Sucrose Unloading in Phloem at Sink

Steps:

• Sucrose unloads from phloem sieve tube into shoot tip, reducing solute concentration inside tube.
• Lower solute concentration raises water potential (makes it less negative) in sieve tube.
• Water follows sucrose out by osmosis, decreasing liquid volume in sieve tube.
• This maintains mass flow toward sink in phloem transport.

Why A is correct:

• Unloading sucrose decreases solute potential, making overall water potential less negative per the formula ψ = ψ_s + ψ_p.

Why the others are wrong:

• B: More negative potential and volume increase occur during sucrose loading at sources, not unloading.
• C: Identical to A, but listed as duplicate; no unique error.
• D: More negative potential contradicts reduced solutes from unloading.

Final answer: A