The Weibel Lung model was developed after an extensive study of the gas exchange system. The model includes detailed measurements of airway diameters (lumen diameters of the airways). In the model, different parts of the gas exchange system are identified with a generation number, as outlined in Fig. 6.1.

1. (a)The Weibel Lung model describes how each airway divides into two. Name the airways in generation 1, labelled X in Fig. 6.1, that branch from generation 0.[1]
2. (b)The airways are well supplied with blood. However, the airways from generation 0 to generation 16, shown in Fig. 6.1, are not able to carry out gas exchange. Suggest why the airways from generation 0 to generation 16 are not able to carry out gas exchange.[2]
3. (c)(i)High-resolution computed tomography (HRCT) is an imaging technique that is used to obtain measurements of airway diameters in people with a pulmonary (lung) disease. Regular, repeated imaging must be avoided because it involves exposure to harmful radiation. Scientists researched the use of a different technique, HP gas MRI, that does not involve harmful radiation. Two types of MRI image, known as projection and multi-Slice, were used to obtain measurements of airway diameters. Fig. 6.2 shows the results of the HP gas MRI study compared with the Weibel Lung model, for generations 0 to 5. The Weibel Lung model was used as a standard reference for airway diameters. State the relationship shown in Fig. 6.2 between airway diameter and airway generation for the Weibel Lung model data.[1]
4. (c)(ii)With reference to the data in Fig. 6.2, explain whether HP gas MRI could be a useful alternative to HRCT in obtaining airway diameter measurements.[3]

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