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Plant Phys > Photosynthesis: Physiological and Ecological Considerations - 6 > Flashcards

Photosynthesis: Physiological and Ecological Considerations - 6 Flashcards

1
Q

What is the limiting factor hypothesis

A

that the rate of photosynthesis is limited by the slowest step in the process (the “limiting factor”)

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2
Q

What are the 3 major metabolic processes that have been identified as important for photosynthesis performance and where do these processes all occur

A
  1. rubisco capacity
  2. regeneration of ribulose 1,5-bisphosphate (RuBP)
  3. metabolism of the triose phosphates
    In the chloroplasts!
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3
Q

What is the supply and demand perspective of photosynthesis

A

that overall net photosynthetic rates of leaves are impacted by by the supply (by guard cells) and demand (in mesophyll cells) of carbon dioxide

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4
Q

define irradiance

A

the amount of energy that falls on a flat sensor or known area per unit of time (W m^-2)

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5
Q

Define quantum flux or photon flux density (PFD)

A

the number of incident quanta striking the leaf (mol m^-2 s_-1)

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6
Q

Define photosynthetic photo flux density (PPFD)

A

the amount of photosynthetically active photons hitting a surface per unit per time, how light is expressed in photosynthesis
how much is actually useful for photosynthesis

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7
Q

What percentage of the energy of sunlight striking vegetation is converted to carbs by photosynthesis and why

A

5%
lots of the light is wavelengths outside of the range for photosynthesis, some reflected or used in metabolism lost as heat

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8
Q

How much radiant energy from the sun reaches each square meter of earth’s surface

A

340 W

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9
Q

What are the 4 specific anatomical structures of leaves that make them specialized for light absorption and function

A
  1. transparent epidermal cells (convex to focus light reaching chloroplasts - channel light)
  2. palisade mesophyll cells in columns (tightly packed)
  3. spongy mesophyll cells (irregular shapes, that reflect, refract and scatter light, so more light can be captured)
  4. specialized structures (hair, glands, epicuticular wax to reduce overheating and excess solar energy)
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10
Q

Why do shaded leaves have lower photosynthetic rates

A

they experience lower light levels and different light quality than the leaves at the top of the canopy

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11
Q

What determines the amount of incident light (light that falls on a subject)

A

angle of the leaf relative to the sun (changes with time of day and orientation of leaf)

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12
Q

leaves near top of canopy are at angle to allow _____ while leaves further down are closer to ______

A

sunlight to penetrate the canopy (go through)
horizontal (to obtain as much as possible)

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13
Q

Define solar tracking

A

way for leaves to maximize light absorption by adjusting their leaf blade to remain perpendicular to the sun

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14
Q

Solar tracking is what kind of response

A

blue-light response which occurs in specialized regions of the leaf or stem

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15
Q

Define pulvinus

A

a specialized organ that controls leaf orientation found at the junction between the leaf blade and petiole.

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16
Q

Define acclimation

A

developmental process, where leaves express biochemical and morphological adjustments that are suited to the environment that they are exposed to

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17
Q

Define plasticity

A

how much adjustment can take place

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18
Q

How do shade leaves increase light capture (3)

A

by increasing total chlorophyll per reaction center, having a higher ratio between chlorophyll b to chlorophyll a (), and a thinner laminae than sun leaves (easier CO2 diffusion)

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19
Q

How do sun leaves increase CO2 assimilation (2)

A
  1. having more Rubisco
  2. large pool of xanthophyll-cycle components that dissipate excess light energy
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20
Q

Sun leaves have thicker ____ and a larger ____ than shade leaves

A

leaves
palisade layer (rich in chloroplasts)

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21
Q

What are two ways that some shade plants increase light absorption

A
  1. produce a higher ratio of PSII to PSI reaction centers
  2. add antenna chlorophyll to PSII
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22
Q

far-red light is absorbed primarily by PSI but also ____ which is proportionally more abundant in _____ habitats

A

phytochrome
shady

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23
Q

What do light response curves display

A

the photosynthetic photon flux density, where photosynthesis is limited by light or by carboxylation capacity

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24
Q

Why is there a negative uptake of CO2 of plants in darkness

A

little photosynthetic carbon fixation occurs in the dark while respiration continues, so CO2 is given off by plants making it a negative UPTAKE

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25
Q

Define light compensation point

A

where PPFD value where photosynthesis is equal to the rate of respiration, anything above is net assimilation of CO2

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26
Q

_____ allow shade plants to survive in light limited environments

A

low respiration rates

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27
Q

the slope of the light response curve provides what information

A

the maximum quantum yield of photosynthesis for the leaf (maximum number of events resulting from minimum amount of photons absorbed)

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28
Q

at higher PPFD in the light response curve, the photosynthetic response starts to level off and approaches ____

A

saturation (holding as much moisture as possible)

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29
Q

what occurs to photosynthesis beyond the saturation point in the light response curve and what explains this

A

net photosynthesis no longer increases, indicating that other factors other than incident light (ex. electron transport chain, Rubisco activity, or metabolism of trios phosphates) have become the limiting factor

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30
Q

What must plants do as a result of being exposed to excess light

A

leaves must dissipate the extra energy absorbed to prevent damage to the photosynthetic apparatus

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31
Q

What is the most important avenue for dissipation of excess light energy

A

xanthophyll cycle

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32
Q

Define xanthophyll cycle

A

cycle comprised of 3 carotenoids, violaxanthin, antheraxanthin, and zeaxanthin that has the ability to dissipate excess light energy in the leaf
uses NADPH

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33
Q

xanthophyll cycle also operates in plants that grow in low light of the understory because of what

A

sunflecks, the sunlight that is able to penetrate the understory through the canopy

34
Q

explain the difference in chloroplast movement in dark or weak light areas compared to high light

A

dark = gather at the cell surfaces perpendicular to the incident light to maximize light absorption
high = chloroplasts move so they are parallel to avoid excess absorption of light

35
Q

chloroplast movement can reduce light absorbed by what percentage

A

15%

36
Q

chloroplast movement in leaves is a typical ____ response

A

blue light

37
Q

what regulates chloroplast movement

A

calcium ions

38
Q

chloroplasts move along ______ in the ____

A

actin microfilaments in the cytoplasm

39
Q

Define photoinhibition

A

reduction in plants capacity for photosynthesis caused by exposure to strong light/intense illumination

40
Q

What is dynamic photoinhibition

A

when there is moderate excess of light and the quantum yield decreases but the maximum photosynthetic rate remains unchanged

41
Q

What causes dynamic inhibition

A

the diversion of absorbed light energy by the xanthophyll cycle and is often temporary

42
Q

Define chronic inhibition

A

results from exposure to high levels of excess light that damages the photosynthetic system and decreases both quantum yield and maximum photosynthetic rate

43
Q

In what conditions is photoinhibition more pronounced

A

at low temperatures and becomes chronic under more extreme climatic conditions

44
Q

The water loss from leaves also removes heat through ____ even under full ____

A

evaporative cooling
sunlight

45
Q

What percentage of total solar energy does leaves absorb

A

50%

46
Q

What 3 processes is the typical heat load of a leaf dissipated through

A
  1. radiative heat loss (long wavelength radiation)
  2. sensible heat loss (convection away from the leaf to the air, to cool leaf)
  3. latent heat loss (evaporative cooling, from water loss)
47
Q

Define Bowen ratio

A

ratio of sensible heat loss to evaporative heat loss
sensible/evaporative

48
Q

in well watered crops, transpiration is _____ so the Bowen ratio is ____

A

high
low

49
Q

When evaporative cooling is ______ the bowen ratio is ____

A

limited
high

50
Q

The amount of evaporative cooling (and therefore the bowen ratio) is influenced by what

A

influenced by the degree of which the stomata stay open (because closed stomata reduce evaporative cooling and increases the bowen ratio)

51
Q

Plants with high Bowen ratios conserve _____ but may experience high ____

A

water
temperatures

52
Q

High bowen ratios is associated with what

A

reduced growth because of the stomatal closures

53
Q

Define photosynthetic thermal optimum

A

is the peak photosynthesis rate across a range of temperatures
which reflects biochemical, genetic and environmental components

54
Q

photosynthetic rates decreases when the optimal temperature is _______

A

exceeded

55
Q

what does the optimal temperature range for photosynthesis in species often reflect

A

the environment in which they are evolved

56
Q

Plants with a higher thermal plasticity are capable of what

A

to grow over a wider range of temperatures

57
Q

In what temperature would hot desert plants be able to achieve a positive photosynthetic rate compared to artic plants

A

hot desert at high temperatures (50) and artic near 0 are capable of CO2 uptake

58
Q

Why is temperature optimum often higher in C4 plants

A

because CO2 is concentrated near the Rubisco enzyme (meaning there is already so much CO2 ready for the sunlight!)

59
Q

at low temperatures, what is C3 photosynthesis limited by

A

phosphate availability in the chloroplast

60
Q

____ and ____ synthesis decreases rapidly with ____ temperature which reduces the demand for ________

A

starch
sucrose
decreasing
triose phosphates

61
Q

What results in C3 photosynthesis with the slowing of triose phosphates

A

phosphate uptake in the chloroplast becomes inhibited and photosynthesis becomes phosphate-limited

62
Q

Explain the changes that occur in quantum yield in C4 and C3 plants

A

remains constant in C4 plants, reflecting low rates of photorespiration
is higher at low temperatures but decreases with temperature as photorespiration increases

63
Q

What 3 things do temperature-sensitivity curves identify

A
  1. temperature range where enzymatic events are stimulated
  2. range for optimal photosynthesis
  3. range where deleterious events occur
64
Q

Below what temperature is the quantum yield higher in C3 plants than C4 plants

A

30
vise versa

65
Q

What leads to the differences in the photosynthetic capacities of C3 and C4 plants

A

the reduced quantum yield and increased photorespiration due to temperature effects

66
Q

how has atmospheric concentrations of CO2 changed and how have plants evolved

A

doubled and plants therefore were evolved back then to live in low CO2 world

67
Q

Concentrations of CO2 have increased from ____ to ___ per year primarily due to what

A

1 to 3
burning of fossil fuels and deforestation

68
Q

what can the gaseous phase of plants be divided into

A

boundary layer, stomata, and intercellular spaces of the leaf

69
Q

boundary layer resistance decreases with what two factors

A

smaller leaf size and greater wind speed

70
Q

when the air is still around a plant, the boundary layer is smaller than what

A

stomatal resistance

71
Q

What has the greatest effect on CO2 diffusion into a leaf

A

stomatal resistance

72
Q

Define intracellular air space resistance

A

the resistance to CO2 diffusion in the air spaces that separate substomatal cavity from the walls of the mesophyll cells

73
Q

Define mesophyll resistance

A

resistance of CO2 diffusion in the liquid phase in C3 leaves, includes diffusion from intracellular leaf spaces to the carboxylation sites in the chloroplast

74
Q

Define CO2 compensation point

A

point where net assimilation of CO2 by the leaf is zero (compensates for CO2 released by respiration)

75
Q

enrichment of CO2 above the natural atmospheric levels results in increased what

A

photosynthesis and productivity

76
Q

where is the CO2 compensation point for C4 plants and C3 plants

A

C4 = near zero (low levels of photorespiration)
C3 = 50-100ppm at 25 degrees, representing CO2 production because of photorespiration

77
Q

ancestral pathway is ___ plants while ____ is the derived pathway
why has the derived pathway come to be

A

C3
C4
in earth’s warmest regions when global atmosphere CO2 concentrations fell below a threshold value

78
Q

few shade-adapted plants are C4 because of what

A

C4 plants use water and nitrogen more efficiently but reduces light-use efficiency which wouldnt be good for shade plants

79
Q

What is the main photosynthetic constraint on CAM metabolism

A

the capacity to store malic acid is limited and this restricts total CO2 uptake

80
Q

Due to changes in CO2 concentrations and greenhouse gases, how will photosynthetic rates change

A

right now photosynthesis in C3 plants are CO2 limited, but will change as CO2 rises. most C3 plants grow 30% faster when reaches 600-750 ppm. above this, they will instead be limited by nutrient availability

81
Q

What do free air CO2 enrichment (FACE) experiments show

A

that C3 plants are more responsive to elevated CO2 than C4 plants

Plant Phys (15 decks)

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