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

What occurs in the fourth stage of mitosis?

1. New chromosomes are formed

2. Chromosomes are aligned

3. Membranes form around the chromosome sets

4. Cell fibers pull chromosomes apart

The correct answer is: Membranes form around the chromosome sets

In the fourth stage of mitosis, known as telophase, new nuclear membranes indeed form around the sets of chromosomes that have reached opposite poles of the cell. This stage is crucial because it signals the end of mitosis for the chromosomes. As the chromosomes decondense back into their more relaxed chromatin form, the cellular machinery prepares for the final separation of the two daughter cells. The activities that occur in this stage ensure the integrity of genetic information as the cell divides. The formation of membranes around each set of chromosomes helps establish distinct nuclei for the forming daughter cells, a key feature that differentiates mitosis from other processes like cytokinesis, which follows shortly after. While some choices involve important processes in mitosis, they pertain to different stages. New chromosomes do not form in this stage, as the aim is to create two sets of the existing chromosomes. Similarly, aligning chromosomes occurs during metaphase, and pulling chromosomes apart is a critical function of anaphase. The understanding of each stage in mitosis is essential for grasping how cells replicate and maintain genetic fidelity.