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Breathing and Exchange of Gases

NCERT Class 11 Biology Chapter 14

Breathing and Exchange of Gases for Class 11 Biology and NEET: human respiratory system, mechanism of breathing, gas exchange and transport, and disorders.

6 topics Updated 8 Nov 2026

For: Class 11 and NEET

In the syllabus: NEET Class 11 syllabus

With your textbook

NCERT Biology (Class 11), Chapter 14 “Breathing and Exchange of Gases”, reprint 2026-27.

Open the official NCERT chapter (PDF, 2.1 MB, ncert.nic.in)

Checked on 19 Oct 2026.

Learn in this order

  1. Respiratory organs and the human respiratory system

    Organs in animals, the airway to the alveoli with a labelled diagram, and breathing vs respiration.

    NCERT Section 14.1 11 min read 5 solved examples 7 practice questions

  2. Mechanism of breathing and lung volumes

    Inspiration vs expiration, the diaphragm and intercostals, respiratory volumes and capacities, with examples.

    NCERT Section 14.2 11 min read 6 solved examples 7 practice questions

  3. Exchange of gases and partial pressures

    Diffusion at the alveoli and tissues, pO and pCO from NCERT Table 14.1, and the three-layer diffusion membrane.

    NCERT Section 14.3 9 min read 4 solved examples 7 practice questions

  4. Transport of oxygen and carbon dioxide

    Oxyhaemoglobin, the oxygen dissociation curve and its shifts, the Bohr effect, bicarbonate, carbonic anhydrase.

    NCERT Section 14.4 13 min read 5 solved examples 7 practice questions

  5. Regulation of respiration

    Medulla, pons, CO and H sensing, and the important response to low arterial oxygen.

    NCERT Section 14.5 9 min read 4 solved examples 6 practice questions

  6. Disorders of the respiratory system

    Asthma vs emphysema, occupational disorders such as silicosis, and what each one damages.

    NCERT Section 14.6 7 min read 4 solved examples 6 practice questions

Key formulas in this chapter

Respiratory organs

  • airway: nostrils → nasal chamber → pharynx → larynx → trachea → bronchi → bronchioles → alveoli
  • conducting part: nostrils to terminal bronchioles; exchange part: alveolated respiratory region
  • NCERT: trachea divides at the 5th thoracic vertebra
  • steps: breathing → alveolar diffusion → transport → tissue diffusion → cellular respiration

Mechanism of breathing

  • IC = TV + IRV; EC = TV + ERV
  • FRC = ERV + RV
  • VC = ERV + TV + IRV
  • TLC = VC + RV = RV + ERV + TV + IRV
  • TV about 500 mL; 12–16 breaths a minute; 6000–8000 mL a minute

Exchange of gases

  • alveoli: pO 104, pCO 40 mm Hg; tissues: pO 40, pCO 45 mm Hg
  • deoxygenated blood: pO 40, pCO 45; oxygenated blood: pO 95, pCO 40
  • atmospheric air: pO 159, pCO 0.3 mm Hg
  • solubility of CO = 20–25 × that of O
  • diffusion membrane: squamous epithelium + basement substance + endothelium

Transport of gases

  • NCERT O shares: 97 per cent as oxyhaemoglobin, 3 per cent dissolved
  • CO: 70 per cent bicarbonate, 20–25 per cent carbamino-haemoglobin, 7 per cent dissolved
  • CO + HO ⇌ HCO ⇌ HCO + H (carbonic anhydrase)
  • 100 mL blood: delivers about 5 mL O; about 4 mL CO
  • up to 4 O per haemoglobin molecule

Regulation of respiration

  • respiratory rhythm centre: medulla (primary control)
  • pneumotaxic centre: pons; can shorten inspiration
  • chemosensitive area: beside the rhythm centre; senses CO and H
  • aortic arch and carotid artery receptors: sense CO and H
  • oxygen: small influence near normal pO; strong peripheral drive when arterial pO falls substantially

Disorders of respiratory system

  • asthma: inflamed bronchi and bronchioles; wheezing
  • emphysema: damaged alveolar walls; less respiratory surface; smoking
  • dust-related occupational fibrosis: hazardous dust → inflammation → scarring
  • protection: control dust at source; use appropriate fitted respirators when required

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