Which of the following obstructs apolastic pathway of water in roots?

Options

A. Casparian strips of the pericycle
B. Casparian strips of the endodermis
C. Casparian strips of the hypodermis
D. Lignin strips of the endodermis

Answer

To solve the question "Which of the following obstructs the apoplastic pathway of water in roots?", we need to understand the concept of the apoplastic pathway and the role of Casparian strips in plant roots.

### Step-by-Step Solution:

1. **Understand the Apoplastic Pathway**:
- The apoplastic pathway refers to the movement of water and solutes through the cell walls and intercellular spaces of plant roots, bypassing the cytoplasm of cells. This pathway allows for the rapid movement of water but does not allow for selective absorption of solutes.

2. **Identify the Role of Casparian Strips**:
- Casparian strips are bands of cell wall material that are impregnated with suberin, a waxy substance. They are found in the endodermis of roots and play a crucial role in regulating the movement of water and minerals into the vascular system of the plant.

3. **Determine the Obstruction of the Apoplastic Pathway**:
- The presence of Casparian strips in the endodermis creates a barrier that forces water and solutes to enter the symplastic pathway (through the cytoplasm of cells) instead of continuing through the apoplastic pathway. This is because the Casparian strips prevent water from moving freely through the cell walls.

4. **Analyze the Options Provided**:
- A. Casparian strips of pericycle: Not primarily responsible for obstructing the apoplastic pathway.
- B. Casparian strips of endodermis: Correct answer, as these strips block the apoplastic pathway.
- C. Casparian strips of hypodermis: Not a significant factor in obstructing the apoplastic pathway.
- D. Lignin strips of endodermis: While lignin can provide structural support, it does not specifically obstruct the apoplastic pathway like Casparian strips do.

5. **Conclusion**:
- Based on the understanding of the apoplastic pathway and the function of Casparian strips, the correct answer is **B. Casparian strips of endodermis**.