Question

During which phase of the cell cycle does DNA replication occur?

• A. \(G_1\) phase
• B. S phase
• C. \(G_2\) phase
• D. M phase

Hint:

Remember the sequence \(G_1 \rightarrow S \rightarrow G_2 \rightarrow M\). The S phase is the only phase where DNA synthesis occurs.

Answer 1

The Correct Option is B

Step 1: Understand the cell cycle.
The cell cycle is the set of steps a cell goes through to grow and then divide. It has a long interphase followed by the M phase (division).

Step 2: Name the parts of interphase.
Interphase is split into three parts in this order: $G_1$ phase, then S phase, then $G_2$ phase.

Step 3: Look at the $G_1$ phase.
In $G_1$ the cell grows bigger and makes proteins and organelles. No DNA copying happens here.

Step 4: Look at the S phase.
The letter S stands for Synthesis. In this phase the DNA copies itself, so the genetic material doubles and each chromosome forms two sister chromatids.

Step 5: Look at $G_2$ and M phases.
In $G_2$ the cell gets ready to divide, and in the M phase the actual division (mitosis) takes place. No DNA copying happens in these.

Step 6: Conclude.
So DNA replication takes place only during the S phase.
\[ \boxed{\text{S phase}} \]