E.R. is made of

Options

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

Answer

**Step-by-Step Solution:**

1. **Definition of E.R.:**
- E.R. stands for Endoplasmic Reticulum, which is an essential cellular organelle found in eukaryotic cells.

2. **Structure of E.R.:**
- The Endoplasmic Reticulum consists of a network of membranes that form tubules and flattened sacs. These structures can be classified into two main types: tubule-like structures and cisternae (flattened sacs).

3. **Types of Endoplasmic Reticulum:**
- There are two types of Endoplasmic Reticulum:
- **Rough Endoplasmic Reticulum (RER):** This type has ribosomes attached to its surface, giving it a "rough" appearance. It is involved in protein synthesis and processing.
- **Smooth Endoplasmic Reticulum (SER):** This type lacks ribosomes, making it "smooth." It is involved in lipid synthesis, detoxification, and calcium ion storage.

4. **Formation of Vesicles:**
- The Endoplasmic Reticulum can also form vesicles, which are small membrane-bound sacs that transport materials within the cell.

5. **Conclusion:**
- In summary, the Endoplasmic Reticulum is made up of tubule-like structures, cisternae, and can also form vesicles. It is classified into rough and smooth types based on the presence or absence of ribosomes.