Summary: Breathing and Exchange of Gases

Respiration is the process by which organisms obtain energy by oxidation of food molecules. In humans, it involves breathing, exchange of gases, transport of gases, and regulation of respiration.

Key Concepts Recap

Breathing vs Respiration

  • Breathing: Physical process of inhalation and exhalation
  • Respiration: Biochemical oxidation of food to release ATP

Respiratory Organs

  • Simple organisms: body surface
  • Earthworm: skin
  • Fish: gills
  • Insects: tracheal system
  • Humans: lungs

Human Respiratory System

  • Air passage: nostrils → nasal cavity → pharynx → larynx → trachea → bronchi → bronchioles → alveoli
  • Alveoli are primary sites of gas exchange
  • Right lung has three lobes, left lung has two lobes

Mechanism of Breathing

  • Inspiration: diaphragm contracts, thoracic volume increases
  • Expiration: diaphragm relaxes, thoracic volume decreases
  • Driven by pressure gradients

Lung Volumes & Capacities

  • TV ≈ 500 mL
  • RV prevents lung collapse
  • VC = IRV + TV + ERV
  • TLC = VC + RV

Exchange of Gases

  • Occurs by simple diffusion due to partial pressure gradients
  • CO₂ diffuses faster than O₂
  • Respiratory membrane is extremely thin

Transport of Gases

  • O₂: 97% bound to haemoglobin
  • CO₂: 70% as bicarbonate, 20–25% carbamino-Hb
  • Bohr effect: promotes O₂ release in tissues
  • Haldane effect: promotes CO₂ release in lungs

Regulation of Respiration

  • Controlled by medullary respiratory centre
  • CO₂ is the primary regulator
  • Hering–Breuer reflex prevents over-inflation

Respiratory Disorders

  • Asthma: airway narrowing
  • Emphysema: alveolar wall destruction
  • Occupational diseases: silicosis, asbestosis

NEET Exam Tips (High Priority)

  • NCERT lines are asked directly (especially lung volumes & gas transport)
  • CO₂ is the main respiratory regulator → very frequent MCQ
  • Emphysema = alveolar damage (not mucus)
  • O₂–Hb dissociation curve → right shift = more O₂ unloading
  • Know exact percentages of gas transport

IAT (IISER Aptitude Test) Exam Tips

  • Focus on conceptual reasoning, not rote facts
  • Questions may link:
  • Physics (pressure gradients)
  • Chemistry (pH, buffering, solubility)
  • Biology (diffusion, membranes)
  • Expect assertion–reason and multi-step logic questions
  • Be clear on Bohr vs Haldane effect mechanisms

This chapter is medium weightage for NEET but concept-heavy and important for IAT.