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

2. Overview: Underground Plants
Stone plants (Lithops) are adapted to life in the desert
Two succulent leaf tips are exposed above ground; the rest of the plant lives below ground
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3. Figure 29.1
Figure 29.1 Plants or pebbles? 3

4. 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
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5. Concept 29.1: Adaptations for acquiring resources were key steps in the evolution of vascular plants
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
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6. 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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7. Xylem transports water and minerals from roots to shoots
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
Phloem transports photosynthetic products from sources to sinks
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8. 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 8

9. 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 9

10. 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 10

11. Adaptations in each species represent compromises between enhancing photosynthesis and minimizing water loss
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12. Shoot Architecture and Light Capture
Stems serve as conduits for water and nutrients and as supporting structures for leaves
Shoot height and branching pattern affect light capture
There is a trade-off between growing tall and branching
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13. Phyllotaxy, the arrangement of leaves on a stem, is specific to each species
Most angiosperms have alternate phyllotaxy with leaves arranged in a spiral
The angle between leaves is 137.5 and likely minimizes shading of lower leaves
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14. Figure 29.3 24 32 42 29 40 16 11 19 21 27 8 3 34 6 14 13 26
Shoot
apical
meristem 1 22 5 9 18
Buds 10 4 2 31 17
Figure 29.3 Emerging phyllotaxy of Norway spruce 23 7 12 15 20 25 28
1 mm 14

15. Figure 29.3a
Figure 29.3a Emerging phyllotaxy of Norway spruce (part 1: SEM, small) 15

16. Figure 29.3b 24 32 42 29 40 16 11 19 21 27 34 8 3 6 14 13 26
Shoot
apical
meristem 1 5 22 9 18 10 4 2 31 17 7 12
Figure 29.3b Emerging phyllotaxy of Norway spruce (part 2: SEM, enlarged) 23 15 20 25 28
1 mm 16

17. The productivity of each plant is affected by the depth of the canopy, the leafy portion of all the plants in the community
Shedding of lower shaded leaves when they respire more than photosynthesize, self-pruning, occurs when the canopy is too thick
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18. Leaf orientation affects light absorption
In low-light conditions, horizontal leaves capture more sunlight
In sunny conditions, vertical leaves are less damaged by sun and allow light to reach lower leaves
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19. Root Architecture and Acquisition of Water and Minerals
Soil is a resource mined by the root system
Root growth can adjust to local conditions
For example, roots branch more in a pocket of high nitrate than in a pocket of low nitrate
Roots are less competitive with other roots from the same plant than with roots from different plants
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20. Mutualisms with fungi helped plants colonize land
Roots and the hyphae of soil fungi form mutualistic associations called mycorrhizae
Mutualisms with fungi helped plants colonize land
Mycorrhizal fungi increase the surface area for absorbing water and minerals
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21. Concept 29.2: Different mechanisms transport substances over short or long distances
There are two major transport pathways through plants
The apoplast
The symplast
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22. The Apoplast and Symplast: Transport Continuums
The apoplast consists of everything external to the plasma membrane
It includes cell walls, extracellular spaces, and the interior of vessel elements and tracheids
The symplast consists of the cytosol of the living cells in a plant, as well as the plasmodesmata
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23. Three transport routes for water and solutes are
The apoplastic route, through cell walls and extracellular spaces
The symplastic route, through the cytosol
The transmembrane route, across cell walls
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24. Cell wall Apoplastic route Cytosol Symplastic route
Figure 29.4
Cell wall
Apoplastic route
Cytosol
Symplastic route
Transmembrane route
Key
Figure 29.4 Cell compartments and routes for short-distance transport
Plasmodesma
Apoplast
Plasma membrane
Symplast 24

25. Short-Distance Transport of Solutes Across Plasma Membranes
Plasma membrane permeability controls short-distance movement of substances
Both active and passive transport occur in plants
In plants, membrane potential is established through pumping H by proton pumps
In animals, membrane potential is established through pumping Na by sodium-potassium pumps
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26. (a) H+ and membrane potential
Figure 29.5
CYTOPLASM
EXTRACELLULAR
FLUID H+ H+ S H+ H+ H+
Hydrogen
ion H+ H+ S H+ S H+ H+ H+ H+ H+ H+ H+ S H+ S H+ S
Proton
pump H+ H+
H+/sucrose
cotransporter
Sucrose
(neutral solute)
(a) H+ and membrane potential
(b) H+ and cotransport of neutral solutes H+ H+
NO3−
NO3− H+ H+ K+
Potassium ion H+ H+ K+
Nitrate H+ K+
Figure 29.5 Solute transport across plant cell plasma membranes K+ H+
NO3−
NO3−
NO3− K+
NO3− K+ K+ H+
H+/NO3−
cotransporter H+ H+
Ion channel
(c) H+ and cotransport of ions
(d) Ion channels 26

27. (a) H and membrane potential
Figure 29.5a
EXTRACELLULAR
FLUID
CYTOPLASM H+
Hydrogen
ion H+ H+ H+ H+ H+ H+
Proton
pump
Figure 29.5a Solute transport across plant cell plasma membranes (part 1: membrane potential) H+
(a) H and membrane potential 27

28. (b) H and cotransport of neutral solutes
Figure 29.5b H+ S H+ H+ H+ H+ H+ H+ S S H+ H+ H+ S S S H+
Figure 29.5b Solute transport across plant cell plasma membranes (part 2: neutral solutes)
H/sucrose
cotransporter
Sucrose
(neutral solute)
(b) H and cotransport of neutral solutes 28

29. (c) H+ and cotransport of ions
Figure 29.5c H+ H+
NO3−
NO3− H+ H+ H+ H+
Nitrate H+ H+
NO3−
NO3−
NO3−
NO3− H+
Figure 29.5c Solute transport across plant cell plasma membranes (part 3: ions)
H+/NO3−
cotransporter H+ H+
(c) H+ and cotransport of ions 29

30. K+ Potassium ion K+ K+ K+ K+ K+ K+ Ion channel (d) Ion channels
Figure 29.5d K+
Potassium ion K+ K+ K+ K+ K+ K+
Figure 29.5d Solute transport across plant cell plasma membranes (part 4: ion channels)
Ion channel
(d) Ion channels 30

31. Plant cells use the energy of H gradients to cotransport other solutes by active transport
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32. Plant cell membranes have ion channels that allow only certain ions to pass
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33. Short-Distance Transport of Water Across Plasma Membranes
To survive, plants must balance water uptake and loss
Osmosis determines the net uptake or water loss by a cell and is affected by solute concentration and pressure
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34. Water potential determines the direction of movement of water
Water potential is a measurement that combines the effects of solute concentration and pressure
Water potential determines the direction of movement of water
Water flows from regions of higher water potential to regions of lower water potential
Potential refers to water’s capacity to perform work
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35.   0 MPa for pure water at sea level and at room temperature
Water potential is abbreviated as  and measured in a unit of pressure called the megapascal (MPa)
  0 MPa for pure water at sea level and at room temperature
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36. How Solutes and Pressure Affect Water Potential
Both pressure and solute concentration affect water potential
This is expressed by the water potential equation:   S  P
The solute potential (S) of a solution is directly proportional to its molarity
Solute potential is also called osmotic potential
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37. Pressure potential (P) is the physical pressure on a solution
Turgor pressure is the pressure exerted by the plasma membrane against the cell wall, and the cell wall against the protoplast
The protoplast is the living part of the cell, which also includes the plasma membrane
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38. Water Movement Across Plant Cell Membranes
Water potential affects uptake and loss of water by plant cells
If a flaccid (limp) cell is placed in an environment with a higher solute concentration, the cell will lose water and undergo plasmolysis
Plasmolysis occurs when the protoplast shrinks and pulls away from the cell wall
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39. (a) Initial conditions: cellular   environmental 
Figure 29.6
Initial flaccid cell: P S 
−0.7
0.4 M sucrose
solution:
−0.7 MPa  
Pure water:  P S
Plasmolyzed
cell at osmotic
equilibrium
with its
surroundings
−0.9  P S
Turgid cell
at osmotic
equilibrium
with its
surroundings
0 MPa  
−0.9 MPa  
−0.9  P S
0.7  P S
−0.7
−0.9 MPa  
0 MPa  
Figure 29.6 Water relations in plant cells
(a) Initial conditions:
cellular   environmental 
(b) Initial conditions:
cellular   environmental  39

40. (a) Initial conditions: cellular   environmental 
Figure 29.6a
Initial flaccid cell: P S 
−0.7
0.4 M sucrose
solution:  
−0.7 MPa 
Plasmolyzed
cell at osmotic
equilibrium
with its
surroundings P S
−0.9  
−0.9 MPa P S 
−0.9
Figure 29.6a Water relations in plant cells (part 1: plasmolyzed cell)  
−0.9 MPa
(a) Initial conditions:
cellular   environmental  40

41. (b) Initial conditions: cellular   environmental 
Figure 29.6b
Initial flaccid cell: P S 
−0.7
Pure water:  
−0.7 MPa P S 
Turgid cell
at osmotic
equilibrium
with its
surroundings  
0 MPa P S 
0.7
−0.7
Figure 29.6b Water relations in plant cells (part 2: turgid cell)  
0 MPa
(b) Initial conditions:
cellular   environmental  41

42. If a flaccid cell is placed in a solution with a lower solute concentration, the cell will gain water and become turgid (firm)
Turgor loss in plants causes wilting, which can be reversed when the plant is watered
Video: Turgid Elodea
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43. Figure 29.7
Wilted
Turgid
Figure 29.7 A moderately wilted plant can regain its turgor when watered. 43

44. Figure 29.7a
Wilted
Figure 29.7a A moderately wilted plant can regain its turgor when watered. (part 1: wilted plant) 44

45. Figure 29.7b
Turgid
Figure 29.7b A moderately wilted plant can regain its turgor when watered. (part 2: turgid plant) 45

46. Aquaporins: Facilitating Diffusion of Water
Aquaporins are transport proteins in the cell membrane that allow the passage of water
These affect the rate of water movement across the membrane
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47. Long-Distance Transport: The Role of Bulk Flow
Efficient long-distance transport of fluid requires bulk flow, the movement of a fluid driven by pressure
Water and solutes move together through tracheids and vessel elements of xylem and sieve-tube elements of phloem
Efficient movement is possible because mature tracheids and vessel elements have no cytoplasm, and sieve-tube elements have few organelles in their cytoplasm
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48. Concept 29.3: Plants roots absorb essential elements from the soil
Water, air, and soil minerals contribute to plant growth
80–90% of a plant’s fresh mass is water
96% of plant’s dry mass consists of carbohydrates from the CO2 assimilated during photosynthesis
4% of a plant’s dry mass is inorganic substances from soil
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49. Macronutrients and Micronutrients
More than 50 chemical elements have been identified among the inorganic substances in plants, but not all of these are essential to plants
There are 17 essential elements, chemical elements required for a plant to complete its life cycle
Researchers use hydroponic culture, the growth of plants in mineral solutions, to determine which chemical elements are essential
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50. containing all minerals Experimental: Solution without potassium
Figure 29.8
Technique
Figure 29.8 Research method: hydroponic culture
Control: Solution
containing all minerals
Experimental: Solution
without potassium 50

51. Table 29.1
Table 29.1 Essential elements in plants 51

52. Nine of the essential elements are called macronutrients because plants require them in relatively large amounts
The macronutrients are carbon, oxygen, hydrogen, nitrogen, phosphorus, sulfur, potassium, calcium, and magnesium
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53. Plants with C4 and CAM photosynthetic pathways also need sodium
The remaining eight are called micronutrients because plants need them in very small amounts
The micronutrients are chlorine, iron, manganese, boron, zinc, copper, nickel, and molybdenum
Plants with C4 and CAM photosynthetic pathways also need sodium
Micronutrients function as cofactors, nonprotein helpers in enzymatic reactions
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54. Symptoms of Mineral Deficiency
Symptoms of mineral deficiency depend on the nutrient’s function and mobility within the plant
Deficiency of a mobile nutrient usually affects older organs more than young ones
Deficiency of a less mobile nutrient usually affects younger organs more than older ones
The most common deficiencies are those of nitrogen, potassium, and phosphorus
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55. Healthy Phosphate-deficient Potassium-deficient Nitrogen-deficient
Figure 29.9
Healthy
Phosphate-deficient
Potassium-deficient
Figure 29.9 The most common mineral deficiencies, as seen in maize leaves
Nitrogen-deficient 55

56. Soil Management
Ancient farmers recognized that crop yields would decrease on a particular plot over the years
Soil management, by fertilization and other practices, allowed for agriculture and cities
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57. Fertilization
In natural ecosystems, nutrients are recycled through decomposition of feces and humus, dead organic material
Soils can become depleted of nutrients as plants and the nutrients they contain are harvested
Fertilization replaces mineral nutrients that have been lost from the soil
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58. Organic fertilizers are composed of manure, fishmeal, or compost
Commercial fertilizers are enriched in nitrogen (N), phosphorus (P), and potassium (K)
Excess minerals are often leached from the soil and can cause algal blooms in lakes
Organic fertilizers are composed of manure, fishmeal, or compost
They release N, P, and K as they decompose
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59. Adjusting Soil pH
Soil pH affects cation exchange and the chemical form of minerals
Cations are more available in slightly acidic soil, as H+ ions displace mineral cations from clay particles
The availability of different minerals varies with pH
For example, at pH 8 plants can absorb calcium but not iron
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60. At present, 30% of the world’s farmland has reduced productivity because of soil mismanagement
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61. The Living, Complex Ecosystem of Soil
Plants obtain most of their mineral nutrients from the topsoil
The basic physical properties of soil are
Texture
Composition
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62. Soil Texture
Soil particles are classified by size; from largest to smallest they are called sand, silt, and clay
Topsoil is formed when mineral particles released from weathered rock mix with living organisms and humus
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63. Soil solution consists of water and dissolved minerals in the pores between soil particles
After a heavy rainfall, water drains from the larger spaces in the soil, but smaller spaces retain water because of its attraction to clay and other particles
Loams are the most fertile topsoils and contain equal amounts of sand, silt, and clay
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64. Topsoil Composition
A soil’s composition refers to its inorganic (mineral) and organic chemical components
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65. Most soil particles are negatively charged
Inorganic components of the soil include positively charged ions (cations) and negatively charged ions (anions)
Most soil particles are negatively charged
Anions (for example, NO3–, H2PO4–, SO42–) do not bind with negatively charged soil particles and can be lost from the soil by leaching
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66. Cations (for example, K, Ca2, Mg2) adhere to negatively charged soil particles; this prevents them from leaching out of the soil through percolating groundwater
During cation exchange, cations are displaced from soil particles by other cations
Displaced cations enter the soil solution and can be taken up by plant roots
Animation: Minerals from Soil
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67. Soil particle Root hair Cell wall K+ K+ Ca2+ Ca2+ Mg2+ K+ H+ H2O + CO2
Figure 29.10
Soil particle K+ K+
Ca2+
Ca2+
Mg2+ K+ H+
H2O + CO2
H2CO3
HCO3− + H+
Figure Cation exchange in soil
Root hair
Cell wall 67

68. Humus forms a crumbly soil that retains water but is still porous
Organic components of the soil include decomposed leaves, feces, dead organisms, and other organic matter, which are collectively named humus
Humus forms a crumbly soil that retains water but is still porous
It also increases the soil’s capacity to exchange cations and serves as a reservoir of mineral nutrients
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69. These organisms help to decompose organic material and mix the soil
Living components of topsoil include bacteria, fungi, algae and other protists, insects, earthworms, nematodes, and plant roots
These organisms help to decompose organic material and mix the soil
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70. Concept 29.4: Plant nutrition often involves relationships with other organisms
Plants and soil microbes have a mutualistic relationship
Dead plants provide energy needed by soil-dwelling microorganisms
Secretions from living roots support a wide variety of microbes in the near-root environment
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71. Soil Bacteria and Plant Nutrition
Soil bacteria exchange chemicals with plant roots, enhance decomposition, and increase nutrient availability
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72. Rhizobacteria
The soil layer surrounding the plant’s roots is the rhizosphere
Rhizobacteria thrive in the rhizosphere, and some can enter roots
The rhizosphere has high microbial activity because of sugars, amino acids, and organic acids secreted by roots
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73. Rhizobacteria known as plant-growth-promoting rhizobacteria can play several roles
Produce hormones that stimulate plant growth
Produce antibiotics that protect roots from disease
Absorb toxic metals or make nutrients more available to roots
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74. 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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75. (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 75

76. (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 76

77. (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 77

78. 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 78

79. 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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80. Nitrogen is lost to the atmosphere when denitrifying bacteria convert NO3– to N2
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81. Nitrogen-Fixing Bacteria: A Closer Look
Nitrogen is abundant in the atmosphere but unavailable to plants due to the triple bond between atoms in N2
Nitrogen fixation is the conversion of nitrogen from N2 to NH3:
Some nitrogen-fixing bacteria are free-living; others form intimate associations with plant roots
N2  8 e–  8 H  16 ATP  2 NH3  H2  16 ADP  16
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82. 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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83. Figure 29.12
Nodules
Figure Soybean root nodules
Roots 83

84. 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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85. 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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86. The Two Main Types of Mycorrhizae
Mycorrhizal associations consist of two major types
Ectomycorrhizae
Arbuscular mycorrhizae
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87. Mantle (fungal sheath)
Figure 29.13
Epidermis
Cortex
Mantle (fungal sheath)
Epidermal
cell
(Colorized SEM)
Endodermis
Fungal
hyphae
between
cortical
cells
1.5 mm
Mantle
(fungal sheath)
(LM)
50 m
(a) Ectomycorrhizae
Epidermis
Cortex
Cortical cell
Figure Mycorrhizae
Endodermis
Fungal
hyphae
Fungal
vesicle
Casparian
strip
Root
hair
10 m
Arbuscules
Plasma
membrane
(LM)
(b) Arbuscular mycorrhizae (endomycorrhizae) 87

88. Mantle (fungal sheath)
Figure 29.13a
Epidermis
Cortex
Mantle (fungal sheath)
Epidermal
cell
Endodermis
(Colorized SEM)
Fungal
hyphae
between
cortical
cells
1.5 mm
Mantle
(fungal sheath)
Figure 29.13a Mycorrhizae (part 1: ectomycorrhizae)
(LM)
50 m
(a) Ectomycorrhizae 88

89. (Colorized SEM) 1.5 mm Mantle (fungal sheath) Figure 29.13aa
Figure 29.13aa Mycorrhizae (part 1a: ectomycorrhizae, SEM)
1.5 mm
Mantle
(fungal sheath) 89

90. Epidermal cell Fungal hyphae between cortical cells (LM) 50 m
Figure 29.13ab
Epidermal
cell
Fungal
hyphae
between
cortical
cells
Figure 29.13ab Mycorrhizae (part 1b: ectomycorrhizae, LM)
(LM)
50 m 90

91. (b) Arbuscular mycorrhizae (endomycorrhizae)
Figure 29.13b
Epidermis
Cortex
Cortical cell
Endodermis
Fungal
hyphae
Fungal
vesicle
Casparian
strip
Root
hair
10 m
Arbuscules
Plasma
membrane
Figure 29.13b Mycorrhizae (part 2: endomycorrhizae)
(LM)
(b) Arbuscular mycorrhizae (endomycorrhizae) 91

92. Cortical cell 10 m Arbuscules (LM) Figure 29.13ba
Figure 29.13ba Mycorrhizae (part 2a: endomycorrhizae, LM)
(LM) 92

93. In ectomycorrhizae, the mycelium of the fungus forms a dense sheath over the surface of the root
These hyphae form a network in the apoplast but do not penetrate the root cells
Ectomycorrhizae occur in about 10% of plant families, most of which are woody (for example, pine, birch, and eucalyptus)
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94. The arbuscules are important sites of nutrient transfer
In arbuscular mycorrhizae, microscopic fungal hyphae extend into the root
These mycorrhizae penetrate the cell wall but not the plasma membrane to form branched arbuscules within root cells
The arbuscules are important sites of nutrient transfer
Arbuscular mycorrhizae occur in about 85% of plant species, including most crops
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95. Agricultural and Ecological Importance of Mycorrhizae
Seeds can be inoculated with fungal spores to promote formation of mycorrhizae
Some invasive exotic plants disrupt interactions between native plants and their mycorrhizal fungi
For example, garlic mustard slows growth of other plants by preventing the growth of mycorrhizal fungi
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96. Experiment Results 300 200 plant biomass (%) Increase in 100 Invaded
Figure 29.14
Experiment
Results
300
200
plant biomass (%)
Increase in
100
Invaded
Uninvaded
Sterilized
invaded
Sterilized
uninvaded
Soil type 40 30
colonization (%)
Mycorrhizal
Figure Inquiry: Does the invasive weed garlic mustard disrupt mutualistic associations between native tree seedlings and arbuscular mycorrhizal fungi? 20
Seedlings 10
Sugar maple
Red maple
Invaded
Uninvaded
White ash
Soil type 96

97. Figure 29.14a
Experiment
Figure 29.14a Inquiry: Does the invasive weed garlic mustard disrupt mutualistic associations between native tree seedlings and arbuscular mycorrhizal fungi? (part 1: experiment) 97

98. Results 300 200 plant biomass (%) Increase in 100 Invaded Uninvaded
Figure 29.14b
Results
300
200
plant biomass (%)
Increase in
100
Invaded
Uninvaded
Sterilized
invaded
Sterilized
uninvaded
Soil type 40
Figure 29.14b Inquiry: Does the invasive weed garlic mustard disrupt mutualistic associations between native tree seedlings and arbuscular mycorrhizal fungi? (part 2: results) 30
colonization (%)
Mycorrhizal 20
Seedlings 10
Sugar maple
Red maple
Invaded
Uninvaded
White ash
Soil type 98

99. 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
© 2014 Pearson Education, Inc. 99

100. Epiphytes grow on other plants and obtain water and minerals from rain, rather than tapping their hosts for sustenance
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101. Staghorn fern, an epiphyte
Figure 29.15a
Figure 29.15a Exploring unusual nutritional adaptations in plants (part 1: epiphytes)
Staghorn fern, an epiphyte
101

102. 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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102

103. 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
103

104. Mistletoe, a photosynthetic parasite
Figure 29.15ba
Figure 29.15ba Exploring unusual nutritional adaptations in plants (part 2a: parasitic, mistletoe)
Mistletoe, a photosynthetic
parasite
104

105. Dodder, a nonphoto- synthetic parasite (orange) Figure 29.15bb
Figure 29.15bb Exploring unusual nutritional adaptations in plants (part 2b: parasitic, dodder)
Dodder, a nonphoto-
synthetic parasite
(orange)
105

106. Indian pipe, a nonphoto- synthetic parasite of mycorrhizae
Figure 29.15bc
Figure 29.15bc Exploring unusual nutritional adaptations in plants (part 2c: parasitic, indian pipe)
Indian pipe, a nonphoto-
synthetic parasite of
mycorrhizae
106

107. Carnivorous plants are photosynthetic but obtain nitrogen by killing and digesting mostly insects
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108. Carnivorous plants Sundew Pitcher plants Venus flytraps Figure 29.15c
Figure 29.15c Exploring unusual nutritional adaptations in plants (part 3: carnivorous plants)
108

109. Pitcher plants Figure 29.15ca
Figure 29.15ca Exploring unusual nutritional adaptations in plants (part 3a: carnivorous, pitcher plants)
Pitcher plants
109

110. Pitcher plants Figure 29.15cb
Figure 29.15cb Exploring unusual nutritional adaptations in plants (part 3b: carnivorous, pitcher plant)
Pitcher plants
110

111. Figure 29.15cc
Figure 29.15cc Exploring unusual nutritional adaptations in plants (part 3c: carnivorous, sundew)
Sundew
111

112. Venus flytrap Figure 29.15cd
Figure 29.15cd Exploring unusual nutritional adaptations in plants (part 3d: carnivorous, venus fly trap)
Venus flytrap
112

113. Venus flytrap Figure 29.15ce
Figure 29.15ce Exploring unusual nutritional adaptations in plants (part 3e: carnivorous, venus fly trap)
Venus flytrap
113

114. 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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114

115. 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
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115

116. The concentration of essential minerals is greater in the roots than in the soil because of active transport
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116

117. Transport of Water and Minerals into the Xylem
The endodermis is the innermost layer of cells in the root cortex
It surrounds the vascular cylinder and is the last checkpoint for selective passage of minerals from the cortex into the vascular tissue
Water can cross the cortex via the symplast or apoplast
Animation: Transport in Roots
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117

118. The endodermis: controlled entry to the vascular cylinder (stele) 5
Figure 29.16
Casparian strip
Endodermal
cell
Pathway along
apoplast 4
Pathway
through
symplast 5 1
Apoplastic
route
Casparian strip
Plasma
membrane
Apoplastic
route 1 2
Symplastic
route 3
Figure Transport of water and minerals from root hairs to the xylem 2 4 5
Vessels
(xylem)
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
118

119. 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
119

120. The endodermis: controlled entry to the vascular cylinder (stele)
Figure 29.16b
Casparian strip
Endodermal
cell
Pathway along
apoplast 4
Pathway
through
symplast 5
Figure 29.16b Transport of water and minerals from root hairs to the xylem (part 2) 4
The endodermis: controlled entry
to the vascular cylinder (stele) 5
Transport in the xylem
120

121. 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
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121

122. 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
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122

123. Water and minerals now enter the tracheids and vessel elements
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
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123

124. Bulk Flow Transport via the Xylem
Xylem sap, water and dissolved minerals, is transported from roots to leaves by bulk flow
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
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124

125. 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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125

126. 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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126

127. 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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127

128. 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
128

129. 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
129

130. 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
130

131. 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 
131

132. 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
132

133. 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
133

134. 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)
134

135. 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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135

136. Thick secondary walls prevent vessel elements and tracheids from collapsing under negative pressure
Drought stress or freezing can cause cavitation, the formation of a water vapor pocket by a break in the chain of water molecules
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136

137. Xylem Sap Ascent by Bulk Flow: A Review
Bulk flow is driven by a water potential difference at opposite ends of xylem tissue
Bulk flow is driven by evaporation and does not require energy from the plant; like photosynthesis, it is solar powered
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137

138. Bulk flow differs from diffusion
It is driven by differences in pressure potential, not solute potential
It occurs in hollow dead cells, not across the membranes of living cells
It moves the entire solution, not just water or solutes
It is much faster
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138

139. 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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139

140. 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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140

141. 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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141

142. Guard cells turgid/Stoma open Guard cells flaccid/Stoma closed
Figure 29.19
Guard cells turgid/Stoma open
Guard cells flaccid/Stoma closed
Radially oriented
cellulose microfibrils
Cell
wall
Vacuole
Guard cell
(a) Changes in guard cell shape and stomatal opening and
closing (surface view)
H2O
H2O
H2O
H2O
Figure Mechanisms of stomatal opening and closing
H2O K+
H2O
H2O
H2O
H2O
H2O
(b) Role of potassium ions (K+) in stomatal opening and closing
142

143. 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)
143

144. 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
144

145. Changes in turgor pressure result primarily from the reversible uptake and loss of potassium ions (K) by the guard cells
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145

146. 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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146

147. Drought stress can cause stomata to close during the daytime
The hormone abscisic acid (ABA) is produced in response to water deficiency and causes the closure of stomata
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147

148. 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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148

149. Adaptations That Reduce Evaporative Water Loss
Xerophytes are plants adapted to arid climates
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149

150. 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)
150

151. Ocotillo (leafless) Figure 29.20a
Figure 29.20a Some xerophytic adaptations (part 1: leafless ocotillo)
Ocotillo (leafless)
151

152. Ocotillo after heavy rain
Figure 29.20b
Figure 29.20b Some xerophytic adaptations (part 2: ocotillo with leaves)
Ocotillo after heavy rain
152

153. Ocotillo leaves Figure 29.20c
Figure 29.20c Some xerophytic adaptations (part 3: ocotillo leaves)
Ocotillo leaves
153

154. Upper epidermal tissue
Figure 29.20d
Thick cuticle
Upper epidermal tissue
100 m
Figure 29.20d Some xerophytic adaptations (part 4: oleander, LM)
Trichomes
(“hairs”)
Crypt
Stoma
Lower
epidermal
tissue
Oleander leaf cross section
154

155. Oleander flowers Figure 29.20e
Figure 29.20e Some xerophytic adaptations (part 5: oleander)
155

156. Figure 29.20f
Figure 29.20f Some xerophytic adaptations (part 6: old man cactus)
Old man cactus
156

157. 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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157

158. Concept 29.7: Sugars are transported from sources to sinks via the phloem
The products of photosynthesis are transported through phloem by the process of translocation
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158

159. Movement from Sugar Sources to Sugar Sinks
In angiosperms, sieve-tube elements are the conduits for translocation
Phloem sap is an aqueous solution that is high in sucrose
It travels from a sugar source to a sugar sink
A sugar source is an organ that is a net producer of sugar, such as mature leaves
A sugar sink is an organ that is a net consumer or storer of sugar, such as a tuber or bulb
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159

160. A storage organ can be both a sugar sink in summer and sugar source in winter
Sugar must be loaded into sieve-tube elements before being exported to sinks
Depending on the species, sugar may move by symplastic or both symplastic and apoplastic pathways
Companion cells enhance solute movement between the apoplast and symplast
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160

161. (a) Sucrose manufactured in mesophyll cells
Figure 29.21
Apoplast
Symplast
Companion
(transfer) cell
Mesophyll cell
High H+ concentration
Cotransporter
Cell walls (apoplast) H+
Sieve-tube
element
Proton
pump
Plasma
membrane S
Plasmodesmata
Figure Loading of sucrose into phloem H+ H+
Sucrose
Mesophyll
cell
Bundle-
sheath cell
Phloem
parenchyma cell S
Low H+ concentration
(a) Sucrose manufactured in mesophyll cells
can travel via the symplast (blue arrows)
to sieve-tube elements.
(b) A chemiosmotic mechanism is
responsible for the active transport of
sucrose.
161

162. (a) Sucrose manufactured in mesophyll cells
Figure 29.21a
Companion
(transfer) cell
Mesophyll cell
Cell walls (apoplast)
Sieve-tube
element
Plasma
membrane
Plasmodesmata
Apoplast
Figure 29.21a Loading of sucrose into phloem (part 1)
Bundle-
sheath cell
Phloem
parenchyma cell
Mesophyll
cell
Symplast
(a) Sucrose manufactured in mesophyll cells
can travel via the symplast (blue arrows)
to sieve-tube elements.
162

163. (b) A chemiosmotic mechanism is
Figure 29.21b
High H concentration
Cotransporter H+
Proton
pump S H+
Sucrose H+
Figure 29.21b Loading of sucrose into phloem (part 2) S
Low H concentration
(b) A chemiosmotic mechanism is
responsible for the active transport of
sucrose.
163

164. In most plants, phloem loading requires active transport
Proton pumping and cotransport of sucrose and H+ enable the cells to accumulate sucrose
At the sink, sugar molecules diffuse from the phloem to sink tissues and are followed by water
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164

165. Bulk Flow by Positive Pressure: The Mechanism of Translocation in Angiosperms
Phloem sap moves through a sieve tube by bulk flow driven by positive pressure called pressure flow
Animation: Phloem Translocation Spring
Animation: Phloem Translocation Summer
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165

166. Sieve tube (phloem) Vessel (xylem)
Figure 29.22
Sieve
tube
(phloem)
Source cell
(leaf)
Vessel
(xylem) 1
Loading of sugar
H2O 1
Sucrose
H2O 2 2
Uptake of water
Bulk flow by negative pressure
Bulk flow by positive pressure 3
Unloading of sugar
Sink cell
(storage
root)
Figure Bulk flow by positive pressure (pressure flow) in a sieve tube 4
Recycling of water 4 3
Sucrose
H2O
166

167. Sometimes there are more sinks than can be supported by sources
Self-thinning is the dropping of sugar sinks such as flowers, seeds, or fruits
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167

168. Figure 29.UN01a
Figure 29.UN01a Skills exercise: calculating and interpreting temperature coefficients (part 1)
168

169. Figure 29.UN01b
Figure 29.UN01b Skills exercise: calculating and interpreting temperature coefficients (part 2)
169

170. H2O CO2 O2 O2 CO2 Minerals H2O Figure 29.UN02
Figure 29.UN02 Summary of key concepts: acquiring resources O2
CO2
Minerals
H2O
170

171. Figure 29.UN03
Figure 29.UN03 Test your understanding: root uptake
171