D.2.3 Water Potential

Solvent

Liquid the solute dissolves in

Solute

substance dissolve

Solution

solute dissolves in solvent

Solvation

the ability of a substance to dissolve solutes to form a solution

Solvent property

Allows many substances to dissolve in water

Polar substances

dissolve in water

Isotonic

A solution that has the same concentration as another solution

Hypertonic

Having a higher concentration of solute than another solution.

Hypotonic

Having a lower concentration of solute than another solution

Water movement

Water moves from low solute concentration to high solute concentration

Limitation on water movement

Some are too large or polar & require a protein channel

Aquaporins

water channel proteins

Osmosis

Movement of water across a semipermeable membrane from a solution

dynamic equilibrium

when the solution is isotonic, but with moving water

Where cell walls exist

plants, algae, prokaryotes, fungi

Experience of a hypotonic medium in cells with a cell wall

high turgor pressure

Experience of hypertonic solution cells with a cell wall

Will become plasmalyzed

Cells in hypertonic solutions

Cells will swell and lyse

Cells in hypotonic solutions

Cells will shrink

Unicellular organism --> water=hypertonic BUT organism=hypotonic

water is going to rush in

Kidney's role in multicellular organism

filters blood to maintain set point for water & salts

Reason why organs must be in isotonic solution when delivered

Hypotonic solution will rush in water and leading to explosion of cells. Hypertonic solution will allow water to escape leading to shrinking of organ.

Water potential

energy of water per unit volume compared to pure water

Use of water potential

To predict movement of water

Unit of water potential

kilopascals (kPa)

Potential energy

stored energy

Water movement based on potential energy

High to low

Reason why water moves from high to low potential

Higher water potential molecules have more free energy

Water potential formula

Ψ = Ψs + Ψp

Characteristic of solute potential

can range from zero down since water in solutes is busy therefore reducing free energy

Characteristic of pressure potential

Positive inside cells as they make plant cells turgid increasing the ability of water to move outwards easily

Pressure potential in xylems

Negative

Reason why pressure potential in xylems are negative

Because there's a pull on water which makes it less free for it to move

Water potential in plant cells in hypotonic solution

cell=negative, solute=less negative --> water will move into the cell since it has a lower water potential than the solute

Water potential in plan cells in hypertonic solution

cell=negative, solute=more negative --> water will move out of the cell