess CO₂.

Difficulty: Medium Question 20 of 20

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