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Plant Phys > Photosynthesis: Light Reactions - 4 > Flashcards

Photosynthesis: Light Reactions - 4 Flashcards

1
Q

What is absorbed, released, and created by plants in photosynthesis

A

plants use light energy from the sun to create carbohydrates stored in plants from carbon dioxide and water while releasing oxygen as a by-product

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2
Q

What is the most photosynthetically active tissue in plants

A

mesophyll of leaves

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3
Q

Define mesophyll

A

inner tissue of leaves that contain chloroplasts, which contain light-absorbing green pigments, the chlorophylls

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4
Q

What are the 3 major steps of photosynthesis

A
  1. absorb light (requires pigment system)
  2. transfer of electrons away from the excited pigment (results in 3 things)
  3. atmospheric CO2 converted to carbs using ATP and NADPH
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5
Q

In the second step of photosynthesis when electrons are transfered away from the excited pigment molecule, what 3 things can be done with that electron

A
  1. used for ATP synthesis
  2. used in NADPH formation
  3. O2 evolution
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6
Q

Where is the site of photosynthesis

A

chloroplasts

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7
Q

How many membranes does a chloroplast have

A

2, inner and outer

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8
Q

Define thylakoid membrane

A

separates the 2 compartments inside the chloroplast (lumen and stroma)

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9
Q

define lumen

A

inside the thylakoid membrane

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10
Q

define stroma

A

outside the thylakoid membrane

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11
Q

Light has characteristics of both ____ and _____

A

light and wave

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12
Q

What three things can results from light-energized chlorophyll

A
  1. fluoresce
  2. transfer energy to another molecule
  3. use its energy to drive chemical reactions
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13
Q

what wavelengths are shorter than visible light and what are longer

A

shorter = ultraviolet
longer = infrared

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14
Q

what is sunlight made of

A

photons of different wavelengths

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15
Q

Define absorption spectrum

A

provides information about what light energy is absorbed by a molecule or substance based on the wavelength of the light

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16
Q

absorption spectrums are determined by a

A

spectrophotometer, by non-absorbing solvents

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17
Q

what wavelengths are absorbed by chlorophyll

A

400nm-700nm

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18
Q

why does chlorophyll appear to be green

A

because it strongly absorbs red and blue light

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19
Q

what occurs when a molecule of chlorophyll absorbs a photon

A

it transitions into a higher energy level, excited state

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20
Q

What happens to the chlorophylls state when in a higher excited state

A

it is unstable and rapidly gives up some energy to its surroundings as heat, then enters the lowest excited state for a short time

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21
Q

What are the 4 pathways for disposing excited chlorophylls available energy

A
  1. Fluorescence (emit a photon)
  2. release as heat only
  3. energy transfer (transfers its energy to another molecule)
  4. photochemistry (chemical reaction occurs)
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22
Q

what chlorophylls are abundant in green plants and which are found in some protists and cyanobacteria

A

a and b
c, d, and f

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23
Q

Besides chlorophylls, what are the 3 other main pigments that participate in photosynthesis

A

carotenoids, bacteriochlorophylls, and billin pigments

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24
Q

Define structure of carotenoids

A

linear molecules with multiple conjugate double bonds that transfer electrons to chlorophylls for photosynthesis. they are accessory pigments that absorb 400-500nm (therefore orange)

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25
Q

Explain the molecular structure of chlorophylls

A

complex ring structure that contain Mg at the centre with surrounding Ns both for light absorption. Contain long hydrocarbon tail

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26
Q

What is the purpose of the hydrocarbon tail of chlorophylls

A

anchors the chlorophyll to the hydrophobic portion of the environment

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27
Q

What differs between chlorophyll a and b in their ring structure

A

a = CH3
b = CHO

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28
Q

Define action spectrum

A

a graphic representation of magnitude of biological effectiveness to different wavelengths of light

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29
Q

What are action spectrum constructed by, what do they measure to produce results

A

measure the photosynthetic production of O2 at different wavelengths which explains their effectiveness

30
Q

What was engelmann’s experiment explanation

A

used a prism to disperse sunlight into a rainbow onto an algal filament. He used O2 seeking bacteria to identify which wavelengths of light results in the most O2 production by the algae

31
Q

What were the results of engelmann’s experiments

A

bacteria gathered in areas of blue and red light which is supported by the absorption of blue and red by chlorophylls.

32
Q

How many photosystems operate in series to carry out early reactions of photosynthesis

A

2, photosystem I and photosystem II

33
Q

What two subunits do photosystems consist of

A
  1. antenna complex
  2. reaction center
34
Q

Define antenna complex

A

“light harvesting complexes”
that consist of chlorophyll and carotenoids attached to a protein structure serving to absorb and pass on solar energy to the reaction center

35
Q

Define reaction center

A

protein component that consists of a complex arrangement of several gene products (proteins and chlorophyll) that initiate electron transfer reactions

36
Q

Define what light PSI absorbs and what it produces

A

far-red light (700) and produces strong reductant (reducing NADP+ and weak oxidant)

37
Q

Define what light PSII absorbs and what it produces

A

red-light (680) and produces very strong oxidant capable of oxidizing water and weaker reductant than PSI

38
Q

Explain Z scheme of photosynthesis

A

far red light absorbed by PSII - produces strong oxidant and weak reductant - far red light absorbed by PSI - produces weak oxidant and strong reductant - strong oxidant from PSII oxidizes water - strong reductant by PSI reduces NADP+`

39
Q

where is the site of light reactions in photosynthesis

A

thylakoid membranes

40
Q

define grana lamellae

A

stacks of thylakoids

41
Q

where do the carbon-reduction reactions take place

A

in the stroma (outside of the thylakoid membranes)

42
Q

stroma lamellae

A

exposed membranes of the thylakoid (connections thylakoids)

43
Q

Define chloroplast envelope

A

double membrane surrounding most types of chloroplasts

44
Q

many essential proteins for photosynthesis are _____

A

embedded in the thylakoid membrane
ex. electron carrier proteins and antennae pigment protein complexes

45
Q

explain the unique orientation of integral membrane proteins

A

one region toward stromal side and one toward lumen

46
Q

How are chlorophylls and accessory light gathering pigments specifically organized to optimize energy transfer with minimal waster processes

A

associated in noncovalent, but highly specific way with proteins to form pigment protein complexes

47
Q

Where are PSII, PSI, and cytochrome b6f complex predominately located

A

PSII = grana lamellae
PSI = stroma lamellae and edges of grana lamellae
b6f = evenly distributed

48
Q

the two photochemical systems are spatially separated implying what

A

one or more of the electron carriers that function between the photosystems diffuse from grana to stroma

49
Q

What are the two diffusible carriers called

A

plastocyanin (PC)
plastoquinone (PQ)

50
Q

___ centers feed reducing equivalents into an intermediate pool of lipid soluble electron carriers ____ where ___ reaction centers ____ the reducing equivalents from the common pool

A

PSII
PQ
PSI
remove

51
Q

the antenna systems ____ energy to the _____

A

funnel
reaction centers

52
Q

Define fluorescence resonance energy transfer (FRET)

A

is the physical mechanism which energy of excitation is transferred from chlorophyll that absorbs light to an adjacent molecule

53
Q

how efficient is energy transfer usually

A

95-99%

54
Q

How is FRET distinct from electron transfer

A

because electron transfer involves redox reactions

55
Q

What makes energy transfer from one pigment to another in the antennae complex so efficient

A

because the transfer is directional and essentially irreversible

56
Q

What is the name of proteins that are primarily associated with PSII and what are the ones primarily associated with PSI

A

light harvesting complex II proteins (LCHII)
LCHI

57
Q

What does the Z scheme identify

A

the flow of electrons through carriers in PSII and PSI from H20 to NADP+

58
Q

What are the 4 large protein complex transfer electrons

A

PSII
cytochrome b6f complex
PSI
ATP synthase

59
Q

What is PSII’s specific role in electron transport

A

it oxidizes water to oxygen in the thylakoid lumen and protons are released into the lumen. PQH2 is the reduced product of PSII

60
Q

What is cytochrome b6f complex’s specific role in electron transport

A

oxidizes PQH2 and delivers electrons to PSI by the PC. this process is also coupled with proton transfer into the lumen from the stoma which generates a proton motive force

61
Q

What is PSI’s specific role in electron transport

A

it reduces NADP+ into NADPH in the stroma by the electron carriers, ferredoxin and FNR

62
Q

What is ATP synthase’s specific role in electron transport

A

it produces ATP as protons diffuse back across the membrane from the lumen into the stroma

63
Q

the PSII reaction center is a ____ protein pigment complex

A

multi-subunit

64
Q

What ions are required to oxidize water

A

manganese ions

65
Q

How many hydrophobic PQ’s accept electrons from the PSII

A

2

66
Q

what also occurs when electrons pass through the cytochrome b6f complex

A

protons are transported into the lumen

67
Q

NADP+ is reduced by PSI by using #___ ____ centers as electron carriers

A

3 Fe-S

68
Q

ATP is generated by _____ while NADPH is generated by ____

A

cyclic electron flow
proton pumping

69
Q

DCMU

A

blocks electron flow by competing for the binding site of PQ

70
Q

What can block electron transport flow

A

herbicides

71
Q

Paraquats

A

accepts electrons from PSI and reacts with oxygen to form superoxide = a reactive oxygen species very damaging to chloroplast components

72
Q

During catalysis, the _____ portion of the ____ rotates like a miniature motor

A

CF0
ATP synthase

Plant Phys (15 decks)

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