8.3 Capturing Sunlight Into Chemical Forms

Question 1

visible light

Answer 1

the portion of the electromagnetic spectrum apparent to our eyes

Question 2

each point along the electromagnetic spectrum has:

Answer 2

a different energy level and a corresponding wavelength

Question 3

pigments are molecules that absorb:

Answer 3

some wavelengths of visible light

Question 4

pigments look coloured because:

Answer 4

they reflect light enriched in the wavelengths that they do not absorb

Question 5

chlorophyll

Answer 5

the major photosynthetic pigment contained in the thylakoid membrane; it plays a key role in the chloroplast’s ability to capture energy from sunlight. chlorophyll appears green because it is poor at absorbing green wavelengths

Question 6

describe a molecule of chlorophyll

Answer 6

large, light absorbing “head” containing a magnesium atom at its centre and a long hydrocarbon “tail”

Question 7

chlorophyll molecules are bound by their tail regions to :

Answer 7

integral membrane proteins in the thylakoid membrane

Question 8

photosystem

Answer 8

a protein-pigement complex that absorbs light energy to drive redox reactions and thereby sets the photosynthetic electron transport chain in motion

Question 9

accessory pigment

Answer 9

a light-absorbing pigment other than chlorophyll in the photosynthetic membrane; carotenoids are important accessory pigments

Question 10

accessory pigments allow photosynthetic cells to absorb:

Answer 10

a broader range of visible light than would be possible with chlorophyll alone

Question 11

when visible light is absorbed by a chlorophyll molecule, what happens?

Answer 11

one of its electrons is elevated to a higher energy state

Question 12

in labs, chlorophyll molecules which have absorbed light energy, rapidly release the energy as:

Answer 12

heat or light (fluorescence)

Question 13

absorption of visible light by an isolated chlorophyll molecule results in:

Answer 13

the release of heat and fluorescence when the electron returns to its ground energy state

Question 14

absorption of visible light by an antenna chlorophyll results in:

Answer 14

the transfer of energy to an electron in a neighbouring chlorophyll molecule (little energy is lost as heat)

Question 15

most chlorophyll molecules in the thylakoid membrane function as an antenna, meaning:

Answer 15

energy is transferred between chlorophyll molecules until it is finally transferred to a specially configured pair of chlorophyll molecules (reaction centre)

Question 16

reaction centre

Answer 16

specially configured chlorophyll molecules where light energy is converted into electron transport

Question 17

the reaction centre is where light energy is converted into:

Answer 17

chemical energy as a result of the excited electron’s transfer to an adjacent molecule

Question 18

the reaction centre chlorophylls have a distinct configuration from antenna chlorophylls which results in:

Answer 18

when excited, the reaction centre transfer an electron to an adjacent molecule (oxidized photosystem) that acts as an electron acceptor, converts light energy into chemical, electron transfer initiates chain of redox reactions that ultimately lead to formation of NADPH

Question 19

once the reaction centre has lost an electron:

Answer 19

it can no longer absorb light or contribute additional electrons, another electron must replace it and reduce the photosystem

Question 20

replacement electrons for reduced photosystems ultimately come from:

Answer 20

water

Question 21

why is water a challenging electron donor?

Answer 21

it takes a lot of energy to pull electrons from water

Question 22

how is there enough energy to extract an electron from water AND reduce NADP+?

Answer 22

two photosystems are arranged in a series, first photosystem pulls electrons from water, second photosystem allows electrons to be transferred to NADP+, both use energy separately

Question 23

why do electrons move in one “direction” through the series of redox reactions that make up the photosynthetic electron transport chain?

Answer 23

because these reactions are exergonic, running the reactions in the opposite way would require an input of energy

Question 24

Z scheme

Answer 24

another name for the photosynthetic electron transport chain, so called because the overall energy trajectory resembles a “Z”

Question 25

absorption of light energy at PSII allows:

Answer 25

electrons pulled from water to enter the photosynthetic electron transport hain

Question 26

a second input of light energy by PSI produces:

Answer 26

electron donor molecules capable of reducing NADP+

Question 27

the use of water as an electron donor requires:

Answer 27

input of light energy at two places in the photosynthetic electron transport chain

Question 28

photosystem II

Answer 28

the photosystem that supplies electrons to the beginning of the electron transport chain. when photosystem II loses an electron, it can pull electrons from water

Question 29

photosystem I

Answer 29

the photosystem that energizes electrons with a second input of light energy so they have enough energy to reduce NADP+

Question 30

associate photosystem II with strong….

Answer 30

OXIDATION and photosystem I with strong REDUCTION

Question 31

cytochrome f complex (cut)

Answer 31

part of the photosynthetic electron transport chain, through which electrons pass between photosystem II and photosystem I

Question 32

what are some compounds that convey electrons between protein complex (PSII, Cyt, PSI)

Answer 32

plastoquinone (Pq)-lipid soluble, similar to coenzyme Q, carries electrons from PSII to Cyt
plastocyanin (Pc)-water soluble carries electrons from Cyt to PSI through thylakoid lumen

Question 33

during photosynthetic electron transport, protons accumulate in the:

Answer 33

thylakoid lumen, protons flow back into the stroma through the ATP synthase

Question 34

where does water splitting occur?

Answer 34

on the lumen side of photosystem II (inside)

Question 35

NADPH is formed when electrons are passed from PSI to a membrane-associated protein called:

Answer 35

ferredoxin (Fd) and its associated enzyme ferredoxin-NADP+ reductase which catalyzes formation of NADPH

Question 36

in the chloroplasts, just like the mitochondria, ATP is synthesized by:

Answer 36

ATP synthase, a transmembrane protein powered by a proton gradient

Question 37

in chloroplasts, the ATP synthase results in the movement of protons from:

Answer 37

the thylakoid lumen to the stroma

Question 38

what are two features that lead to accumulation of protons in the thylakoid lumen?

Answer 38

oxidation of water releases protons and oxygen into the lumen, Cyt complex functions as a proton pump

Question 39

in photosynthesis, the proton pump involves:

Answer 39

1. the transport of two electrons and two protons, by the diffusion of Pq from the stroma side of PSII to the lumen side of the Cyt complex
2. the transfer of electrons within the Cyt complex to a different molecule of Pq which results in additional protons being picked up from the stroma and released into the lumen

Question 40

the accumulation of protons on one side of the thylakoid membrane can then be used to power:

Answer 40

the synthesis of ATP by oxidative phosphorylation

Question 41

an additional pathway for electrons is needed to:

Answer 41

increase the production of ATP (the Calvin cycle requires more ATP than NADPH)

Question 42

cyclic electron transport

Answer 42

an alternative pathway for electrons during the Calvin cycle that increases the production of ATP

Question 43

describe the process of cyclic electron transport:

Answer 43

electrons from PSI are redirected from ferredoxin back to the electron transport chain. electrons reenter by plastoquinone where they eventually return to PSI. as they pass through Cyt complex, more protons are pumped=more energy for ATP synthesis