During which phase does the nuclear membrane and nucleolus disassemble?

During prophase, the nuclear membrane and nucleolus disassemble, marking a crucial step in the cell division process. Prophase is the first stage of mitosis, where chromatin condenses into distinct chromosomes, making them visible under a microscope. The disassembly of both the nuclear membrane and nucleolus is essential because it allows the spindle apparatus to access the chromosomes and facilitates their movement towards the metaphase plate.

The breakdown of the nuclear membrane ensures that the chromosomes are no longer contained within the nucleus, which is critical for their separation during the later stages of mitosis. This disassembly signals the cell's readiness to proceed with division and is a clear indicator of the transition from interphase to active mitotic division.