1. LG 3 – Plant Transport Material Transport –
Plant Material Transport
Material Transport –
Passive and Active Transport –
Water Movement in Plants –
Transport in Roots
Water in Roots –
Mineral Active Transport –
Transport of Water and Minerals in Xylem –
Mechanical Properties of Water
Transpiration –
Cohesion-tension Mechanisms of Water Transport –
Cohesion-Tension in Tallest Trees -
Leaf Anatomy
Stomata –
Physiology of Stomata-
Arid Adaptations –
Transport of Organic Substances in Phloem
Organic Compounds –
Sources and Sinks -

2. Examine how materials are transported throughout the body of a plant.
Unit II Plants
Learning Goal 3
Examine how materials are transported throughout the body of a plant.

3. Plant Material Transport
Short distances between cells
Long distances between roots and leaves (xylem and phloem)

4. A new plant species from Idaho. Sacajawea’s bitterroot (Lewisia
Sugar from
photosynthesis
Mineral ions
c. Long distance transport
throughout the plant
Sugar from
photosynthesis
Cells load and unload
organic molecules
(including CO2) into and
out of phloem (purple
arrows to/from phloem).
Xylem:
transport of
H2O and O2
b. Transport in
vascular tissues
Phloem:
sugars
Vascular tissue
distributes substances
throughout the plant,
sometimes over
great distances.
Water and mineral ions travel
from root hairs into xylem
vessels by passing through
or between cells (black arrow
into/out of xylem).
a. Short distance
transport across cell
membranes into roots
Minerals
Water and solutes from
soil enter plant roots by
passive or active transport
through the plasma
membrane of root hairs.
A new plant species from Idaho. Sacajawea’s bitterroot (Lewisia
sacajaweana) was formally described in It is named in honor
of Sacajawea, the Native American woman who guided Lewis and
Clark in their exploration of the Pacifi c Northwest in the early 1800s.
Stepped Art
Fig. 32.2, p. 739

5. Passive and Active Transport
Passive transport requires no metabolic energy
Substance moves down concentration or electrochemical gradient or by membrane potential
Active transport requires metabolic energy (ATP)
Substance moves against gradient

6. Water Movement in Plants
Bulk flow of water due to pressure differences
Xylem sap
Dilute water movement from roots to leaves
Osmosis
Passive movement of water across cell membrane
Water potential (Ψ)
Driving force (pressure and/or solutes)

7. Transport in Roots Water in Roots
Apoplastic pathway: Water does not cross cell membrane, includes dead xylem transport
Symplastic pathway: Water moves through plasmodesmata (openings between plant cells).
Transmembrane pathway:
Water moves between living cells through cell membranes.
Casparian strip in root endodermis forces apoplastic water to symplast

8. A new plant species from Idaho. Sacajawea’s bitterroot (Lewisia
In the apoplastic pathway
(red), water moves through
nonliving regions–the continuous network of adjoining cell walls and tissue air spaces. However, when it reaches the endodermis, it passes through one layer of living cells.
Cell wall
Tonoplast
Plasmodesma
Air space
Endodermis with
Casparian strips
Root hair
Xylem
vessel
in stele
In the symplastic pathway
(green), water passes into and through living cells. After being taken up into root hairs water diffuses through the cytoplasm and passes from one living cell
to the next through plasmo-desmata.
In the transmembrane
pathway (black), water that enters the cytoplasm moves between living
cells by diffusing across
cell membranes, including
the plasma membrane and perhaps the tonoplast.
A new plant species from Idaho. Sacajawea’s bitterroot (Lewisia
sacajaweana) was formally described in It is named in honor
of Sacajawea, the Native American woman who guided Lewis and
Clark in their exploration of the Pacifi c Northwest in the early 1800s.
Root cortex
Epidermis
Fig. 32.6, p. 743

9. Casparian Strips in Roots

10. A new plant species from Idaho. Sacajawea’s bitterroot (Lewisia
a. Root
b. Stele in cross section
(stained)
Exodermis
Primary
xylem
Primary
phloem
Root
cortex
Stele
Endodermis
Abutting walls of
endodermal cells
c. Casparian strip (from above)
A new plant species from Idaho. Sacajawea’s bitterroot (Lewisia
sacajaweana) was formally described in It is named in honor
of Sacajawea, the Native American woman who guided Lewis and
Clark in their exploration of the Pacifi c Northwest in the early 1800s.
Stele
Endodermal cells with
Casparian strip
In root cortex, water molecules
move through the apoplast,
around cell walls and through
them (arrows).
Fig. 32.7, p. 744

11. A new plant species from Idaho. Sacajawea’s bitterroot (Lewisia
d. Movement of water into the stele
Tracheids and vessels in xylem
Stele
Sieve tubes in phloem
Pericycle (one or more cells thick)
Endodermis (one cell thick)
Radial
wall region
impregnated
with suberin
A new plant species from Idaho. Sacajawea’s bitterroot (Lewisia
sacajaweana) was formally described in It is named in honor
of Sacajawea, the Native American woman who guided Lewis and
Clark in their exploration of the Pacifi c Northwest in the early 1800s.
Wall of endodermal
cell facing root cortex
Transverse wall regions
impregnated with suberin
Route water takes
into the stele
Waxy, water-impervious Casparian strip (gold) in abutting walls of endodermal
cells that control water and nutrient uptake
Fig. 32.7, p. 744

12. Mineral Active Transport
Most minerals for growth are more concentrated in root than in soil
Active transport into symplast
Active transport at Casparian strip across membrane
Minerals loaded into apoplast of dead xylem in root stele
Transported long distance to other tissues

13. Transport of Water and Minerals in the Xylem
Mechanical properties of water have key roles in its transport
Leaf anatomy contributes to cohesion-tension forces
In the tallest trees, the cohesion-tension mechanism may reach its physical limit

14. Root pressure contributes to upward water movement in some plants
Stomata regulate the loss of water by transpiration
In dry climates, plants exhibit various adaptations for conserving water

15. Mechanical Properties of Water
Transpiration
Evaporation of water out of plants
Greater than water used in growth and metabolism
Cohesion-tension mechanism of water transport
Evaporation from mesophyll walls
Replacment by cohesion (H-bonded) water in xylem
Tension, negative pressure gradient, maintained by narrow xylem walls, wilting is excess tension

16. A new plant species from Idaho. Sacajawea’s bitterroot (Lewisia
Mesophyll
Vein
Upper epidermis
The driving force of evaporation into dry air
1 Transpiration is the evaporation of water molecules from above ground plant parts, especially at stomata. The process puts the water in the xylem sap in a state of tension that extends from roots to leaves.
Stoma
Vascular
cambium
Water uptake in
growth regions
Xylem
Phloem
Cohesion in the xylem of roots, stems, and leaves
Growing
cells also
remove
small
amounts
of water
from xylem.
2 The collective strength
of hydrogen bonds among
water molecules, which are
confined within the
tracheids and vessels in
xylem, imparts cohesion to
the water.
A new plant species from Idaho. Sacajawea’s bitterroot (Lewisia
sacajaweana) was formally described in It is named in honor
of Sacajawea, the Native American woman who guided Lewis and
Clark in their exploration of the Pacifi c Northwest in the early 1800s.
Water uptake from soil by roots
Stele
cylinder
Endodermis
Cortex
Water
molecule
Root
hair
3 As long as water
molecules continue to
escape by transpiration, that tension will drive the uptake of replacement water molecules from soil water.
Fig. 32.8, p. 746

17. Cohesion-Tension in Tallest Trees
Transpiration follows atmospheric evaporation
Driving forces: Dryness and radiation
Tallest trees (>110m) near physical limit of cohesion
Root pressure occurs in moist to wet soils
Moves water up short distances
Guttation
Water movement under pressure out leaves

18. Guttation

19. Leaf Anatomy
Stomata
Transpiration losses of water must be regulated to prevent rapid dessication
Cuticle limits H2O loss but also prevents CO2 uptake
Water is always lost when stomata open for photosynthesis

20. A new plant species from Idaho. Sacajawea’s bitterroot (Lewisia
a. Open stoma
b. Closed stoma
Guard cell
Guard cell
Chloroplast
(guard cells
are the only
epidermal
cells that
have these
organelles)
A new plant species from Idaho. Sacajawea’s bitterroot (Lewisia
sacajaweana) was formally described in It is named in honor
of Sacajawea, the Native American woman who guided Lewis and
Clark in their exploration of the Pacifi c Northwest in the early 1800s.
Stoma
Fig , p. 748

21. Physiology of Stomata
Stomata must balance H2O loss and CO2 uptake by responding to many signals, biological clock
Stomata open to increase photosynthesis
Increasing light (blue)
Decreasing CO2 concentration in leaf
Stomata close under water stress
Abscisic acid is hormonal signal for closure, synthesized by roots and leaves

22. Arid Adaptations
Xenophytes have adaptations to aridity
Thickened cuticle, sunken stomata, water storage in stems

23. Transport of Organic Substances in the Phloem
Organic compounds are stored and transported in different forms
Organic solutes move by translocation
Phloem sap moves from source to sink under pressure

24. Transport of Organic Substances in the Phloem
Organic Compounds
Translocation
Long-distance transport of substances via phloem
Phloem flow under pressure, moves any direction
Macromolecules broken down into constituents for transport across cell membranes
Phloem sap composed of water and organic compounds that move through sieve tubes

25. Sources and Sinks
Source: Any region of plant where organic substance is loaded into phloem
Companion and transfer cells, use free energy
Sink: Any region of plant where organic substance is unloaded from phloem
Pressure flow mechanism moves substance by bulk flow under pressure from sources to sinks
Based on water potential gradients

26. A new plant species from Idaho. Sacajawea’s bitterroot (Lewisia
Sieve tube of the phloem
1 Active transport
mechanisms move
solutes into the
companion cells
and then into the
sieve tube, against
concentration
gradients.
Source
(for example,
mature leaf cells)
Solute
Water
2 As a result of
the increased solute con-centration, the water potential is
decreased in the
sieve tube, and
water moves in by osmosis, increasing turgor pressure.
3 The pressure
then pushes solutes by bulk flow between
a source and a sink, with water moving into and out of the system all along the way.
bulk
flow
4 Pressure and
solute con-centrations
gradually decrease between the source and the sink as substances move into the sink from phloem.
A new plant species from Idaho. Sacajawea’s bitterroot (Lewisia
sacajaweana) was formally described in It is named in honor
of Sacajawea, the Native American woman who guided Lewis and
Clark in their exploration of the Pacifi c Northwest in the early 1800s.
5 Solutes are
unloaded into sink cells, and the water potential in those
cells is lowered.
Water moves out of the seive tube and into sink cells.
Sink
(for example,
developing
root cells)
Fig , p. 752

27. LG 3 Vocab Terms Passive Transport - Active Transport - Osmosis -
Water Potential -
Apoplastic vs Symplastic Pathway -
Casparian Strip -
Cohesion-Tension Mechanism -
Source -
Sink -
Pressure Flow Mechanism -