What role do cilia play in the respiratory system?

The role of cilia in the respiratory system is primarily to filter out dust and other particulate matter from the airways. Cilia are tiny, hair-like structures that line the respiratory tract and beat in a coordinated manner, moving mucus, which traps inhaled particles such as dust, bacteria, and pollutants, toward the throat. This action helps to keep the airways clear and protects the lungs from potential infections and irritants.

In the context of the other options, while cilia are important in the overall function of the respiratory system, they do not directly facilitate gas exchange (which primarily occurs in the alveoli), nor do they themselves secrete mucus (this is the role of goblet cells). Although cilia play a role in the movement of mucus that contains various substances, their primary function in this context is effectively the mechanical filtering of incoming air, making filtration by cilia the correct focus.