In which stage of mitosis do chromosomes condense and the nucleolus disappears?

The correct answer is prophase, as this is the stage in mitosis where several key events occur that are crucial for the successful division of the cell. During prophase, the chromatin—the loose material that makes up chromosomes—begins to condense into visible, distinct chromosomes. This condensation makes it easier to separate the genetic material during later stages of mitosis.

Additionally, during prophase, the nucleolus, which is the site of ribosome synthesis within the nucleus, disappears. This dissolution is significant as it marks the beginning of the cell's transition from interphase—when the cell is preparing for division—to the active division phase of mitosis. The disappearance of the nucleolus is an indicator that the cell is moving toward the segregation of its genetic material.

This stage also involves the formation of the mitotic spindle, which is crucial for the movement of chromosomes. Understanding prophase is fundamental as it sets the stage for the subsequent actions of metaphase, anaphase, and telophase, which all build on the events initiated in prophase.