Final answer:
During metaphase in an onion root tip cell, the chromosomes line up in the middle of the cell in a circular arrangement called the metaphase plate.
Step-by-step explanation:
During metaphase in an onion root tip cell, the chromosomes line up in the middle of the cell. This is because the spindle fibers attach to the centromeres of the chromosomes and pull them towards the center. The cell appears to have a circular arrangement of chromosomes in the middle, known as the metaphase plate.