What is the role of the diaphragm in breathing?

The diaphragm is a dome-shaped muscular sheet at the base of the thorax. During inspiration, it contracts and flattens downward, increasing thoracic volume and reducing pressure, drawing air in. During expiration, it relaxes and moves upward, decreasing thoracic volume and pushing air out. It performs ~75% of the work of normal breathing.

What is vital capacity?

Vital Capacity (VC) is the maximum volume of air a person can exhale after a maximum inhalation. VC = Tidal Volume + Inspiratory Reserve Volume + Expiratory Reserve Volume = 500 + 2500 + 1000 = ~4000 mL (varies by age, sex, fitness). It does NOT include Residual Volume (air always remaining in lungs).

How is carbon dioxide transported in blood?

CO₂ is transported in three ways: (1) ~70% as bicarbonate ions (HCO₃⁻) — CO₂ + H₂O → H₂CO₃ → H⁺ + HCO₃⁻ (catalysed by carbonic anhydrase in RBCs); (2) ~23% as carbamino-haemoglobin (CO₂ bound to amino groups of Hb); (3) ~7% dissolved directly in plasma.

Mechanism of Breathing

Breathing and Exchange of Gases • Class 11 Biology • NCERT • CBSE

Breathing involves inspiration (diaphragm contracts and moves down, external intercostals contract, thoracic volume increases, pressure decreases — air flows in) and expiration (diaphragm relaxes, thoracic volume decreases, pressure increases — air flows out). Oxygen transport: 97% by haemoglobin as oxyhaemoglobin.

Frequently Asked Questions

What is the role of the diaphragm in breathing?: The diaphragm is a dome-shaped muscular sheet at the base of the thorax. During inspiration, it contracts and flattens downward, increasing thoracic volume and reducing pressure, drawing air in. During expiration, it relaxes and moves upward, decreasing thoracic volume and pushing air out. It performs ~75% of the work of normal breathing.
What is vital capacity?: Vital Capacity (VC) is the maximum volume of air a person can exhale after a maximum inhalation. VC = Tidal Volume + Inspiratory Reserve Volume + Expiratory Reserve Volume = 500 + 2500 + 1000 = ~4000 mL (varies by age, sex, fitness). It does NOT include Residual Volume (air always remaining in lungs).
How is carbon dioxide transported in blood?: CO₂ is transported in three ways: (1) ~70% as bicarbonate ions (HCO₃⁻) — CO₂ + H₂O → H₂CO₃ → H⁺ + HCO₃⁻ (catalysed by carbonic anhydrase in RBCs); (2) ~23% as carbamino-haemoglobin (CO₂ bound to amino groups of Hb); (3) ~7% dissolved directly in plasma.

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