Fig. 5.1 is a photomicrograph of a transverse section of a bronchus in the lungs. [Fig. 5.1]

1. (a)(i)Identify the tissue labelled T in Fig. 5.1.[1]
2. (a)(ii)Describe the function of smooth muscle in the bronchus.[2]
3. (b)(i)The walls of alveoli contain some specialised epithelial cells called type II epithelial cells. These cells secrete surfactant. Surfactant helps to prevent the alveoli collapsing during breathing. Surfactant contains phospholipid, cholesterol and protein. The components of surfactant are synthesised in the rough endoplasmic reticulum and smooth endoplasmic reticulum and then passed to the Golgi body. The surfactant that is produced is stored in secretory organelles called lamellar bodies. The surfactant in the lamellar bodies is released onto the surface of the alveolar epithelium by exocytosis, as shown in Fig. 5.2. [Fig. 5.2] Each lamellar body is surrounded by a single membrane. Draw a diagram to show the arrangement of phospholipid molecules in the membrane surrounding the lamellar body.[2]
4. (b)(ii)Scientists studying the production and secretion of lung surfactant have discovered that a reduction in cholesterol in the cell surface membrane of type II epithelial cells reduces the secretion of surfactant. Suggest why secretion of surfactant is affected by a reduction in cholesterol in the cell surface membranes of type II epithelial cells.[2]
5. (b)(iii)Lung surfactant is engulfed by macrophages that are in close contact with the type II epithelial cells. Suggest why macrophages engulf surfactant.[1]

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