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The tiny air sacs in lungs where gas exchange occurs are called ________.
- Bronchi
- Bronchioles
- Alveoli
- Trachea
Answer: Alveoli
Alveoli are microscopic sacs surrounded by capillaries. Oxygen diffuses into blood, CO₂ diffuses out. Their large surface area (~70 m²) enables efficient respiration. Key anatomy concept. [[NCERT Biology Class 11]]