Which of the following is a main source of cellular membranes :–

Options

A. Endoplasmic reticulum
B. Golgi body
C. Mitochondria
D. Nucleus

Answer

### Step-by-Step Solution:

1. **Understanding Cellular Membranes**:
- Cellular membranes are crucial structures that define the boundaries of cells and organelles. They are primarily composed of lipids and proteins.

2. **Identifying the Main Source**:
- The question asks for the main source of cellular membranes. To answer this, we need to consider which organelle is primarily responsible for the synthesis and transport of membrane components.

3. **Role of Endoplasmic Reticulum (ER)**:
- The endoplasmic reticulum (ER) is the key organelle involved in the production of cellular membranes. It comes in two forms: rough endoplasmic reticulum (RER) and smooth endoplasmic reticulum (SER).
- The RER is studded with ribosomes, which are involved in protein synthesis. The proteins synthesized here can be integrated into membranes or secreted.
- The SER, on the other hand, is primarily involved in lipid synthesis, which is essential for membrane formation.

4. **Transport of Lipids**:
- The smooth endoplasmic reticulum synthesizes lipids and transports them to the cell membrane, contributing to the formation of the phospholipid bilayer that makes up the cell membrane.

5. **Conclusion**:
- Based on the functions of the endoplasmic reticulum, we conclude that it is the main source of cellular membranes. Other options like Golgi apparatus, mitochondria, and nucleus do not primarily contribute to membrane synthesis.

6. **Final Answer**:
- The correct answer is the **endoplasmic reticulum**.