What is the role of mucus and cilia?

• A. Trap smaller particles/pathogens
• B. Oxygenate blood
• C. Digest fats
• D. Regulate blood glucose

Answer: (A)

Key idea: mucociliary clearance in the airways. Mucus coats the lining and traps small particles and pathogens, forming a sticky barrier that prevents them from reaching deeper lung tissues. The cilia on the airway epithelium beat in coordinated waves to move that mucus upward toward the throat, where it can be swallowed or expelled. This system is a primary defense of the respiratory tract, helping keep the lungs clear of irritants and infections. The other options describe processes elsewhere in the body—gas exchange in the alveoli, fat digestion in the gastrointestinal tract, and hormonal regulation of blood glucose—so they don’t fit the role of mucus and cilia.