Restriction endonucleases are obtained from

Options

A. Bacteria
B. All prokaryotic cells
C. Bacteriophages
D. Plasmids

Answer

### Step-by-Step Solution:

1. **Understanding Restriction Endonucleases**:
- Restriction endonucleases are enzymes that cut DNA at specific sequences. They are crucial tools in molecular biology for gene cloning and DNA manipulation.

2. **Identifying the Source**:
- These enzymes are primarily derived from bacteria. They function by recognizing specific nucleotide sequences in the DNA and cleaving the strands at these sites.

3. **Analyzing the Options**:
- **Option A: Bacteria** - This is the correct answer, as restriction endonucleases are indeed bacterial enzymes.
- **Option B: All Prokaryotic Cells** - This is incorrect because not all prokaryotic cells produce restriction enzymes. For example, archaebacteria and cyanobacteria do not.
- **Option C: Bacteriophages** - This is incorrect. Bacteriophages are viruses that infect bacteria and do not produce restriction endonucleases.
- **Option D: Plasmids** - This is also incorrect. Plasmids are extra-chromosomal DNA found in bacteria but do not produce restriction enzymes themselves.

4. **Conclusion**:
- Based on the analysis, the correct answer is **Option A: Bacteria**.