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Trinity Term 1 > Plant energy balance and ecological diversity > Flashcards

Plant energy balance and ecological diversity Flashcards

1
Q

Photosynthesis

A
  • acquiring CO2
  • reactions catalysed by Rubisco
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2
Q

Rubisco

A

ribulose-1,5-bisphosphate carboxylase-oxygenase

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3
Q

Describe Calvin’s lollipop

A
  • pulse feeding with 14CO2
  • mercury-vapour lamps symmetrically placed either side of a culture of Chlorella
  • tap for draining off an aliquot into conical flask of hot ethanol below
  • timer
  • carbon allocation during photosynthesis across time
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4
Q

Describe dismutation

A
  • CO2 + RuBP -> 2 × 3-PGA
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5
Q

Summarise the stoichiometry of the Calvin–Benson–Bassham cycle

A
  • carboxylation
  • phosphorylation
  • reduction
  • regeneration
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6
Q

Summarise the Calvin-Benson-Bassham cycle

A

9 ATP + 6 NADPH required per 3 CO2 fixed

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7
Q

What is the net product of the Calvin-Benson-Bassham cycle

A

1 in every 6 triose-P (GAP / DHAP)

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8
Q

List some problems with RUBISCO

A
  • large multi-subunit enzyme (L8S8)
  • requires heavy investment in protein nitrogen
  • very low turnover number (~3s−1)
  • relatively high KMCO2; only ~50% CO2-saturated in C3 plants under present-day conditions
  • relatively poor selectivity for CO2 vs. O2 under typical physiological conditions
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9
Q

DEscibre some advantages of RUBISCO

A

extremely abundant protein (~50 % of soluble protein in photosynthetic tissues)

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10
Q

Describe Rubisco oxygenase

A

catalyses photorespiration (and consequent loss of CO2)

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11
Q

Describe the relationship between photorespiration and temperature

A
  • increases steeply
  • oxygenase activity of Rubisco increases more than carboxylase activity
  • concentration of dissolved CO2 in solution declines more than that of O2
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12
Q

Describe C4 plants

A
  • Kranz anatomy: ‘wreath’ or ‘ring’ surrounding RUBISCO
  • large bundle sheath cells surround the vascular bundles
  • contain prominent chloroplasts in centrifugal location
  • vascular bundles are quite closely spaced (separated by only two mesophyll cells on average)
  • mesophyll cells
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13
Q

Give an example of a C4 plant

A

Zea mays

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14
Q

centrifugal location

A

arranged around their outer walls

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15
Q

What is the C4 pathway

A

an energetically costly “CO2-concentrating mechanism”

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16
Q

List the key enzymes in the C4 pathway

A
  • carbonic anhydrase
  • phosphoenolpyruvate carboxylase
  • decarboxylase, e.g. malic enzyme
  • PPDK
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17
Q

carbonic anhydrase

A

CO2 + H2O → H2CO3 → HCO3− + H+

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18
Q

phosphoenolpyruvate carboxylase

A

HCO3− + PEP → OAA + Pi

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19
Q

malic enzyme

A

malate + NADP+ → pyruvate + CO2 + NADPH

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20
Q

PPDK

A
  • PEP regeneration, pyruvate, Pi dikinase
  • pyruvate + Pi + ATP → PEP + PPi + AMP
  • AMP + ATP → 2 ADP)
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21
Q

assimilation requirement

A

mol water consumed / mol CO2 fixed

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22
Q

assimilation requirement in C3 v C4

A
  • C3: 700-1300
  • C4: 400-600
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23
Q

Describe sugarcane

A
  • C4
  • exceptionally high productivity refined sugar
  • bioenergy crop
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24
Q

List some major C4 crops

A
  • sugarcane
  • maize (corn)
  • sorghum
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25
Q

Describe natural C4 biomes

A
  • tropical savannas dominated by C4 grasses
  • saline habitats with C4 halophytes
  • Queensland, Australia
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26
Q

Describe the global distribution of C4 photosynthesis

A

predominantly tropical savannas and subtropical grasslands

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27
Q

Describe air carbon composition

A

normal air contains 1.1% by volume of the stable isotope 13C

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28
Q

Describe the kinetic isotope effect wrt carbon

A

enzymes discriminate against 13C compared with 12C, but to different degrees

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29
Q

Describe PEP carboxylase

A
  • used for initial fixation of CO2 (as
    HCO3−) in C4 and CAM plants
  • discriminates against 13C to a lesser
    extent than does Rubisco
  • useful in large surveys of photosynthetic plant pathways - 1mg sufficient, applicable to herbarium species and fossils
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30
Q

Describe the major Monocot families of C4 plants

A
  • Poaceae (grasses)
  • Cyperaceae (sedges)
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31
Q

How many C4 plants are there?

A
  • c.8000 spp.
  • > 65 independent lineages
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32
Q

Describe the major Edict families of the C4 plants

A
  • Amaranthaceae (incl. Chenopodiaceae)
  • Euphorbiaceae
  • Asteraceae
  • Polygonaceae
  • Acanthaceae
  • Portulacaceae
    • 10 other minor families
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33
Q

Describe the Poaceae

A
  • 61% of all C4
  • 46% C4
34
Q

Describe the Cyperacaea

A
  • 18% of all C4
  • 27% C4
35
Q

Describe the Amaranthaceae (incl. Chenopodiaceae)

A
  • 10% of all C4
  • 30% C4
36
Q

Describe the Euphorbiaceae

A
  • 3% of all C4
  • 5% C4
37
Q

Describe the Asteraceae

A
  • 1% of all C4 plants
  • 1% C4
38
Q

Describe the Polygonaceae

A
  • 1% of all C4
  • 7% C4
39
Q

Describe the Acanthaceae

A
  • 1% of all C4
  • 3% C4
40
Q

Describe the Portulacacaea

A
  • 1% of all C4
  • 16% C4
41
Q

What percentage of angiosperms are C4?

A

3%

42
Q

What are the two main ecological C4 groups?

A
  • tropical and subtropical grasses and sedges
  • highly stress-tolerant plants (e.g. halophytic eudicots)
43
Q

Describe the physiological properties of C4 plants

A
  • high maximum rates of photosynthesis and growth
  • approx. 2-fold more water-use efficient than C3 plants
44
Q

C4 plants are responsible for approximately … of terrestrial NPP globally

A

20–25%

45
Q

C4 plants

A
  • do not suffer from significant photorespiratory CO2 loss
  • amongst the most productive plants on Earth
  • superior biomass crops for production of bioethanol
46
Q

Describe the productivity of C4 plants

A
  • ## up to 80 tonnes dry matter ha−1 year−1
47
Q

List some C4 plants

A
  • maize (corn): Zea mays
  • sugarcane: Saccharum
  • switch grass: Miscanthus
48
Q

Describe maize usage in the USA

A

up to 35 % used for production of bioethanol by fermentation rather than for food / animal feed

49
Q

Describe losses at different stages in energy transduction - general

A
  • 51% outside usable spectrum
  • 5% reflected and transmitted
  • 7% photochemical inefficiency
50
Q

Describe losses at different stages in energy transduction - C4

A
  • 28.5% carbohydrate synthesis
  • 0% photorespiration
  • 2.5% respiration
  • (6% remaining)
51
Q

Describe losses at different stages in energy transduction - C3

A
  • 25.5% carbohydrate synthesis
  • 5.1% photorespiration
  • 1.9% respiration
  • (4.6% remaining)
52
Q

Describe CAM succulents

A
  • simultaneous uptake of O2 and CO2 at night by cacti
  • nocturnal acidification of tissues
  • “Inverse rhythm” of stomatal opening
  • carbohydrate levels fluctuate inversely with organic acids
53
Q

CAM

A

crassulacean acid metabolism

54
Q

What is the “inverse rhythm” of stomatal opening

A

stomata closed during day, open at night

55
Q

Describe the day–night cycle of CAM

A
  • temporal separation of PEPC and Rubisco activity
  • night: CO2 + PEP → malic acid
  • day: malic acid → CO2 photosynthesis
56
Q

Describe the phases of CAM

A
  • Phase I: acidification; net CO2 fixation; PEPC
  • Phase II: PEPC -> RUBISCO
  • Phase III: deacidification; CO2 refixation; RUBISCO
  • Phase IV: net CO2 fixation, RUBISCO, PEPC
57
Q

Phase I of CAM

A
  • open stomata
  • vacuole: pH 6->3
58
Q

Phase III of CAM

A
  • closed stomata
  • vacuole: pH 3->6
59
Q

Describe Cactaceae

A
  • CAM
  • almost exclusively Neotropical (apart from more widely dispersed epiphytic Rhipsalis)
  • e.g. Mammillaria sp.
    Sonoran Desert, California, USA
60
Q

Describe Sonoran Desert cacti

A
  • ‘slow-growing, stress-tolerant’ end of life-history spectrum
  • Ferocactus acanthodes
  • Opuntia bigelovii
61
Q

Describe Euphorbias

A
  • Palaeotropics: the ‘Old World’
  • Euphorbia candelabra, Tanzania
62
Q

Describe the succulent biome

A
  • unique assemblages of CAM plants in Madagascar
  • spiny thicket
  • Alluaudia procera (Didiereaceae) with shrubby euphorbias
63
Q

Describe the canopy of tropical rainforests

A

ecological niche for diverse epiphytes and CAM plants

64
Q

Many CAM plants are

A

tropical epiphytes (e.g. bromeliads and orchids)

65
Q

List the principal Monocotyledon families of CAM plants

A
  • Asparagaceae (Agavoideae): 270
  • Asphodelaceae (Alooideae): 450
  • Bromeliaceae: 1,400
  • Orchidaceae: 6,250
66
Q

List the principal Eudicotyledon families of CAM plants

A
  • Apocynaceae (Asclepiadoideae): 435
  • Aizoaceae: 1,360
  • Cactaceae: 1,584
  • Crassulaceae: 1,050
  • Euphorbiaceae: 400
67
Q

How many CAM families are there?

A

37

68
Q

How many CAM species are there?

A

17,000

69
Q

What percentage of angiosperms are CAM?

A

5%

70
Q

Describe Ananas comosus

A
  • pineapple
  • CAM
  • international trade value ~US$ 9 billion per year
71
Q

Describe Agave tequilana

A
  • tequila
  • Jalisco, Mexico
72
Q

Describe Agave sisalensis

A
  • Sisal fibre
  • Brazil, Tanzania, Kenya, Madagascar
73
Q

Describe Vanilla planifolia

A
  • Orchidaceae
  • second-most valuable plant product per unit mass
  • cultivation in Madagascar
74
Q

C3 grasses are favoured at

A

higher levels of CO2

75
Q

Describe decline in CO2 during the Devonian

A
  • approx. 10-fold decline in atmospheric CO2 from Early (~410Mya) to
    Late (~360Mya) Devonian
  • transition from small vascular plants with microphylls (e.g. Cooksonia) to plants with true leaves (megaphylls), including tall trees (e.g. Lepidodendron)
76
Q

What caused the Devonian CO2 decline?

A
  • shoot systems of high-biomass plants absorbing large amounts of CO2
  • root systems promote weathering of silicate rocks, trapping CO2 in insoluble carbonates
    Burial of lignified plant organic matter resistant to microbial degradation in sediments locks up further CO2 → coal-forming swamps of Carboniferous; lasted to Early Permian (280 Ma)
    Consequence is steep decline in atmospheric CO2
    and increase in atmospheric O2 up to 35 % (giant insects, etc.)
77
Q

Describe trapping of CO2 in insoluble carbonates

A

CO2 + Ca,MgSiO3 → Ca,MgCO3 + SiO2

78
Q

Describe the “Carbon dioxide starvation hypothesis” for the origin of C4 plants

A
  • how to explain long delay between timing of minimum CO2 concentrations (~25Mya) and emergence of C4-dominated ecosystems (~ 6Mya)?
  • declining CO2 during Eocene associated with progressive cooling
  • further major cooling at end of Miocene and in Pliocene associated with gradual aridification; restricted tree cover, allowing C4 grasses to become dominant
  • drier ecosystems are more fire-prone; favours grasses over trees
  • ecosystem eventually reached a “tipping point” when it switched from a C3- to a C4-dominated biome
  • transition from closed forest to open savanna
79
Q

Why is CO2 decline associated with cooling

A

CO2 is a greenhouse gas

80
Q

Evolution of early hominins is likely to have been

A
  • profoundly influenced by ecosystem change
  • transition to C4 domination

Trinity Term 1 (38 decks)

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