Question

The figure given above shows a small part of human lung where exchange of gases takes place. In which one of the options given below, the one part A, B, C or D is correctly identified along with its function.

• A. C : Arterial capillary - Passes oxygen to tissues
• B. A : Alveolar cavity - Main site of exchange of respiratory gases
• C. D : Capillarywall - Exchange of $O_2$ and ${CO}_2$ takes place here
• D. B : Red blood cell - Transport of ${CO}_2$ mainly

Answer 1

Answer: (B)

A : Alveolar cavity - Main site of exchange of respiratory gases

• In the given diagram, A represents the alveolar cavity, B represents the red blood cell, C represents the alveolar wall, and D represents the basement membrane.
• The exchange of respiratory gases, oxygen, and carbon dioxide takes place in the alveoli of the lungs.
• Oxygen which is inhaled from the atmosphere diffuses through the walls of the alveoli and reaches the adjacent capillaries into the red blood cells. It binds to hemoglobin present in red blood cells and is transported to all the tissues of the body.
• Carbon dioxide produced by the metabolism reaches the lungs via the blood. It then diffuses across the capillary and alveolar wall into the air to be exhaled out from the body.
• The alveoli of the lungs have a specialized structure for the efficient exchange of respiratory gases. It has extremely thin walls. It has a large surface area to volume. It is surrounded by many blood capillaries.

So, the correct answer is option B.