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BIOL 120 Plant Biology > Photosynthesis I > Flashcards

Photosynthesis I Flashcards

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1
Q

where does plant respiration occur?

A

in mitochondria, where stored energy is converted to ATP in presence of O2

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2
Q

all organisms must extract energy from food through ____

A

respiration

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3
Q

photosynthesis and respiration are ____ processes

A

interdependent

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4
Q

ATP stands for?

A

adenosine triphosphate

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5
Q

___% of solar energy received on Earth is visible light?
leaves absorb ___% of visible light reaching them?

A

40
80

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6
Q

pigment colour is determined by absorbed/reflected light?

A

reflected light, NOT absorbed light!

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7
Q

chlorophyll absorbs photons in the blue (__nm) and red (__nm) of visible spectrum (400-700nm), green reflected

chlorophyll a reflects _____
chlorophyll b reflects _____

A

430
680

blue-green
yellow-green

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8
Q

what colour do carotenoids absorb and reflect?

A

absorb blue-green,
reflect yellow or yellow-orange

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9
Q

where are carotenoids and anthocyanin stored? types + colour?

A

carotenoids: stored in plastids
- beta-carotene (orange)
- xanthophyll (yellow)

anthocyanin: stored in vacuole
- flavonoids (blue, purple, red depending on pH)

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10
Q

colours of autumn are from?

A

deciduous trees:
when chlorophyll is broken down,
accessory pigments carotenoids and anthocyanin become visible

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11
Q

photosynthesis is divided into 2 reactions?;
where do they occur?

A
  1. light-dependent; occurs in chloroplast thylakoid membranes
  2. light-independent; occurs in chloroplast stroma
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12
Q

light-dependent reaction in thylakoid membranes:
what steps + photosystems? (Detailed)

A
  • water molecules split, releasing e-, H+, O2
  • e- pass along electron transport chain
  • ATP made and NADP+ reduced to form NADPH (to power light-independent reactions in stroma)
  • chlorophyll pigment: magnesium and nitrogen ring ABSORBS light photons and lipid tail ANCHORS into thylakoid membrane
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13
Q

what are photosystems? (detailed)

A

pigments clustered in discrete units of organization

  • each PS contains 200-300 pigments and associated proteins
  • PS’s occur repeatedly throughout thylakoid membranes
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14
Q

photosystem structures (2):

A
  1. reaction centre
    - chlorophyll a molecule and primary e- acceptor
    - <1% of pigments in a PS are chlorophyll a
  2. antenna pigment molecules
    - chlorophyll and accessory pigments gather and transfer light energy to reaction centre
    - accessory pigments play critical role dissipating and funnelling light energy to chlorophyll a
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15
Q

light-dependent reaction: electron energy steps

A
  • when pigments absorb light photons, energy levels of e- are raised
  • excited e- energy released when it drops to “ground state”
    – energy can be heat, fluoresence, photochemistry
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16
Q

light-dependent reaction: reaction centre

A
  • upon reaching reaction centre, light energy causes an e- to be ejected from chlorophyll a molecule
  • e- transferred to a primary electron receptor
  • chlorophyll a molecules of reaction centres behave differently than other chlorophyll: absorb light at slightly longer wavelengths (lower energy)
17
Q

light-dependent reaction: PSI and PSII (antenna pigment molecules, reaction centre)

A

two kinds of photosystems with their own unique chlorophyll a in reaction centres:

PSII:
- antenna pigment molecules: chlorophyll a, chlorophyll b, beta-carotene
- reaction centre: chlorophyll a P680 and primary electron acceptor (pheophytin)

PSI:
- antenna pigment molecules: chlorophyll a>chlorophyll b, carotenoids
- reaction centre: chlorophyll a P700 and primary electron acceptor (iron-sulphur proteins)

18
Q

light-dependent reaction: Z-scheme

A

PSII and PSI are linked together in a zigzag pattern (Z-SCHEME)
- consists of a series of protein-based electron carriers that form a pathway for electron movement
- electron movement in each Z-scheme constitutes the light-dependent reactions

19
Q

PQ stands for?
PC?
Fd?

A

plastoquinone
plastocyanin
ferredoxin

20
Q

light-dependent reaction: Z-scheme steps (DETAILED) (6)

A
  1. light funnelled to P680, energize e- in chlorophyll a. excited e- -> pheophytin (primary electron acceptor) -> PQ in electron transport chain -> PSI
  2. each rejected P680 e- replaced by e- from H2O after enzymatic splitting of water (photolysis) into: 2e- + 2H+ + O
  3. e- passed on from primary electron acceptor slowly loses energy as they move through protein complexes in electron transport chain: plastoquinone, cytochrome complexes, plastocyanin
  4. energy released by e- used to move H+ across thylakoid membrane (chemiosmosis)
    - buildup H+ gradient indirectly powers ATP synthesis (photophosphorylation)
  5. light funnelled to P700, energizing e- in chlorophyll a
    - excited e- passed to iron-sulphur electron acceptor
    - electrons ejected from P700 replaced by e- from PSII
  6. excited e- moves through through second electron transport chain (ferredoxin -> NADP+ reductase, NADP+ reduced to NADPH)

OVERALL: movement of e- from H2O -> PSII -> PSI -> NADPH known as NONCYCLIC ELECTRON FLOW

21
Q

PSII and PSI operate ____

A

simultaneously

22
Q

light-dependent reaction: chemiosmosis (detailed)

A

light reactions make ATP using energy from chemiosmosis
- as e- move through electron transport chain from PSII to PSI, lose energy
– energy used to pump H+ (stroma -> thylakoid lumen) using concentration graident of H+ across thylakoid membrane (chemiosmosis)
– charge diff is also a pH diff
– protons move across thylakoid membrane through protein channel, ATPase, producing ATP
– movement of H+ from thylakoid back to stroma releases energy; when protons flow through ATP synthase, energy is used to add inorganic phosphate to ADP, making ATP

23
Q

light-dependent reactions: O2, ATP, NADPH (how are they made?)
what is efficiency % (light -> chemical energy)

A
  • light-dependent reactions use energized e- from PSII to make ATP, make oxygen via photolysis, and use re-energized e- from PSI to make NADPH
  • ~27%
24
Q

primitive photosystems: cyclic electron flow

A
  • PSI can work independently of PSII
  • energized e- from P700 are recycled back via ferredoxin to plastoquinone instead of being passed on to NADP+ reductase
  • e- pass back down to PSI driving H+ transport across thylakoid membrane, making MORE ATP
  • no water molecules split, so NO OXYGEN OR NADPH made
25
Q

light-independent reaction (chloroplast stroma): dark reaction?

A

AKA calvin cycle uses chemical energy made in light-dependent reactions to make simple sugar phosphates, often called DARK reactions

26
Q

what is light-independent reaction/calvin officially known as? why?

A

calvin-benson-bassham cycle
- named after melvin calvin, with students andrew benson and james bassham

(Determined pathyway by which plants convert Co2 into sugars)

27
Q

what is first product of calvin cycle?

A

3-carbon sugar (3PGA)
3-phosphoglyceric acid

also known as C3 pathway

28
Q

starting compound of calvin cycle (which is regenerated at end of cycle) is?

A

RuBP, or Ribulose-1,5-bisphophate

29
Q

light-independent cycle/calvin cycle steps (around 6)

A
  1. one ATP powers addition of a phosphate to 5-carbon sugar phosphate
  2. CO2 added to 5-carbon sugar phosphate (catalyzed by RUBISCO, ribulose 1,5 bisphosphate carboxylase/oxygenase)
    resulting 6- carbon is short-lived, breaks into 2 3-carbon PGAs
  3. two ATPs add phosphates to PGA; 2 PGAs are made into 2 1,3-bisphosphoglycerate (BPG)
  4. BPG reduced by NADPH into glyceraldehyde-3- phosphate (G3P)
  5. one G3P per 3 cycle turns contributes to sugar (majority is for replenish RuBP)
  6. ATP from light-dependent reaction used to phosphorylate Ru5p to regenerate RuBP
30
Q

___ turns of calvin cycle makes 1 G3P?
need ___ turns for 1 6-carbon sugar? (glucose to sucrose)

A

3
6

31
Q

for one 6-carbon sugar, need __ ATP and __ NADPH

A

18 and 12

32
Q

calvin cycle needs more ATP than NADPH (3:2)
where does extra ATP come from?

A

cyclic electron flow that takes place in PSI makes extra ATP

33
Q

once 6-carbon sugar is made, it can remain in chloroplast and be made into ___ or transported to other areas as ___

A

starch
sucrose

BIOL 120 Plant Biology (28 decks)

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