Advanced Placement (AP) Biology Practice Exam

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What occurs during the S phase of the cell cycle?

Cell growth
Replication of DNA
Separation of chromosomes
Formation of the mitotic spindle

The correct answer is: Replication of DNA

During the S phase of the cell cycle, replication of DNA occurs. This phase is crucial because it ensures that when a cell eventually divides, each daughter cell receives an identical set of genetic material. During this phase, the entire genome is duplicated, resulting in the formation of two complete sets of chromosomes. This process is tightly regulated and involves various enzymes, including DNA polymerase, which synthesizes new strands of DNA by matching nucleotides to the existing strands, ensuring that the genetic information is accurately copied. This replication is essential for cell division, as it guarantees that both cells produced will have the same genetic instructions necessary for proper function and development. The successful completion of the S phase is critical for the subsequent phases of the cell cycle, particularly the G2 phase where the cell prepares for mitosis, and ultimately results in the accurate division of genetic material during the M phase.