During which phase does the centrosome become more defined?

The centrosome becomes more defined during prometaphase due to the significant changes that occur in the cell's structure at this stage of mitosis. During prometaphase, the nuclear envelope breaks down, which allows the microtubules to access the chromosomes that have already condensed and are visible. As the centrosomes move to opposite poles of the cell, they begin to anchor microtubules that will connect to the kinetochores of the chromosomes. This organization and anchoring are crucial for the proper alignment and separation of chromosomes that will occur in metaphase and anaphase. The increased prominence and functioning of the centrosome in this phase are essential for ensuring that the chromosomes can be accurately divided, highlighting the importance of the centrosome's role in cell division.