Final answer:
The cilia in the upper respiratory tubules propel mucus upward to trap and remove foreign particles and pathogens, keeping the respiratory system healthy.
Step-by-step explanation:
The cilia in the upper respiratory tubules play a crucial role in protecting the respiratory system from potentially harmful substances in the air. Specifically, they propel mucus upward, which is essential in the mucociliary escalator mechanism. The mucus traps particles and pathogens, and the cilia continuously move to sweep this mucus, along with the trapped debris, away from the lungs and toward the throat where it can be swallowed and destroyed by stomach acids. This action helps prevent infection and maintains respiratory health.