Transcript Ch. 36 - Crestwood Local Schools

Question ?
How
do plants
move materials
from one organ
to the other ?
Levels of Plant
Transport
1. Cellular
2. Short Distance
3. Long Distance
Cellular Transport
The
transport
of solutes and
water across
cell
membranes.
Types of transport:
1. Passive Transport
2. Active Transport
3. Water Transport
1. Passive Transport
Diffusion
and Osmosis.
Requires no cellular energy.
Materials diffuse down
concentration gradients.
Problems
Usually
very slow.
How can diffusion be
assisted?
Transport Proteins
Ex.
K+ channel
Potassium Channel
Found
in most plant cell
membranes.
Allow K+ but not Na+ to pass.
Often “gated” to respond to
environmental stimuli
(see cell signaling)
2. Active Transport
Requires
cell energy.
Moves solutes against a
concentration gradient.
Ex: Proton Pumps
Proton Pump
Uses
ATP to move H+ out of
cells.
H+ creates a membrane
potential.
H+ allows cotransport.
Membrane Potentials
Allow
cations to moved into
the cell.
Ex: Ca+2, Mg+2
Allow anions to move by cotransport.
Ex: NO3
Summary
3. Water Transport
Osmosis
- water moves from
high concentration to low
concentration.
Water Potential
The
potential energy of water
to move from one location to
another.
Abbreviated
as
y
Problem
Cell
wall creates a pressure
in the cells.
Water potential must account
for this pressure.
Pressure counteracts the
tendency for water to move
into plant cells.
Water Potential
Has
two components:
Pressure
Solute
potential:
potential:
y = y r + yp
yr
yp
Comment
See
the Ts lab handout for
more on water potential.
Bulk Flow
The
movement of water
between two locations due to
pressure or tension.
Bulk Flow
Much
faster than osmosis.
Tension (negative pressure)
pulls water from place to
place.
May cause bulk flow against
the diffusion gradient.
Plant Vacuoles
Create
Turgor Pressure
against the cell wall.
Affect water potential by
controlling water concentrations
inside cells.
Tonoplast
Name
for the vacuole
membrane.
Has proton pumps.
Comment – genetic
modification of these pumps
gives plants salt tolerance.
Proton Pumps
Drives
solutes inside the
vacuole.
water potential (yp )
inside the vacuole.
Lowers
Result
Water
moves into the vacuole.
Vacuole swells.
Turgor pressure increases.
Turgor Pressure
Important
for non-woody
plant support.
Wilting:
Loss
of turgor pressure.
Loss of water from cells.
Flaccid
Turgid
Aquaporins
Water
specific facilitated
diffusion transport channels.
Help water move more
rapidly through lipid bilayers.
Aquaporins with GFP
Short Distance
Transport
1. Transmembrane route
2. Symplast route
3. Apoplast route
1. Transmembrane
Materials
cross
from cell to cell
by crossing each
cell's membranes
and cell walls.
2. Symplast
The
continuum
of cytoplasm by
plasmodesmata
bridges
between cells.
3. Apoplast
Extracellular
pathway
around and
between cell
walls.
Long Distance
Transport
Problem:
diffusion is too
slow for long distances.
Answer: tension and bulk
flow methods.
Root Hairs
 Main
site of
absorption of
water and
minerals.
 Comment - older
roots have cork
and are not very
permeable to
water.
Root Cortex
Very
spongy.
Apoplast
route very
common.
Problem
Can't
control uptake of
materials if the apoplast route
is used.
Solution
Endodermis
with its
Casparian
Strip.
Casparian Strip
Waxy
layer of suberin.
Creates a barrier between the
cortex and the stele.
Forces materials from
apoplast into endodermis
symplast.
Casparian Strip
Endodermis
Result
Plant
can now control
movement of materials into
the stele.
Xylem Sap
Solution
of water and
minerals loaded into the
xylem by the endodermis.
Endodermis - also prevents
back flow of water and
minerals out of the stele.
Xylem Sap
Transport Methods
1. Root Pressure
2. Transpiration (Ts)
Root Pressure
Root
cells load minerals into
xylem.
potential (yp) is
lowered.
Water flows into xylem.
Water
Result
Volume
of water in xylem
increases
Xylem sap is pushed up the
xylem tissues creating
root pressure.
Comments
 Root
Pressure:
limited way to
move xylem sap.
 Most apparent at
night.
 Excess water may
leave plant
through Guttation.
Transpiration (Ts)
Evaporation
of water from
aerial plant parts.
Major force to pull xylem sap
up tall trees.
TCTM Theory
Transpiration
Cohesion
Tension
Mechanism
How does TCTM work?
Water
evaporates from
leaves, especially from the
cell walls of the spongy
mesophyll.
Reason: water potential of
the air is usually much less
than that of the cells.
As water evaporates:
Cohesion:
water molecules
sticking together by H bonds.
Adhesion: water molecules
sticking to other materials
(cell walls etc.).
Result
The
loss of water from the
leaves creates “tension” or
negative pressure between
the air and the water in the
plant.
Tension causes:
Xylem
sap to move to replace
the water lost from the
mesophyll cells.
Xylem Sap
Is
“pulled” by the resulting
tension all the way down the
plant to the roots and soil.
Ts Summary
Xylem
sap moves along a
continual chain of water
potential from:
air leaf stem roots soil
Factors that Affect
Transpiration Rate
1. Environmental
2. Plant
Structures
Stomatal Crypt
Multiple Layer Epidermis
Homework
– Chapter 36, 39
Chapter 36 – Mon. 4/16
Test 2 – next week – Chapters
29, 30, 35, 36. A few
questions may come from 37,
38 and possible 39.
Read
Environmental Factors
1. Humidity
2. Temperature
3. Light
4. Soil Water Content
5. Wind
Plant Structure Factors
1. Cuticle
2. Stomate Number
3. Hairs
Stomates
Openings
in the epidermis
that allow water and gas
exchange.
Controlled by Guard Cells.
Control rate of Ts and Ps.
Guard Cells
Turgid:
Swell - open stomata.
Flaccid: Shrink - close
stomata.
Size of the cells is a result of
turgor pressure changes.
Turgid - Open
Flaccid - Closed
Turgor Pressure of
Guard cells
Controlled
by K+ concentrations.
+
K
Movement
Regulated
by proton pumps
and K+ channels.
Controlled by:
Light
(Blue)
CO2 concentrations
Abscisic Acid (water stress)
Comment
Plant
must balance loss of
water by transpiration with
CO2 uptake for Ps.
Phloem Transport
Moves
sugars (food).
Transported in live cells.
Ex:
Sieve & Companion Cells
Source - Sink Transport
Model
for movement of
phloem sap from a Source to
a Sink.
Source
Sugar
production site
Ex: Ps
Starch breakdown in a
storage area.
Sink
Sugar
uptake site.
Ex: Growing areas
Storage areas
Fruits and seeds
Comment
The
same organ can serve as
a source or a sink depending
on the season.
Result
Phloem
transport can go in
two directions even in the
same vascular bundle.
Xylem Transport:
In Contrast to Phloem
Usually
unidirectional.
Endodermis prevents back
flow.
Dead cells.
Phloem Loading at the
Source:
1. Diffusion
2. Transfer Cells
3. Active Transport
Phloem Loading
Transfer Cells
Modified
cell with ingrowths
of cell wall to provide more
surface area for sugar
diffusion.
Result
Sugar
loaded into phloem.
potential (yp)
decreases.
Bulk flow is created.
Water
Bulk Flow
Movement
of water into
phloem.
Pressure forces phloem sap
to move toward the sink.
At the Sink:
Sugar
is removed.
Water potential is raised.
Water moves out of phloem
over to xylem.
Phloem: summary
Source
- builds pressure.
Sink - reduces pressure.
Pressure caused by:
Sugar
content changes
Water potential changes
Comment
Plants
move materials
without "moving" parts,
unlike animals.
Summary
Know
various ways plants
use to move materials.
Know how Ts works and the
factors that affect Ts.
Know how phloem transport
works.