1. Plant Transport
Chapters 28 & 29

2. REVIEW Transport – movement of molecules
Passive transport – down a concentration gradient with out energy
Osmosis – water
Aquaporins – assist water through bilayer
Facilitated Diffusion - large / polar molecules with transport protein
Simple diffusion – small molecules directly through bilayer
Active transport – against a concentration gradient with energy
Endocytocis – engulf large molecules
Exocytosis – remove large molecules
Pumps – ions / large molecules

4. Proton Pumps Cotransport
Creates a proton concentration gradient using ATP so other molecules can passively enter the plant cell.
Sugar, NO3-

6. Water Potential and Osmosis
Water moves from a higher water potential to a lower water potential
Ψ = Ψs + Ψp
Ψs = solute potential (osmotic potential)
Adding solutes to a solution lowers the solute potential and there fore the overall water potential
Ψp = pressure potential

9. Osmosis and Plant Cells
Isotonic – external solute concentration the same as the internal solute concentration
Water moves in and out at the same rate
Dynamic Equilibruim
Flaccid or wilty
Hypertonic – external solute concentration greater than the internal solute concentration
Water moves out of cell
Plasmolyszed
Hypotonic – internal solute concentration greater that external solute concentration
Water moves in
Turgid
Healthy plant

11. s = –0.9
(a)
0.4 M sucrose solution:
 = 0
s = –0.9
 = –0.9 MPa
 = 0
s = –0.7
 = –0.7 MPa
Initial flaccid cell:
 = 0
s = 0
 = 0 MPa
Distilled water:
Plasmolyzed
cell at osmotic
equilibrium
with its
surroundings
 = 0
 = –0.9 MPa
 = 0.7
s = –0.7
 = 0 MPa
Turgid cell
at osmotic
Initial conditions: cellular  > environmental . The cell
loses water and plasmolyzes. After plasmolysis is complete,
the water potentials of the cell and its surroundings are the
same.
Initial conditions: cellular  < environmental . There
is a net uptake of water by osmosis, causing the cell to
become turgid. When this tendency for water to enter is
offset by the back pressure of the elastic wall, water
potentials are equal for the cell and its surroundings.
(The volume change of the cell is exaggerated in this
diagram.)
(b)

12. Plant Cell Cell wall Cytoplasm Vacuole Plasmodesta (plasmadesmata)
Vacuolar membrane is called the tonoplast
Transport proteins in
the plasma membrane
regulate traffic of
molecules between
the cytosol and the
cell wall.
the vacuolar
membrane regulate
traffic of molecules
between the cytosol
and the vacuole.
Plasmodesma
Vacuolar membrane
(tonoplast)
Plasma membrane
Cell wall
Cytosol
Vacuole
Cell compartments. The cell wall, cytosol, and vacuole are the three main
compartments of most mature plant cells.
(a)
Figure 36.8a

14. Movement of materials Symplast Apoplast Bulk Flow
Movement of materials through the cytoplasm of the cell through the plasmodesta
Must cross cell membrane
Apoplast
Movement of material through the cell wall and extracellular spaces
Doesn’t have to cross cell membrane until it reaches the Casparian strip in the endodermis
Bulk Flow
Long distance transport
Xylem or phloem

17. Roots to Xylem
Root Pressure – pushing of water from the root to the xylem
Water and minerals travel through
The epidermis of the root
The cortex
The stele (inside the endodermis) which contains the tracheary elements
Xylem - tracheids – dead cells

19. Symplast vs. Apoplast Symplast Path Apoplast Path
In cytoplasm (protoplasm)
In cell walls
Water enters the root cells by crossing the plasma membrane
Water does not enter the root cells, but stays in the cell walls
Not blocked by the Casparian strip
Blocked at the endodermis by the Casparian strip
Can continue to xylem
Cannot continue to xylem unless it passes into the root cells through the plasma membrane

21. Key Symplast Apoplast Transmembrane route The symplast is the
continuum of
cytosol connected
by plasmodesmata.
The apoplast is
the continuum
of cell walls and
extracellular
spaces.
Transmembrane route
Symplastic route
Apoplastic route
Transport routes between cells. At the tissue level, there are three passages:
the transmembrane, symplastic, and apoplastic routes. Substances may transfer
from one route to another.
(b)

22. Bulk Flow – Water and Minerals
Transpiration – “pulling” of water from the roots to the leaves of plants
Hydrogen Bonding
Cohesion – keeps H2O together as it is pulled upward
Adhesion – keeps H2O from falling with gravity
Sticks to the sides of the xylem

23. Transpiration – pg 589 Chain Reaction
Water evaporates through open stomata
Pulls water from mesophyll cells to the stomata
Plant cells shrink (plasmolysize) due to the loss of water
Tension is created which pulls the water in the xylem up the plant to replace the water in the plasmolysized cells

24. Water potential gradient
Xylem
sap
Outside air Y
= –100.0 MPa
Leaf Y (air spaces)
= –7.0MPa
Leaf Y (cell walls)
= –1.0 MPa
Trunk xylem Y
= – 0.8 MPa
Water potential gradient
Root xylem Y
= – 0.6 MPa
Soil Y
= – 0.3 MPa
Mesophyll
cells
Stoma
Water
molecule
Atmosphere
Transpiration
Adhesion
Cell
wall
Cohesion, by
hydrogen
bonding
Root
hair
Soil
particle
Cohesion
and adhesion
in the xylem
Water uptake
from soil

25. Factors that affect transpiration
Heat – increases rate
CAM plants only have stomata on the underside of the leaves to conserve H2O
Wind – increases rate
Humidity – decreases rate
# of stomata – increases rate

26. Transpiration Regulation
Guard cells around the stomata in the epidermis of the plant leaf
CO2 enters, O2 leaves and H2O evaporates
Light stimulates the stomata to open to allow CO2 to enter for photosynthesis

27. 20 µm

28. Xylem vs. Phloem Transport – Bulk Flow
Dead Cells – Tracheids
Living Cells – Sieve Tube Members
Water and Minerals
Organic Compounds (sugar)
Unidirectional Movement (up)
Bi-Directional Movement (down, up, side to side)
Fast – max rate 15 meters / hr
Slow – max flow rate 1 meter / hr
NO ATP
ATP
Transpiration
Translocation

29. Translocation
Photosynthesis occurs in the leaves and produces organic compounds (sugar) for the plant.
These organic substances travel via translocation in the phloem from source to sink
Source – an organ that produces more sugar than it requires (leaf)
Sink – an organ that does not make enough sugar for its own needs (flower, developing bud, root, or fruit)

30. Source (Leaf) to Sink (Organ of need)
Mesophyll cell produces sugars via photosynthesis
Sugars are transported through bundle sheath cells and companion cells before entering the sieve tube members.
This process occurs via the symplast through the plasmodesta of the cell walls.
Once in the sieve tubes, sugars are transported to the organ of need (sink).

31. Mesophyll cell
Cell walls (apoplast)
Plasma membrane
Plasmodesmata
Companion
(transfer) cell
Sieve-tube
member
Phloem
parenchyma cell
Bundle-
sheath cell

32. Pressure Flow Model – pg 594
Sugars are pumped by active transport into companion cells and sieve tube members (phloem).
As sugars (solutes) accumulate, water enters the sieve tube via osmosis from nearby xylem.
Turgor pressure builds in the sieve tube at the source end and the fluid is pushed to the sink organ, which has a lower turgor pressure.

33. Pressure Flow Model – pg 594
Sugars are removed using active transport at the sink cells.
Removed sugars are either used (metabolized) or converted into starch for storage.
Left over water in the phloem is pulled into the nearby xylem and transported back up the plant.