Final answer:
During prophase, changes such as the breakup of the nuclear envelope, movement of centrosomes, and coiling of sister chromatids occur. These changes continue into metaphase, where chromosomes align along the metaphase plate.
Step-by-step explanation:
During prophase, several changes occur within the cell. The nuclear envelope breaks up into small vesicles, while the Golgi apparatus and endoplasmic reticulum fragment and disperse towards the periphery of the cell. The nucleolus disappears, and the centrosomes move towards opposite poles of the cell. Microtubules extend between the centrosomes, forming the mitotic spindle, and the sister chromatids coil tightly and become visible under a light microscope. These changes continue into metaphase, where all the chromosomes align along the metaphase plate, and the sister chromatids remain tightly attached to each other by cohesin proteins. The chromosomes are maximally condensed at this stage.