Which of the following does not lose their nucleus at maturity?

Options

A. companion cells
B. Red blood cells
C. Vessel
D. Sieve tube cells

Explanation

To solve the question "Which of the following does not lose their nucleus at maturity?", we will analyze the options provided and determine which cell type retains its nucleus.

### Step-by-Step Solution:

1. **Identify the Options**: The question provides several options, including companion cells, red blood cells (RBCs), vessels, and sieve tube cells.

2. **Analyze Companion Cells**:
- Companion cells are part of the phloem tissue in plants.
- They are involved in the translocation of sugars.
- At maturity, companion cells retain their nucleus.

3. **Analyze Red Blood Cells (RBCs)**:
- RBCs are found in blood and are responsible for carrying oxygen.
- At maturity, RBCs lose their nucleus to create more space for hemoglobin, which allows them to carry more oxygen.

4. **Analyze Vessels**:
- Vessels are part of the xylem tissue in plants.
- They are involved in the transport of water and minerals.
- At maturity, vessels also lose their nucleus.

5. **Analyze Sieve Tube Cells**:
- Sieve tube cells are part of the phloem and are involved in the transport of food.
- Similar to vessels, sieve tube cells lose their nucleus at maturity.

6. **Conclusion**:
- Among the options analyzed, only the companion cells retain their nucleus at maturity.
- Therefore, the correct answer to the question is **companion cells**.

### Final Answer:
The cell type that does not lose its nucleus at maturity is **companion cells**.

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