Question

Functional unit of lungs is

• A. Bronchus
• B. Alveolus
• C. Trachea
• D. Pleura

Hint:

Alveoli are the functional units of lungs because they are the sites of gas exchange.

Answer 1

The Correct Option is B

Concept:
The lungs are respiratory organs responsible for exchange of gases.

Step 1: Understanding alveoli.
Alveoli are tiny air sacs present at the end of bronchioles.

Step 2: Function of alveoli.
Gas exchange occurs through the thin walls of alveoli. Oxygen enters the blood and carbon dioxide leaves the blood. \[ O_2 \rightarrow \text{blood}, \qquad CO_2 \rightarrow \text{alveoli} \]

Step 3: Why alveolus is functional unit.
Since the main function of lungs is gaseous exchange and alveoli perform this function, alveolus is the functional unit of lungs.

Step 4: Checking other options.
Bronchus and trachea are air passages.
Pleura is the covering of lungs.
Alveolus is the site of gas exchange. \[ \boxed{\text{Alveolus}} \]