“Gaseous Exchange” is the 13th Chapter in the new course of Biology for intermediate premedical students. In this chapter the students will learn about the Respiratory gases and need of respiratory gas exchange. Air and water as respiratory medium, Exchange of O2 and CO2 by diffusion in leaves, stem and roots. Photorespiration and its consequences, Properties of respiratory surfaces. Respiratory organs of aquatic and terrestrial animals (Hydra Earthworm, Cockroach, Fish, Frog, Bird), Air passage ways, lungs, Mechanism of breathing, rate of breathing and its involuntary and voluntary control, Disorders of respiratory tract: lung cancer, tuberculosis, asthma emphysema and O2 carrying and CO2 carrying capacities of blood and factor affecting these capacities. Lung capacities. Role of hemoglobin and myoglobin.