11 Bio Chapter Summary

Exchange of Gases

Chapter Summary

  • The process of exchange of O2 (from the atmosphere) with CO2 (produced by cells) is called breathing. This process is commonly known as respiration.
  • The human respiratory system is composed of pharynx, larynx, trachea, bronchi and lungs.
  • The lungs are composed of the branching network of bronchi, bronchioles and alveoli. Each lung is covered by a double-layered pleura.
  • The conducting part is constituted by the external nostrils, pharynx, larynx, bronchi and the terminal bronchioles.
  • The exchange part of the respiratory system is composed of the alveoli and their ducts. Actual diffusion of O2 and CO2 (between blood and atmospheric air) takes place in the exchange part of the respiratory system.
  • The lungs are situated in the thoracic chamber. This is anatomically an air-tight chamber.



  • Breathing involves two stages, viz. inspiration and expiration.
  • The volume of air inspired or expired during a normal respiration is called Tidal Volume.
  • Additional volume of air, a person can inspire by a forcible inspiration is called Inspiratory Reserve Volume.
  • Additional volume of air, a person can expire by a forcible expiration is called Expiratory Reserve Volume.
  • The volume of air remaining in the lungs even after a forcible expiration is called Residual Volume.
  • The total volume of air a person can inspire after a normal expiration is called Inspiratory Capacity.
  • The total volume of air a person can expire after a normal inspiration is called Expiratory Capacity.
  • The volume of air which remains in the lungs after a normal expiration is called Functional Residual Capacity.
  • The maximum volume of air a person can breathe in after a forceful expiration is called Vital Capacity.
  • Total volume of air accommodated in the lungs at the end of a forced inspiration is called Total Lung Capacity.
  • Alveoli are the main sites of exchange of gases. However, exchange of gases also occurs between blood and tissues. The exchange of O2 and CO2 at these sites happens by simple diffusion which is mainly based on pressure/concentration gradient.
  • About 97% of oxygen is transported by RBCs. The remaining 3% of oxygen is carried in a dissolved state through the plasma.
  • About 20-25% of carbon dioxide is transported by RBCs. About 70% of carbon dioxide is carried as bicarbonate and about 7% is carried in a dissolved state through plasma.
  • Oxygen can bind with haemoglobin in a reversible manner to form oxyhaemoglobin.
  • The respiratory rhythm centre is present in the medulla and is mainly responsible for the regulation of respiration.