Chapter 19. The Light Reactions of Photosynthesis

Question 1

a dimer of bacterial chlorophyll-b molecules, called the special pair, that absorb light maximally at 960 nm. P960 initiates charge separation in bacterial photosynthesis.

Answer 1

P960

Question 2

a substituted tetrapyrrole that is the principal photoreceptor in plants.

Answer 2

Chlorophyllα

Question 3

in chloroplasts, the reactions in which light is used to create reducing potential and to generate oxygen.

Answer 3

Light reactions

Question 4

the excitation of an electron from its ground state to a higher energy level by light absorption, and the subsequent movement of the excited electron from the initial molecule to an acceptor, resulting in a positive charge on the initial molecule and a negative charge on the acceptor molecule.

Answer 4

Photoinduced charge separation

Question 5

the special pair of photosystem II in green plants. Absorption of light by P680 results in the transfer of electrons from water to plastoquinone, which generates a proton gradient.

Answer 5

P680

Question 6

pile or stack of thylakoid membranes in the chloroplast.

Answer 6

Granum

Question 7

the plant organelle in which photosynthesis takes place.

Answer 7

Chloroplast

Question 8

in chloroplasts, a photosynthetic unit that includes a light-harvesting complex, a reaction center and an electron-transport chain. The system catalyzes the light-driven transfer of electrons from reduced plastoquinone to ferredoxin, which in turn drives the formation of NADPH; it requires light of wavelength shorter than 700 nm.

Answer 8

Photosystem I (PS I)

Question 9

extended polyenes that absorb light between 400 and 500 nm and serve as accessory pigments in photosynthesis by funneling the energy to the photosynthetic reaction center

Answer 9

Carotenoid

Question 10

molecular assembly of the inner mitochondrial membrane responsible for the respiratory chain driven synthesis of ATP; also called Complex V, mitochondrial ATPase, H+-ATPase, or F0F1-ATPase.

Answer 10

ATP synthase (CF 1-CF 0 complex)

Question 11

in photosynthesis, the generation of ATP without concomitant formation of NADPH. Electron cycling from the reaction center of photosystem I to ferredoxin and then back to the reaction center via cytochrome bf and plastoquinone generates a proton gradient that is used to drive ATP formation.

Answer 11

Cyclic photophosphorylation

Question 12

a cytochrome complex that links photosystem II and photosystem I in green plants. Cytochrome bf contributes to the proton gradient by oxidizing plastoquinol to plastoquinone.

Answer 12

Cytochrome bf

Question 13

the special pair of photosystem I in green plants. Absorption of light by P700 results in the transfer of electrons that generates ferredoxin, and ultimately NADPH.

Answer 13

P700

Question 14

complexes of light-absorbing pigments and protein that completely surround the reaction center of photosynthesis. The complex funnels the energy of absorbed light to the reaction center.

Answer 14

Light-harvesting complex

Question 15

the matrix of the chloroplast, which contains thylakoids as well as soluble enzymes; the stroma is enclosed by the inner membrane of the chloroplast.

Answer 15

Stroma

Question 16

In chloroplasts, a membranous sac, or vesicle, that contains the energy-transducing machinery of photosynthesis, including light-harvesting proteins, reaction centers, electron-transport chains, and ATP synthase.

Answer 16

Thykaloid

Question 17

the site of oxygen generation in photosynthesis in green plants. The center is a complex, which includes four manganese ions, that donates electrons to positively charged P680. After donating four electrons, the manganese center oxidizes two molecule of water to replenish its electrons and thus forms a single molecule of molecular oxygen and four protons.

Answer 17

water-oxidizing complex (WOC) (manganese center)

Question 18

in chloroplasts, a photosynthetic unit that includes a light-harvesting complex, a reaction center, and an electron-transport chain. The system catalyzes the light-driven transfer of electrons from water to plastoquinone, with the concomitant generation of oxygen; it requires light of wavelength shorter than 680 nm.

Answer 18

Photosystem II (PS II)

Question 19

in a photosynthetic unit, a specialized chlorophyll molecule that collects excitation energy from other chlorophylls and mediates the transformation of light into chemical energy.

Answer 19

Reaction center

Question 20

in a photosynthetic reaction center, the pair of chlorophyll molecules that collect excitation energy from antenna chlorophylls and then transfer high-energy electrons to other electron acceptors.

Answer 20

Special pair

Question 21

the energy inherent in the proton gradient established during the functioning of the respiratory chain; consists of a membrane potential as well as a chemical gradient.

Answer 21

Proton-motive force

Question 22

the pathway of electron flow between photosystem I and II. It is called such because the redox diagram from P680 to P700+ looks like the letter Z.

Answer 22

Z scheme of photosynthesis