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

What is the main purpose of the S phase in the cell cycle?

1. To prepare the cell for division

2. To ensure DNA integrity

3. To replicate DNA

4. To create new organelles

The correct answer is: To replicate DNA

The main purpose of the S phase in the cell cycle is to replicate DNA. During this phase, the entire genome is duplicated to ensure that each daughter cell receives an identical set of chromosomes when the cell divides in the subsequent mitotic phases. This is crucial for maintaining genetic consistency across cell generations. While preparing the cell for division is important and takes place in other phases, such as the G2 phase, the actual replication of DNA is specifically the hallmark task of the S phase. Ensuring DNA integrity also plays a role in the overall cell cycle but is more about the checks that occur before and after S phase. Similarly, the creation of new organelles is a process that occurs mainly in the G1 phase and not specifically tied to the S phase. Thus, the replication of DNA stands out as the primary focus of the S phase.