Final answer:
Ciliated epithelial cells with hair-like cilia propel mucus secreted by goblet cells, which traps dust and particles, up the respiratory tract to the throat to keep the lung surface clear.
Step-by-step explanation:
Ciliated epithelial cells and goblet cells play a pivotal role in keeping the lung surface clear of dust and other particles. The goblet cells secrete mucus that traps incoming particles, such as dust and bacteria, preventing them from reaching the lungs. The mucus containing the trapped particles is then moved by the cilia, which are hair-like projections on the surface of ciliated epithelial cells, in a wave-like motion. This motion propels the mucus upwards towards the throat, where it can be swallowed and safely digested in the stomach. The ciliated epithelial cells in the respiratory system form what is known as the mucociliary escalator, which effectively moves mucus and trapped particles out of the respiratory tract, thereby protecting the lungs from potential harm.