Which of the following subcellular structures cannot be isolated ?

Options

A. nuclei
B. lysosomes
C. Mitochondria
D. endoplasmic reticulum

Answer

To solve the question "Which of the following subcellular structures cannot be isolated?", we will analyze each option provided in the context of cell biology and the methods used to isolate cellular components.

### Step-by-Step Solution:

1. **Understanding Subcellular Structures**:
- Subcellular structures are components within a cell that perform specific functions. Common examples include the nucleus, lysosomes, mitochondria, and endoplasmic reticulum.

2. **Isolation Techniques**:
- The isolation of subcellular structures typically involves three main steps:
- **Extraction**: Breaking open the cells to release their contents.
- **Homogenization**: Mixing the cell contents to ensure a uniform solution.
- **Centrifugation**: Spinning the mixture at high speeds to separate components based on size and density.

3. **Analyzing Each Option**:
- **Option 1: Nuclei**:
- Nuclei can be isolated using lysis of the cell followed by centrifugation. Therefore, this option is incorrect.
- **Option 2: Lysosomes**:
- Lysosomes can also be isolated from animal tissues using differential centrifugation. Thus, this option is incorrect.
- **Option 3: Mitochondria**:
- Mitochondria can be isolated using similar techniques as nuclei and lysosomes. Therefore, this option is incorrect.
- **Option 4: Endoplasmic Reticulum**:
- The endoplasmic reticulum is more complex to isolate due to its continuous connection with the nuclear membrane and its extensive network throughout the cytoplasm. This makes it difficult to isolate as a distinct entity.

4. **Conclusion**:
- Based on the analysis, the endoplasmic reticulum is the subcellular structure that cannot be easily isolated from the cell. Therefore, the correct answer is **Option 4: Endoplasmic Reticulum**.

### Final Answer:
**Option 4: Endoplasmic Reticulum**