RBCs in human are :

Options

A. Biconcave and nucleated
B. Biconvex and nucleated
C. Biconvex and enucleated
D. Biconcave and enucleated

Answer

### Step-by-Step Solution:

1. **Understanding RBCs**: RBCs stand for red blood cells, which are also known as erythrocytes. They play a crucial role in transporting oxygen throughout the body.

2. **Shape of RBCs**: The shape of human RBCs is described as biconcave. This means they have a disc-like shape that is indented on both sides, resembling a doughnut without a hole.

3. **Nucleus Presence**: In most animals, RBCs contain a nucleus. However, in mammals, including humans, RBCs are unique because they do not have a nucleus. This characteristic makes them enucleated.

4. **Analyzing Options**:
- **Option 1**: Biconcave and nucleated - Incorrect, as human RBCs are enucleated.
- **Option 2**: Biconvex and nucleated - Incorrect, as the shape is biconcave, not biconvex.
- **Option 3**: Biconvex and enucleated - Incorrect, as the shape is biconcave.
- **Option 4**: Biconcave and enucleated - Correct, as this accurately describes human RBCs.

5. **Conclusion**: The correct answer to the question "RBCs in humans are:" is **biconcave and enucleated**.