Final answer:
The phase where chromosomes are physically pulled apart is anaphase, during which sister chromatids are separated and move towards opposite cell poles.
Step-by-step explanation:
The phase during which chromosomes are physically pulled apart is called anaphase. Anaphase is known as the “upward phase” and is characterized by the separation of sister chromatids. The cohesin proteins that hold sister chromatids together degrade, which allows the chromatids to be pulled apart at the centromere. After they separate, each sister chromatid, now considered an individual chromosome, is pulled rapidly towards the centrosome of the cell. This action is facilitated by the mitotic spindle microtubules that attach to the chromosomes. During anaphase, the cell elongates, and the chromosomes are moved to opposite poles, preparing for the formation of two new cells.
Visible Chromosomes and Mitotic Stages
It's also important to note that the individual chromosomes become visible under a light microscope during prophase. This is part of the process of mitosis, and the visibility is due to the chromosomes condensing, which makes them appear more distinct.