(i) How does the air necessary for breathing enter the body of a human being?

(ii) What other function is performed by this part of our respiratory system?

(i) Oxygen enters the body in the mouth and nose, passes through the larynx and the trachea.

As shown in the diagram given below:

(ii) Nose - The nose is the primary organ of smell and also functions as part of the body's respiratory system.

Mouth – Mostly the breathing is done through nose i.e. nasal cavity. But, it can be done through oral cavity as well.