Chapter 36 Notes

Concept 36.1

Concept 36.1
Transport in plants occurs on 3 levels
- the uptake and loss of water by individual cells
- short distance transport of substances from cell to cell at the level of tissues and organs
- long distance transport of sap within xylem and phloem of the whole plant

Concept 36.1
Uptake and loss of water by cells
- plant cell membranes are selectively permeable
- use of transport proteins
/selective channels
- transport can be active or passive

Concept 36.1
- proton pump: hydrolyzes ATP and uses the released energy to pump H + ions out of the cell
- forms a H + gradient
- plant cells use the energy from the gradient to drive the transport of many different solutes
- ex. movement of K +

Concept 36.1

Concept 36.1
Differences in water potential drive water transport in plant cells
Osmosis: the net uptake or loss of water by a cell
- high concentration to low
In plants, the cell wall makes physical pressure a factor of osmosis

Concept 36.1
Water potential: the combined effect of solute concentration and pressure.
- psi ( Y )
- water will move from the solution with the higher water potential to the solution with the lower water potential

Concept 36.1

Concept 36.1
The combined effects of pressure and concentration
Y = Y
P
+ Y
S
Y
P
: pressure potential
Y
S
: solute potential

Concept 36.1

Concept 36.1
Bulk flow functions in long distance transport
Bulk flow: the movement of fluid driven by pressure
- water and solutes move the xylem vessels and sieve tubes
- transpiration reduces pressure in xylem which creates tension

Concept 36.2
Most absorption occurs near root tips
- soil particles adhere to root hairs
- the soil sln. flows into the walls of the epidermal cells and into the root cortex
- mycorrhizae absorb water and minerals and then transfers them to the plant

Concept 36.2

Concept 36.2

Concept 36.3
Root pressure: water flows in from the root cortex, generating a positive pressure that forces fluid up the xylem
Root pressure causes guttation: when more water enters leaves than is transpired and the excess is forced out
Root pressure can only force water up a few meters, not the major force

Concept 36.3
Pulling up xylem sap: Transpiration-
Cohesion-Tension Theory
Transpiration
-when stomata open water exits the leaf
- move from [high] to [low]

Concept 36.3

Concept 36.3
Cohesion
- water molecules will bond to each other with hydrogen bonds
- water molecules exiting the xylem tug on adjacent molecules
- the pull is relayed

Concept 36.3
Tension
- the upward pull creates tension within the xylem
- the small diameter of the tracheids helps overcome the force of gravity