Question

Residual air mostly occurs in
A) Alveoli
B) Bronchus
C) Nostrils
D) Trachea

Answer 1

Hint: Lungs is the organ for respiration. The amount of air that remains in the lungs following a maximal expiration. In some unhealthy conditions like an asthma attack and diffuse obstructive emphysema, the residual volume is higher than the normal one as most air remains obstructed in the lungs.

Complete answer:
The respiratory system comprises tissues and organs through which we breathe. The air we inhale is taken through the nostrils (nose which contains fine hairs and lines with mucous). After the nostrils, it moves through the trachea (cartilaginous rings like tube which is lined with mucous) and reaches the lungs.

The lungs are the main organ for respiration. The air enters the lungs through the bronchus. The Alveoli are the small air sacs like structure which are the main units where exchange of gases takes place. They are the functional unit of the lungs. Once the oxygen is diffused, the carbon dioxide is exhaled from the lungs back to the atmosphere through nostrils.

The structure of the respiratory system is as follows-

After expiration, some amount of air is left in the alveoli. This is called the residual volume. The residual volume is the amount of air that is left in the alveoli of the lungs after expiratory reserve volume is exhaled. The lungs are not ever completely empty, there is always some air in the lungs after a maximal exhalation. If residual volume didn’t exist and lungs emptied completely then tissues of lungs would stick together.

Thus the correct answer is option A i.e Alveoli.

Note: The residual air is important for following
1) Providing sufficient time for oxygen to be absorbed and for the carbon dioxide to be released.
2) It also helps from collapsing of lung passage
The portion of air contained in the lungs which can not be expelled by the most violent expiratory effort amounts to from 75 to 100 cubic inches. Forced expiratory volume is also decreased during obstructive lung diseases.