L6 photosynthesis part 2

Question 1

everything happens inside the…. and in the … in particular

Answer 1

chlorplast
thylakoid membranes

Question 2

what is on the surface of the thylakoid membrane?

Answer 2

-pigment molecules (chlorophyll a and b and carotenoids)
-embedded in thylakoid, in association with proteins

Question 3

how are pigment molecules organized on the thylakoid membrane?

Answer 3

in discrete membranes, photosystems

Question 4

how many pigments do photosystems each carry?

Answer 4

approx. 250-400 pigments

Question 5

what are the two components of the photosystems?

Answer 5

antenna complex and reaction center

Question 6

photosystems are surrounded by … (ones without reaction centers)

Answer 6

many light-harvesting complexes

Question 7

photosystems + light-harvesting complexes = ….

Answer 7

photosystem complex

Question 8

what is resonance energy transfer?

Answer 8

energy moving from one pigment to the next

Question 9

what is chlorophyll a’s role?

Answer 9

to absorb energy and boost electrons to a higher energy level, which initiates energy flow

i.e., chlorophyll a becomes oxidized

Question 10

photosynthesis occurs between two ….

Answer 10

photosystems, photosystem I (P700) and photosystem II (P680). they work simultaneously

Question 11

what are PSI and PSII linked by

Answer 11

the electron transport chain

Question 12

what happens in photosystem II?

Answer 12

water is oxidized to oxygen. water is split into hydrogen protons and oxygen molecules. two electrons are stripped and passed onto the complex. these electrons replaces the electrons that are lost by the reaction center, p680

Question 13

what is the PSII complex made up of?

Answer 13

an intricate network of manganese, oxygen, and calcium ions, that strip electrons off water. this intricate network is embedded in the psII protein complex, located at the base of the photosystem, facing the thylakoid lumen

Question 14

explain the process that occurs in PSII (P680)

Answer 14

light energy is absorbed by chlorophyll a in reaction center, exciting electrons. the excited electrons are then passed on to the electron acceptor, known as pheophytin. the electron transport chain then follows. This entails electrons being passed thorugh plastoquinone (Qa) and plastoquinone (Qb), to the Cyt b6/f complex

Question 15

what is pheophytin?

Answer 15

modified chlorophyll a molecule, magnesium atom replaced by two protons

Question 16

how many protons does Plastoquinone B (PQb) picks up?

Answer 16

two protons

Question 17

how are electrons and protons moved thought the Cyt b6/f complex?

Answer 17

2 electrons are donated to the complex (one at a time), and 2 protons are funelled into the lumen. reduced cytochrome f donates electrons to plastocyanin

Question 18

what happens in photosystem I?

Answer 18

light energy excited antenna molecules, A0 being the primary acceptor where electrons are then passed downhill on the stromal side of the membrane. the final acceptor is Ferredoxin (mobile iron-sulfur protein). NADP+ is reduced to NADPH

Question 19

summary of what happens between PSII and PSI:

Answer 19

electrons flow continuously from PSII and PSI, ultimately to NADP+, oxidation of water, reduction of NADP, a non-cyclic electron flow
PSII supplies electrons for PSI, with 6 electrons at each turn, producing 6 ATP + 6 NADPH

Question 20

what is cyclic phosphorylation?

Answer 20

a process that bypasses PSII. electrons excited in PSI pass through cascade to cytochrome complex, on to plastocyanin and back to PSI. protons are pumped into the lumen which drives ATP synthesis

Question 21

what is cyclic phosphorylation necessary for?

Answer 21

carbon fixation (3:2 ratio of ATP to NADPH)

Question 22

what does the ATP synthase complex do?

Answer 22

releases protons into thylakoid membrane during the oxidation of water via the cytochrome b6/f complex. this generates an electrochemical proton gradient (lumen:stroma)
part of photo-phosphorylation