Chapter 36: Resource Acquisition
and Transport in Plants
36.1
Admit Slip
3. List 3 words you think of
when you look at the
picture/diagram
2. Write 2 ideas you have
based on the picture and
your words. If possible, use
your words as you write your
ideas.
1. Write 1 question you have.
Transport
• Begins with the movement of water and
solutes across a cell membrane
– Solutes diffuse down electrochemical gradients
– Passive Transport: No energy required to move
materials across the membrane
• Diffusion, Osmosis
– Active Transport: energy is required to move
materials across the membrane
• Usually requires a transport protein in membrane
• Proton pump=most important transport protein
Transport
• Proton Pump
– Creates electrochemical gradient by using ATP to
pump H+ ions across a membrane. This changes
the electrochemical gradient of the membrane
and powers transport
Transport of Water
• Osmosis is the passive transport of water
across a membrane
– Water moves from high water potential to low
water potential
Movement of water in plants
• Water relations in
plant cells is based on
water potential
cells are flaccid
plant is wilting
– osmosis through
aquaporins
• transport proteins
– water flows from high
potential to low
potential
cells are turgid
2009
Transport in Water
• Potential water equation: Ѱ= Ѱs+ Ѱp
• Ѱ=water potential, Ѱs=solute potential, Ѱp=
pressure potential
• The Ѱs of pure water=0. Adding solutes lowers
the potential (always negative)
• Pressure Potential refers to the cell contents
pressing on the plasma membrane, (turgor
Pressure). If the cell loses water, the pressure
potential becomes more negative (wilting of
plant)
Practice Calculation
Potential water equation: Ѱ= Ѱs+ Ѱp
– Ѱ=water potential, Ѱs=solute potential, Ѱp= pressure potential
• 1. If a cell’s ΨP = 3 bars and its ΨS = -4.5 bars, what is the
resulting Ψ?
• 2. The cell from question #1 is placed in a beaker of sugar
water with ΨS = -4.0 bars. In which direction will the net
flow of water be?
Transport in Water
• Aquaporins: transport proteins (channels) in
the membrane that allow the passage of
water through the hydrophobic region of the
lipid bilayer.
• Bulk Flow: movement of water through the
plant
– Moves from regions of high pressure to regions of
low pressure
– Xylem and Phloem move materials through bulk
flow
Chapter 36: Resource Acquisition
and Transport in Plants
36.2
Absorption of Water and Minerals
from the Soil
• Most absorption happens near the
root tips through the root hairs
• Pathway of water/minerals: root
epidermiscortexvascular
cylindertracheidsshoot
system
• Roots and fungi have a symbiotic
relationship called mycorrhizae.
Increases absorption and uptake
of water/minerals by plants
Chapter 36: Resource Acquisition
and Transport in Plants
36.3
Lateral Transport from Roots to Shoots
• Apoplastic Route: movement of water and
minerals between cells
• Symplastic Route: occurs after the solution
crosses a plasma membrane
• Casparian Strip: waxy material that blocks
passage of materials, control point for passage
of materials (passing the casparian strip the
solution passes the plasma membrane
Lateral Transport
Transport
• Once water and minerals get to the xylem,
they are transported through the plant by bulk
flow. Eventually they exit the plant through
the leaves
• Transpiration: loss of water vapor primarily
from the leaves or other parts in contact with
air.
– This plays an important part in the movement of
water through the plant
Water Movement in Plants
• 2 mechanisms:
1. Root Pressure: water entering the cortex creates
positive pressure. This pushes water up the
xylem.
•
Does not have the force to push water up to the top
of trees
2. Transpiration-cohesion-tension Mechanism:
water is lost through transpiration due to lower
water potential of air. Cohesion and adhesion of
water (from hydrogen bonding) enables it to
create a column and be drawn up through the
xylem
Rise of water in a tree by bulk flow
• Transpiration pull
– adhesion & cohesion
• H bonding
– brings water & minerals
to shoot
• Water potential
– high in soil 
low in leaves
• Root pressure push
– due to flow of H2O from
soil to root cells
– upward push of xylem
sap
Chapter 36: Resource Acquisition
and Transport in Plants
36.4
Stomata
• Help regulate the rate of transcription
• Large surface area increases photosynthesis
(gas into plant cell)/increases water loss
• Guard cells open and close the stomata
– Control gases coming in and water moving out
• Control the size of
stomata by changing
shape
– When guard cells take up
K+ from surrounding
cells, water potential
decreases in guard
cells=take up water. Cells
swell and buckle=open
pore
– Guard cells lose K+, cells
lose water, become less
bowed=pore closes
Guard Cells
Guard Cells
• Stimulated to open by:
– Light
– Loss of carbon dioxide in leaf
– Normal circadian rhythms
• Circadian rhythms=part of plants internal clock
mechanism. Cycle with intervals for 24 hours.