What is the core of cilia?

• A. Actin
• B. Keratin
• C. Intermediate filaments
• D. Microtubules (axoneme)

Answer: (D)

The moving shaft of a cilium is built around microtubules, organized into the axoneme. In most motile cilia, this axoneme has a characteristic 9+2 arrangement—nine outer microtubule doublets surrounding a central pair. These microtubules provide the scaffold for dynein motor proteins, which generate the beating motion by causing sliding between adjacent doublets; the structural connections convert that sliding into bending. The central pair and associated links regulate this activity to produce coordinated movement. Other filaments, like actin, keratin, and intermediate filaments, do important roles in different parts of the cell but do not form the core structural framework of the ciliary axoneme. So the core of cilia is microtubules (axoneme).