In the mammalian respiratory system. exchange of gases occurs in the?

1. Analyze the question The question asks for the exact structure in the mammalian respiratory system where gaseous exchange (oxygen in, carbon dioxide out) takes place.

2. Explain the concept Air travels along this pathway: Nostrils → Trachea → Bronchi → Bronchioles → Alveoli

• Trachea, bronchi and bronchioles are air passages. They carry air but have thick walls, so no gaseous exchange takes place there.
• Alveoli are tiny air sacs at the ends of the bronchioles. They are the actual site of gaseous exchange.

Alveoli are well adapted for this job:

• Their walls are only one cell thick, so gases diffuse over a very short distance.
• They are surrounded by a dense network of blood capillaries, which keeps a steep concentration gradient.
• They have a large total surface area (millions of alveoli in each lung).
• Their surfaces are moist, so gases can dissolve and diffuse easily.

3. Step-by-step solution

• A. Lungs: The lungs are the whole organ. Gaseous exchange happens inside them, but the question asks for the specific site. This is a general answer, not the precise one.
• B. Bronchi: These are air tubes only. No exchange occurs.
• C. Bronchioles: These are smaller air tubes. They carry air to the alveoli, and no exchange occurs.
• D. Alveoli: Oxygen diffuses from the alveolar air into the blood, and carbon dioxide diffuses from the blood into the alveolar air. This is correct.

4. Answer The correct option is D. alveoli.

5. Exam tip Remember: "Tubes transport, alveoli exchange." When JAMB asks for the site of gaseous exchange, choose the most specific structure (alveoli) rather than the broader organ (lungs). Also watch for the word "exchange": it points to thin-walled, capillary-rich surfaces.