ER is extensively developed and abundant in

Options

A. liver
B. sperms
C. resting cells
D. all correct

Answer

### Step-by-Step Solution:

1. **Understanding Endoplasmic Reticulum (ER)**:
- The endoplasmic reticulum (ER) is a membrane-bound organelle found in eukaryotic cells. It plays a crucial role in the synthesis of proteins and lipids.

2. **Types of Endoplasmic Reticulum**:
- There are two main types of ER:
- **Rough Endoplasmic Reticulum (RER)**: This type has ribosomes on its surface, which are involved in protein synthesis.
- **Smooth Endoplasmic Reticulum (SER)**: This type lacks ribosomes and is involved in lipid synthesis, carbohydrate metabolism, and detoxification processes.

3. **Analyzing the Options**:
- **Option A: Liver**: The liver is known for its extensive smooth endoplasmic reticulum, which is involved in detoxification of drugs and alcohol. It also has a significant amount of rough endoplasmic reticulum for protein synthesis.
- **Option B: Sperms**: Sperm cells primarily contain Golgi apparatus and mitochondria, but they do not have a significant amount of endoplasmic reticulum.
- **Option C: Resting Cells**: Resting cells do not actively divide and therefore do not require extensive ER, as they are not synthesizing proteins or lipids at a high rate.
- **Option D: All Correct**: This option suggests that all previous options are correct, which is not accurate based on the analysis.

4. **Conclusion**:
- The endoplasmic reticulum is most extensively developed and abundant in the **liver** due to its roles in detoxification and metabolism. Therefore, the correct answer is **Option A: Liver**.