Chapter 14 of Class 11 Biology is Breathing and Exchange of Gases. It covers the human respiratory system, the mechanism of breathing, and gas exchange/transport in the body. These Class 11 Biology Chapter 14 solutions are also useful as quick revision notes before exams.
Human Respiratory System
Air passes through: nostrils → nasal cavity → pharynx → larynx → trachea → bronchi → bronchioles → alveoli (site of gas exchange, thin-walled, richly vascularized).
Mechanism of Breathing
Inspiration: diaphragm contracts (flattens) and external intercostal muscles contract, increasing thoracic volume, decreasing pressure, drawing air in. Expiration: diaphragm relaxes (domes upward), thoracic volume decreases, pressure increases, air is pushed out. Governed by Boyle’s Law (pressure inversely proportional to volume).
Lung Volumes and Capacities
Tidal volume (~500mL, normal breath), vital capacity (maximum volume that can be forcibly exhaled after maximum inhalation), residual volume (air remaining after maximal exhalation, cannot be expelled).
Gas Exchange
Occurs by simple diffusion across the alveolar membrane, driven by partial pressure gradients: O₂ diffuses from alveoli (high pO₂) into blood (low pO₂); CO₂ diffuses from blood (high pCO₂) into alveoli (low pCO₂).
Transport of Gases
O₂ transport: ~97% bound to haemoglobin as oxyhaemoglobin, ~3% dissolved in plasma. CO₂ transport: ~70% as bicarbonate ions (HCO₃⁻), ~20-25% bound to haemoglobin as carbaminohaemoglobin, ~7% dissolved in plasma.
Regulation of Respiration
Controlled by the respiratory rhythm centre in the medulla oblongata, primarily sensitive to CO₂ concentration (and pH) in the blood, rather than O₂ levels directly.
Class 11 Biology Chapter 14 – Notes and Extra Questions
Along with these NCERT Solutions, students can also use the Class 11 Biology Chapter 14 Extra Questions and Class 11 Biology Chapter 14 Revision Notes for quick revision and extra practice.
