OCR General Certificate of Secondary Education (GCSE) Biology Practice Exam

What happens during the second stage of mitosis?

1. DNA is replicated

2. Chromosomes condense into X-shaped structures

3. The cell divides into two

4. The chromosomes align at the cell's edge

The correct answer is: Chromosomes condense into X-shaped structures

During the second stage of mitosis, also known as prophase, chromosomes condense into X-shaped structures. This is a crucial step in the cell division process. As the cell prepares to divide, the chromatin (a complex of DNA and proteins) becomes tightly coiled and condenses, resulting in distinct chromosomes that are visible under a microscope. Each chromosome consists of two sister chromatids joined at a region called the centromere. The condensation of chromosomes is essential because it enables the chromosomes to be moved efficiently and accurately to opposite ends of the cell during the later stages of mitosis. If chromosomes did not condense, they would remain in a tangled and less organized state, making it difficult to ensure that each new daughter cell receives the correct number of chromosomes. The other options do not accurately describe the second stage of mitosis. DNA replication occurs during the S phase of interphase, not during mitosis itself. The cell division into two actually takes place during cytokinesis, which follows mitosis. The alignment of chromosomes at the cell's edge occurs during metaphase, the third stage of mitosis, when the chromosomes line up in the center of the cell.