I. ER is also called the control center of the cell.
II. It modifies chemicals that are toxin to the cell.
III. SER is a major site for the synthesis of proteins.
IV. ER is a network of interconnected cisternae , tubules, and vesicles present in the endoplasm.
Which of the following statements is /are not true about the ER.

Options

A. None
B. I and III
C. All except III
D. All

Answer

To determine which statements about the endoplasmic reticulum (ER) are not true, we will analyze each statement one by one.

### Step-by-Step Solution:

1. **Statement I: "ER is also called the control center of the cell."**
- This statement is **not true**. The control center of the cell is the nucleus, not the endoplasmic reticulum. Therefore, this statement is incorrect.

2. **Statement II: "It modifies chemicals that are toxin to the cell."**
- This statement is **true**. The smooth endoplasmic reticulum (SER) is involved in detoxifying harmful substances and modifying chemicals that can be toxic to the cell. Hence, this statement is correct.

3. **Statement III: "SER is a major site for the synthesis of proteins."**
- This statement is **not true**. The rough endoplasmic reticulum (RER) is the site for protein synthesis due to the presence of ribosomes on its surface. The smooth endoplasmic reticulum does not play a major role in protein synthesis. Therefore, this statement is incorrect.

4. **Statement IV: "ER is a network of interconnected cisternae, tubules, and vesicles present in the endoplasm."**
- This statement is **true**. The endoplasmic reticulum is indeed a network of interconnected structures, including cisternae, tubules, and vesicles, found in the cytoplasm (endoplasm) of the cell. Thus, this statement is correct.

### Conclusion:
The statements that are **not true** about the endoplasmic reticulum are:
- Statement I
- Statement III

### Final Answer:
The correct option indicating the statements that are not true is **Option 2: First and Third.**

---