AP BIOLOGY

Detailed explanation-1: -At the beginning of nuclear division, two wheel-shaped protein structures called centrioles position themselves at opposite ends of the cell forming cell poles. Long protein fibers called microtubules extend from the centrioles in all possible directions, forming what is called a spindle.

Detailed explanation-2: -In animal cells, spindle fibres extend from the centrioles. But in plant cells, which lack centrioles, spindle fibres originate from the centrosome region of the cell.

Detailed explanation-3: –centrioles organize to form spindle fibres.