What occurs during interphase before a cell divides?

During interphase, which is the phase of the cell cycle that occurs before cell division, the primary event is the duplication of chromosomes. This is a critical process as it ensures that each daughter cell will have an identical set of chromosomes after cell division. Interphase is divided into three sub-phases: G1 (gap 1), S (synthesis), and G2 (gap 2).

During the S phase, DNA replication occurs, resulting in the synthesis of identical sister chromatids for each chromosome. This chromosomal duplication is essential for maintaining genetic continuity across generations of cells.

The other processes mentioned, such as the disappearance of the cell membrane (which does not happen until cell division begins), the alignment of chromosomes at the metaphase plate (which occurs during metaphase, part of mitosis), and the division of the nucleus (which occurs during mitosis), do not take place during interphase. Thus, the correct answer highlights the importance of chromosome duplication as a preparatory step for successful cell division.