Water potential gradient drives flow toward xylem

Steps:

• Water flows from higher (less negative) to lower (more negative) water potential.
• Xylem has the lowest water potential, creating a pull.
• Water enters xylem from cell D, so ψ_D > ψ_xylem.
• Gradient decreases from cell A (farthest) through B, C, D toward xylem, making A least negative.

Why A is correct:

• Cell A has the highest water potential as the source in the symplastic pathway gradient, per water potential definition (ψ = ψ_s + ψ_p).

Why the others are wrong:

• B has lower ψ than A due to proximity to xylem.
• C has even lower ψ, closer to flow path end.
• D has lowest ψ among cells, just above xylem to enable entry.

Final answer: A