Q.The period of cell cycle during which synthesis or replication of DNA takes place is

Before a cell can safely divide by mitosis, it has to earn the right — it must first get itself ready. Splitting a cell that is not prepared would be like trying to hand two people a complete copy of a book when you only have one copy: someone ends up short. So mitosis has a genuine prerequisite, and that preparation happens during the long, busy period before division called interphase.

The single most important requirement is that the genetic material must be duplicated in advance. This copying does not happen during mitosis itself; it takes place earlier, in the S phase of interphase. During S phase the amount of DNA in the cell doubles, so that when division comes, there is a full second copy of every chromosome ready to be handed to the second daughter cell.

Alongside copying its DNA, the cell must also build up enough of its own materials so that each new cell it forms is complete and functional:

• In G1, the cell is metabolically active and grows steadily, but it does not yet copy its DNA.
• In the S phase, DNA replication occurs and the DNA content doubles.
• In G2, the cell makes the proteins needed for mitosis and continues to grow. …