Copyright Notice!
This PowerPoint slide set is copyrighted by Ross Koning
and is thereby preserved for all to use from
plantphys.info for as long as that website is available.
Images lacking photo credits are mine and, as long as
you are engaged in non-profit educational missions, you
have my permission to use my images and slides in your
teaching. However, please notice that some of the images
in these slides have an associated URL photo credit to
provide you with the location of their original source within
internet cyberspace. Those images may have separate
copyright protection. If you are seeking permission for use
of those images, you need to consult the original sources
for such permission; they are NOT mine to give you
permission.
Figure 36-3 Page 793
The shoot system
produces
carbohydrates (etc.)
by photosynthesis.
These solutes are
transported to the
roots in the phloem
tissue:
Translocation
Node
Internode
Transpiration
Carbohydrate
etc.
Node
Leaves
Branch
Stem
Transpiration
The root system
removes water and
minerals from the soil
environment. These
solutes are
transported to the
shoot in the xylem
tissue:
Apical bud
Axillary bud
Translocation
Lateral roots
Water and
Minerals
Taproot
Figure 36-3 Page 793
Node
Internode
Because these
pathways involve
solutes in water
passing in the
adjacent tissues of a
narrow vascular
bundle, this is a
circulation system!
Apical bud
Axillary bud
Carbohydrate
etc.
Node
Leaves
Branch
Stem
Transpiration
Translocation
Transpiration and
Translocation
Lateral roots
The water is moving
up the xylem, and
down the phloem,
making a full circuit!
Water and
Minerals
Taproot
Mendocino Tree (Coastal Redwood) Sequoia sempervirens
Ukiah, California
112 m tall (367.5 feet)!
This tree is more
than ten times taller
than is “theoretically
possible” based
solely upon the
length of the column
of uncavitated water.
How could this be
achieved?
http://www.nearctica.com/trees/conifer/tsuga/Ssemp10.jpg
Transpiration in a tall tree
has at least 3 critical
components:
Evaporation: pulling up water from above
Capillarity: climbing up of water within xylem
Root Pressure: pushing up water from below
©1996 Norton Presentation Maker, W. W. Norton & Company
Transpiration: root pressure (osmotic “push”)
Solutes from
translocation of
sugars
accumulate in
roots.
guttation
Water from the
soil moves in by
osmosis.
Accumulating
water in the
root rises in the
xylem.
This is not “dew” condensing!
Water escapes
from
hydathodes.
Transpiration: root pressure (osmotic “push”)
The veins (coarse and
fine) show that no cell in
a leaf is far from xylem
and phloem (i.e.water
and food!).
The xylem of the veins
leaks at the leaf margin
in a modified stoma
called the hydathode.
These droplets are
xylem sap.
http://img.fotocommunity.com/photos/8489473.jpg
Root pressure accounts
for maybe a half-meter
of “push” up a tree
trunk.
Capillarity: maximum height of unbroken water column
glass tube
vacuum created
gravity pulls
water down
10.4m
atmospheric pressure
keeps water in tube
water
The small diameter of
vessels and tracheids
and the surface
tension of water
provide capillary
(“climb”).
Cohesion of water,
caused by hydrogen
bonds, helps avoid
cavitation.
A tree taller than
10.4 m would need
some adaptations to
avoid “cavitation”
Transpiration: evaporation (“pull”)
water
Water
evaporating
from a porous
clay cap also
lifts the
mercury!
mercury
Transpiration
can lift the
mercury
above its
normal
cavitation
height!
vacuum
76 cm
mercury
PHLOEM
XYLEM
Transpiration is
Unidirectional
Lower
pressure
sucrose
sucrose
H+
Apical
Bud
Translocation is
Bidirectional
High
pressure
sucrose
Leaf
H+
Translocation is
Bidirectional
Lower
pressure
sucrose
sucrose
H+
Root
Transpiration
Evaporation:
Water evaporates from
mesophyll into
atmosphere.
Water molecules are
pulled up the xylem by
virtue of cohesion.
Capillarity:
Water climbs in the
xylem cell walls by
adhesion.
Water molecules
follow by cohesion.
Node
Internode
Apical bud
Axillary bud
Carbohydrate
etc.
Node
Leaves
Branch
Stem
Transpiration
Translocation
Lateral roots
Root Pressure:
Water moves into the
root because of
solutes from phloem.
Pressure pushes the
water up the stem.
Water and
Minerals
Taproot
Figure 36-3 Page 793
Node
Internode
Apical bud
Axillary bud
Carbohydrate
etc.
Node
Leaves
Branch
Stem
Transpiration
Translocation
Lateral roots
Water and
Minerals
Taproot
Figure 36-3 Page 793
Translocation
Leaf = Source
Photosynthesis
produces solutes.
Solutes loaded into
phloem by active
transport.
Water follows by
osmosis, increasing
pressure.
Root (etc.) = Sinks
Solutes removed from
phloem by active
transport.
Water follows by
osmosis, reducing
pressure.
Pressure = Bulk Flow
The pressure gradient
forces phloem sap away
from leaves to all sinks
(bidirectionally).