Which forms the core of both cilia and flagella and also constitutes the spindle apparatus during cell division?

• A. Microfilaments
• B. Microtubules
• C. Intermediate filaments
• D. Keratin

Answer: (B)

Microtubules form the structural framework of both cilia and flagella and also organize the spindle apparatus during cell division. In cilia and flagella, the core axoneme is built from microtubule doublets arranged in a 9+2 pattern, with dynein motors causing microtubule sliding that generates the characteristic bending movement. In cell division, microtubules assemble into the spindle, creating kinetochore connections to chromosomes and dynamic fibers that lengthen and shorten to separate sister chromatids during anaphase.

The other options don’t fit this dual role: microfilaments are primarily actin-based and drive cortical movement and shape changes; intermediate filaments provide mechanical support and structural integrity; keratin is a type of intermediate filament protein found in epithelial cells, not involved in forming cilia/flagella cores or the mitotic spindle.