A nucleus is absent in the mature

Options

A. Sieve tube cells
B. Mammalian erythrocytes
C. Monocytes
D. Both A and B

Answer

**Step-by-Step Solution:**

1. **Understanding the Question**: The question asks which cells lack a nucleus in their mature form. The options provided include sieve tube cells, mammalian erythrocytes (red blood cells), monocytes, and both A and B.

2. **Identifying Sieve Tube Cells**: Sieve tube cells are specialized cells found in the phloem of vascular plants. Their primary function is to transport nutrients, particularly sugars, throughout the plant. During their maturation, these cells lose their nucleus.

3. **Identifying Mammalian Erythrocytes**: Mammalian erythrocytes, commonly known as red blood cells (RBCs), are responsible for transporting oxygen in the blood. During their development in the bone marrow, they also lose their nucleus and other organelles to maximize space for hemoglobin, the protein that carries oxygen.

4. **Considering Monocytes**: Monocytes are a type of white blood cell that plays a role in the immune response. Unlike sieve tube cells and erythrocytes, monocytes do contain a nucleus in their mature form.

5. **Analyzing the Options**: Based on the information gathered:
- Sieve tube cells (A) - no nucleus in mature form.
- Mammalian erythrocytes (B) - no nucleus in mature form.
- Monocytes - have a nucleus in mature form.
- Therefore, the correct answer is both A (sieve tube cells) and B (mammalian erythrocytes).

6. **Final Answer**: The correct choice is option D: both A and B.

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