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2. Carbohydrate etc. Transpiration Translocation Water and Minerals
Figure 36-3 Page 793
Apical bud
The shoot system produces carbohydrates (etc.) by photosynthesis. These solutes are transported to the roots in the phloem tissue:
Translocation
Axillary bud
Node
Carbohydrate etc.
Internode
Node
Shoot system
Leaves
Branch
Stem
Transpiration
Translocation
The root system removes water and minerals from the soil environment. These solutes are transported to the shoot in the xylem tissue:
Transpiration
Lateral roots
Root system
Water and Minerals
Taproot

3. Dicot circulation: stem anatomy Dicots start with one ring of bundles…
Let’s take a closer look at the vascular tissues
©1996 Norton Presentation Maker, W. W. Norton & Company

4. Cell Divison: More Xylem and Phloem
Dicot stem anatomy: vascular bundle
phloem fibers
Support of Stem
functional phloem
Translocation
vascular cambium
Cell Divison: More Xylem and Phloem
xylem
Transpiration
As a dicot grows, how does it add vascular capacity to become a tree?
©1996 Norton Presentation Maker, W. W. Norton & Company

5. Carbohydrate etc. Transpiration Translocation Water and Minerals
Figure 36-3 Page 793
Apical bud
Axillary bud
Node
Carbohydrate etc.
Internode
Because these pathways involve solutes in water passing in the adjacent tissues of a narrow vascular bundle, this is a circulation system!
Transpiration and Translocation
The water is moving up the xylem, and down the phloem, making a full circuit!
Node
Shoot system
Leaves
Branch
Stem
Transpiration
Translocation
Lateral roots
Root system
Water and Minerals
Taproot

6. 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?

7. 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

8. Transpiration: root pressure (osmotic “push”)
Solutes from translocation of sugars accumulate in roots.
Water from the soil moves in by osmosis.
Accumulating water in the root rises in the xylem.
Water escapes from hydathodes.
guttation
©1996 Norton Presentation Maker, W. W. Norton & Company
This is not “dew” condensing!

9. 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.
Root pressure accounts for maybe a half-meter of “push” up a tree trunk.

10. Capillarity: maximum height of unbroken water column
glass tube
vacuum created
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”
gravity pulls water down
10.4m
atmospheric pressure keeps water in tube
water

11. Transpiration: evaporation (“pull”)
Transpiration can lift the mercury above its normal cavitation height!
vacuum
water
mercury
Water evaporating from a porous clay cap also lifts the mercury!
76 cm
mercury

12. This is a cross-section of a “typical” leaf: Syringa vulgaris (lilac)
soil mineral entry
evaporative cooling means the solute concentration increases!

13. Translocation is Bidirectional XYLEM PHLOEM
Lower pressure
Apical Bud
sucrose
sucrose H+
Translocation is Bidirectional
XYLEM
PHLOEM
Transpiration is Unidirectional
High pressure
sucrose
Leaf H+
Translocation is Bidirectional
Lower pressure
sucrose
Root
sucrose H+

14. Transpiration Carbohydrate etc. Transpiration Translocation
Apical bud
Axillary bud
Node
Evaporation:
Water evaporates from mesophyll into atmosphere.
Water molecules are pulled up the xylem by virtue of cohesion.
Carbohydrate etc.
Internode
Node
Shoot system
Leaves
Branch
Capillarity:
Water climbs in the xylem cell walls by adhesion.
Water molecules follow by cohesion.
Stem
Transpiration
Translocation
Lateral roots
Root Pressure:
Water moves into the root because of solutes from phloem.
Pressure pushes the water up the stem.
Root system
Water and Minerals
Taproot
Figure 36-3 Page 793

15. Translocation Carbohydrate etc. Transpiration Translocation
Apical bud
Axillary bud
Node
Leaf = Source
Photosynthesis produces solutes.
Solutes loaded into phloem by active transport.
Water follows by osmosis, increasing pressure.
Carbohydrate etc.
Internode
Node
Shoot system
Leaves
Branch
Stem
Transpiration
Translocation
Root (etc.) = Sinks
Solutes removed from phloem by active transport.
Water follows by osmosis, reducing pressure.
Lateral roots
Root system
Pressure = Bulk Flow
The pressure gradient forces phloem sap away from leaves to all sinks (bidirectionally).
Water and Minerals
Taproot
Figure 36-3 Page 793