Question

What structure does act as a door at the entrance of trachea?

Answer 1

Epiglottis

Explanation:

It is a leaf-shaped structure located at the base of tongue surrounding the upper end of trachea.

Importance:
It is a muscularly controlled structure. It acts like a lid. It's salient because it automatically closes the opening of wind pipe(trachea) during the action of swallowing.
Thus in a nutshell, epiglottis prevents the entry of food and liquid in wind pipe and hence prevents us from choking.

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