Which of the following properties of alveoli is/are helpful in gaseous exchange during respiration in human beings? I. The epithelial lining of alveoli is very thin. II. Elastic fibres are present in alveolar wall. III. Wall of alveoli is surrounded by many blood capillaries. Select the correct answer using the code given below.
B. I and III only
Gaseous exchange in the alveoli occurs primarily through simple diffusion. A very thin epithelial lining of the alveoli minimizes the diffusion distance for gases, which significantly increases the rate of gaseous exchange. Thus, statement I is correct. The presence of a dense network of blood capillaries surrounding the alveolar walls continuously removes oxygen and brings carbon dioxide. This maintains a steep concentration gradient essential for efficient diffusion. Thus, statement III is correct. Although elastic fibres are present in the alveolar wall to aid in the expansion and recoil of lungs during breathing mechanics, they do not directly facilitate the diffusion of gases across the respiratory membrane. Therefore, only statements I and III describe properties directly helpful in gaseous exchange.
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