Fig. 3.1 shows the structure of an alveolus and surrounding structures in a mammalian lung. The lining of each alveolus is formed by two types of epithelial cell, alveolar type 1 and alveolar type 2. [Figure 3.1]

1. (a)Explain how the structure of an alveolar type 1 cell is adapted to its function.[2]
2. (b)Alveolar type 2 cells secrete pulmonary surfactant into the watery fluid that lines the alveolus. The surfactant reduces the surface tension of the fluid so that the alveolus does not collapse. Pulmonary surfactant is a mixture of phospholipids and proteins. The phospholipids form a monolayer on the surface of the fluid. Explain how phospholipids interact with water to form a monolayer on the surface of the fluid.[2]
3. (c)Macrophages and neutrophils are found in the lungs, as shown in Fig. 3.1. Describe the role of macrophages in the lungs.[3]
4. (d)(i)Neutrophils leave the blood and secrete the extracellular enzyme, elastase. Suggest why neutrophils secrete elastase.[2]
5. (d)(ii)The protein alpha-1 antitrypsin is produced in cells in the liver and is transported to the lungs, where it inhibits the action of elastase. Some people produce a different form of this protein that remains within liver cells. These people are at an increased risk of developing emphysema, in which alveolar walls break down. Emphysema is one of the conditions associated with chronic obstructive pulmonary disease (COPD). Explain why these people are at increased risk of developing emphysema.[3]

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