Florida Biology EOC Practice Test

In which stage of mitosis do chromosomes become visible and the nuclear membrane breaks down?

1. Anaphase

2. Interphase

3. Metaphase

4. Prophase

The correct answer is: Anaphase

The stage of mitosis where chromosomes become visible and the nuclear membrane breaks down is prophase. During prophase, the chromatin condenses into distinct chromosomes, making them visible under a microscope. Each chromosome consists of two sister chromatids joined at the centromere. Additionally, the nuclear membrane begins to disintegrate, allowing the spindle fibers to access the chromosomes. This is a crucial step leading up to the alignment and separation of chromosomes that occurs in later stages of mitosis. Anaphase, in contrast, is the stage where sister chromatids are pulled apart toward opposite poles, while metaphase is characterized by chromosomes aligning at the cell's equatorial plane. Interphase is not a stage of mitosis but rather the phase where the cell prepares for division, including DNA replication and other growth activities.