Summary
Breathing and Exchange of Gases is the process by which oxygen from the atmosphere is continuously supplied to cells and harmful carbon dioxide produced during metabolism is released out. It involves respiratory organs, gas diffusion across alveolar membranes, transport of gases by blood, and cellular utilization of oxygen.
Chapter 14 covers the human respiratory system and how organisms exchange oxygen and carbon dioxide. The respiratory tract includes nostrils, nasal passage, pharynx, larynx, trachea, bronchi, bronchioles, and alveoli. Breathing occurs in two stages—inspiration (air drawn in by diaphragm and intercostal muscle contraction) and expiration (air released by muscle relaxation). Gas exchange happens primarily at the alveoli through simple diffusion based on partial pressure gradients. Oxygen is transported mainly as oxyhaemoglobin in red blood cells; carbon dioxide is transported as bicarbonate, carbamino-haemoglobin, and dissolved plasma. Respiratory rhythm is regulated by the medulla's respiratory centre, pons pneumotaxic centre, and chemosensitive areas responsive to CO2 and hydrogen ions.
Key points & formulas
- 01Respiration involves breathing, gas diffusion across alveolar membranes, gas transport by blood, tissue diffusion, and cellular utilization of oxygen
- 02Inspiration increases thoracic volume via diaphragm contraction and external intercostal muscle action, decreasing intra-pulmonary pressure below atmospheric pressure
- 03Expiration occurs when diaphragm and intercostal muscles relax, increasing intra-pulmonary pressure to release air from lungs
- 04Oxygen (97%) is transported primarily as oxyhaemoglobin; carbon dioxide (70%) is transported as bicarbonate with carbonic anhydrase enzyme
- 05Gas exchange occurs by simple diffusion across the thin alveolar-capillary diffusion membrane (~0.1 mm) following partial pressure gradients
- 06Respiratory rate (~12-16 breaths/minute in healthy humans) is regulated by neural centres in the medulla and modulated by CO2 and hydrogen ion concentration
Frequently asked questions
01What are the main parts of the human respiratory system?
The human respiratory system consists of the nasal passage, pharynx, larynx (sound box), trachea, bronchi, bronchioles, and lungs containing alveoli. The lungs are covered by pleural membranes with pleural fluid between them. The thoracic cavity, formed by the vertebral column, sternum, ribs, and diaphragm, houses the lungs.
02How does the diaphragm work during breathing?
During inspiration, the diaphragm contracts and moves downward, increasing the antero-posterior volume of the thoracic chamber. This reduces intra-pulmonary pressure below atmospheric pressure, forcing air into the lungs. During expiration, the diaphragm relaxes and returns to its normal position, decreasing thoracic volume and expelling air.
03What is the role of haemoglobin in oxygen transport?
Haemoglobin is an iron-containing pigment in red blood cells that reversibly binds oxygen to form oxyhaemoglobin. Each haemoglobin molecule can carry four oxygen molecules. In the lungs (high pO2), oxygen binds to haemoglobin; in tissues (low pO2, high pCO2, high H+), oxygen dissociates from haemoglobin for cellular use. About 97% of oxygen is transported this way.
04Is the NCERT Class 11 Biology Chapter 14 PDF free to download?
Yes, the NCERT Class 11 Biology Chapter 14 PDF is free to download.
More chapters in Biology
This is the complete Biology Chapter 14 as published by NCERT — every diagram, solved example, and exercise included, free. Browse all NCERT Class 11 textbooks.
Read offline with notes, solutions & mock tests
CBSE Prepmaster — free on iOS & Android