AP BIOLOGY

Detailed explanation-1: -The first and longest phase of mitosis is prophase. During prophase, chromatin condenses into chromosomes, and the nuclear envelope (the membrane surrounding the nucleus) breaks down.

Detailed explanation-2: -During prophase, the chromatin (DNA) coils up into visible chromosomes, each made up of two sister chromatids held together by the centromere. Also during this phase, the nucleolus disappears, and the spindle begins to form from the centrioles.

Detailed explanation-3: -In prophase, the chromatin fibers condense into chromosomes that are visible through a light microscope, each replicated chromosome appears as two identical sister chromatids joined at their centromeres, and the mitotic spindle begins to form.

Detailed explanation-4: -The yarn that fills the interphase nucleus is chromatin, which consists of DNA coiled around histone proteins.