Phloem loading drives osmotic water influx Steps:

• Sucrose is actively loaded from mesophyll cells into the phloem sieve tube element.
• Solute concentration rises inside the sieve tube.
• Water potential decreases (becomes more negative) due to lower solute potential.
• Osmosis draws water from xylem or mesophyll, increasing liquid volume in the sieve tube.

Why B is correct:

• Osmosis dictates that higher solute concentration lowers water potential (ψ_s more negative in ψ = ψ_s + ψ_p), prompting water entry that expands phloem sap volume and builds turgor pressure.

Why the others are wrong:

• A: Water potential becomes less negative (incorrect; solutes make it more negative); volume decreases (incorrect; water influx increases it).
• C: Water potential becomes less negative (incorrect; loading makes it more negative); volume increases (effect is right but ψ is wrong).
• D: Water potential becomes more negative (correct); volume decreases (incorrect; osmosis increases volume).

Final answer: B