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Chapter 36 Notes
Transport in Plants
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 = YP + YS
- YP: pressure potential
- YS: 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: TranspirationCohesion-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