BIOC 385 FINAL EXAM TEST BANK B
– 180 QUESTIONS WITH VERIFIED
ANSWERS & RATIONALES | LATEST
2026/2027 ARIZONA UNIVERSITY
BIOCHEM 385 FINAL EXAM
Photosynthesis & The Calvin Cycle
1. The Biosphere 2 project, a sealed terrarium in Tucson, Arizona, had to be
interrupted after only a few months primarily because:
A) The humans ran out of food.
B) Levels of CO2 rose to dangerous levels.
C) The plants stopped producing oxygen.
D) The rate of photosynthesis was too high.
Answer: B
Rationale: The project was interrupted because CO2 levels rose to dangerous levels,
disrupting the balance between respiration and photosynthesis.
2. The __________ is driven directly by photons from the sun in the light reactions
of photosynthesis.
A) pumping of protons
B) synthesis of ATP
C) transfer of electrons
D) synthesis of glucose
Answer: C
Rationale: Photons directly drive the transfer of electrons through the photosystems,
initiating the light-dependent reactions.
3. Which of the following is a photosynthetic light-harvesting pigment?
A) FeS cluster
B) NADPH
C) Plastoquinone
D) β-carotene
Answer: D
Rationale: β-carotene is an accessory pigment that absorbs light energy and transfers it
to the reaction center chlorophyll.
,4. Approximately how many light-harvesting chromophores are found per
photosystem enzyme, such as in PSI or PSII?
A) 2
B) About a dozen
C) About 100 to 200
D) About 1000 to 2000
Answer: C
Rationale: Each photosystem contains a large antenna complex of about 100 to 200
chromophores to maximize light absorption.
5. The photosynthetic Z scheme describes the:
A) Synthesis of glucose from CO2.
B) Movement of electrons driven by the absorption of light energy.
C) Production of O2.
D) Reduction of NADPH.
Answer: B
Rationale: The Z scheme illustrates the energy profile of electron transfer from water to
NADP+ through PSII and PSI, driven by light.
6. In chloroplasts, Photosystem I (PSI) generally localizes in the __________,
whereas Photosystem II (PSII) localizes in the __________.
A) thylakoid lumen; thylakoid grana
B) thylakoid lamellae; thylakoid grana
C) stroma; thylakoid lumen
D) thylakoid grana; thylakoid lamellae
Answer: B
Rationale: PSI is found in the unstacked thylakoid lamellae, while PSII is primarily in
the stacked grana membranes.
7. What is the overall balanced reaction for the light reactions of
photosynthesis?
A) 6 CO2 + 6 H2O → C6H12O6 + 6 O2
B) 2 H2O + 8 photons + 2 NADP+ + 3 ADP + 3 Pi → O2 + 2 NADPH + 3 ATP
C) 2 H2O + 4 photons + 2 NADP+ + 3 ADP + 3 Pi → O2 + 2 NADPH + 3 ATP
D) CO2 + H2O → CH2O + O2
Answer: B
Rationale: The balanced equation for the light reactions shows the input of water, light,
NADP+, and ADP/Pi to produce oxygen, NADPH, and ATP.
8. The energy derived from photosynthesis and used to make ATP is manifested
in what form?
A) A proton gradient (acidic thylakoid lumen)
B) A sodium gradient
C) An electric potential across the stroma
,D) Heat
Answer: A
Rationale: The light reactions pump protons into the thylakoid lumen, creating an
electrochemical gradient (proton motive force) used by ATP synthase.
9. Under what conditions does cyclic photophosphorylation take place?
A) With high levels of NADPH
B) In the dark
C) When PSII is damaged
D) When CO2 levels are high
Answer: A
Rationale: Cyclic photophosphorylation occurs when NADPH levels are high, and the
electron transport chain cycles electrons back to the cytochrome b6f complex to
produce only ATP.
10. The Calvin cycle requires which species from the light reactions?
A) ATP and NADPH
B) Reducing electrons only
C) CO2 and ATP
D) NADH and FADH2
Answer: A
Rationale: The Calvin cycle uses the ATP and NADPH generated by the light reactions
to fix CO2 into sugars.
11. The first stage of the three-stage Calvin cycle is catalyzed by the enzyme:
A) Rubisco
B) Phosphoglycerate kinase
C) Glyceraldehyde-3-phosphate dehydrogenase
D) Aldolase
Answer: A
Rationale: The first committed step of the Calvin cycle is the carboxylation of ribulose-
1,5-bisphosphate by rubisco.
12. Overall, the net balanced reaction of the Calvin cycle converts 3 CO2 into
one:
A) Glucose molecule
B) Glyceraldehyde-3-phosphate
C) Ribulose-1,5-bisphosphate
D) Pyruvate
Answer: B
Rationale: Three turns of the Calvin cycle fix three CO2 molecules to produce one net
molecule of glyceraldehyde-3-phosphate (G3P).
, 13. The third stage of the three-stage Calvin cycle:
A) Generates CO2.
B) Uses ATP and NADPH from the light reactions.
C) Regenerates a C5 sugar for the Calvin cycle to continue.
D) Is catalyzed by rubisco.
Answer: C
Rationale: The regeneration phase (stage 3) rearranges carbon skeletons to regenerate
ribulose-1,5-bisphosphate, allowing the cycle to continue.
14. Under what condition(s) do the wasteful side reaction of O2 with rubisco
become significant?
A) Low temperature and low light
B) Increased temperature and intense light
C) High CO2 and low O2
D) In the dark
Answer: B
Rationale: Photorespiration is favored when stomata close on hot, bright days, leading
to high internal O2 and low CO2, causing rubisco to fix O2 instead of CO2.
15. The herbicide paraquat operates by stealing electrons from photosystem I
(PSI). Which of the following is true of chloroplasts treated with paraquat?
A) NADPH levels drop.
B) Photosystem II is not re-reduced.
C) Plastocyanin has nowhere to donate electrons.
D) No protons are pumped across the chloroplast membranes.
Answer: A
Rationale: By diverting electrons away from ferredoxin, paraquat prevents the
reduction of NADP+ to NADPH, causing NADPH levels to drop.
16. The cytochrome b6f complex of the photosynthetic electron transport
system is responsible for translocating 8 H+ into the thylakoid space. A total of
12 H+ accumulate inside the thylakoid space. What is the origin of the other 4
H+?
A) From the stroma
B) From the oxidation of 2 H2O to form O2 + 4H+ + 4e-
C) From the reduction of NADP+
D) From ATP hydrolysis
Answer: B
Rationale: The oxidation of water by PSII releases 4 protons directly into the thylakoid
lumen, contributing to the proton gradient.
17. In C4 and CAM plants, CO2 is first incorporated into __________, which is then
converted to malate.
A) Ribulose-1,5-bisphosphate
– 180 QUESTIONS WITH VERIFIED
ANSWERS & RATIONALES | LATEST
2026/2027 ARIZONA UNIVERSITY
BIOCHEM 385 FINAL EXAM
Photosynthesis & The Calvin Cycle
1. The Biosphere 2 project, a sealed terrarium in Tucson, Arizona, had to be
interrupted after only a few months primarily because:
A) The humans ran out of food.
B) Levels of CO2 rose to dangerous levels.
C) The plants stopped producing oxygen.
D) The rate of photosynthesis was too high.
Answer: B
Rationale: The project was interrupted because CO2 levels rose to dangerous levels,
disrupting the balance between respiration and photosynthesis.
2. The __________ is driven directly by photons from the sun in the light reactions
of photosynthesis.
A) pumping of protons
B) synthesis of ATP
C) transfer of electrons
D) synthesis of glucose
Answer: C
Rationale: Photons directly drive the transfer of electrons through the photosystems,
initiating the light-dependent reactions.
3. Which of the following is a photosynthetic light-harvesting pigment?
A) FeS cluster
B) NADPH
C) Plastoquinone
D) β-carotene
Answer: D
Rationale: β-carotene is an accessory pigment that absorbs light energy and transfers it
to the reaction center chlorophyll.
,4. Approximately how many light-harvesting chromophores are found per
photosystem enzyme, such as in PSI or PSII?
A) 2
B) About a dozen
C) About 100 to 200
D) About 1000 to 2000
Answer: C
Rationale: Each photosystem contains a large antenna complex of about 100 to 200
chromophores to maximize light absorption.
5. The photosynthetic Z scheme describes the:
A) Synthesis of glucose from CO2.
B) Movement of electrons driven by the absorption of light energy.
C) Production of O2.
D) Reduction of NADPH.
Answer: B
Rationale: The Z scheme illustrates the energy profile of electron transfer from water to
NADP+ through PSII and PSI, driven by light.
6. In chloroplasts, Photosystem I (PSI) generally localizes in the __________,
whereas Photosystem II (PSII) localizes in the __________.
A) thylakoid lumen; thylakoid grana
B) thylakoid lamellae; thylakoid grana
C) stroma; thylakoid lumen
D) thylakoid grana; thylakoid lamellae
Answer: B
Rationale: PSI is found in the unstacked thylakoid lamellae, while PSII is primarily in
the stacked grana membranes.
7. What is the overall balanced reaction for the light reactions of
photosynthesis?
A) 6 CO2 + 6 H2O → C6H12O6 + 6 O2
B) 2 H2O + 8 photons + 2 NADP+ + 3 ADP + 3 Pi → O2 + 2 NADPH + 3 ATP
C) 2 H2O + 4 photons + 2 NADP+ + 3 ADP + 3 Pi → O2 + 2 NADPH + 3 ATP
D) CO2 + H2O → CH2O + O2
Answer: B
Rationale: The balanced equation for the light reactions shows the input of water, light,
NADP+, and ADP/Pi to produce oxygen, NADPH, and ATP.
8. The energy derived from photosynthesis and used to make ATP is manifested
in what form?
A) A proton gradient (acidic thylakoid lumen)
B) A sodium gradient
C) An electric potential across the stroma
,D) Heat
Answer: A
Rationale: The light reactions pump protons into the thylakoid lumen, creating an
electrochemical gradient (proton motive force) used by ATP synthase.
9. Under what conditions does cyclic photophosphorylation take place?
A) With high levels of NADPH
B) In the dark
C) When PSII is damaged
D) When CO2 levels are high
Answer: A
Rationale: Cyclic photophosphorylation occurs when NADPH levels are high, and the
electron transport chain cycles electrons back to the cytochrome b6f complex to
produce only ATP.
10. The Calvin cycle requires which species from the light reactions?
A) ATP and NADPH
B) Reducing electrons only
C) CO2 and ATP
D) NADH and FADH2
Answer: A
Rationale: The Calvin cycle uses the ATP and NADPH generated by the light reactions
to fix CO2 into sugars.
11. The first stage of the three-stage Calvin cycle is catalyzed by the enzyme:
A) Rubisco
B) Phosphoglycerate kinase
C) Glyceraldehyde-3-phosphate dehydrogenase
D) Aldolase
Answer: A
Rationale: The first committed step of the Calvin cycle is the carboxylation of ribulose-
1,5-bisphosphate by rubisco.
12. Overall, the net balanced reaction of the Calvin cycle converts 3 CO2 into
one:
A) Glucose molecule
B) Glyceraldehyde-3-phosphate
C) Ribulose-1,5-bisphosphate
D) Pyruvate
Answer: B
Rationale: Three turns of the Calvin cycle fix three CO2 molecules to produce one net
molecule of glyceraldehyde-3-phosphate (G3P).
, 13. The third stage of the three-stage Calvin cycle:
A) Generates CO2.
B) Uses ATP and NADPH from the light reactions.
C) Regenerates a C5 sugar for the Calvin cycle to continue.
D) Is catalyzed by rubisco.
Answer: C
Rationale: The regeneration phase (stage 3) rearranges carbon skeletons to regenerate
ribulose-1,5-bisphosphate, allowing the cycle to continue.
14. Under what condition(s) do the wasteful side reaction of O2 with rubisco
become significant?
A) Low temperature and low light
B) Increased temperature and intense light
C) High CO2 and low O2
D) In the dark
Answer: B
Rationale: Photorespiration is favored when stomata close on hot, bright days, leading
to high internal O2 and low CO2, causing rubisco to fix O2 instead of CO2.
15. The herbicide paraquat operates by stealing electrons from photosystem I
(PSI). Which of the following is true of chloroplasts treated with paraquat?
A) NADPH levels drop.
B) Photosystem II is not re-reduced.
C) Plastocyanin has nowhere to donate electrons.
D) No protons are pumped across the chloroplast membranes.
Answer: A
Rationale: By diverting electrons away from ferredoxin, paraquat prevents the
reduction of NADP+ to NADPH, causing NADPH levels to drop.
16. The cytochrome b6f complex of the photosynthetic electron transport
system is responsible for translocating 8 H+ into the thylakoid space. A total of
12 H+ accumulate inside the thylakoid space. What is the origin of the other 4
H+?
A) From the stroma
B) From the oxidation of 2 H2O to form O2 + 4H+ + 4e-
C) From the reduction of NADP+
D) From ATP hydrolysis
Answer: B
Rationale: The oxidation of water by PSII releases 4 protons directly into the thylakoid
lumen, contributing to the proton gradient.
17. In C4 and CAM plants, CO2 is first incorporated into __________, which is then
converted to malate.
A) Ribulose-1,5-bisphosphate
