Phloem loading lowers water potential and raises pressure

Steps:

• Sucrose is actively transported into sieve tubes, raising solute concentration.
• Increased solutes make water potential more negative via osmotic effects.
• More negative water potential pulls water from xylem into sieve tubes.
• Inflow of water increases hydrostatic (turgor) pressure for transport.

Why D is correct:

• Per pressure-flow hypothesis, sucrose loading decreases water potential (more negative) while increasing hydrostatic pressure to drive flow.

Why the others are wrong:

• A: Water potential becomes more negative, not less negative, and pressure rises.
• B: Water potential does not become less negative; it decreases osmotically.
• C: Hydrostatic pressure increases with water influx, not decreases.

Final answer: D