Which of the following describes prophase?

• A. Chromosomes line up in the middle of the cell
• B. Chromosomes become visible, nuclear envelope dissolves, spindle forms
• C. The chromosomes separate and move to opposite ends of the cell
• D. The chromosomes become longer, thinner, and less distinct; the nuclear membrane forms

Answer: (B)

Prophase is the stage of mitosis when chromatin condenses into visible chromosomes, the nucleolus disappears, the nuclear envelope breaks down, and the spindle apparatus forms outside the nucleus. These changes prepare chromosomes to be guided and separated in the next stages. The description that combines chromosomes becoming visible, the nuclear envelope dissolving, and the spindle forming matches these events precisely, so it is the best description of prophase. In contrast, lining up at the cell’s middle is metaphase, chromosomes separating to opposite poles is anaphase, and the reformation of the nuclear membrane with chromosomes decondensing describes telophase.