Final answer:
During mitotic metaphase, chromosomes are maintained in the equatorial plane by a tug-of-war between balanced pulling forces exerted by chromosomal spindle fibers from opposite poles. This alignment is achieved as spindle fibers attach to kinetochores and the chromosomes line up at the notional metaphase plate.
Step-by-step explanation:
Chromosomes are maintained in the equatorial plane during mitotic metaphase largely due to the actions of spindle fibers. These spindle fibers attach to the centromere of each pair of sister chromatids at a structure known as the kinetochore. During metaphase, chromosomes align on the metaphase plate, or equatorial plane. The correct answer to the provided question is: A: by a tug-of-war between balanced pulling forces exerted by chromosomal spindle fibers from opposite poles. This is because the chromosomal spindle fibers from the centrosomes at each pole of the cell exert balanced pulling (or tension) forces on the kinetochores of the sister chromatids. This synchronized pulling aligns the chromosomes at the metaphase plate. It is important to note that the metaphase plate does not actually bind the chromosomes; rather, it is a notional plane where the chromosomes align due to these forces. Additionally, astral spindle fibers with from the poles also play a role but are involved in spindle orientation and the regulation of mitosis rather than directly maintaining chromosome alignment.