Question

Water potential is a measure of

• A. Free energy status of water
• B. Free chemical energy status of water
• C. Free thermal energy status of water
• D. Entropy of water

Hint:

Water potential is a thermodynamic measure of the free energy of water. Pure water has the highest free energy status, defined as zero, while soil water potentials are typically negative.

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
Water potential (\(\psi\)) is a fundamental thermodynamic concept used to describe the energy state of water in soil, plants, and the atmosphere.
Water always moves spontaneously from an area of higher water potential to an area of lower water potential.
Detailed Explanation:
Thermodynamically, water potential is defined as the difference between the free energy of water in a given system and the free energy of pure, free water at standard reference conditions (same temperature, pressure, and elevation).
It represents the potential energy of water per unit volume relative to pure water.
Pure water is assigned a reference water potential of \( 0 \).
The presence of dissolved solutes (osmotic potential) or capillary forces in soil pores (matric potential) restricts the movement of water molecules, lowering their free energy status to a negative value.
Therefore, water potential is a direct measure of the free energy status of water, which drives its movement through the soil-plant-atmosphere continuum.

Step 2: Final Answer:
Water potential is a measure of the free energy status of water.