Final answer:
The upper respiratory tract is lined with pseudostratified ciliated columnar epithelium with goblet cells for trapping debris; the alveoli, however, are lined with simple squamous epithelium to facilitate gas exchange through the respiratory membrane.
Step-by-step explanation:
The epithelium of the upper respiratory tract is primarily composed of pseudostratified ciliated columnar epithelial cells with goblet cells. This type of tissue appears to be multiple layers due to the varied positioning of nuclei, but in fact, it is a single layer. These ciliated cells and goblet cells serve an important role in trapping debris and pathogens in the mucus, which is then moved out of the respiratory tract via the mucociliary escalator mechanism.
In contrast, the alveoli are lined with simple squamous epithelium, which is thinner to facilitate the exchange of gases. Here, there are no cilia or goblet cells; the alveolar epithelium, along with the surrounding capillary endothelium, forms the respiratory membrane. This membrane is crucial for enabling gas exchange by simple diffusion and is the site where oxygen enters the blood and carbon dioxide is released from the blood.