AP BIOLOGY

Detailed explanation-1: -During metaphase, the nuclear membrane disappears and the chromosomes become aligned half way between the centrioles. The centromere of each doubled chromosome becomes attached by thread-like spindle fibers to the centrioles which are at polar opposite sides of the cell.

Detailed explanation-2: -During prophase, the chromosomes condense, the nucleolus disappears, and the nuclear envelope breaks down.

Detailed explanation-3: -In order for these processes to occur, the nuclear membrane must be dissolved during the earliest mitotic phase: prophase. During prophase, DNA condenses into chromosomes, the nuclear membrane dissolves, and the chromosomes enter the cytoplasm.

Detailed explanation-4: -In the third step of mitosis, called metaphase, each chromosome lines up in a single file line at the center of the cell. By this point in time, the membrane enclosing the nucleus has dissolved, and mitotic spindles have attached themselves to each chromatid in all the chromosomes.