2.4 | Adaptations in Respiratory Systems

The respiratory structures of most organisms including humans have three features to ensure an efficient gaseous exchange with the surroundings. These three features are as follows:

• Moist surface of respiratory structures such as the moist surface of alveoli.

• Thin respiratory structures such as the walls of alveolus and blood capillaries which are one cell thick.

• Large surface area of respiratory structures such as the surface area of millions of alveoli.

Gills

• Fish is an organism that can only live in water. Therefore, the respiratory structure of fish, namely gills can adapt to increase the efficiency of gaseous exchange in water. Gills are made up of two rows of fine filaments that have many thin and flat projections known as lamellae. The number of filaments and lamellae produces a large surface area to facilitate gaseous exchange. Since fish live in water, their gills are surrounded by water and this causes the respiratory gases to dissolve and diffuse easily.

Trachea

• The respiratory system of insects is the trachea system made up of air tubes known as trachea. Air enters or leaves the trachea through breathing pores known as spiracles. The opening and closing of spiracles are controlled by valves which allow air to leave and enter the body.

• Trachea is divided into fine branches known as tracheoles. Tracheoles have thin and moist walls to increase the efficiency of gaseous exchange. The large number of tracheoles also provides a large surface area to facilitate gaseous exchange through diffusion directly into the cells. Some insects such as grasshoppers have air sacs in their trachea system. These sacs are filled with air to increase the rate of exchange of respiratory gases between tissues and the surroundings during energetic activities.