Transcript Passive and Active Transport

LG 3 – Plant 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 StomataArid Adaptations –
Transport of Organic Substances in Phloem
Organic Compounds –
Sources and Sinks -
Unit II
Plants
Learning Goal 3
Examine how materials are
transported throughout the body of
a plant.
Plant Material Transport
• Material transport
– Short distances between cells
– Long distances between roots and leaves
(xylem and phloem)
c. Long distance transport
throughout the plant
Cells load and unload
organic molecules
(including CO2) into and
out of phloem (purple
arrows to/from phloem).
b. Transport in
vascular tissues
Sugar from
photosynthesis
Phloem:
transport of
sugars
Xylem:
transport of
H2O and O2
a. Short distance
transport across cell
membranes into roots
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).
Water and solutes from
soil enter plant roots by
passive or active transport
through the plasma
membrane of root hairs.
Minerals
Mineral ions
Sugar from
photosynthesis
Stepped Art
Fig. 32.2, p. 739
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
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)
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
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.
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 plasmodesmata.
Cell wall
Tonoplast
Plasmodesma
Root hair
Air space
Endodermis with
Casparian strips
Xylem
vessel
in stele
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.
Root cortex
Epidermis
Fig. 32.6, p. 743
Casparian Strips in Roots
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)
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
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
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
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
Transport of Water and
Minerals in the Xylem
• Mechanical properties of water have key
roles in its transport
• Leaf anatomy contributes to cohesiontension forces
• In the tallest trees, the cohesion-tension
mechanism may reach its physical limit
• 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
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
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
Cohesion in the
xylem of roots,
stems, and
leaves
Water uptake from soil
by roots
Vascular
cambium
Xylem
Phloem Water uptake in
growth regions
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.
Root
Stele Endodermis Cortex Water
molecule hair
cylinder
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
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
Guttation
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
a. Open stoma
Guard cell
b. Closed stoma
Guard cell
Chloroplast
(guard cells
are the only
epidermal
cells that
have these
organelles)
Stoma
Fig. 32.10, p. 748
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
Arid Adaptations
Xenophytes have
adaptations to
aridity
Thickened
cuticle, sunken
stomata, water
storage in
stems
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
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
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
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
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.
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.
bulk
flow
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.
4 Pressure and
solute concentrations
gradually decrease
between the
source and the
sink as substances
move into the sink
from phloem.
Sink
(for example,
developing
root cells)
Fig. 32.15, p. 752
LG 3 Vocab Terms
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Passive Transport Active Transport Osmosis Water Potential Apoplastic vs Symplastic Pathway Casparian Strip Cohesion-Tension Mechanism Source Sink Pressure Flow Mechanism -