D2.3.8 Water potential as the potential energy of water per unit volume (HL)

In which units is water potential measured?

Kilopascals (kPa) or megapascals (MPa).

Why is potential energy meaningful only when describing differences or gradients?

Because potential energy is relative, and movement is driven by differences.

What effect do solutes have on water potential?

Solutes lower water potential.

What is solute potential and its value when solutes are added?

Solute potential (Ψs) is always negative because solutes reduce water potential.

How does positive pressure affect water potential?

It increases water potential.

What is the formula for calculating water potential?

Ψ = Ψs + Ψp.

What does a more negative water potential value indicate?

Lower water potential.

Why is water potential important for plant cells?

It explains turgidity in hypotonic solutions and plasmolysis in hypertonic solutions.

How does water potential drive water transport in plants?

Water moves from higher to lower water potential, helping move water from soil to leaves.

What is the relationship between solute concentration and water potential?

Higher solute concentration → lower (more negative) water potential.

What are the two main factors that determine water potential?

Solute concentration and pressure.

What is the reference point for measuring water potential?

Pure water at standard pressure and 20°C, with Ψ = 0 kPa.

What effect does pressure have on water potential?

Pressure can raise or lower water potential.

What is the difference between solute potential and pressure potential?

Solute potential (Ψs) is always negative; pressure potential (Ψp) can be positive or negative.

Give an example of how negative pressure affects water potential.

Negative pressure in xylem during transpiration lowers water potential.

How do organisms like Paramecium use water potential?

They use it to regulate water balance in their cells.

What happens to water potential in a turgid plant cell?

It increases because of positive pressure.

What happens to water potential in a plasmolyzed plant cell?

It decreases because pressure is lost.

Can water potential be measured absolutely?

No, it is measured relative to a reference point.

What is water potential?

Water potential (Ψ) is the potential energy of water per unit volume, showing the direction water will move.