Which of the following is a living cell which lacks nucleus on maturity ?

Options

A. Complementary cell
B. Mature sieve tube element
C. Mature vessel element
D. Companion cell

Answer

To solve the question "Which of the following is a living cell which lacks nucleus on maturity?", we need to analyze the options provided and understand the characteristics of each cell type mentioned.

### Step-by-Step Solution:

1. **Understanding Cell Types**:
- **Sieve Tube Elements**: These are part of the phloem tissue and are responsible for the transport of nutrients. They are living cells but lose their nucleus at maturity.
- **Vessel Elements**: These are part of the xylem tissue and are involved in the transport of water. They are dead cells at maturity and do not have a nucleus.
- **Companion Cells**: These cells are also part of the phloem and are closely associated with sieve tube elements. They are living cells and retain their nucleus at maturity.

2. **Identifying Living Cells**:
- We need to focus on living cells that lack a nucleus when they mature.
- Sieve tube elements fit this description as they are living cells that lose their nucleus during maturation.

3. **Eliminating Incorrect Options**:
- **Vessel Elements**: These are not living cells at maturity, so they cannot be the answer.
- **Companion Cells**: These retain their nucleus and are thus not the correct answer.

4. **Conclusion**:
- The only cell type that is living and lacks a nucleus at maturity is the **Sieve Tube Element**.

### Final Answer:
The correct answer is **Sieve Tube Element**.

---