Water moves from higher to lower water potential

Steps:

• Water potential (Ψ) decreases from leaf cell to air spaces to air for evaporation to occur.
• Compare Ψ values: higher Ψ in source means water flows to lower Ψ in sink.
• Sequence must show Ψ leaf cell > Ψ air spaces > Ψ air (all negative for tension).
• Only option A shows decreasing Ψ gradient from cell (-1 MPa) to spaces (-7 MPa) to air (-100 MPa).

Why A is correct:

• Water flows down the gradient per the water potential equation (Ψ = Ψ_s + Ψ_p), enabling transpiration from leaf to atmosphere.

Why the others are wrong:

• B: Positive Ψ in air spaces blocks flow; gradient reverses (cell lowest).
• C: Positive Ψ in air spaces and air prevents evaporation; no decreasing gradient.
• D: Positive Ψ in cell and air spaces indicates no tension for water movement.

Final answer: A