The diagram of an alveolus is labelled as follows: 1 Alveolar wall, 2 Capillary network, 3 Type I pneumocyte, 4 Type II pneumocyte, 5 Surfactant layer.
(i) Which labelled structure is primarily responsible for reducing surface tension in the alveolus?
(ii) The surface tension of the alveolar fluid is $0.07\ \text{N\ m}^{-1}$ when no surfactant is present and $0.02\ \text{N\ m}^{-1}$ when surfactant is present. Approximating the alveolus as a sphere of radius $0.10\ \text{mm}$, calculate the factor by which the mechanical work required to inflate the alveolus is reduced by the presence of surfactant. (Assume work ≈ surface tension × surface area.)

Question

The diagram of an alveolus is labelled as follows: 1 Alveolar wall, 2 Capillary network, 3 Type I pneumocyte, 4 Type II pneumocyte, 5 Surfactant layer.  
(i) Which labelled structure is primarily responsible for reducing surface tension in the alveolus?  
(ii) The surface tension of the alveolar fluid is $0.07\ \text{N\ m}^{-1}$ when no surfactant is present and $0.02\ \text{N\ m}^{-1}$ when surfactant is present. Approximating the alveolus as a sphere of radius $0.10\ \text{mm}$, calculate the factor by which the mechanical work required to inflate the alveolus is reduced by the presence of surfactant. (Assume work ≈ surface tension × surface area.)

Accepted Answer

Structure 4 (type II pneumocyte); work reduced to ≈0.29 × the original (≈29 % of the work)

Gce Model Questions Vol1 2023 Biology Question 9

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