[A]: Root pressure is largely responsible for ascent of sap in harbaceous plants.
[R]: Root pressure develops due to DPD & is maintained by the living cells.

Options

A. (a) If both A and R are true and R is the correct explanation of A
B. (b) If both A and R are true but R is not the correct explanation of A
C. (c) If A is true and R is false
D. (d) If both A and R are false

Answer

**Step-by-Step Solution:**

1. **Understanding the Assertion:**
- The assertion states that "Root pressure is largely responsible for the ascent of sap in herbaceous plants." This is a true statement. Root pressure plays a significant role in the movement of water and nutrients from the roots to the aerial parts of the plant.

2. **Understanding the Reason:**
- The reason given is that "Root pressure develops due to DPD (Diffusion Pressure Deficit) and is maintained by the living cells." This statement is also true. DPD is the difference in water potential between the root cells and the surrounding soil, which drives the uptake of water into the roots.

3. **Explaining the Mechanism:**
- In herbaceous plants, root pressure is generated when water is absorbed by the root hairs. This absorption occurs due to the DPD, which is a result of the concentration gradient between the soil and the root cells.
- The living cells in the roots actively transport minerals, which leads to an increase in solute concentration inside the root cells. This causes water to move into the roots, creating pressure that pushes water upward through the xylem.

4. **Ascent of Sap:**
- The ascent of sap refers to the upward movement of water from the roots to the leaves. In herbaceous plants, this is primarily facilitated by root pressure, which is effective due to the shorter height of these plants.
- Additionally, adhesion forces between water molecules and the xylem walls also contribute to this upward movement.

5. **Conclusion:**
- While both the assertion and reason are true, the reason does not directly explain the assertion. The assertion focuses on the role of root pressure in herbaceous plants, while the reason discusses the mechanism of root pressure development.

6. **Final Answer:**
- Therefore, the correct answer is option (B): Both assertion and reason are true, but the reason is not the correct explanation of the assertion.

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