What is the mitotic spindle?

• A. A ribosome-rich organelle.
• B. A structure made of microtubules that controls chromosome movement during mitosis.
• C. A lipid membrane around the nucleus.
• D. A mitochondrion.

Answer: (B)

Mitotic spindle is the structure that organizes and drives chromosome segregation during cell division. It is built mainly from microtubules, organized at opposite poles by centrosomes, and it reaches out to chromosomes to move them. The spindle attaches to chromosomes at kinetochores and coordinates their alignment at the metaphase plate, then shortens some microtubules while others lengthen to pull sister chromatids apart during anaphase. The other options don’t fit because ribosome-rich organelles are for protein synthesis, a lipid membrane around the nucleus is the nuclear envelope, and a mitochondrion is involved in energy production. So the mitotic spindle is a microtubule-based apparatus that controls chromosome movement during mitosis.