Breathing and Exchange of Gases covers the structure of the human respiratory system, the mechanics of inspiration and expiration, all the respiratory lung volumes and capacities (with their numeric values), gas exchange by diffusion, oxygen and carbon dioxide transport in blood, and neural regulation of breathing. NEET asks 3–4 questions from this chapter — the respiratory volumes table, Bohr effect, and CO₂ transport as bicarbonate are the most tested.
Different animals have evolved different respiratory surfaces — skin (earthworms), gills (fish), book lungs (spiders), and lungs (mammals). In humans, the lungs are the chief respiratory organs.
Human airway: Nostrils → nasal cavity (filters, warms, moistens air) → pharynx → larynx (voice box) → trachea (C-shaped cartilaginous rings keep it open) → primary bronchi → secondary bronchi → bronchioles → terminal bronchioles → alveolar ducts → alveoli.
Each lung has ~300 million alveoli, providing a total surface area of ~70 m². The alveolar wall is extremely thin (0.2 µm) and richly supplied with blood capillaries.
Breathing depends on creating pressure differences between the atmosphere and the lungs using the diaphragm and intercostal muscles.
Inspiration (active process):
Expiration (passive during quiet breathing):
During forced expiration, the internal intercostal muscles contract to push ribs further inward, and the abdominal muscles help compress the abdomen.
Lung volumes are measured with a spirometer. Key values to memorise for NEET:
| Term | Value | Definition |
|---|---|---|
| Tidal Volume (TV) | 500 mL | Air moved per normal breath |
| Inspiratory Reserve Volume (IRV) | 2500–3000 mL | Extra air inhaled after normal inspiration |
| Expiratory Reserve Volume (ERV) | 1000–1100 mL | Extra air exhaled after normal expiration |
| Residual Volume (RV) | 1100–1200 mL | Air left after maximum expiration |
| Vital Capacity (VC) | ~4600 mL | TV + IRV + ERV |
| Total Lung Capacity (TLC) | ~5800 mL | VC + RV |
| Functional Residual Capacity (FRC) | ~2300 mL | ERV + RV |
Gas exchange occurs by simple diffusion across the thin alveolar and capillary walls, driven by partial pressure gradients.
Oxygen transport:
Carbon dioxide transport:
Breathing is regulated by the respiratory centre in the medulla oblongata and pons.
Respiratory disorders:
Use this section after the first reading. It connects facts into mechanisms, comparisons, and NEET-style decision rules.
Air moves because pressure changes, not because lungs actively pull air. During inspiration, diaphragm contraction increases thoracic volume, so intrapulmonary pressure falls below atmospheric pressure and air enters. During quiet expiration, elastic recoil reduces thoracic volume, pressure rises, and air leaves.
Oxygen is transported mainly as oxyhaemoglobin, while carbon dioxide is transported mainly as bicarbonate. Tissue conditions are designed for oxygen unloading: high CO2, high H+ concentration, and higher temperature reduce haemoglobin affinity for oxygen. This is the Bohr effect in exam form.
Use this process after reading the notes. It turns NCERT lines into exam-ready recall, diagrams, and MCQ decisions.
Memory mistake: make a two-column comparison table.
Diagram mistake: redraw the labelled structure from memory.
Process mistake: rewrite the sequence with arrows.
Assertion-reason mistake: check truth of each statement first, then relation.
Practice these before starting MCQs. They are designed to lock core concepts with minimum theory load.
Diaphragm. It contracts and flattens, increasing thoracic volume.
VC = TV + IRV + ERV.
As bicarbonate ions (HCO3-) in plasma.
High CO2, high temperature, low pH, and high 2,3-BPG promote oxygen unloading.
Carbon dioxide level, through its effect on blood/CSF pH.
Chapter note placement for Breathing and Exchange of Gases.
Test your understanding of Breathing and Exchange of Gases with focused sectional tests and a full-length NEET-style module test. Each chapter now runs 5 practice tests of 25 questions each, and every question has a 90-second timer — matching real NEET exam pacing.
5 focused sessions: respiratory organs & airway, mechanics of breathing, lung volumes & capacities, gas transport (O₂ and CO₂), and regulation & disorders — 15 NEET MCQs each.
Open Session TestsNEET-style 125-question module test on Breathing and Exchange of Gases with timer, palette, answer review, and subtopic accuracy breakdown.
Open Full MockInline banner shown in the practice section — high-intent placement for test-prep and coaching campaigns.
Move straight from chapter-wise questions into a subject test, then loop back into weaker areas instead of ending the session here.