1. Resource Acquisition, Nutrition, and Transport in Vascular Plants29
Resource Acquisition, Nutrition, and Transport in Vascular Plants

2. Important Topics
Roots: mutualistic adaptations with bacteria and their role in the nitrogen cycle
Stems: xylem and phloem collectively make up vascular plants
Leaves: stomata/guard cells
Transpiration: adhesion/cohesion and its role in the transport of water from roots all the way to the leaves
Special plant adaptations for different circumstances

3. The evolution of plants requires key adaptations
What might be the advantage of this plant structure?
What might the disadvantages be?
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4. Early nonvascular land plants lived in shallow water
ancestors of land plants absorbed water, minerals, and CO2 directly from surrounding water
Early nonvascular land plants lived in shallow water
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5. Xylem transports water and minerals from roots to shoots
Phloem transports photosynthetic products
What benefit do xylem and phloem provide in the evolution of plants?
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6. H2O H2O and minerals Figure 29.2-1
Figure An overview of resource acquisition and transport in a vascular plant (step 1)
H2O
and
minerals 6

7. 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 7

8. O2 CO2 Light Sugar H2O O2 H2O and minerals CO2 Figure 29.2-3
Figure An overview of resource acquisition and transport in a vascular plant (step 3) O2
H2O
and
minerals
CO2 8

9. Roots What is the purpose of roots in a plant?
Roots and the hyphae of soil fungi form mutualistic associations called mycorrhizae
Mycorrhizal fungi increase the surface area for absorbing water and minerals
Mutualisms with fungi helped plants colonize land
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10. Bacteria in the Nitrogen Cycle
Nitrogen can be an important limiting nutrient for plant growth
The nitrogen cycle transforms atmospheric nitrogen and nitrogen-containing compounds
Plants can only absorb nitrogen as either NO3– or NH4
Most usable soil nitrogen comes from actions of soil bacteria
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11. (dead organic material)
Figure 29.11
ATMOSPHERE N2
SOIL N2
ATMOSPHERE N2
Nitrate and
nitrogenous
organic
compounds
exported in
xylem to
shoot system
SOIL
Proteins from humus
(dead organic material)
Nitrogen-fixing
bacteria
Microbial
decomposition
Figure The roles of soil bacteria in the nitrogen nutrition of plants
Amino acids
NH3
(ammonia)
Denitrifying
bacteria
Ammonifying
bacteria
NH4+ H+
(from soil)
NH4+
(ammonium)
NO2−
(nitrite)
NO3−
(nitrate)
Nitrifying
bacteria
Nitrifying
bacteria
Root 11

12. (dead organic material) SOIL
Figure 29.11a N2
ATMOSPHERE N2
Nitrate and
nitrogenous
organic
compounds
exported in
xylem to
shoot system
Proteins from humus
(dead organic material)
SOIL
Nitrogen-fixing
bacteria
Microbial
decomposition
Amino acids
NH3
(ammonia)
Denitrifying
bacteria
Ammonifying
bacteria
NH4+ H+
(from soil)
NH4+
(ammonium)
NO2−
(nitrite)
NO3−
(nitrate)
Figure 29.11a The roles of soil bacteria in the nitrogen nutrition of plants (part 1)
Nitrifying
bacteria
Nitrifying
bacteria
Root 12

13. (dead organic material) SOIL
Figure 29.11b N2
ATMOSPHERE
Proteins from humus
(dead organic material)
SOIL
Nitrogen-fixing
bacteria
Microbial
decomposition
Amino acids
NH3
(ammonia)
Ammonifying
bacteria H+
(from soil)
Figure 29.11b The roles of soil bacteria in the nitrogen nutrition of plants (part 2)
NH4+
(ammonium)
NO2−
(nitrite)
Nitrifying
bacteria 13

14. N2 Nitrate and nitrogenous organic compounds exported in xylem to
Figure 29.11c N2
Nitrate and
nitrogenous
organic
compounds
exported in
xylem to
shoot system
Denitrifying
bacteria
NH4+
Figure 29.11c The roles of soil bacteria in the nitrogen nutrition of plants (part 3)
NO2−
(nitrite)
NO3−
(nitrate)
Nitrifying
bacteria
Root 14

15. Conversion to NH4 Conversion to NO3–
Ammonifying bacteria break down organic compounds and release ammonium (NH4)
Nitrogen-fixing bacteria convert N2 gas into NH3
NH3 is converted to NH4
Conversion to NO3–
Nitrifying bacteria oxidize NH4 to nitrite (NO2–) then nitrite to nitrate (NO3–)
Different nitrifying bacteria mediate each step
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16. Nitrogen is lost to the atmosphere when denitrifying bacteria convert NO3– to N2
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17. Symbiotic relationships with nitrogen-fixing Rhizobium bacteria provide some legumes with a source of fixed nitrogen
Along a legume’s roots are swellings called nodules, composed of plant cells “infected” by nitrogen-fixing Rhizobium bacteria
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18. Figure 29.12
Nodules
Figure Soybean root nodules
Roots 18

19. Inside the root nodule, Rhizobium bacteria assume a form called bacteroids, which are contained within vesicles formed by the root cell
The plant obtains fixed nitrogen from Rhizobium, and Rhizobium obtains sugar and an anaerobic environment
Each legume species is associated with a particular strain of Rhizobium
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20. Fungi and Plant Nutrition
Mycorrhizae are mutualistic associations of fungi and roots
The fungus benefits from a steady supply of sugar from the host plant
The host plant benefits because the fungus increases the surface area for water uptake and mineral absorption
Mycorrhizal fungi also secrete growth factors that stimulate root growth and branching
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21. Epiphytes, Parasitic Plants, and Carnivorous Plants
Some plants have nutritional adaptations that use other organisms in nonmutualistic ways
Three unusual adaptations are
Epiphytes
Parasitic plants
Carnivorous plants
Video: Sundew Traps Prey
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22. Epiphytes grow on other plants and obtain water and minerals from rain, rather than tapping their hosts for sustenance
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23. Some species parasitize the mycorrhizal hyphae of other plants
Parasitic plants absorb water, sugars, and minerals from their living host plant
Some species also photosynthesize, but others rely entirely on the host plant for sustenance
Some species parasitize the mycorrhizal hyphae of other plants
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24. Mistletoe, a photosynthetic parasite Dodder, a nonphoto-
Figure 29.15b
Parasitic plants
Figure 29.15b Exploring unusual nutritional adaptations in plants (part 2: parasitic plants)
Mistletoe, a photosynthetic
parasite
Dodder, a nonphoto-
synthetic parasite
(orange)
Indian pipe, a nonphoto-
synthetic parasite of
mycorrhizae 24

25. Carnivorous plants are photosynthetic but obtain nitrogen by killing and digesting mostly insects
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26. Carnivorous plants Sundew Pitcher plants Venus flytraps Figure 29.15c
Figure 29.15c Exploring unusual nutritional adaptations in plants (part 3: carnivorous plants) 26

27. 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
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28. The endodermis: controlled entry to the vascular cylinder (stele) 5
Figure 29.16a
Vessels
(xylem)
Casparian strip 1
Apoplastic
route
Plasma
membrane
Apoplastic
route 1 2
Symplastic
route 3 2 4 5
Figure 29.16a Transport of water and minerals from root hairs to the xylem (part 1)
Symplastic
route
Root
hair 3
Transmembrane
route
Epidermis
Endodermis
Vascular
cylinder
(stele)
Cortex 4
The endodermis: controlled entry
to the vascular cylinder (stele) 5
Transport in the xylem 28

29. 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 is normally under negative pressure, or tension
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30. 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
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31. 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
Animation: Transpiration
Animation: Water Transport in Plants
Animation: Water Transport
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32. Cuticle Xylem Upper epidermis Microfibrils in cell wall of
Figure 29.17
Cuticle
Xylem
Upper
epidermis
Microfibrils in
cell wall of
mesophyll cell
Mesophyll
Air
space
Figure Generation of transpirational pull
Lower
epidermis
Cuticle
Stoma
Microfibril
(cross section)
Water
film
Air-water
interface 32

33. Microfibrils in cell wall of mesophyll cell Air space
Figure 29.17a
Cuticle
Xylem
Upper
epidermis
Microfibrils in
cell wall of
mesophyll cell
Mesophyll
Air
space
Figure 29.17a Generation of transpirational pull (part 1)
Lower
epidermis
Cuticle
Stoma 33

34. Microfibrils in cell wall of mesophyll cell Microfibril
Figure 29.17b
Microfibrils in
cell wall of
mesophyll cell
Figure 29.17b Generation of transpirational pull (part 2)
Microfibril
(cross section)
Water
film
Air-water
interface 34

35. Outside air  = −100.0 MPa Leaf  (air spaces) = −7.0 MPa
Figure 29.18
Xylem sap
Outside air 
Mesophyll cells =
−100.0 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
Figure Ascent of xylem sap
Water molecule
Trunk xylem 
Root hair
−0.6 MPa 
Soil particle
Water
Soil 
Water uptake from soil
−0.3 MPa  35

36. Water molecule Root hair Soil particle Water Water uptake from soil
Figure 29.18a
Water molecule
Root hair
Soil particle
Water
Figure 29.18a Ascent of xylem sap (part 1: water uptake)
Water uptake from soil 36

37. Adhesion by hydrogen bonding Xylem cells Cell wall Cohesion
Figure 29.18b
Adhesion by hydrogen
bonding
Xylem
cells
Cell wall
Cohesion
by hydrogen
bonding
Figure 29.18b Ascent of xylem sap (part 2: cohesion and adhesion)
Cohesion
and adhesion
in the xylem 37

38. Xylem sap Mesophyll cells Stoma Water molecule Atmosphere
Figure 29.18c
Xylem sap
Mesophyll cells
Stoma
Water molecule
Atmosphere
Transpiration
Figure 29.18c Ascent of xylem sap (part 3: transpiration) 38

39. Cohesion makes it possible to pull a column of xylem sap
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
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40. Concept 29.6: The rate of transpiration is regulated by stomata
Leaves generally have broad surface areas and high surface-to-volume ratios
These characteristics increase photosynthesis and increase water loss through stomata
Guard cells help balance water conservation with gas exchange for
photosynthesis
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41. Stomata: Major Pathways for Water Loss
About 95% of the water a plant loses escapes through stomata
Each stoma is flanked by a pair of guard cells, which control the diameter of the stoma by changing shape
Stomatal density is under genetic and environmental control
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42. Mechanisms of Stomatal Opening and Closing
Changes in turgor pressure open and close stomata
When turgid, guard cells bow outward and the pore between them opens
When flaccid, guard cells become less bowed and the pore closes
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43. Guard cells turgid/Stoma open Guard cells flaccid/Stoma closed
Figure 29.19a
Guard cells turgid/Stoma open
Guard cells flaccid/Stoma closed
Radially oriented
cellulose microfibrils
Cell
wall
Figure 29.19a Mechanisms of stomatal opening and closing (part 1: cell shape)
Vacuole
Guard cell
(a) Changes in guard cell shape and stomatal opening and
closing (surface view) 43

44. Guard cells turgid/Stoma open Guard cells flaccid/Stoma closed
Figure 29.19b
Guard cells turgid/Stoma open
Guard cells flaccid/Stoma closed
H2O
H2O
H2O
H2O
H2O K+
H2O
H2O
H2O
H2O
H2O
Figure 29.19b Mechanisms of stomatal opening and closing (part 2: K+ ions)
(b) Role of potassium ions (K+) in stomatal opening and closing 44

45. Changes in turgor pressure result primarily from the reversible uptake and loss of potassium ions (K) by the guard cells
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46. Stimuli for Stomatal Opening and Closing
Generally, stomata open during the day and close at night to minimize water loss
Stomatal opening at dawn is triggered by
Light
CO2 depletion
An internal “clock” in guard cells
All eukaryotic organisms have internal clocks; circadian rhythms are 24-hour cycles
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47. Effects of Transpiration on Wilting and Leaf Temperature
Plants lose a large amount of water by transpiration
If the lost water is not replaced by sufficient transport of water, the plant will lose water and wilt
Transpiration also results in evaporative cooling, which can lower the temperature of a leaf and prevent protein denaturation
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48. Adaptations That Reduce Evaporative Water Loss
Xerophytes are plants adapted to arid climates
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49. Oleander (Nerium oleander)
Figure 29.20
Ocotillo
(Fouquieria
splendens)
Oleander (Nerium oleander)
Thick cuticle
Upper epidermal tissue
100 m
Trichomes
(“hairs”)
Crypt
Stoma
Lower epidermal
tissue
Figure Some xerophytic adaptations
Old man cactus
(Cephalocereus
senilis) 49

50. Some desert plants complete their life cycle during the rainy season
Others have leaf modifications that reduce the rate of transpiration
Some plants use a specialized form of photosynthesis called crassulacean acid metabolism (CAM) where stomatal gas exchange occurs at night
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