Biology · Breathing and Exchange of Gases · NEET
Air enters through a pair of external nostrils, goes into the nasal chamber through the nasal passage, then into the pharynx, then through the larynx into the trachea. The trachea divides at the level of the 5th thoracic vertebra into a right and left primary bronchus. Each bronchus divides again and again into secondary and tertiary bronchi, then into smaller bronchioles, ending in the alveoli. Learn this order left to right because NEET often gives a scrambled list and asks the correct sequence.
The conducting part runs from the external nostrils up to the terminal bronchioles. It only transports air; it does not exchange gases. Its jobs are to clear the air of foreign particles, humidify (add moisture) to the air, and bring the air to body temperature. The respiratory part is made of the alveoli and their ducts, and this is the only place where oxygen and carbon dioxide actually diffuse. NEET 2022 asked exactly this.
Gas exchange happens only in the alveoli, which are thin-walled, richly blood-supplied (highly vascularised) bag-like structures. Oxygen from inhaled air diffuses into the blood and carbon dioxide diffuses out. The trachea, bronchi and bronchioles do not exchange gas; they only carry air to the alveoli. Many students wrongly mark trachea or bronchi as the exchange site.
The pharynx is a common passage for both food and air, so it belongs to both systems. Air from the nasal chamber and food from the mouth both pass through it. From the pharynx, air goes through the larynx into the trachea, while food goes into the oesophagus. Because it is a shared passage, the epiglottis closes the larynx during swallowing so food does not enter the airway.
The lungs are covered by a double-layered pleura with pleural fluid between the two layers. This fluid reduces friction on the lung surface during breathing. The outer pleural layer is in close contact with the wall of the thoracic cavity, and the inner layer is in contact with the lung. The lungs sit in the thoracic chamber, which is bounded on the lower side by the dome-shaped diaphragm.
Which of the following is not the function of the conducting part of the respiratory system?
Try the real previous-year questions from this chapter — each with the answer and a full solution.
External nostrils, nasal chamber, pharynx, larynx, trachea, primary bronchi, secondary and tertiary bronchi, bronchioles, and alveoli inside the lungs. The lungs are covered by a double-layered pleura and sit in the thoracic cavity above the diaphragm.
The trachea divides at the level of the 5th thoracic vertebra into a right and left primary bronchus. Each bronchus then divides repeatedly into secondary and tertiary bronchi and bronchioles.
Breathing and Exchange of Gases is a high-yield chapter. NEET regularly asks the sequence of parts, the conducting versus respiratory part, and where diffusion occurs. Knowing the exact NCERT order and function of each part helps you answer both direct and tricky questions.
The larynx is a cartilaginous box that helps in sound production, so it is also called the voice box. Air passes from the pharynx through the larynx into the trachea.
