MoCA Science Practice Test

The S phase, or synthesis phase, is the part of the cell cycle where DNA replication occurs. During this phase, the cell actively synthesizes a complete set of DNA in preparation for cell division. Each chromosome is duplicated, resulting in two sister chromatids for each chromosome. This is crucial because, before a cell can divide and pass on its genetic information to daughter cells, it must ensure that each daughter cell receives the same genetic material as the parent cell.

Growing and ensuring the integrity of the DNA are vital steps in the cell cycle, which is why the S phase is specifically focused on this process. While the G1 phase also involves cell growth and preparation for DNA synthesis, it does not include the actual replication of DNA. The G2 phase focuses on further growth and preparation for mitosis after the DNA has been replicated. The M phase is when mitosis and cytokinesis occur, resulting in the division of the cell itself. Therefore, the S phase is key for both cell growth in terms of preparing to divide and for the critical process of DNA replication.