1. The Chapter 29 Homework is due on Thursday, March 14
The Chapter 29 Homework is due on Thursday, March 14. (We will be completely skipping section 29.3.)
Integrating Chapter 29 Homework – due Tuesday, March 12 at 11:59 pm
There will be a Test on Chapter 29 on Friday, March 15.

2. Chapter 29
Transpiration

3. You Must Know
How the transpiration cohesion-tension mechanism explains water movement in plants.

4. Concept 29.1: Adaptations for acquiring resources were key steps in the evolution of vascular plants
The success of plants depends on their ability to gather and conserve resources from their environment.
The transport of materials is central to the integrated functioning of the whole plant.
The evolution of adaptations enabling plants to acquire resources from both above and below ground sources allowed for the successful colonization of land by vascular plants. The algal ancestors of land plants absorbed water, minerals, and CO2 directly from surrounding water. Early nonvascular land plants lived in shallow water and had aerial shoots. Natural selection favored taller plants with flat appendages, multicellular branching roots, and efficient transport.
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5. Figure
The plant does not have to expend any energy to transport water through the xylem
H2O
Xylem
What substances do plants need for photosynthesis?
The evolution of xylem and phloem in land plants made possible the development of extensive root and shoot systems that carry out long-distance transport.
Xylem transports water and minerals from roots to shoots.
What substances do plants need for respiration?
H2O
and
minerals 5

6. O2 CO2 H2O O2 H2O and minerals CO2 Figure 29.2-2
Figure An overview of resource acquisition and transport in a vascular plant (step 2) O2
H2O
and
minerals
CO2 6

7. Phloem transports photosynthetic products from sources to sinks.
Figure
CO2 O2
Light
Sugar
H2O
Phloem transports photosynthetic products from sources to sinks. O2
H2O
and
minerals
CO2
Video: water transport 7

8. 60 L of water during a growing season!
Concept 29.5: Transpiration drives the transport of water and minerals from roots to shoots via the xylem
Plants can move a large volume of water from their roots to shoots.
60 L of water during a growing season!
A single maize plant transpires 60 L of water during a growing season. Peak velocities in the transport of xylem sap can range from 15 to 45 m/hr.
15 to 45 mph!
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9. Absorption of Water and Minerals by Root Cells
Most water and mineral absorption occurs near root tips, where root hairs are located and the epidermis is permeable to water.
Root hairs account for much of the absorption of water by roots.
After soil solution enters the roots, the extensive surface area of cortical cell membranes enhances uptake of water and selected minerals.
The concentration of essential minerals is greater in the roots than in the soil because of active transport.
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10. Cell compartments and routes for short-distance transport
Cell wall
Apoplastic route
Cytosol
Symplastic route
Transmembrane route
Key
Plasmodesma
Water can cross the cortex via the symplast or apoplast.
Apoplast
Plasma membrane
Symplast 10

11. Vessels (xylem) Casparian strip 1 Apoplastic route Plasma membrane
Figure 29.16a
Vessels
(xylem)
Casparian strip 1
Apoplastic
route
Plasma
membrane
Apoplastic
route 1 2 3
Symplastic
route 2 5
Symplastic
route
Root
hair
Water and minerals can travel to the vascular cylinder through the cortex via
The apoplastic route, along cell walls and extracellular spaces.
The symplastic route, in the cytoplasm, moving between cells through plasmodesmata .
The transmembrane route, moving from cell to cell by crossing cell membranes and cell walls.
The waxy Casparian strip of the endodermal wall blocks apoplastic transfer of minerals from the cortex to the vascular cylinder.
Water and minerals in the apoplast must cross the plasma membrane of an endodermal cell to enter the vascular cylinder.
The endodermis regulates and transports needed minerals from the soil into the xylem.
Water and minerals move from the protoplasts of endodermal cells into their cell walls.
Diffusion and active transport are involved in this movement from symplast to apoplast.
Water and minerals now enter the tracheids and vessel elements. 3
Transmembrane
route
Epidermis
Endodermis
Vascular
cylinder
(stele)
Cortex 5
Transport in the xylem 11

12. Pulling Xylem Sap: The Cohesion-Tension Hypothesis
According to the cohesion-tension hypothesis, transpiration and water cohesion pull water from shoots to roots.
Xylem sap, water and dissolved minerals, is transported from roots to leaves by bulk flow, the movement of a fluid driven by pressure. The transport of xylem sap involves transpiration, the loss of water vapor from a plant’s surface. Transpired water is replaced as water travels up from the roots.
Xylem sap is normally under negative pressure, or tension.
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13. Ascent of xylem sap Water molecule Root hair Soil particle Water
Water uptake from soil 13

14. Adhesion by hydrogen bonding Xylem cells Cell wall Cohesion
Figure 29.18b
Adhesion by hydrogen
bonding
Xylem
cells
Cell wall
Cohesion
by hydrogen
bonding
Cohesion and adhesion in the ascent of xylem sap: Water molecules are attracted to each other through cohesion.
Cohesion makes it possible to pull a column of xylem sap. Water molecules are attracted to hydrophilic walls of xylem cell walls through adhesion. Adhesion of water molecules to xylem cell walls helps offset the force of gravity. 14

15. Xylem sap Mesophyll cells Stoma Water molecule Atmosphere
Figure 29.18c
Xylem sap
Mesophyll cells
Stoma
Water molecule
Atmosphere
Transpiration
Transpirational pull is generated when water vapor in the air spaces of a leaf diffuses down its water potential gradient and exits the leaf via stomata.
As water evaporates, the air-water interface retreats farther into the mesophyll cell walls and becomes more curved.
Due to the high surface tension of water, the curvature of the interface creates a negative pressure potential.
This negative pressure pulls water in the xylem into the leaf.
The pulling effect results from the cohesive binding between water molecules.
The transpirational pull on xylem sap is transmitted from leaves to roots. 15

16. Outside air  = -100.0 MPa Leaf  (air spaces) = -7.0 MPa
Figure 29.18
Xylem sap
Outside air 
Mesophyll cells =
MPa
Stoma
Leaf  (air spaces)
Water molecule =
-7.0 MPa
Atmosphere
Transpiration
Leaf  (cell walls)
Adhesion by hydrogen
bonding =
-1.0 MPa
Xylem
cells
Cell wall
Water potential gradient
Trunk xylem 
Cohesion
by hydrogen
bonding
−0.8 MPa 
Cohesion
and adhesion
in the xylem
Water molecule
Trunk xylem 
Root hair
−0.6 MPa 
Soil particle
Water
Soil 
Water uptake from soil
−0.3 MPa  16