Answer: Microtubules.
- A Actin filaments
- B Microtubules
- C Intermediate filaments
- D Collagen fibers
Correct answer: B. Microtubules
Explanation: Spindle fibers are made of microtubules (tubulin protein). They attach to chromosomes at kinetochores and pull them to poles.
The cell cycle: G1 (growth and preparation), S (DNA replication, chromosome number stays 2n but DNA content doubles), G2 (final checks before division), and M (mitosis itself) - together, G1+S+G2 make up interphase.
Concept context
Mitosis and meiosis: how cells divide for growth, repair, and reproduction.