If a cell does not meet the criteria for entrance into the S phase, it will remain in which phase?

If a cell does not meet the criteria for entrance into the S phase, it will remain in which phase?

• A. G0
• B. G1
• C. S
• D. G2

Answer: (A)

Key idea: progression through the cell cycle is governed by checkpoints that decide whether a cell should commit to DNA replication. To enter S phase, a cell must have adequate growth signals, nutrients, and intact DNA. If these criteria aren’t met, the cell does not commit to replication and instead exits the cycle into a non-dividing, resting state called G0. In G0 the cell is metabolically active but not preparing to divide; many differentiated cells reside there, and some can re-enter the cycle if conditions improve. So when entrance into S phase isn’t met, the cell remains in G0 rather than advancing to S (or the later phases).

Key idea: progression through the cell cycle is governed by checkpoints that decide whether a cell should commit to DNA replication. To enter S phase, a cell must have adequate growth signals, nutrients, and intact DNA. If these criteria aren’t met, the cell does not commit to replication and instead exits the cycle into a non-dividing, resting state called G0. In G0 the cell is metabolically active but not preparing to divide; many differentiated cells reside there, and some can re-enter the cycle if conditions improve. So when entrance into S phase isn’t met, the cell remains in G0 rather than advancing to S (or the later phases).