Question

why do the walls of trachea don't collapse even when there is less air in it

Answer 1

Heya!!

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Trachea is supported by C-shaped rings of cartilage which hold them in place when there is less air inside it. So, the walls of trachea do not collapse even when there is a little air.

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Hope it helps

Answer 2

BECAUSE WALL OF TRACHEA CONTAINS INCOMPLETE CARTILAGENIOUS  RINGS WHICH PREVENT TRACHEA FROM COLLAPSING