In plant physiology, which statement correctly describes water potential and its role in plant water transport?

• A. Water moves from higher to lower water potential; solute and pressure potentials influence flow from roots to leaves.
• B. Water moves from lower to higher water potential.
• C. Water potential is determined only by temperature.
• D. Water moves independently of solute potentials.

Answer: (A)

Water moves along a water-potential gradient, from higher to lower water potential, and in plants this gradient drives water from roots up to the leaves. Water potential (Ψ) is the sum of solute potential (Ψs) and pressure potential (Ψp). Adding solutes lowers Ψ (Ψs becomes more negative), while positive turgor in cells raises Ψ (Ψp). Along the plant, soil water usually has a higher Ψ than the leaf air spaces, where transpiration makes Ψ very negative, creating a continuous pull that moves water upward through the xylem and into cells along the path. Temperature doesn’t determine water potential, and water movement is not independent of solute potentials; the solute and pressure components together set the direction and flow of water.