What are centrioles?

• A. A minute cylindrical organelle near the nucleus in animal cells, occurring in pairs and involved in the development of spindle fibers in cell division
• B. DNA segments that regulate transcription
• C. Clusters of ribosomes on the endoplasmic reticulum
• D. Cellular structures that store calcium ions

Answer: (C)

Centrioles are minute cylindrical organelles located near the nucleus in many animal cells, usually existing as a pair. Their main function is to organize the spindle apparatus that forms during cell division, guiding the separation of chromosomes so each daughter cell ends up with the correct genetic material. They duplicate during the cell cycle and move to opposite poles to anchor the spindle fibers. They are not ribosomes on the endoplasmic reticulum (that structure is the rough ER involved in protein synthesis), nor are they DNA segments that regulate transcription, nor calcium-storage structures (calcium is stored elsewhere, such as in the sarcoplasmic reticulum). So centrioles are best described as paired, near-nucleus cylindrical organelles that help develop spindle fibers during cell division.