Ch 10.1: Photosynthesis

Question 1

What happens when a pigment molecule absorbs light?

Answer 1

one of its electrons goes from a ground state to an excited state, which is unstable

Question 2

What happens to an excited chlorophyll molecule in isolation?

Answer 2

excited electrons fall back to the ground state, releasing excess energy as heat or light, an afterglow called flourescence

Question 3

What is a photosystem?

Answer 3

consists of a reaction-center complex surrounded by light-harvesting complexes

Question 4

What is a reaction-center complex?

Answer 4

an association of proteins holding a special pair of chlorophyll a molecules and a primary electron acceptor

Question 5

What is the light-harvesting complex?

Answer 5

it consists of various pigment molecules bound to proteins

Question 6

What does the light-harvesting complex do?

Answer 6

is transfers the energy of photons to the chlorophyll a molecules in the reaction-center complex

Question 7

How are these chlorophyll a molecules special?

Answer 7

they are special because they can transfer an excited electron to a different molecule

Question 8

What accepts the excited electron?

Answer 8

a primary electron acceptor in the reaction center accepts the excited electrons and is reduced as a result

Question 9

What is the first step of the light reactions?

Answer 9

solar-powered transfer of an electron from a chlorophyll a molecule to the primary electron acceptor

Question 10

What are the two types of photosystem in the thylakoid membrane?

Answer 10

photosystem II and photosystem I

Question 11

Photosystem II

Answer 11

called P680 because its reaction-center chlorophyll a is best at absorbing light with a wavelength of 680 nm

Question 12

Photosystem I

Answer 12

called P700 because its reaction-center chlorophyll a is best at absorbing light with a wavelength of 700 nm

Question 13

What are the two possible routes for electron flow during the light reactions?

Answer 13

cyclic and linear

Question 14

What is the linear electron flow?

Answer 14

the primary pathway, involves both photosystems and produces ATP and NADPH using light energy

Question 15

First step in linear electron flow:

Answer 15

a photon hits a pigment in a light-harvesting complex of PS II, and its energy is passed among pigment molecules until it excites P680

Question 16

Second step in linear electron flow:

Answer 16

an excited electron from P680 is transferred to the primary electron acceptor; we refer to the oxidized form as P680+

Question 17

Third step in linear electron flow:

Answer 17

an enzyme catalyzes the split of H20 into two electrons, two hydrogen ions (H+), and an oxygen atom. The electrons are transferred to the P680+ pair, reducing it back to P680. The H+ are released into the thylakoid space. The oxygen atom combines with another oxygen atom generated by the splitting of a different H20 and forms 02

Question 18

Fourth step in linear electron flow:

Answer 18

electrons are passed in a series of redox reactions from the primary electron acceptor of PS II down an electron transport chain to PS I

Question 19

Fifth step in linear electron flow:

Answer 19

potential energy stored in the proton gradient drives production of ATP by chemiosmosis

Question 20

Sixth step in linear electron flow:

Answer 20

in PS I, transferred light energy excites P700, which loses an electron to the primary electron acceptor, P700+ accepts an electron passed down from PS II via the electron transport chain

Question 21

Seventh step in linear electron flow:

Answer 21

electrons are passed from the primary electron acceptor of PS I down a second electron transport chain to the protein ferredoxin (Fd)

Question 22

Eighth step in linear electron flow:

Answer 22

the enzyme NADP+ reductase catalyzes the transfer of electrons from Fd to NADP+

Question 23

What is the cyclic electron flow?

Answer 23

photoexcited electrons cycle back from Fd to the cytochrome complex instead of being transferred to NADP+, uses only photosystem I, produces ATP, but no NADPH or oxygen results from this process

Question 24

Similarities of chloroplasts and mitochondria

Answer 24

chloroplasts and mitochondria both generate ATP by chemiosmosis, some of the electron carriers, including iron-containing proteins called cytochromes, are very similar in mitochondria and chloroplasts, and the ATP synthase complexes are also very similar.

Question 25

What are the differences between photophosphorylation and oxidative phosphorylation?

Answer 25

in chloroplasts, high-energy electrons drop down the transport chain from water, while in mitochondria, they are extracted from organic molecules. Mitochondria transfer chemical energy from food to ATP; chloroplasts transform light energy into the chemical energy of ATP

Question 26

What happens during the calvin cycle?

Answer 26

the ca;vin cycle uses the chemical energy of ATP and NADPH to reduce CO2 to sugar

Question 27

Is the calvin cycle anabolic or catabolic?

Answer 27

its anabolic, it builds sugar from smaller molecules by using ATP and the reducing power of electrons carried by NADPH

Question 28

What is the name of the made sugar in the calvin cycle?

Answer 28

glyceraldehyde 3-phosphate (G3P)

Question 29

How many times must the calvin cycle go around for net synthesis of one G3P?

Answer 29

the cycle must take place three times, fixing three molecules of CO2, one for each turn of the cycle

Question 30

What are the three phases of the calvin cycle?

Answer 30

carbon fixation, reduction, and regeneration of the CO2 acceptor

Question 31

Phase 1: Carbon fixation

Answer 31

the binding of CO2 to a five-carbon sugar named ribulose bisphosphate (RuBP) is catalyzed by RuBP carboxylase-oxygenase, or rubisco, the six-carbon intermediate molecules is immediately split into two molecues of 3-phosphoglycerate

Question 32

Phase 2: Reduction

Answer 32

each molecule of 3-phosphoglycerate is altered through phosphorylation by six ATP and reduction by six NADPH to ultimately produce a G3P sugar

Question 33

Phase 3: Regeneration of the CO2 acceptor (RuBP)

Answer 33

the remaining five molecules of G3P are rearranged in a complex series of reactions yielding three molecules of RuBP and three additional molecules of ATP are used to facilitate the regeneration of RuBP

Question 34

What does the calvin cycle consume for the net synthesis of one G3P molecule?

Answer 34

the calvin cycle consumes nine molecules of ATP and six molecules of NADPH