Which structure of the respiratory system plays the main role in carry out the system’s primary function? trachea pharynx alveoli nose

The correct answer would be alveoli.

Alveoli (singular alveolus) are the functional unit of the respiratory system.

They are sac like structures present at the end of respiratory tree (in lungs).

They are arranged in the form of clusters such as found in cluster of grapes.

The exchange of oxygen and carbon dioxide takes place at alveolar level.

These are one celled thick which helps in easy diffusion of oxygen (from inhaled air into the blood stream) and carbon dioxide (from blood stream to exhaled air).

In addition, they are highly supplied with blood capillaries which bring the carbon dioxide from the cells and take oxygen to them.

trachea, alveoli, lung capillaries, arteries