Which of the following events occur during prophase?

• A. Sister chromatids are pulled apart to opposite poles.
• B. The nuclear envelope re-forms around each set of chromosomes.
• C. The cell membrane pinches in to divide the cytoplasm.
• D. Chromosomes condense and become visible.

Answer: (D)

Verified step by step guidance

1. Begin by understanding the stages of mitosis, which include prophase, metaphase, anaphase, and telophase. Each stage has distinct events that occur within the cell.
2. Focus on prophase, the first stage of mitosis. During prophase, several key events occur that prepare the cell for division.
3. Recognize that during prophase, the chromatin fibers condense into visible chromosomes. This is a crucial step as it allows the chromosomes to be easily segregated later in mitosis.
4. Understand that the nuclear envelope begins to break down during prophase, allowing the spindle fibers to interact with the chromosomes.
5. Note that the other events listed, such as sister chromatids being pulled apart, the nuclear envelope re-forming, and the cell membrane pinching in, occur in later stages of mitosis, not during prophase.