Write short note on Modes of respiration in animals

The four basic categories of animal gas exchange mechanisms are diffusion through the body surface, gills, lungs & trachea. The design of respiratory surface & the mechanism of breathing is related to the nature of the medium in which the animal lives.

a) Many organisms like protozoans, flatworms etc obtain oxygen by diffusion through their body surface.

b) Most aquatic animals like fish exchange gases through gills that are evaginations of respiratory surface. Diffusion of oxygen in water is slow, therefore, aquatic animals must expend energy to the move large volume of water over the respiratory surfaces.

c) Terrestrial animals that exchange gases with the atmosphere do so by means of highly branched internal surfaces that are protected from drying out. Many vertebrates have sac-like lungs.

d) Insects have a special respiratory system. Insects have evolved a separate system for gas exchange tracheal system independent of the circulatory system.