The upper part of the respiratory tract is provided with small hair-like structures called ______.

cilia

The correct answer is Option (2) - cilia

The upper part of the respiratory tract is provided with small hair-like structures called cilia. These are microscopic, hair-like projections on the surface of the cells lining the respiratory passages, particularly in the trachea and bronchi. The coordinated movement of cilia helps in the clearance of mucus and trapped particles, such as dust and pathogens, from the respiratory system. This mechanism is essential for maintaining the health of the respiratory system by preventing the accumulation of foreign particles and facilitating their expulsion through mechanisms like coughing and swallowing.