NEET Biology — Breathing and Exchange of Gases Complete Chapter Guide

Chapter Overview & Weightage

Breathing and Exchange of Gases covers the respiratory system, mechanics of breathing, gas exchange at alveoli, transport of $O_2$ and $CO_2$ in blood, and respiratory volumes. The oxygen dissociation curve is a NEET favourite.

Key Concepts You Must Know

Tier 1 (Core)

• Respiratory pathway: nostrils → pharynx → larynx → trachea → bronchi → bronchioles → alveoli
• Mechanism of breathing: inspiration (diaphragm contracts, volume increases, pressure decreases) and expiration (reverse)
• Gas exchange at alveoli: down partial pressure gradient ($O_2$ into blood, $CO_2$ out)
• $O_2$ transport: 97% as oxyhaemoglobin ($HbO_2$), 3% dissolved in plasma
• $CO_2$ transport: 70% as $HCO_3^-$ (bicarbonate), 23% as carbaminohaemoglobin, 7% dissolved

Tier 2 (Frequently tested)

• Oxygen-haemoglobin dissociation curve (sigmoid shape) and factors affecting it (Bohr effect)
• Respiratory volumes: tidal volume (TV = 500 mL), inspiratory reserve (IRV = 2500-3000 mL), expiratory reserve (ERV = 1000-1100 mL), residual volume (RV = 1100-1200 mL)
• Respiratory capacities: vital capacity (VC = TV + IRV + ERV), total lung capacity (TLC = VC + RV)
• Chloride shift (Hamburger phenomenon)

Tier 3 (Occasionally tested)

• Disorders: asthma, emphysema, occupational lung diseases (silicosis, asbestosis)
• Role of respiratory centre in medulla oblongata
• Pneumotaxic centre in pons

Important Formulas

Solved Previous Year Questions

PYQ 1 — NEET 2024

Problem: Bohr effect refers to:

(A) Effect of $CO_2$ on $O_2$ binding (B) Effect of $O_2$ on $CO_2$ transport (C) Effect of temperature on breathing rate (D) Effect of altitude on haemoglobin

Solution:

The Bohr effect describes how increased $CO_2$ concentration (and the resulting decrease in pH) reduces the affinity of haemoglobin for $O_2$. This shifts the oxygen dissociation curve to the right, promoting $O_2$ release at the tissue level.

Answer: (A) Effect of $CO_2$ on $O_2$ binding

PYQ 2 — NEET 2023

Problem: The volume of air remaining in the lungs after a forceful expiration is called:

(A) Tidal volume (B) Residual volume (C) Expiratory reserve volume (D) Vital capacity

Solution:

After a forceful expiration, you’ve pushed out everything you can, but some air still remains — this is the residual volume (about 1100-1200 mL). This air can never be voluntarily expelled; it keeps the alveoli from collapsing.

Answer: (B) Residual volume

PYQ 3 — NEET 2022

Problem: Maximum volume of $CO_2$ is transported as:

(A) Dissolved in plasma (B) Carbaminohaemoglobin (C) Bicarbonate ions (D) Carbonic acid

Solution:

70% of $CO_2$ is transported as bicarbonate ions ($HCO_3^-$) in plasma. The enzyme carbonic anhydrase in RBCs catalyses: $CO_2 + H_2O \rightarrow H_2CO_3 \rightarrow H^+ + HCO_3^-$. The $HCO_3^-$ moves out of RBCs into plasma (chloride shift).

Answer: (C) Bicarbonate ions

Difficulty Distribution

Expert Strategy

Day 1: Learn the respiratory pathway and mechanism of breathing. Understand the pressure changes: inspiration = volume up, pressure down, air flows in. This is Boyle’s law applied to lungs.

Day 2: Gas transport — this is the highest-yield topic. Memorise the exact percentages for $O_2$ and $CO_2$ transport. Understand the Bohr effect conceptually (not just as a fact) and the chloride shift mechanism.

Day 3: Respiratory volumes and capacities. Draw the spirogram from NCERT. Know the exact formula relationships (VC = TV + IRV + ERV, TLC = VC + RV). Practice calculating one capacity from given volumes.

Common Traps