According to the pressure flow hypothesis
A. Phloem loading produces a hypertonic condition in the sieve tubes.
B. Water potential gradient facilitates the mass movement in the phloem.
C. Phloem unloading is a passive process .

Options

A. A&B are incorrect
B. B &C are incorrect
C. A & B are correct
D. A & C are correct

Answer

**Step-by-Step Solution:**

1. **Understanding the Pressure Flow Hypothesis**: The pressure flow hypothesis, proposed by scientist Munch, explains how substances are transported in plants, particularly through the phloem. It describes the movement of sugars (mainly sucrose) from the source (where they are produced) to the sink (where they are utilized).

2. **Phloem Loading**: When photosynthesis occurs in the leaves, glucose is produced and converted into sucrose. This sucrose is then loaded into the sieve tubes of the phloem. This process creates a hypertonic condition in the sieve tubes because the concentration of sucrose is higher than that in the surrounding tissues.

3. **Water Movement**: The hypertonic condition in the sieve tubes causes water from the adjacent xylem vessels to move into the phloem by osmosis. This influx of water increases the pressure within the sieve tubes, creating a high-pressure area at the source.

4. **Mass Flow**: The high pressure at the source drives the movement of the sucrose solution through the phloem towards the sink, where the pressure is lower. This movement is facilitated by the water potential gradient.

5. **Phloem Unloading**: At the sink, sucrose is unloaded from the phloem. This unloading process typically requires energy, meaning it is an active transport process rather than a passive one.

6. **Evaluating the Statements**:
- **Statement A**: "Phloem loading produces a hypertonic condition in the sieve tubes." - This statement is **true**.
- **Statement B**: "Water potential gradient facilitates the mass movement in the phloem." - This statement is **true**.
- **Statement C**: "Phloem unloading is a passive process." - This statement is **false** as unloading often requires active transport.

7. **Conclusion**: Based on the evaluation of the statements, the correct answers are A and B, while C is incorrect.

**Final Answer**: A and B are correct; C is incorrect.

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