Exam 1 - Photosynthesis Light Reactions

Question 1

What is the overall equation for photosynthesis?

Answer 1

Energy + 6CO2 + 6H2O —> C6H12O6 + 6O2

Question 2

What is reduced in photosynthesis, and what is oxidized?

Answer 2

CO2 is reduced and H2O is oxidized

Question 3

What is the overall equation for respiration?

Answer 3

C6H12O6 + 6O2 —> 6CO2 + 6H2O + Energy

Question 4

What is reduced in respiration, and what is oxidized?

Answer 4

O2 is reduced and C6H12O6 is oxidized

Question 5

How are photosynthesis and respiration related?

Answer 5

photosynthesis reverses the direction of electron flow compared to respiration (and vice versa)

Question 6

What is reduction?

Answer 6

the gaining of an electron/the reduction of charge

Question 7

What is oxidation?

Answer 7

the losing of an electron/the raising of charge

Question 8

What are the main products of the light reactions of photosynthesis?

Answer 8

ATP and NADPH

Question 9

What substrates are used by the carbon reactions of photosynthesis?

Answer 9

ATP and NADPH

Question 10

What steps of the light reactions occur in the thylakoids?

Answer 10

• split H2O and release O2
• reduce NADP+ to NADPH
• generate ATP from ADP and Pi by photophosphorylation

Question 11

What energy conversion occurs in the thylakoids?

Answer 11

conversion of light energy into chemical energy

Question 12

What steps of the carbon reactions occur in the stroma?

Answer 12

• formation of sugar from CO2

- use of ATP and reducing power of e- carried by NADPH

Question 13

What is the first step of the Calvin cycle?

Answer 13

carbon fixation

Question 14

Why are the light reactions and carbon reactions interdependent?

Answer 14

• light reactions produce ATP and NADPH, the substrates of the carbon reactions, from ADP and NADP+
• carbon reactions turn use ATP and NADPH and produce ADP and NADP+, which is needed by the light reactions

Question 15

What is chlorophyll a?

Answer 15

the main photosynthetic pigment

Question 16

What is the role of accessory pigments, such as chlorophyll b?

Answer 16

to broaden the spectrum of light used for photosynthesis

Question 17

What is the role of carotenoids?

Answer 17

to absorb excessive light that would damage the chlorophyll

Question 18

Why do we compare absorption and action spectra?

Answer 18

to determine if what is absorbing the light actually shows a response

Question 19

What does a photosystem consist of?

Answer 19

a reaction-center complex surrounded by light-harvesting complexes

Question 20

What is the role of light-harvesting complexes in photosystems?

Answer 20

transfer the energy of photons to the reaction center

Question 21

What are the characteristics of photosystem II?

Answer 21

• functions first
• best at absorbing light at a wavelength of 680 nm
• reaction-center chlorophyll a is called P680

Question 22

What are the characteristics of photosystem I?

Answer 22

• functions second
• best at absorbing light at a wavelength of 700 nm
• reaction-center chlorophyll a is called P700

Question 23

What is the chloroplast coupling center of ATP synthase?

Answer 23

uses proton gradient across thylakoid membrane to synthesize ATP (couples ATP synthesis with the proton gradient)

Question 24

Why is it important that P680 is a strong oxidant?

Answer 24

its “electron hole” must be filled, which greatly facilitates transfer of electrons from split water molecules

Question 25

Why is more light required in photosystem I, despite there already being light input in photosystem II?

Answer 25

as electrons move down the ETC from PSII to PSI, they lose energy; light energy is needed to get back to the higher energy state

Question 26

What are the “big picture” key points about the light reactions?

Answer 26

• use solar energy to generate ATP and NADPH
• provide chemical energy and reducing power to synthesize carbohydrates in the Calvin cycle
• light and carbon rxns are dependent on each other and on the presence of light

Question 27

What is linear electron flow?

Answer 27

• primary electron pathway
• involves PSII and PSI
• electron transport chain between the two photosystems
• produces ATP and NADPH using light energy

Question 28

What is cyclic electron flow?

Answer 28

• uses only PSI
• produces ATP, but not NADPH
• no oxygen released
• generates a surplus of ATP to satisfy demand of Calvin cycle
• sends e- flow back through cytochrome complex rather than to NADP reductase