Water Potential

What is happening during water potential?

solutions separated by semi permeable membranes create a potential for water to move

Water potential (Ψ)

tendency for water molecules to enter/leaves a solution by osmosis

How is water potential calculated?

Calculated by comparing phloem sap water potential to its surrounding environment or any two adjacent cells

Which way does water always move in?

It always moves toward the negative Ψ side until the concentration of molecules equalizes (from high to low water potential)

Where is water potential used?

In plants

Equation for water potential

Ψ_cell=Ψ_s+Ψ_p

The equation involves…

solute and pressure potential

Pressure potential (Ψ_p)

hydrostatic pressure to which water is subjected to by a plant cell wall

What number is pressure potential in?

Usually a positive number (because plant cells are turgid under normal conditions)

→ 0 when cell is in equilibrium

What’s another name for pressure potential? How is it also measured (unit)?

Turgor pressure measured in kPA (kilopascals)

Solute potential (Ψ_s)

measure of the reduction of water due to the pressure of solute molecules (osmotic pressure/potential)

What number is solute potential in?

negative number

Characteristics of hypotonic solutions

-less negative solute potential

-less negative water potential

-loses water by osmosis to the solution on the other side of the membrane

Characteristics of hypertonic solutions

-more negative solution potential

-more negative water potential

-gains water by osmosis from the other side of the membrane

Water always goes from ____ to ____

Hypo to hyper

What is the normal condition of a plant cell?

Turgor/turgid pressure

What’s another explanation of water potential?

measure of potential energy in water based on potential water movement between 2 systems (difference in potential energy between any given water sample and pure water)

What are the two factors that alter water potential?

Solute and pressure potential

What happens when more solute is added?

It decreases water potential

What happens when solute is removed?

It increases water potential

What is the difference in water potential under equilibrium?

No difference since water is not moving

Why does the fluid in xylem have a negative pressure potential value?

Because transpiration pull causes tension

Note: When plant cells are so full of water that they bulge, they are said to have high turgor pressure. This affects plant structure since there’s no inner skeleton

How does wilting occur in plants?

When the plant is under a very dry and hot environment; over fertilized