xylem part 1

What physical properties does the shape of water molecules give

Excellent solvent

High specific heat capacity and latent heat of vaporization

Surface tension - adhesion and cohesion

Tensile strength

What bonds do water molecules make

H bonds and can form up to 4 with other water molecules

Water contact angle

The angle between a water droplet and surface to measure if the surface is hydrophilic (less than 90) or hydrophobic (greater than 90)

Diffusion

Spontaneous movement of solutes from regions of higher to lower concentration

Spontaneous processes occur towards

More entropy (disorder)/ less free energy

The time required for diffusion across a certain distance is proportional to

The square of the distance

Osmosis

Diffusion of water across a selectively permeable barrier

What is osmosis limited by

The volume of the cell wall. The cell wall resists deformation and creates an inward force increasing hydrostatic pressure within cell but not volume.

what does free energy drive into the plant

Biochemical rxns, solute concentration, and long distance transport

Free energy

The potential for performing work

G = force * distance

Chemical potential

Relative quantitative expression of free energy associated with a substance

Water potential

Chemical potential of water divided by the volume of 1 mol of water.

Free energy of water per unit volume

Unit for water potential

Pascal (Pa)

How does water move

From high to low water potential

What factors influence water potential

Concentration, pressure, gravity

Does gravity play a part in water potential on the cellular level

No

Water potential formula

Solute potential

Reduce free energy of water by diluting the water. Lowers water potential

What is solute potential independent of

The nature of the solute

Solute potential formula

S = -RTc

The more solute the more -ve solute potential

What do solutes lower

Water potential in the -ve range

Pressure potential

Positive hydrostatic pressure raises water potential – turgor

Negative hydrostatic pressure lowers water potential – tension

How is hydrostatic pressure measured?

As the deviation from standard atmospheric pressure

When does pressure potential equal zero for water

Add atmospheric pressure

Gravity potential

= pgh

pgh has a constant value of

0.01 MPa m-1

Gravity potential in cells

Typically omitted

What part of the tree has more water potential?

The roots because water moves from high to low water potential

When does wilting occur?

When turgor pressure reaches zero

For water to move up the tree, which part should have a lower water potential

The leaves

What do rigid cell walls allow

Plant cells to accommodate changes in water potential with large changes and pressure potential

Aquaporins

Water specific channels to facilitate water movement across membranes. Can be reversibly gated based on cellular stimuli