Advanced Placement (AP) Biology Practice Exam

Which process ensures that the chromosome number is conserved during cell division?

1. Meiosis

2. DNA replication

3. Mitosis

4. Cytokinesis

The correct answer is: Mitosis

During cell division, the process that ensures the chromosome number is conserved is mitosis. Mitosis is the process by which a single eukaryotic cell divides to produce two genetically identical daughter cells, each containing the same number of chromosomes as the original cell. This is achieved through several phases: prophase, metaphase, anaphase, and telophase. In prophase, the chromosomes condense and become visible, while the nuclear envelope begins to disintegrate. During metaphase, the chromosomes line up at the cell's equatorial plane, and during anaphase, the sister chromatids are pulled apart to opposite poles of the cell by spindle fibers. Finally, in telophase, the chromosomes reach the poles, and the nuclear envelope reforms around each set of chromosomes, resulting in two distinct nuclei. Since the entire process of mitosis is designed to ensure that each daughter cell receives an exact copy of the parent’s chromosome set, it plays a crucial role in maintaining the organism’s chromosome number across generations of cells. This is essential for growth, repair, and asexual reproduction in organisms. In contrast, meiosis reduces the chromosome number by half to produce gametes for sexual reproduction. DNA replication is the process that