Biology · Breathing and Exchange of Gases · NEET
Two reasons. First, the cartilage keeps the airway open so it does not collapse when the pressure inside the airway falls (this happens during forceful breathing). Second, the open gap at the back faces the food pipe (oesophagus). When a big bolus of food goes down, the oesophagus needs room to bulge. A full ring of hard cartilage would block this. The soft open gap lets the food pipe expand. So the C-shape does two jobs at once: hold the airway open and give the food pipe space.
NCERT lists them exactly: the trachea, the primary, secondary and tertiary bronchi, and the initial bronchioles are supported by incomplete cartilaginous rings. As the airway gets smaller, the cartilage slowly disappears. Terminal bronchioles and the alveoli have NO cartilage. Remember: cartilage is only in the conducting part where the tube must stay stiff and open; it is absent in the thin exchange part.
The rings are indeed C-shaped, meaning open on one side. But NCERT itself uses the words 'incomplete cartilaginous rings', not 'C-shaped'. For NEET, learn the exact NCERT phrase 'incomplete cartilaginous rings' because options often test the precise wording. C-shaped and incomplete mean the same thing.
During inspiration the pressure inside the airway drops below atmospheric pressure. A soft tube with no support would be sucked flat and close, cutting off air flow. The cartilage acts like the rigid rings in a vacuum-cleaner hose: it keeps the tube permanently open so air can always pass, no matter what the pressure inside is.
Cartilage belongs only to the conducting part (nostrils to terminal bronchioles), whose job is to carry, clean, warm and humidify air. The exchange part (alveoli and their ducts) does actual gas diffusion and has thin walls with no cartilage. So cartilage marks the conducting zone, not the site of gas exchange.
Try the real previous-year questions from this chapter — each with the answer and a full solution.
'The tracheae, primary, secondary and tertiary bronchi, and initial bronchioles are supported by incomplete cartilaginous rings.' Learn this word for word.
Because the oesophagus (food pipe) lies just behind the trachea. The soft open gap lets the oesophagus expand when a food bolus passes down during swallowing.
Only the initial bronchioles have some cartilage support. As bronchioles get smaller, cartilage disappears, and terminal bronchioles have none.
To keep the airway tube open and stop it from collapsing when the pressure inside the airway falls, so air can always flow.
Yes, but separately. NCERT calls the larynx a 'cartilaginous box' (the sound box). That is different from the incomplete rings of the trachea and bronchi.
