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BISC 101 Mid2 > Photosynthesis > Flashcards

Photosynthesis Flashcards

Lecture 9

1
Q

(photo) autotrophs function

A

use light energy to drive the synthesis of organic molecules from CO2 and water

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2
Q

where is the site of photosynthesis

A

chloroplasts

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3
Q

what is photosynthesis

A

harnesses sunlight to make carbohydrate (sugar)

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4
Q

what do the light-capturing reactions do?

A

convert solar energy to ATP and NADPH in photosystems using chlorophyll

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5
Q

Calvin cycle does what?

A

uses chemical energy of ATP and NADPH to reduce CO2 to sugar

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6
Q

where have alternative mechanisms of carbon fixation evolved

A

hot, arid climates

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7
Q

Redox reaction of photosynthesis

A

carbon is reduced and oxygen is oxidised

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8
Q

what happens to the potential energy in photosynthesis

A

electrons are held more loosely in products than reactants so their potential energy increases; requires energy

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9
Q

what do plants take in with the help of sunlight?

A

CO2 and H2O

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10
Q

chloroplasts characteristics

A
  • double membrane
  • inside has fluid-filled stroma
  • contains thylakoids
  • contains enzymes and pigments (chlorophyll)
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11
Q

thylakoids characteristics

A

stacked “pancake-like” in grana

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12
Q

enzymes and pigments (chlorophyll) function and characteristics

A

they run photosynthesis and are embedded in thylakoid membrane or stroma

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13
Q

pigments

A

substances that absorb visible light

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14
Q

why does chlorophyll (and leaves) appear green?

A

because chlorophyll absorbs violet-blue and red wavelength light while reflecting green light

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15
Q

spectrophotometer measures what?

A

the ability of a pigment to absorb various wavelengths of light

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16
Q

what happens when a photon of light strikes a chlorophyll molecule?

A

energy is transferred to an electron [in the chlorophyll]

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17
Q

if the excited electron falls back to its “ground” or unexcited state what happens?

A

it emits extra energy as heat and light

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18
Q

what happens to the energy from the electron in chloroplasts?

A

passed around: Antenna complex -> reaction centre -> electron acceptor

it can be passed among many chlorophyll molecules of an antenna complex then to a reaction center and then an electron can be transferred to an electron acceptor

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19
Q

how do chlorophyll molecules work?

A

they work in groups within chloroplasts

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20
Q

where do the antenna complex, reaction centre, and electron acceptor occur?

A

in photosystems on the thylakoid membrane

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21
Q

What are the 2 types of photosystem

A

PS 2 and PS 1

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22
Q

Photosystem 2 does what?

A

feeds high-energy electrons to an electron transport chain

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23
Q

what does energy reaching the reaction centre do?

A

excites an electron within a specialized chlorophyll molecule

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24
Q

what does the excited electron bind to in PS 2

A

electron acceptor = pheophytin

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25
"high energy" electrons that reach pheophytin are passed where?
to an electron transport chain in the thylakoid membrane
26
ETC function
generates a proton-motive force and produces ATP by chemisosmosis
27
plastoquinone in ETC function
carriers electrons to a cytochrome complex
28
energy is used to transport what in photosystem 2
transport protons from the stroma to the thylakoid lumen
29
the transport of protons does what across the thylakoid membrane
creates a large proton gradient
30
How do Proton’s flow in the thylakoid membrane? What do they drive?
flow down their concentration gradient. Drives photophosphorylation of ADP to ATP by ATP synthase
31
Photosystem 1 does what?
produces NADPH via an electron transport chain not coupled to chemiosmosis
32
what does ferrodoxin move in PS 1?
high-energy electrons are passed through an electron transport chain by this molecule
33
NADP+ reductase function
transfers 2 electrons + 1H+ to NADP+ reducing it to NADPH
34
ATP production in PS 2
generates a proton-motive force and produces ATP by chemisosmosis
35
ATP production in PS 1
this ETC does not involve chemiosmosis so ATP is not produced. NADPH is produced by PS1
36
How is PS 1 energy stored
this photosystem stores energy as NADPH
37
what happens to the electrons lost from PS 2
they are replaced by the splitting of water. The H+ ions are released into thylakoid lumen
38
Plastocyanin function
transfers electrons from cytochrome of PS 2 to PS 1
39
what are the outputs of light-capturing reaction
ATP and NADPH (and O2)
40
How does the Calvin cycle fix carbon?
by addition of CO2 to an existing organic compound (RuBP)
41
what kind of reaction is the Calvin cycle
anabolic. It builds complex CHO from smaller molecules and consumes energy
42
rubisco function
catalyses reaction between CO2 and RuBP
43
what is the first phase of the Calvin cycle and what does it do?
CO2 fixation. It uses ATP and NADHP and regenerates RuBP
44
What does one turn of the Calvin cycle do?
fixes 1 CO2
45
what do three turns of the Calvin cycle do?
produces 1 x G3P
46
What does photosynthesis require?
CO2 that enters via stomata on the leaf
47
what is the stomata the main route of?
for evaporative loss of water via transpiration
48
why do plants on hot, dry days close their stomata?
to conserve water
49
what happens when the stomata is closed?
limits access to CO2 and reduces photosynthetic yield and causes build up of O2 in air spaces of leaf from light reactions
50
Why are most plants called C3 plants
because rubisco initially fixes carbon as a 3C molecule
51
what type of enzyme is rubisco?
a slow and inefficient enzyme
52
what will rubisco bind together?
will bind O2 to RuBP equally as well as CO2 (when CO2 is scarce)
53
Photorespiration
consumes ATP and releases "fixed" CO2 so it decreases the efficiency of photosynthesis
54
C4 and CAM plants trick
store CO2 when its available to maintain constant supply for Calvin cycle when stomata are closed
55
C4 photosynthesis
CO2 is fixed initially as a 4C-compound in outer mesophyll cells
56
PEP carboxylase has high affinity for...
CO2
57
PEP carboxylase does NOT have high affinity for...
O2 so carbon fixation occurs even at low CO2
58
where are 4C products exported
bundle-sheath cells
59
4C products in bundle-sheath cells maintain what?
a supply of CO2 for the Calvin cycle
60
Why do CAM plants take up CO2 at night?
when the stomata can be open and incorporate it into organic acids
61
where do CAM plants store taken up CO2?
In vacuole of mesophyll cells
62
When is the stored CO2 in CAM plants released
during the day

BISC 101 Mid2 (5 decks)

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