Final answer:
Prophase is the first phase of mitosis in which chromatin condenses into visible chromosomes. The nucleolus disappears and the nuclear envelope disintegrates. The centrosomes move to opposite poles and microtubules form the mitotic spindle.
Step-by-step explanation:
Prophase is the first phase of mitosis where chromatin condenses into visible chromosomes. Each chromosome becomes visible with its identical partner attached, forming sister chromatids. The nucleolus disappears early in prophase, and the nuclear envelope disintegrates. The centrosomes start to move to opposite poles of the cell, and microtubules form the mitotic spindle that pushes them apart. Overall, prophase is a crucial stage of mitosis where the cell prepares for chromosome segregation.