Which of the following is not true about the S phase?

Options

A. DNA and histones are synthesized
B. Amount of DNA per cell become half
C. Even after S phase chromosome number become double
D. All are not true

Answer

To solve the question "Which of the following is not true about the S phase?", we will analyze the characteristics of the S phase of the cell cycle step by step.

### Step 1: Understand the S Phase
The S phase, or synthesis phase, is part of the cell cycle where DNA replication occurs. During this phase, the cell synthesizes a complete copy of the DNA in its nucleus.

**Hint:** Remember that the S phase is specifically focused on DNA synthesis and replication.

### Step 2: Identify Key Characteristics of the S Phase
1. **DNA Replication**: The primary function of the S phase is the replication of DNA, resulting in the doubling of the amount of DNA.
2. **Chromosome Number**: Although the amount of DNA doubles, the number of chromosomes remains the same until the cell divides in the subsequent phases (M phase).
3. **Histone Synthesis**: Histones, which are proteins that package and order DNA into structural units called nucleosomes, are also synthesized during this phase.

**Hint:** Focus on the relationship between DNA amount and chromosome number during the S phase.

### Step 3: Analyze the Options
Now, let's evaluate the options provided in the question:

1. **Option 1**: "DNA and histones are synthesized." - This statement is true because both DNA and histones are synthesized during the S phase.
2. **Option 2**: "Amount of DNA per cell becomes half." - This statement is false; the amount of DNA actually doubles during the S phase.
3. **Option 3**: "Even after S phase chromosome number becomes double." - This statement is also false; the chromosome number remains the same during the S phase.
4. **Option 4**: "All are not true." - This option suggests that all previous statements are false, which is incorrect since option 1 is true.

**Hint:** Evaluate each option carefully to determine which statements are true or false about the S phase.

### Step 4: Conclusion
Based on the analysis:
- Option 1 is true.
- Options 2 and 3 are false.
- Therefore, the correct answer to the question "Which of the following is not true about the S phase?" is **Option 2 and Option 3**.

However, since the question asks for a single answer, we conclude that **Option 4** is misleading because not all statements are false. The most appropriate response is to identify the specific false statements (Options 2 and 3).

**Final Answer:** The statements that are not true about the S phase are Options 2 and 3.