Adult human RBCs are enucleate. Which of the following statement (s) is/are most appropriate explanation for this feature ?
(1) They do not need to reproduce
(2) They are somatic cells
(3) They do not metabolise
(4) All their internal space is available for oxygen transport.

Options

A. Only (iv)
B. Only (i)
C. (i), (iii) and (iv)
D. (ii) and (iii)

Answer

To determine the most appropriate explanation for why adult human red blood cells (RBCs) are enucleate, we will evaluate each of the given statements:

1. **They do not need to reproduce**:
- This statement is true. RBCs do not reproduce themselves because they lack a nucleus, which is essential for cell division. Instead, they are produced in the bone marrow and have a limited lifespan.

2. **They are somatic cells**:
- This statement is misleading. While RBCs are indeed somatic cells (as opposed to germ cells), the presence or absence of a nucleus does not define them as somatic. Therefore, this statement is not a relevant explanation for their enucleate nature.

3. **They do not metabolize**:
- This statement is also true. Adult human RBCs lack organelles, including a nucleus, which means they do not carry out metabolic processes in the same way that other cells do. Their primary function is to transport oxygen, and they rely on anaerobic metabolism for energy.

4. **All their internal space is available for oxygen transport**:
- This statement is correct. The absence of a nucleus allows more space within the RBC for hemoglobin, the protein responsible for oxygen transport. This adaptation maximizes their efficiency in carrying oxygen throughout the body.

### Conclusion:
The most appropriate explanations for the enucleate nature of adult human RBCs are statements (1), (3), and (4).

### Final Answer:
- The correct statements are: (1) They do not need to reproduce, (3) They do not metabolize, and (4) All their internal space is available for oxygen transport.