When does the nuclear membrane and nucleolus disappear? When do they reappear?

Prophase

Explanation:

The nucleus during mitosis. Micrographs illustrating the progressive stages of mitosis in a plant cell. During prophase, the chromosomes condense, the nucleolus disappears, and the nuclear envelope breaks down.

The nuclear membrane dissolves in the first part of mitosis, so that the cell can grow and divide.  It is prophase.

Explanation:

answer; ///i believe the answer your looking for is (ribosomes);

during the process of dna replication, brdu can replace thymidine and incorporate into the newly synthesized dna, cell proliferation thus can be reflected in the extent of brdu incorporation.