Q.Which of the following statements is incorrect regarding respiratory system?

Alveoli And Respiratory Surface

Why Alveoli Exist

If your lungs were just two empty balloons, the exchange surface available for oxygen to enter blood would be no bigger than a tabletop — nowhere near enough to supply the whole body. The lungs solve this by packing themselves with millions of microscopic air pockets called alveoli (singular: alveolus), the way a sponge packs air into countless tiny chambers instead of one big cavity.

What Are Alveoli?

Alveoli are the terminal, balloon-like sacs at the very end of the airway tree. Air travels down the trachea, through the bronchi, and into progressively finer bronchioles before finally reaching them. A single adult lung holds roughly 300–500 million alveoli.

The Respiratory Surface

The wall of each alveolus, together with the capillary wrapped around it, forms the respiratory surface — the only place in the lung where gases actually cross into and out of the blood. Several features make it efficient:

1. Extremely thin walls — each alveolar wall is a single layer of flat (squamous) epithelial cells, only one cell thick.
2. Rich blood supply — a dense network of capillaries surrounds every alveolus; capillary walls are also just one cell thick. Air and blood end up separated by only two cell layers, about 0.5 micrometres in total.
3. A moist lining — a thin film of fluid coats the inside of each alveolus. Gases must dissolve in this fluid before crossing the membrane; a dry surface cannot exchange gases.
4. Enormous total area — with hundreds of millions of alveoli, the combined surface area is huge, which compensates for how slowly a single gas molecule diffuses across a membrane.

How Gas Exchange Happens Here …