Photosynthesis I Flashcards
where does plant respiration occur?
in mitochondria, where stored energy is converted to ATP in presence of O2
all organisms must extract energy from food through ____
respiration
photosynthesis and respiration are ____ processes
interdependent
ATP stands for?
adenosine triphosphate
___% of solar energy received on Earth is visible light?
leaves absorb ___% of visible light reaching them?
40
80
pigment colour is determined by absorbed/reflected light?
reflected light, NOT absorbed light!
chlorophyll absorbs photons in the blue (__nm) and red (__nm) of visible spectrum (400-700nm), green reflected
chlorophyll a reflects _____
chlorophyll b reflects _____
430
680
blue-green
yellow-green
what colour do carotenoids absorb and reflect?
absorb blue-green,
reflect yellow or yellow-orange
where are carotenoids and anthocyanin stored? types + colour?
carotenoids: stored in plastids
- beta-carotene (orange)
- xanthophyll (yellow)
anthocyanin: stored in vacuole
- flavonoids (blue, purple, red depending on pH)
colours of autumn are from?
deciduous trees:
when chlorophyll is broken down,
accessory pigments carotenoids and anthocyanin become visible
photosynthesis is divided into 2 reactions?;
where do they occur?
- light-dependent; occurs in chloroplast thylakoid membranes
- light-independent; occurs in chloroplast stroma
light-dependent reaction in thylakoid membranes:
what steps + photosystems? (Detailed)
- 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
what are photosystems? (detailed)
pigments clustered in discrete units of organization
- each PS contains 200-300 pigments and associated proteins
- PS’s occur repeatedly throughout thylakoid membranes
photosystem structures (2):
- reaction centre
- chlorophyll a molecule and primary e- acceptor
- <1% of pigments in a PS are chlorophyll a - 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
light-dependent reaction: electron energy steps
- 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
light-dependent reaction: reaction centre
- 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)
light-dependent reaction: PSI and PSII (antenna pigment molecules, reaction centre)
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)
light-dependent reaction: Z-scheme
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
PQ stands for?
PC?
Fd?
plastoquinone
plastocyanin
ferredoxin
light-dependent reaction: Z-scheme steps (DETAILED) (6)
- light funnelled to P680, energize e- in chlorophyll a. excited e- -> pheophytin (primary electron acceptor) -> PQ in electron transport chain -> PSI
- each rejected P680 e- replaced by e- from H2O after enzymatic splitting of water (photolysis) into: 2e- + 2H+ + O
- e- passed on from primary electron acceptor slowly loses energy as they move through protein complexes in electron transport chain: plastoquinone, cytochrome complexes, plastocyanin
- energy released by e- used to move H+ across thylakoid membrane (chemiosmosis)
- buildup H+ gradient indirectly powers ATP synthesis (photophosphorylation) - 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 - 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
PSII and PSI operate ____
simultaneously
light-dependent reaction: chemiosmosis (detailed)
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
light-dependent reactions: O2, ATP, NADPH (how are they made?)
what is efficiency % (light -> chemical energy)
- 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%
primitive photosystems: cyclic electron flow
- 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
light-independent reaction (chloroplast stroma): dark reaction?
AKA calvin cycle uses chemical energy made in light-dependent reactions to make simple sugar phosphates, often called DARK reactions
what is light-independent reaction/calvin officially known as? why?
calvin-benson-bassham cycle
- named after melvin calvin, with students andrew benson and james bassham
(Determined pathyway by which plants convert Co2 into sugars)
what is first product of calvin cycle?
3-carbon sugar (3PGA)
3-phosphoglyceric acid
also known as C3 pathway
starting compound of calvin cycle (which is regenerated at end of cycle) is?
RuBP, or Ribulose-1,5-bisphophate
light-independent cycle/calvin cycle steps (around 6)
- one ATP powers addition of a phosphate to 5-carbon sugar phosphate
- 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 - two ATPs add phosphates to PGA; 2 PGAs are made into 2 1,3-bisphosphoglycerate (BPG)
- BPG reduced by NADPH into glyceraldehyde-3- phosphate (G3P)
- one G3P per 3 cycle turns contributes to sugar (majority is for replenish RuBP)
- ATP from light-dependent reaction used to phosphorylate Ru5p to regenerate RuBP
___ turns of calvin cycle makes 1 G3P?
need ___ turns for 1 6-carbon sugar? (glucose to sucrose)
3
6
for one 6-carbon sugar, need __ ATP and __ NADPH
18 and 12
calvin cycle needs more ATP than NADPH (3:2)
where does extra ATP come from?
cyclic electron flow that takes place in PSI makes extra ATP
once 6-carbon sugar is made, it can remain in chloroplast and be made into ___ or transported to other areas as ___
starch
sucrose
