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H2 Biology > Photosynthesis > Flashcards

Photosynthesis Flashcards

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1
Q

what is site of photosynthesis?

A
  1. thylakoid membrane of chloroplast: light dependent photophosphorylation
  2. stroma (calvin cycle)
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2
Q

what is the final e- acceptor for non-cyclic photophosphorylation?

A
  1. NADP+
    -> generate NADPH for calvin cycle
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3
Q

what is the general pathway of non-cyclic ppp?

A

PSII -> PSI -> NADP+

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4
Q

what is the process of non-cyclic ppp?

A

[photoactivation]
1. light energy absorbed by accessory pigment molecules in LHC of PSII & PSI
2. e- gets excited
3. energy is transferred to other pigment molecules via resonance transfer of energy until it reaches 1 (out of 2) of Chl a in reaction centre (P700 in PSI, P680 in PSII)
4. chl a absorbed energy -> excited e- gets emitted
5. e- hole in PSII & PSI
6. excited e- is captured by primary electron acceptor in reaction centre

[photolysis]
1. enzyme split H2O -> 2e- + 2H+ + 1/2O2 to generate & replace e- lost to primary electron accepter from PSII & PSI
2. O atom will combine with another O atom to release O2 as a by-product
3. H+ will remain in thylakoid space

[1st ETC from PSII to PSI]
1. excited e- flow down the chain of e- carriers of ETC with increasing electronegativity
2. energy released is coupled to the pumping of H+ from stroma to thylakoid space, generating a proton-motive force
3. H+ diffuses down (conc. gradient) across ATP synthase back to stroma via facilitated diffusion
4. ADP is phosphorylated to ATP via chemo osmosis

[2nd ETC from PSI to NADP+]
1. photoexcited e- passed from PSI’s primary e- acceptor down 2nd ETC
2. no ATP is produced
3. e- is transferred to NADP+, reducing to NADPH (NADP+ +2e- + H+ -> NADPH)
4. catalyzed by NADP reductase

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5
Q

what is the pathway of cyclic ppp?

A

PSI -> PSI

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6
Q

what’s the purpose of cyclic ppp?

A

generates more ATP -> when there’s insufficient under times of stress

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7
Q

what is the process of cyclic ppp?

A

[photoactivation of PSI]
1. light energy is absorbed by accessory pigments molecules in electron carriers of LHC of PSI
2. e- gets excited
3. energy is relayed to other pigment molecules via transfer of resonance energy until chl a in reaction centre (p700 in PSI) is reached
4. when chl a absorbs energy
5. excited e- is emitted
6. e- hole in PSI is formed
7. excited e- is captured by primary e- acceptor in reaction centre

[ETC from PSI to PSI]
1. photoexcited e- passed from P700 (chl a) in PSI is captured by primary e- acceptor
2. e- is transferred back to 1st ETC
3. as excited e- flow down chain of e- carrier of ETC of increasing electronegativity
4. energy released is coupled to pumping of H+ from stroma to thylakoid space, creating a proton-motive force
5. H+ is diffused down the conc. gradient across ATP synthase back into stroma via facilitated diffusion
6. ADP is phosphorylated to ATP via chemiosmosis
7. e- goes through cyclic pathway and return to PSI

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8
Q

what is the process of calvin cycle (light independent)?

A

[carbon fixation]
1. CO2 combines with Ribulose Biphosphate
2. form unstable intermediate 6C compound, catalyzed by RuBP carboxylase

[reduction of GP by NADPH)
1. NADPH acts as a reducing power to reduce GP to G3P
2. ATP used
3. G3P is the first product formed in PS & end product of calvin cycle

[regeneration of RuBP]
1. 5 G3P is used to regenerate 3 RuBP
2. 3ATP from light dependent reaction is required

[fate of G3P & conclusion]
1. net synthesis of 1 molecule of G3P requires 3 CO2 to be fixed
2. 2 G3P may be used to form 1 glucose

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9
Q

what is needed to produce 1 G3P

A

6 NADPH, 9 ATP, 3CO2

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10
Q

why do we need cyclic ppp?

A

more ATP (9) is needed compared to NADPH (6) for calvin cycle

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11
Q

what is light compensation point?

A
  1. rate of photosynthesis = rate of respiration
  2. net gaseous exchange =0 (amt of CO2 produced = used)
  3. no net gain in dry mass & no growth
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12
Q

why does the rate of PS graph plateau? (y-axis: light intensity)

A
  1. chloroplast is saturated w/ light
  2. PS is occurring at max rate
  3. light is no longer limiting
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13
Q

explain the graph at which respiration occurs below light compensation point.

A
  1. respiration rate > photosynthesis -> CO2 is used up faster
  2. low light intensity -> low PS rate
  3. less photons of light strike chlorophyll for photoactivation
  4. decrease formation of ATP & NADPH for light independent reactions
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14
Q

explain [CO2] as limiting factor

A
  1. low [CO2]
  2. decrease freq. of effective collision btw CO2 & RuBP & RuBisCo
  3. decrease formation of ESC
  4. decrease rate of C fixation
  5. limit rate of calvin cycle
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15
Q

explain [O2] as limiting factor

A
  1. O2 is competitive inhibitor of RuBisCo
  2. when CO2 < O2 -> oxygenase function of Rubisco split RuBP into GP & glycolate
  3. broken down into CO2
  4. photorespiration
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16
Q

why does photoinhibition take place?

A

due to excess light

17
Q

what is the point of comparison of light-dependent & light independent reactions

A
  1. location
  2. reactants
  3. products
  4. conditions
  5. reactions involved
18
Q

what is the point of comparison of non-cyclic ppp & cyclic ppp?

A
  1. products
  2. PS involved
  3. source of e-
  4. pathway of e-
  5. final e- acceptor
  6. accumulation of H+ by:
  7. ATP production
  8. location
19
Q

role of NADP

A
  1. coenzyme that is reduced to NADPH -> in light reaction as the final e- acceptor
  2. R.A -> reduce GP to G3P in calvin cycle
  3. high energy e- carrier (from PS in light stage to stroma)
20
Q

structure & function of thylakoid membrane

A
  1. provide large S.A -> embed many photosynthetic pigments for light absorption
  2. maintain sequential arrangement of PS & e- carriers of ETC -> flow of e-
  3. maintain proton gradient for ATP synthesis via chemiosmosis -> since hydrophobic core of membrane is impermeable to protons
  4. embed many ATP synthase -> produce ATP as H+ flow down conc gradient via chemiosmosis from thylakoid space to stroma
21
Q

A plant placed with Radioactive C atoms in the sunlight for 1h. Afterwhich, it is removed from the sun and into the dark, what do you expect the Ribulose Bisphosphate and Glycerate Phosphate levels to change?

A

RB will decrease because no light for light-dependent phase so there is no generation of ATP & NADPH for regeneration of RB

GP levels will plateau as C fixation is stopped due to RB regeneration stopping

22
Q

What’s the purpose of light-dependent phase?

A

To generate NADPH & ATP needed for light-indep phase (Calvin cycle)

23
Q

What is Chl b?

A

Accessory pigment found in the light harvesting complex

Absorbs / harvests light energy

Pass energy to neighbouring accessory pigments until it accumulates and reaches
special chlorophyll a in reaction centre

idea of extending the range of light wavelengths absorbed

24
Q

Factors affecting PS

A
  1. Light intensity
  2. Wavelength of Light
  3. Water
  4. CO2
  5. Temperature
  6. pH

recall still common ideas of enzymes

25
Q

Name the adaptions of the Thylakoid membrane for its role

A
  1. Provides large surface area to –> embed many photosynthetic pigments for light absorption
  2. Maintains the sequential arrangement of the photosystems* & electron carriers of ETC for flow of e-
  3. Maintains proton gradient for ATP synthesis since the Hphobic core* of the membrane is impermeable to protons → allows chemiosmosis to occur
  4. Allows many ATP synthase* to be embedded so ATP can be produced as H+ flow down their gradient
    via chemiosmosis from thylakoid space to stroma
26
Q
A

H2 Biology (20 decks)

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