Final answer:
Cilia are tiny hair-like structures on cell surfaces that function in innate immunity by clearing mucus and trapped particles from the respiratory tract, thus preventing infections. They are found on eukaryotic cells and are essential for maintaining respiratory health, especially as part of the body's natural defenses against inhaled pathogens.
Step-by-step explanation:
Cilia (singular: cilium) are tiny hair-like structures on cell surfaces that play a crucial role in the defense mechanisms of the human body. These microtubule-based extensions are found on eukaryotic cells, such as those lining the respiratory, reproductive, and digestive systems. Cilia use a rapid, flexible, waving motion to move substances over cell surfaces. In the respiratory system, for example, ciliated epithelial cells trap and move mucus secretions and trapped debris away from the lungs in what is known as the 'mucociliary escalator.' This process helps prevent infections by removing dust, germs, and other foreign particles before they can cause harm. Cilia are also present in other biological contexts, such as in ciliates, a group of protozoans like Paramecium and Stentor that use cilia for locomotion and feeding.
It is important to note that innate immunity is a part of the body's natural defenses, with cilia playing a supportive role in these mechanisms. The presence of functional cilia is essential for maintaining health, as damage or loss of cilia can lead to an increased risk of respiratory infections. Smoking, for instance, can impair ciliary function and contribute to lung diseases.