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.

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I, II and III. All three properties genuinely help gas exchange in the lungs. The thin epithelial lining means oxygen and carbon dioxide only cross a very short distance between air and blood. Elastic fibres let the alveolar walls stretch during breathing in and spring back during breathing out. This elastic recoil keeps air moving in and out steadily, which keeps fresh air reaching the exchange surface. A dense network of blood capillaries around each alveolus keeps carrying blood past the surface constantly. This maintains a steady concentration gradient, so diffusion of oxygen and carbon dioxide keeps happening efficiently. So all three properties, I, II and III, support efficient gaseous exchange, making option (d) correct.

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.

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