The smooth E.R. is generally made up of :-

Options

A. Cisternae
B. Tubules
C. Vesicle
D. All the above

Answer

To answer the question "The smooth E.R. is generally made up of:", we will analyze the structure and components of the smooth endoplasmic reticulum (smooth ER).

### Step-by-Step Solution:

1. **Understanding Smooth ER**:
- The smooth endoplasmic reticulum is a type of endoplasmic reticulum that lacks ribosomes on its surface. This distinguishes it from rough ER, which has ribosomes.

2. **Structure of Smooth ER**:
- The smooth ER is primarily composed of tubular structures. These tubules are interconnected and can sometimes branch out, forming a network.

3. **Components of Smooth ER**:
- The smooth ER is not made up of cisternae (which are flattened membrane-bound sacs found in rough ER) or vesicles (small membrane-bound sacs that transport materials within the cell).

4. **Conclusion**:
- Therefore, the smooth endoplasmic reticulum is generally made up of tubules.

5. **Final Answer**:
- The correct option is "tubules".