True for mammalian RBCs

Options

A. Nucleated and biconcave in shape
B. Enucleated and biconcave in shape
C. Enucleated and oval in shape
D. Nucleated and biconvex in shape

Answer

### Step-by-Step Solution:

1. **Understanding Red Blood Cells (RBCs)**:
- Red blood cells, or erythrocytes, are crucial components of blood that primarily function to transport oxygen from the lungs to various tissues in the body.

2. **Structure of Mammalian RBCs**:
- Mammalian RBCs are unique in their structure. They are **biconcave** in shape, which means they have a dip in the middle on both sides, resembling a doughnut without a hole. This shape increases the surface area for gas exchange.

3. **Nucleus in Mammalian RBCs**:
- Unlike many other vertebrates, mammalian RBCs are **enucleated**, meaning they do not contain a nucleus. This adaptation allows more space for hemoglobin, the protein responsible for oxygen transport, thus enhancing their oxygen-carrying capacity.

4. **Conclusion**:
- Based on the characteristics of mammalian RBCs, the correct statement is that they are **enucleated and biconcave in shape**.

### Final Answer:
- The true statement for mammalian RBCs is: **Enucleated and biconcave in shape**.

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