Chapter 8.5: The Light-Dependent Reactions

Question 1

What is a proton pump found in the thylakoid membrane. This complex uses energy from excited electrons to pump protons from the stroma into the thylakoid compartment?

Answer 1

 Cytochrome/b₆-f Complex

Question 2

After  The oxidized P₆₈₀ then removes an electron from a manganese atom. , what is the next step of noncyclic photophosphorylation?

Answer 2

 The oxidized manganes atoms, with the aid of reaction center proteins, remove electrons from oxygen atoms in the two water molecules

Question 3

Which photosystem has a P₇₀₀ reaction center pigment?

Answer 3

photosystem I

Question 4

After  When the reaction center of photosystem II absorbs a photon, an electron in a P₆₈₀ chlorophyll molecule is excited, which transfers this electron to an acceptor, what is the next step of noncyclic photophosphorylation?

Answer 4

 The oxidized P₆₈₀ then removes an electron from a manganese atom.

Question 5

How is ATP generated by chemiosmosis in photosynthesis?

Answer 5

o Protons are pumped from the stroma into the thylakoid compartment by the b₆-f complex o The splitting of water also produces added protons that contribute to the gradient o ATP Synthase  The chloroplast has ATP synthase enzymes in the thylakoid membrane that form a channel, allowing protons to cross back out into the stroma  As protons pass out of the thylakoid through the ATP synthase channel, ADP is phosphorylated to ATP and released into the stroma

Question 6

After charge separation, what is the next stage of the thylakoid reactions?

Answer 6

o Electron Transport  The excited electrons are shuttled along a series of electron carrier molecules embedded with the photosynthetic membrane.  Several of them react by transporting protons across the membrane, generating a proton gradient.  Eventually the electrons are used to reduce a final acceptor, NADPH

Question 7

After electron transport, what is the last stage of the thylakoid reactions?

Answer 7

o Chemiosmosis  The protons that accumulate on one side of the membrane now flow back across the membrane through ATP synthase where chemiosmotic synthesis of ATP takes place, just as it does in aerobic respiration

Question 9

Define  Cytochrome/b₆-f Complex

Answer 9

a proton pump found in the thylakoid membrane. This complex uses energy from excited electrons to pump protons from the stroma into the thylakoid compartment

Question 10

After the primary photoevent, what is the next stage of the thylakoid reactions?

Answer 10

o Charge Separation  This excitation energy is transferred to the reaction center, which transfers an energetic electron to an acceptor molecule, initiating electron transport

Question 11

After photosystem I  Accepts an electron from plastocyanin, what is the next step of noncyclic photophosphorylation?

Answer 11

 The absorption of a photon by photosystem I boosts the electron leaving the reaction center to a very high energy level

Question 12

After  The oxidized manganes atoms, with the aid of reaction center proteins, remove electrons from oxygen atoms in the two water molecules, what is the next step of noncyclic photophosphorylation?

Answer 12

 The primary electron acceptor for the light-energized electrons leaving photosystem II is a quinone molecule  The reduced quinone that results from accepting a pair of electrons passes the excited electron pair to a proton pump called the b₆-f complex

Question 13

After  The absorption of a photon by photosystem I boosts the electron leaving the reaction center to a very high energy level, what is the next step of noncyclic photophosphorylation?

Answer 13

 The electrons are passed to an iron-sulfur protein called ferredoxin

Question 14

Which photosystem has a P₆₈₀ reaction center pigment?

Answer 14

photosystem II

Question 15

Where is cytochrome b₆-f complex located?

Answer 15

borders between grana and lamella

Question 16

After  Arrival of the electron pair causes the b₆-f complex to pump a proton into the thylakoid space, what is the next step of noncyclic photophosphorylation?

Answer 16

 A small, copper containing protein called plastocyanin then carries the electron pair to photosystem I

Question 17

Where is photosystem II located?

Answer 17

grana

Question 18

What is the set of light-dependent reactions of the two plant photosystems, in which excited electrons are shuttled between the two photosystems, producing a proton gradient that is used for the chemiosmotic synthesis of ATP. The electrons are used to reduce NADP to NADPH. Lost electrons are replaced by the oxidation of water producing O₂?

Answer 18

noncyclic photophosphorylation

Question 19

What is the reaction center for photosystem II?

Answer 19

P₆₈₀

Question 20

Where is ATP synthase located?

Answer 20

stroma lamella,  Can also be found on the edges of grana that are not stacked

Question 21

After The reduced quinone that results from accepting a pair of electrons passes the excited electron pair to a proton pump called the b₆-f complex, what is the next step of noncyclic photophosphorylation?

Answer 21

 Arrival of the electron pair causes the b₆-f complex to pump a proton into the thylakoid space

Question 22

What is the first stage of the thylakoid reactions?

Answer 22

o Primary Photoevent  A photon of light is captured by a pigment  Excites an electron within the pigment

Question 23

What does the photosystem II reaction center require?

Answer 23

 Requires the reaction center to absorb four photons to complete the oxidation of two water molecules, producing one O₂ in the process

Question 24

After  A small, copper containing protein called plastocyanin then carries the electron pair to photosystem I, what is the next step of noncyclic photophosphorylation?

Answer 24

photosystem I  Accepts an electron from plastocyanin

Question 25

How is additional ATP produced in photosynthesis?

Answer 25

 The passage of an electron pair from water to NADPH in noncyclic phosphorylation generates one molecule of NADPH and slightly more than one molecule of ATP  To produce the extra ATP, many plant species are capable of short-circuiting photosystem I, switching photosynthesis into a cyclic photophosphorylation mode, so that the light-excited electron leaving photosystem I is used to make ATP instead of NADPH  The energetic electrons are passed back to the b₆-f complex, rather than passing on to NADP⁺  The b₆-f complex pumps protons into the thylakoid space, adding to the proton gradient that drives the chemiosmotic synthesis of ATP

Question 26

What is the first step of noncyclic photophosphorylation?

Answer 26

 When the reaction center of photosystem II absorbs a photon, an electron in a P₆₈₀ chlorophyll molecule is excited, which transfers this electron to an acceptor

Question 27

After  The electrons are passed to an iron-sulfur protein called ferredoxin, what is the last step of noncyclic photophosphorylation?

Answer 27

 The reduced ferrodoxin carries an electron  Two of them, from two molecules of reduced ferredoxin, are then donated to a molecule of NADP⁺ to form NADPH • Reaction catalyzed by the membrane-bound enzyme NADP reductase

Question 28

Define noncyclic photophosphorylation

Answer 28

the set of light-dependent reactions of the two plant photosystems, in which excited electrons are shuttled between the two photosystems, producing a proton gradient that is used for the chemiosmotic synthesis of ATP. The electrons are used to reduce NADP to NADPH. Lost electrons are replaced by the oxidation of water producing O₂

Question 29

What is the reaction center for photosystem I?

Answer 29

P₇₀₀

Question 30

Where is photosystem I located?

Answer 30

stroma lamella,  Can also be found on the edges of grana that are not stacked