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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
Explain the molecular structure of chlorophylls
complex ring structure that contain Mg at the centre with surrounding Ns both for light absorption. Contain long hydrocarbon tail
26
What is the purpose of the hydrocarbon tail of chlorophylls
anchors the chlorophyll to the hydrophobic portion of the environment
27
What differs between chlorophyll a and b in their ring structure
a = CH3 b = CHO
28
Define action spectrum
a graphic representation of magnitude of biological effectiveness to different wavelengths of light
29
What are action spectrum constructed by, what do they measure to produce results
measure the photosynthetic production of O2 at different wavelengths which explains their effectiveness
30
What was engelmann's experiment explanation
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
What were the results of engelmann's experiments
bacteria gathered in areas of blue and red light which is supported by the absorption of blue and red by chlorophylls.
32
How many photosystems operate in series to carry out early reactions of photosynthesis
2, photosystem I and photosystem II
33
What two subunits do photosystems consist of
1. antenna complex 2. reaction center
34
Define antenna complex
"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
Define reaction center
protein component that consists of a complex arrangement of several gene products (proteins and chlorophyll) that initiate electron transfer reactions
36
Define what light PSI absorbs and what it produces
far-red light (700) and produces strong reductant (reducing NADP+ and weak oxidant)
37
Define what light PSII absorbs and what it produces
red-light (680) and produces very strong oxidant capable of oxidizing water and weaker reductant than PSI
38
Explain Z scheme of photosynthesis
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
where is the site of light reactions in photosynthesis
thylakoid membranes
40
define grana lamellae
stacks of thylakoids
41
where do the carbon-reduction reactions take place
in the stroma (outside of the thylakoid membranes)
42
stroma lamellae
exposed membranes of the thylakoid (connections thylakoids)
43
Define chloroplast envelope
double membrane surrounding most types of chloroplasts
44
many essential proteins for photosynthesis are _____
embedded in the thylakoid membrane ex. electron carrier proteins and antennae pigment protein complexes
45
explain the unique orientation of integral membrane proteins
one region toward stromal side and one toward lumen
46
How are chlorophylls and accessory light gathering pigments specifically organized to optimize energy transfer with minimal waster processes
associated in noncovalent, but highly specific way with proteins to form pigment protein complexes
47
Where are PSII, PSI, and cytochrome b6f complex predominately located
PSII = grana lamellae PSI = stroma lamellae and edges of grana lamellae b6f = evenly distributed
48
the two photochemical systems are spatially separated implying what
one or more of the electron carriers that function between the photosystems diffuse from grana to stroma
49
What are the two diffusible carriers called
plastocyanin (PC) plastoquinone (PQ)
50
___ centers feed reducing equivalents into an intermediate pool of lipid soluble electron carriers ____ where ___ reaction centers ____ the reducing equivalents from the common pool
PSII PQ PSI remove
51
the antenna systems ____ energy to the _____
funnel reaction centers
52
Define fluorescence resonance energy transfer (FRET)
is the physical mechanism which energy of excitation is transferred from chlorophyll that absorbs light to an adjacent molecule
53
how efficient is energy transfer usually
95-99%
54
How is FRET distinct from electron transfer
because electron transfer involves redox reactions
55
What makes energy transfer from one pigment to another in the antennae complex so efficient
because the transfer is directional and essentially irreversible
56
What is the name of proteins that are primarily associated with PSII and what are the ones primarily associated with PSI
light harvesting complex II proteins (LCHII) LCHI
57
What does the Z scheme identify
the flow of electrons through carriers in PSII and PSI from H20 to NADP+
58
What are the 4 large protein complex transfer electrons
PSII cytochrome b6f complex PSI ATP synthase
59
What is PSII's specific role in electron transport
it oxidizes water to oxygen in the thylakoid lumen and protons are released into the lumen. PQH2 is the reduced product of PSII
60
What is cytochrome b6f complex's specific role in electron transport
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
What is PSI's specific role in electron transport
it reduces NADP+ into NADPH in the stroma by the electron carriers, ferredoxin and FNR
62
What is ATP synthase's specific role in electron transport
it produces ATP as protons diffuse back across the membrane from the lumen into the stroma
63
the PSII reaction center is a ____ protein pigment complex
multi-subunit
64
What ions are required to oxidize water
manganese ions
65
How many hydrophobic PQ's accept electrons from the PSII
2
66
what also occurs when electrons pass through the cytochrome b6f complex
protons are transported into the lumen
67
NADP+ is reduced by PSI by using #___ ____ centers as electron carriers
3 Fe-S
68
ATP is generated by _____ while NADPH is generated by ____
cyclic electron flow proton pumping
69
DCMU
blocks electron flow by competing for the binding site of PQ
70
What can block electron transport flow
herbicides
71
Paraquats
accepts electrons from PSI and reacts with oxygen to form superoxide = a reactive oxygen species very damaging to chloroplast components
72
During catalysis, the _____ portion of the ____ rotates like a miniature motor
CF0 ATP synthase

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