Apoplast is the system of adjacent cell walls that is continuous throughout the plant except at the

Options

A. Plasmodesmata
B. Casparian strips of the endodermis
C. Tracheids
D. Vessel elements

Answer

### Step-by-Step Solution:

1. **Understanding Apoplast**: The apoplast refers to the system of adjacent cell walls and intercellular spaces that allow for the movement of water and solutes through the plant without crossing the cell membranes (protoplasts).

2. **Identifying the Pathways**: There are three main pathways for water movement in plants:
- **Apoplastic Pathway**: Movement through cell walls and intercellular spaces.
- **Symplastic Pathway**: Movement through the cytoplasm of cells, connected by plasmodesmata.
- **Vascular Pathway**: Involves movement through the vascular tissues (xylem and phloem).

3. **Recognizing Interruptions in the Apoplast**: The apoplastic pathway is generally continuous but is interrupted at certain points. One significant interruption occurs at the Casparian strips of the endodermis, which forces water to enter the symplastic pathway.

4. **Evaluating the Options**:
- **Plasmodesmata**: These are channels between plant cells that facilitate the symplastic pathway, so they do not interrupt the apoplast.
- **Casparian Strips of Endodermis**: These are the correct answer as they interrupt the apoplastic pathway, directing water into the symplastic pathway.
- **Tracheids and Vessel Elements**: These are part of the xylem and facilitate water transport but do not interrupt the apoplast.

5. **Conclusion**: The correct answer to the question is that the apoplast is continuous throughout the plant except at the **Casparian strips of the endodermis**.

### Final Answer:
**The correct answer is B: Casparian strips of endodermis.**

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