1. Transport in Vascular Plants

2. LE 36-2_4
CO2 O2
Light
H2O
Sugar O2
H2O
CO2
Minerals

3. Effects of Differences in Water Potential
measurement that combines the effects of solute concentration and pressure
determines the direction of movement of water
Movement from high to lower water potential

4. Turgor Pressure

5. Bulk Flow in Long-Distance Transport
xylem and phloem
bulk flow
movement of fluid in the is driven by pressure differences at opposite ends of the xylem vessels and sieve tubes

6. Animation: Transport in Roots
Water and mineral salts from the soil
through the epidermis of roots
ultimately flow to the shoot system
Animation: Transport in Roots

7. Absorption Root hairs Mutualism - Mycorrhizae
Much of surface area of roots
Mutualism - Mycorrhizae
Plant roots and fungal hyphae
facilitate absorption of water and minerals from the soil

8. The Endodermis endodermis waxy Casparian strip
innermost layer of cells in the root cortex
surrounds the vascular cylinder
Is last checkpoint for selective passage of minerals from the cortex into the vascular tissue
waxy Casparian strip
Part of endodermal wall
blocks apoplastic transfer of minerals from the cortex to the vascular cylinder

9. Transpirational Pull Water vapor in the airspaces of a leaf
diffuses down its water potential gradient
exits the leaf via stomata
Transpiration
produces negative pressure (tension) in the leaf
exerts a pulling force on water in the xylem
pulling water into the leaf

10. LE 36-12 Y = –0.15 MPa Y = –10.00 MPa Cell wall Air-water interface
Airspace
Low rate of
transpiration
High rate of
transpiration
Cuticle
Upper
epidermis
Cytoplasm
Evaporation
Mesophyll
Airspace
Air
space
Cell wall
Lower
epidermis
Evaporation
Water film
Vacuole
Cuticle
Stoma
CO2 O2
CO2 O2
Xylem

11. Animation: Transpiration
Transpirational pull
facilitated by cohesion and adhesion
Animation: Transpiration

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

13. LE 36-14
20 µm

14. Transpiration and evaporative cooling
can lower the temperature of a leaf
prevent denaturation of various enzymes involved in photosynthesis and other metabolic processes

15. Cells turgid/Stoma open Cells flaccid/Stoma closed
LE 36-15a
Cells turgid/Stoma open
Cells flaccid/Stoma closed
Radially oriented
cellulose microfibrils
Cell
wall
Vacuole
Guard cell
Changes in guard cell shape and stomatal opening and closing
(surface view)

16. Cells turgid/Stoma open Cells flaccid/Stoma closed
LE 36-15b
Cells turgid/Stoma open
Cells flaccid/Stoma closed
H2O
H2O
H2O
H2O
H2O K+
H2O
H2O
H2O
H2O
H2O
Role of potassium in stomatal opening and closing

17. Xerophyte Adaptations That Reduce Transpiration
Xerophytes
plants adapted to arid climates
leaf modifications
stomata are concentrated on the lower leaf surface
often in depressions that provide shelter from dry wind

18. LE 36-16
Cuticle
Upper epidermal tissue
Lower epidermal
tissue
Trichomes
(“hairs”)
Stomata
100 µm

19. Movement from Sugar Sources to Sugar Sinks
Phloem sap
aqueous solution
mostly sucrose
travels from a sugar source to a sugar sink
A sugar source = organ that is net producer of sugar
Ex. mature leaves
A sugar sink = organ that is a net consumer or storer of sugar
Ex. tuber or bulb

20. Pressure Flow: The Mechanism of Translocation in Angiosperms
Movement of sap
through a sieve tube
by bulk flow
driven by positive pressure
Animation: Translocation of Phloem Sap in Summer
Animation: Translocation of Phloem Sap in Spring