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Trinity Term 1 > Vascular plants and life on land > Flashcards

Vascular plants and life on land Flashcards

1
Q

Give an overview of the world’s terrestrial biomes

A
  • tropical forest
  • temperate forest
  • boreal forest
  • savanna
  • grassland/shrubland
  • tundra
  • semi-desert/desert/ice
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2
Q

Which two climate axes help delineate the major biomes

A
  • x: MAT (°C)
  • y: MAP (mm)
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3
Q

MAT

A

mean annual temperature

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4
Q

MAP

A

mean annual precipitation

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5
Q

There is considerable diversity of plant life-forms in

A
  • water-limited biomes
  • e.g. Sonoran Desert, California, USA
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6
Q

List the principal plant life-forms in water-limited environments from high to low productivity

A
  • ephemerals
  • drought-deciduous shrubs
  • phreatophytes
  • evergreen shrubs
  • leaf/stem succulents
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7
Q

Describe ephemerals

A
  • short life cycle
  • dormancy
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8
Q

Describe drought-deciduous shrubs

A

leaf shedding

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9
Q

Describe phreatophytes

A

deep-rooted shrubs and trees

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10
Q

Describe evergreen shrubs

A

year-round growth

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11
Q

Describe leaf/stem succulents

A
  • shallow roots
  • water storage
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12
Q

In drier climates, annual biome NPP is

A

an (almost) linear function of precipitation

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13
Q

Describe the principal plant water interaction

A

movement of water through the SPAC

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14
Q

SPAC

A

soil–plant–atmosphere continuum

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15
Q

Describe the movement of water through the SPAC

A
  • movement from cell-to-cell across semi-permeable membranes is
    osmotic (driven by differences in water potential)
  • movement through open conduits in the long-distance transport pathways, as well as through the soil, is in response to hydrostatic pressure gradients
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16
Q

What are the long-distance transport pathways of plants?

A

xylem and phloem

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17
Q

Describe the gradient across a plant

A
  • soil pressure difference
  • root water potential difference
  • xylem pressure difference
  • leaf air spaces water vapour concentration difference
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18
Q

pressure difference

A

delta-psi-p

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19
Q

water potential difference

A

delta-psi-W

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20
Q

water vapour concentration difference

A

delta-c-W-V

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21
Q

Give the equations for water potential

A
  • psi = (muw - muw0) / Vw
  • psi = P - pi
  • psiW = psip + psis
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22
Q

water potential

A
  • psi
  • units of pressure
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23
Q

muw

A

chemical potential of water in the observed state

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24
Q

muw0

A

chemical potential of pure water

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25
Q

Vw

A

partial molal volume of water

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26
Q

P

A

turgour pressure

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27
Q

pi

A

osmotic pressure

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28
Q

psip

A

pressure potential

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29
Q

psis

A

solute (or osmotic) potential

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30
Q

1MPa =

A
  • 10 bar
  • 10atm
  • 7.6mHg
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31
Q

Describe exploration of the soil by roots

A

mining for water and nutrients below ground

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32
Q

soil is a

A

complex, heterogeneous phase

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33
Q

How does water move into a plant?

A
  • via the root hair or epidermal cell
  • osmotically
  • across a cell membrane
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34
Q

Describe the three pathways for movement into and across a root

A
  1. Apoplastic pathway
  2. Symplastic pathway
  3. Transcellular pathway
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35
Q

apoplastic pathway

A

through cell walls only, up to endodermis

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36
Q

symplastic pathway

A

via cell interior and plasmodesmata

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37
Q

transcellular pathway

A

across walls and membranes

38
Q

Describe movement of water through a plant

A
  • radially across the root cortex to the stele
  • longitudinally through the xylem
39
Q

stele

A

vascular tissue

40
Q

xylem

A

tracheary elements

41
Q

Describe flow blockage through the apoplast

A

hydrophobic deposits (principally lignin) in the endodermis and (sometimes) exodermis

42
Q

What are a plant’s essential above-ground requirements

A
  • sunlight
  • CO2
43
Q

What are a plant’s essential below-ground requirements

A
  • H2O
  • N
  • K
  • Ca
  • Mg
  • P
  • S
  • Si
  • Cl
  • Fe
  • B
  • Mn
  • Na
  • Zn
  • Cu
  • Ni
  • Mo
44
Q

What is the ratio of molybdenum to hydrogen requirement in a plant

A

1:60,000,000

45
Q

Describe long-distance transport in the xylem

A
  • primarily water and dissolved mineral ions
  • water column is under tension
  • water is in metastable state; vulnerable to cavitation
46
Q

What is tension

A

negative hydrostatic pressure

47
Q

cavitation

A

air seeding

48
Q

Describe the tensile strength of water

A

great!

49
Q

Describe the development of xylem elements

A
  • procambial cells form phloem tissue, xylem parenchyma, fibres etc.
  • mesophyll cell dedifferentiates and elongates
  • undergoes secondary wall deposition
  • undegroes apoptosis to form a mature treachery element
50
Q

wood

A

secondary xylem

51
Q

Describe the evolutionary origins of wood

A
  • Early Devonian (~ 400 Ma)
  • early tracheophytic lignophyte
  • pyritised specimens with euphyllophyte affinities sim. to Psilophyton
  • thick-walled tracheids in cortex interpreted as wood (occasional anticlinal divisions typical of lignophytes)
  • single-walled spaces interpreted as rays (not preserved)
  • possible remains of vascular cambium
  • small size of specimens suggests early function of wood more likely associated with efficient water conduction rather than mechanical support
52
Q

Describe fluid flow in xylem elements

A
  • depends strongly on r of conduit
  • described by Hagen–Poiseuille equation
53
Q

radius

A

r

54
Q

Give the Hagen–Poiseuille equation

A

volume of flow rate per tube Jv = (pir^4 / 8eta) dP/dx

55
Q

The Hagen-Poiseuille equation is analogous to

A

Ohm’s law

56
Q

For a given cross-sectional area, volume of flow rate per tube Jv =

A

(r^2/8eta) dP/dx

57
Q

Tracheids are typical of

A
  • gymnosperms
  • some basally diverging angiosperm lineages
  • many monocots
58
Q

Vessels are typical of

A

most eudicots

59
Q

What are the possible mechanisms of long-distance solution transport in the xylem?

A

(3) Root pressure
(4) Cohesion–tension(–adhesion) theory:
* high tensile strength of water (cohesion–tension) * strong forces of adhesion to hydrophilic surfaces * but note vulnerability of fluid under tension to
cavitation (embolism)

60
Q

Give Fick’s laws of diffusion:

A

te = Le^2 / 4Ds

61
Q

te =

A

time

62
Q

Le

A

distance

63
Q

Ds

A

diffusion coefficient of molecule (typically 10^-9m2s-1)

64
Q

Give the equation for capillarity rise

A

(1.49x10^-5m2) / radius

65
Q

Describe root pressure

A
  • positive pressure in the xylem can result from active pumping of solutes from living, metabolically active root cells into the xylem, followed by osmotic influx of water
  • responsible for guttation of water from hydathodes along leaf margins
66
Q

Why isn’t root pressure valid?

A
  • gravitational force on water column is 0.01 MPa m−1 or 0.1 MPa (i.e. 1 bar) for every 10 m
  • typical root pressures = 0.01 to 0.03 MPa
  • root pressure could only raise water column by 1 to 3m
67
Q

Give an example of xylem sap under positive pressure

A

exudation of xylem sap from maple trees

68
Q

Describe exudation of xylem sap from maple trees

A
  • mobilisation of sugars into the xylem in early springtime to support bud break
  • commercial use for xylem sap harvested in NE North America
69
Q

embolism

A

cavitation

70
Q

Describe the structure of a Gymnosperm pit membrane

A

torus-margo

71
Q

Describe the structure of an angiosperm pit membrane

A

homogenous

72
Q

Describe embolism and pit membranes

A

when adjacent tracheary elements are both water-filled, pit membranes are not subject to significant pressure differentials

73
Q

When does embolism occur?

A

in response to drought stress

74
Q

What happens if tension increases?

A

Ψ becomes more negative

75
Q

Describe the propagation of air-seeding in embolism-sensitive species

A

if one tracheary element (on the right side) becomes embolised, and the tension increases in the adjacent fluid-filled element (on the left side), the pressure differential causes the porous pit membrane to deflect, but at a critical point the capillary seal gives way, allowing air-seeding to propagate

76
Q

What are the features of pit membranes that prevent air seeding?

A
  • increased size of the pit torus (gymnosperms)
  • elaborate vestures
  • thickness (angiosperms)
77
Q

Describe some xylem vulnerabilities

A
  • occlusion by microbes, e.g. Xylella fastidiosa
  • occlusion by secretions e.g. tyloses, resins
  • cavitation
78
Q

air seeding occurs on

A

increasing tension

79
Q

What can a plant do to cavitated elements?

A

refill them

80
Q

Describe Sequoia sempervirens

A
  • ## 113m high giant redwood
81
Q

physiological limits of tree height…

A

~ 125 m

82
Q

which factors affect the physiological limit of tree height?

A
  • leaf density
  • CO2
  • water
  • photosynthetic efficiency
83
Q

Describe transfusion tracheids in cycads

A

Contrast with branched vascular anatomy in angiosperm leaves

84
Q

Describe the relationship between both vein density and vein diameter with leaf area

A
  • scale allometrically (logged)
85
Q

Describe the relationship between vein density and leaf area

A

Vein density decreases with leaf area

86
Q

Describe the relationship between vein diameter and leaf area

A

Vein diameter increases with leaf area

87
Q

Describe the scale independence of finest (minor) veins

A

ensures that the entire leaf is hydraulically well connected in angiosperms

88
Q

Describe water transport through the leaf

A

Water vapour exits the leaf, and carbon dioxide enters the leaf, by the same pathway

89
Q

The “conquest of the land” by plants was largely

A

the conquest of a highly desiccating atmosphere

90
Q

The higher capacity for water transport endowed by wide-diameter xylem vessels and a higher density of venation in leaves may have contributed to the evolutionary success of angiosperms.

A

Trinity Term 1 (38 decks)

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