What occurs during the S phase of the cell cycle?

During the S phase of the cell cycle, DNA synthesis occurs where each chromosome is duplicated. This is a crucial step in the cell cycle because it ensures that, when the cell divides during mitosis, each daughter cell will have an identical set of chromosomes. The S phase is specifically designed for this replication process, allowing the cell to prepare for division by doubling its genetic material.

During this phase, enzymes such as DNA polymerases are active as they unwind the double helix structure of the DNA. Each strand serves as a template for creating a complementary strand, resulting in two identical copies of the DNA. This process is vital for maintaining genetic consistency across cell generations and plays a significant role in growth and repair in multicellular organisms.

In contrast, the other options pertain to different phases of the cell cycle or cellular activities that do not occur during the S phase. For instance, checking for DNA errors is associated with the G1 and G2 phases, while protein synthesis primarily takes place during interphase but is not specific to the S phase. Cellular respiration, on the other hand, is a metabolic process used by cells for energy production and is not confined to a single phase of the cell cycle.