The fundamental cause of the sickle-cell disease is a change in the structure of :

Options

A. blood
B. Capillaries
C. hemoglobin
D. red cells

Answer

To solve the question regarding the fundamental cause of sickle-cell disease, we need to analyze the components involved in this condition step by step.

### Step-by-Step Solution:

1. **Understanding Sickle-Cell Disease**: Sickle-cell disease is a genetic disorder that affects the shape and function of red blood cells (RBCs). Under normal circumstances, RBCs are disc-shaped and flexible, allowing them to move easily through blood vessels.

**Hint**: Think about the normal shape of red blood cells and how it relates to their function.

2. **Identifying the Change**: In sickle-cell disease, a mutation occurs in the gene that codes for hemoglobin, the protein in red blood cells responsible for carrying oxygen. This mutation leads to the production of abnormal hemoglobin known as hemoglobin S (HbS).

**Hint**: Consider what component of the red blood cells is responsible for oxygen transport and how a mutation could affect it.

3. **Result of the Mutation**: The presence of hemoglobin S causes red blood cells to become rigid and take on a crescent or sickle shape, especially under low oxygen conditions. This altered shape can block blood flow in small blood vessels, leading to pain and various complications.

**Hint**: Reflect on how the shape of the red blood cells changes and the implications it has for blood circulation.

4. **Conclusion**: The fundamental cause of sickle-cell disease is a change in the structure of hemoglobin due to a genetic mutation. This change directly affects the shape of red blood cells, leading to the characteristic sickle shape.

**Hint**: Summarize the relationship between the mutation, hemoglobin, and the shape of red blood cells.

### Final Answer:
The fundamental cause of sickle-cell disease is a change in the structure of hemoglobin.