Xylem walls are`

Options

A. Positively charged
B. Negatively charged
C. Electrochemically neutral
D. Differentially permeable.

Answer

### Step-by-Step Solution

1. **Understanding Xylem Composition**:
- Xylem is primarily composed of dead cells that have thick lignified secondary cell walls. This composition is crucial for its function in transporting water and minerals from roots to other parts of the plant.

2. **Identifying the Charge of Xylem Walls**:
- The walls of xylem cells are negatively charged. This negative charge is significant for the interaction of xylem with various ions in the plant.

3. **Reason for Negative Charge**:
- The negative charge on xylem walls arises from specific chemical groups present in the cell wall components. Notably, the carboxyl groups found in pectin contribute to this negative charge.

4. **Components Contributing to Charge**:
- Two key components are responsible for the negative charge:
- **Galacturonic Acid**: A component of pectin that contributes to the overall negative charge.
- **Glucuronic Acid**: Found in lignin, another component of the xylem walls, which also contributes to the negative charge.

5. **Interaction with Cations**:
- Due to the negative charge, xylem walls tend to bind with positively charged ions (cations), such as calcium ions. This interaction is essential for maintaining ion balance and facilitating nutrient transport within the plant.

6. **Conclusion**:
- Based on the above points, we conclude that xylem walls are negatively charged due to the presence of carboxyl groups, galacturonic acid, and glucuronic acid in their structure.

### Final Answer
Xylem walls are negatively charged.

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