Summary
Combines solute and pressure potential to predict water movement into and between plant cells.
In depth
Ψ = Ψs + Ψp, measured in kPa or MPa. Pure water has Ψ = 0; solutes lower Ψs; pressure raises Ψp. Water moves from higher to lower Ψ, soil to root to leaf to air. Plasmolysis occurs at Ψp = 0.
Water potential is lower in cells with more solutes, drawing water in. Turgor pressure rises until it balances. Osmotic adjustment lets plants tolerate drought.
Key idea: water always moves from higher (less negative) to lower (more negative) potential.
Water potential is the potential energy of water relative to pure water, driving flow from high to low (less negative to more negative). Solute potential equals minus iRT times concentration, and pressure potential is positive in turgid cells and negative in xylem under tension. A flaccid cell has Ψp of zero, and a turgid cell has Ψp equal to minus Ψs, so Ψ is zero at equilibrium.
Typical gradient: soil (minus 0.3 MPa), root (minus 0.5), stem, leaf (minus 1.0 to minus 2.0), air (minus 50 to minus 100 MPa at 50 percent humidity). Plasmolysis occurs when cells lose water in a hypertonic solution, and the incipient plasmolysis point can estimate Ψs in a tissue, using sucrose dilutions. A pressure chamber (Scholander bomb) measures leaf water status.
Key idea: water moves according to total potential, not concentration alone.
Frequently asked questions
What is Plant Water Potential?
Combines solute and pressure potential to predict water movement into and between plant cells.
Which area of biology covers Plant Water Potential, and how advanced is it?
Plant Water Potential is one of the 56 topics in Plant Biology. It is rated Advanced, so it suits learners who want specialist depth. Related topics in this area include Cohesion-Tension Theory, Abscisic Acid and Drought, Transpiration.
Can you give an example of Plant Water Potential?
Potato tissue in sucrose solutions finds the cell's water potential.
What should I learn before Plant Water Potential?
Work through the Beginner topics in Plant Biology first, such as Plant Kingdom, Photosynthesis, Chlorophyll, then return to Plant Water Potential. Advanced topics assume the Intermediate vocabulary.
What topics are related to Plant Water Potential?
The closest topics to Plant Water Potential are Cohesion-Tension Theory, Abscisic Acid and Drought, Transpiration, Xylem. Comparing them side by side is a good way to see how the ideas connect.
How can I check that I understand Plant Water Potential?
Read the summary and the in-depth section, then use the quick check on the interactive lesson for Plant Water Potential. To practise the whole of Plant Biology, use the Plant Biology quiz.
How is Plant Water Potential different from Cohesion-Tension Theory?
Plant Water Potential: Combines solute and pressure potential to predict water movement into and between plant cells. Cohesion-Tension Theory: Water molecules stick together and to xylem walls, so evaporation tension pulls a continuous water column up. Read both side by side and note what each one explains.
How should I study Plant Water Potential step by step?
First, read the summary and write the definition in your own words. Second, read the in-depth section and note any example. Third, compare it with Cohesion-Tension Theory and explain the difference aloud. Finally, take the Plant Biology quiz and come back to this page for any question you miss.