Deck 12: Photosynthesis

Question 1

The Biosphere 2 project, in Tucson, Arizona, was an experiment involving a large sealed terrarium with humans and photosynthetic plants living in balance. Why did the project have to be interrupted after only a few months?

A) Levels of CO₂ rose to dangerous levels.
B) The humans ran out of food.
C) The plants stopped producing oxygen.
D) The rate of photosynthesis was too high.

Answer 1

Levels of CO₂ rose to dangerous levels.

Question 2

For photosynthesis, sunlight energy drives electron transfer. Where are the electrons ejected from when light is absorbed?

A) photons released by chlorophyll
B) NADPH
C) light-harvesting pigments in PSI and PSII
D) oxygen

Answer 2

light-harvesting pigments in PSI and PSII

Question 3

Which enzyme in the photosynthesis light reactions does NOT transfer electrons?

A) ATP synthase
B) photosystem II
C) photosystem I
D) cytochrome b₆f

Answer 3

ATP synthase

Question 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

Question 5

What is the overall balanced reaction for the light reactions of photosynthesis?

A) O₂ + 2 NADPH + 3 ATP $\rightarrow$ 2 H₂O + 2 NADP⁺ + 3 ADP + 3 P_i
B) 3 CO₂ + 6 NADPH + 9 ATP + 6 H₂O $\rightarrow$ Glyceraldehyde-3-phosphate + 6 NADP⁺ + 9 ADP + 9 P_i
C) O₂ + 8 photons + NADP⁺ + 3 ATP $\rightarrow$ 2 H₂O + NADP⁺ + 3 ADP + 3 P_i
D) 2 H₂O + 8 photons + 2 NADP⁺ + 3 ADP + 3 P_i $\rightarrow$ O₂ + 2 NADPH + 3 ATP

Question 6

The term greenhouse effect refers to the idea that

A) the global production of plant matter is increasing.
B) the capacity of the earth's plant matter to store CO₂ is increasing.
C) the temperature of the earth is increasing because of heat trapped by gases such as CO₂.
D) tropical rainforests are gradually being eliminated.

Question 7

On excitation by a photon, a fate of the excited chlorophyll molecule is to

A) transfer an electron to an acceptor molecule.
B) transfer an electron to ATP.
C) relax and release a proton to a neighboring chlorophyll.
D) relax and accept an electron from a nearby donor.

Question 8

The chloroplast contains a highly folded membrane called the

A) thylakoid.
B) lumen.
C) inner membrane.
D) matrix.

Question 9

The following picture is an example of what phenomenon?

A) resonance energy transfer
B) electron transfer
C) photoexcitation
D) fluorescence

Question 10

Which of the following is a photosynthetic light harvesting pigment?

A) "FeS cluster"
B) "NADPH"
C) "plastoquinone"
D) " $\beta$ -carotene"

Question 11

Resonance energy transfer from one chlorophyll in the photosystems results in

A) a reduced neighboring pheophytin molecule.
B) a neighboring chlorophyll in an excited state.
C) heat release.
D) the release of a photon.

Question 12

The __________ is driven directly by photons from the sun in photosynthesis light reactions.

A) pumping of protons
B) synthesis of ATP
C) transfer of electrons
D) synthesis of glucose

Question 13

Which is the orange pigment commonly found in plant's light harvesting complexes?

A) "chlorophyll"
B) "phycocyanobilin"
C) "porphyrin"
D) " $\beta$ -carotene"

Question 14

Chlorophyll absorbs light energy efficiently because of the

A) metal ion in the center of the molecule.
B) ring structure.
C) planar structure.
D) alternating double and single bonds.

Question 15

In the five steps used by photosynthetic organisms to convert solar energy into chemical energy, which molecules store the solar energy before sugar synthesis?

A) chlorophylls
B) NADH and FADH₂
C) H₂O and O₂
D) ATP and NADPH

Question 16

Heme and chlorophyll have similar overall structures. What is common between the two molecules?

A) color
B) hydrophobic tail
C) polycyclic planar structure
D) metal ion found at their center

Question 17

Chlorophyll absorbs

A) heat energy and reaches an excited state.
B) photon energy and becomes excited or oxidized.
C) an electron during photon excitation.
D) all wavelengths of light.

Question 18

All of the following are true of both chloroplasts and mitochondria EXCEPT that they

A) have one highly folded membrane.
B) produce ATP inside the organelle.
C) produce NADPH inside the organelle.
D) are present in photosynthetic plant cells.

Question 19

The O₂ generated from photosynthesis is derived from

A) CO₂ reduction to glyceraldehyde-3-phosphate.
B) CO₂ reduction to glycerate-3-phosphate.
C) water molecules that directly reduce PSI*.
D) water molecules that directly reduce PSII*.

Question 20

What is the overall reaction for the Calvin cycle, or dark reactions?

A) 2 H₂O + 2 NADP⁺ + 3 ADP + 3 P_i $\rightarrow$ O₂ + 2 NADPH + 3 ATP
B) 3 CO₂ + 6 NADPH + 9 ATP + 6 H₂O $\rightarrow$ Glyceraldehyde-3-phosphate + 6 NADP⁺ + 9 ADP + 9 P_i
C) 6 CO₂ + 6 NADPH + 12 ATP $\rightarrow$ Glucose + NADP⁺ + ADP + P_i
D) Glucose $\rightarrow$ 9 ATP + 12 NADPH + 6 CO₂ + 6 H₂O

Question 21

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.

Question 22

Approximately how many ATP are synthesized per O₂ molecule generated in photosynthesis light reactions?

A) 3
B) 4
C) 8
D) 12

Question 23

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.

Question 24

Which electron carrier molecule in the photosynthetic electron transport chain is largely hydrophobic and found floating in the thylakoid membrane?

A) heme
B) chlorophyll
C) pheophytin
D) plastoquinone

Question 25

Which enzyme in the photosynthetic Z scheme catalyzes the PQ cycle, which is analogous to Complex III and the Q cycle in the mitochondrial electron transport chain?

A) photosystem II
B) plastocyanin
C) cytochrome b₆f
D) photosystem I

Question 26

Per O₂ molecule generated in photosynthesis light reactions, approximately how many protons are moved across the thylakoid membrane?

A) 3
B) 4
C) 8
D) 12

Question 27

Which complex in the photosynthetic electron transport chain pumps protons as electrons pass through it?

A) plastocyanin
B) cytochrome b₆f
C) photosystem I
D) photosystem II

Question 28

To form one O₂, electrons must leave two water molecules, and to form one NADPH, electrons must be delivered to one NADP⁺.

A) 2; 2
B) 2; 4
C) 4; 2
D) 4; 4

Question 29

During photophosphorylation, the protons are pumped into the __________, and the ATP is made in the _.

A) thylakoid lumen; cytoplasm
B) thylakoid lumen; stroma
C) stroma; thylakoid lumen
D) cytoplasm; stroma

Question 30

Which is NOT a correct analogy between the photosynthetic PQ cycle and the mitochondrial electron transport chain Q cycle?

A) Plastocyanin is analogous to cytochrome c.
B) Plastoquinone is analogous to coenzyme Q.
C) Cytochrome b₆f is analogous to Complex III.
D) Photosystem I is analogous to Complex I.

Question 31

In the chloroplasts, photosystem I (PSI) and photosystem II (PSII) are known to localize in different regions. PSI generally localizes in the , whereas PSII localizes in the __________.

A) thylakoid lumen; thylakoid grana
B) thylakoid lamellae; thylakoid grana
C) stroma; thylakoid lumen
D) thylakoid grana; thylakoid lamellae

Question 32

The primary difference between ATP synthesis during the photosynthetic light reactions and ATP synthesis in the mitochondrial electron transport chain is the

A) cellular location of the proton motive force.
B) enzyme catalyzing the ATP synthesis.
C) number of ATP produced per 360 $\degree$ rotation of the F₁ subunit of ATP synthase.
D) number of NADPH required to produce ATP.

Question 33

In addition to the pumping of protons with the photosynthetic electron transport, what else contributes to establishing a proton gradient?

A) the loss of electrons from NADPH
B) the reduction of P680⁺
C) the movement of plastocyanin
D) the formation of O₂ from two H₂O

Question 34

Under what conditions does cyclic photophosphorylation take place?

A) in an acidic stroma
B) with high levels of NADPH
C) with high levels of ATP
D) with an inactivated photosystem I

Question 35

Which of the following is an electron transfer molecule in photosynthesis light reactions?

A) plastoquinone
B) photon
C) paraquat
D) ATP

Question 36

The energy derived from photosynthesis and used to make ATP is manifested in what form?

A) an acidic stroma
B) an electron gradient in the thylakoid membrane
C) an acidic thylakoid lumen
D) an acidic cytoplasm

Question 37

What group in photosystem II (PSII) directly reacts with H₂O during its light-driven oxidation?

A) oxygen evolving center
B) P680
C) tyrosine
D) pheophytin

Question 38

Electrons from plastocyanin are passed on to

A) P700⁺.
B) P680⁺.
C) cytochrome b₆f.
D) O₂.

Question 39

Where do electrons from photosystem II (PSII) come from to re-reduce the oxidized P680⁺ state?

A) O₂
B) NADPH
C) plastocyanin
D) H₂O

Question 40

Which protein or enzyme is NOT involved in the cyclic photophosphorylation pathway?

A) ferredoxin
B) photosystem II
C) cytochrome b₆f
D) plastocyanin

Question 41

Which is a characteristic of the second stage of the three-stage Calvin cycle?

A) It uses ATP and NADPH.
B) It is similar to a series of reactions in pentose phosphate pathway.
C) It is catalyzed by an enzyme called rubisco.
D) It begins and ends with a C₅ sugar.

Question 42

Overall, the net balanced reaction of the Calvin cycle converts 3 CO₂ into one

A) ribulose-5-phosphate.
B) glyceraldehyde-3-phosphate.
C) acetyl-CoA.
D) glucose.

Question 43

In what location of the cell does the Calvin cycle occur?

A) chloroplast grana
B) thylakoid lumen
C) chloroplast stroma
D) cytoplasm

Question 44

The first stage of the three-stage Calvin cycle

A) generates CO₂.
B) uses ATP and NADPH from the light reactions.
C) occurs in the plant cell cytoplasm.
D) is catalyzed by the enzyme rubisco.

Question 45

What is the name of the enzyme that catalyzes the reaction shown below?

A) ribulose bisphosphate carboxylase
B) acetyl-CoA carboxylase
C) glyceraldehyde-3-phosphate dehydrogenase
D) pyruvate carboxylase

Question 46

Which of the following groups of molecules are found in the shuffling reactions of stage 3 of photosynthesis?

A) C₁, C₂, C₃, C₄, C₅, C₆, and C₇ sugars
B) NADPH and ATP
C) erythrose-4-phosphate, glyceraldehyde-3-phosphate, and xylulose-5-phosphate
D) 3-phosphoglycerate, 1,3-bisphosphoglycerate, and glyceraldehyde-3-phosphate

Question 47

The three stages of the Calvin cycle are

A) (1) fix CO₂, (2) make a C₃ sugar, and (3) make glucose.
B) (1) fix CO₂, (2) use NADPH and ATP, and (3) regenerate the starting C₅ molecule.
C) (1) use ATP, NADPH, and CO₂, (2) make a C₃ molecule, and (3) regenerate the starting C₃ molecule.
D) (1) use a C₅ sugar, (2) reduce CO₂ with NADPH, and (3) use ATP to regenerate the starting C₅ molecule.

Question 48

When transketolase acts on fructose-6-phosphate and glyceraldehyde-3-phosphate, the products are

A) 3-phosphoglycerate and two molecules of glyceraldehyde-3-phosphate.
B) dihydroxyacetone phosphate and glucose-6-phosphate.
C) xylulose-5-phosphate and erythrose-4-phosphate.
D) xylulose-5-phosphate and ribose-5-phosphate.

Question 49

Why are Calvin cycle reactions also referred to as the dark reactions?

A) They occur primarily at night.
B) They absorb, and do not reflect, the sunlight energy.
C) They do not absorb sunlight energy.
D) They do not require sunlight energy.

Question 50

Regulation of photosystem II (PSII) enzyme activity is accomplished by phosphorylation. Higher levels of stimulates the phosphorylation and tuning down of PSII activity.

A) oxidized NADP⁺
B) reduced plastoquinone (PQH₂)
C) reduced NADPH
D) ATP

Question 51

Ribulose bisphosphate carboxylase (rubisco)

A) is the most abundant enzyme in the biosphere, comprising as much as 50% of plant cell protein.
B) catalyzes the reaction of C₅ molecule and CO₂ with a C₆ sugar product.
C) is located in the thylakoid lumen.
D) requires NADPH and ATP to fix CO₂.

Question 52

The five-step mechanism of ribulose bisphosphate carboxylase (rubisco)

A) is an overall thermodynamically unstable reaction.
B) involves C₁, C₃, C₄, C₅, and C₆ molecules in the enzyme mechanism intermediates.
C) adds a CO₂ molecule to a C₅ ribulose sugar, yielding an unstable C₆ molecule that cleaves into two C₃ molecules.
D) involves the incorporation of 3 CO₂ molecules to yield one 3-phosphoglycerate molecule.

Question 53

The reactions in stage 2 of the Calvin cycle are the same as those of the gluconeogenesis/glycolysis pathway in the

A) cellular location of the pathways.
B) use of NADPH as reductant.
C) C₃ sugars in the pathways.
D) enzyme locations.

Question 54

The formation of one net glyceraldehyde-3-phosphate during the net Calvin cycle reactions requires __________ NADPH and ATP.

A) 3; 3
B) 3; 6
C) 6; 6
D) 6; 9

Question 55

The Calvin cycle requires which species from the light reactions?

A) ATP and NADPH
B) reducing electrons
C) CO₂ and ATP
D) NADH and FADH₂

Question 56

Which of the following is NOT required to activate rubisco?

A) carbamate formation of the active site lysine
B) activation by CO₂
C) binding of the biotin cofactor
D) binding of Mg²⁺

Question 57

The final product that is formed by the enzyme rubisco is

A) 3-phosphoglycerate.
B) ATP.
C) ribulose-1,5-bisphosphate.
D) glyceraldehyde-3-phosphate.

Question 58

Which of the following is true of stage 2 of the Calvin cycle?

A) Stage 2 involves the net incorporation of CO₂ into the six-carbon glucose molecule.
B) Almost all of the NADPH and ATP from the light reactions are used in stage 2.
C) Stage 2 reactions are localized on the thylakoid membrane of the chloroplasts.
D) C₃, C₄, C₅, and C₆ sugars are all involved in stage 2 reactions.

Question 59

What is a reason for keeping photosystem I (PSI) and photosystem II (PSII) separate in the chloroplasts?

A) They are involved in different pathways and not involved with each other.
B) They would quench each other by energy transfer.
C) They have different sunlight exposure requirements.
D) They have different ATP consumption requirements.

Question 60

The third stage of the three-stage Calvin cycle

A) uses ATP and NADPH from the light reactions.
B) generates a glucose molecule for the plant.
C) is similar to the reactions found in the glycolysis pathway.
D) regenerates a C5 sugar for the Calvin cycle to continue.

Question 61

C₄ plants are thought to be more efficient than C₃ plants because they

A) make larger sugar molecules from CO₂.
B) can concentrate the CO₂ in chloroplasts and therefore minimize side reactions with O₂.
C) can produce sugar molecules at night in addition to during the day.
D) can live in dry climates.

Question 62

Hypothesize how the combustion of large quantities of fossil fuels could affect the cycle shown below. Then explain how this could be further complicated by the global loss of vegetation, such as by the cutting of rain forests.

Question 63

Under what condition(s) do the wasteful side reaction of O₂ with rubisco become significant?

A) higher levels of CO₂ than O₂
B) at night
C) increased temperature and intense light
D) increased rubisco concentrations

Question 64

Which of the following is true of the glyoxylate cycle?

A) It allows plants to produce glucose from fats and two-carbon molecules like acetate.
B) It occurs in plant cells as an alternative to photosynthesis.
C) It bypasses all regulated steps of the TCA cycle.
D) It results in a net production of ATP and NADH without proceeding through the TCA cycle.

Question 65

Which is a way that light controls the Calvin cycle activity?

A) Calvin cycle enzymes are inhibited by the lower H⁺, which is pumped out of the stroma by light reactions.
B) Reduced ferredoxin from the light reactions keeps thioredoxin reduced, which keeps Calvin cycle enzymes in an active form.
C) High levels of ATP and NADPH from the light reactions inhibit the Calvin cycle enzymes.
D) Calvin cycle or dark reaction enzyme activators are present at higher levels in the dark.

Question 66

What is the cellular location of the plant glyoxylate cycle?

A) chloroplast stroma
B) cytoplasm
C) mitochondria
D) glyoxysome

Question 67

List the three possible fates of an electron in an excited state chlorophyll molecule.

Question 68

What is the name of the plant leaf openings that open during the night and close during the day in CAM plants?

A) mesophyll cells
B) stomata
C) guard cells
D) malate pore proteins

Question 69

Which statement regarding CAM plants is true?

A) They use one cell type to absorb and store CO₂ before utilizing it in the Calvin cycle in another cell type.
B) They are more efficient than C₄ plants.
C) They absorb CO₂ at night and release it to the Calvin cycle during the day.
D) They store CO₂ in 3-phosphoglycerate before releasing it to the Calvin cycle.

Question 70

Label the parts of the chloroplast on the figure below.

Question 71

The glyoxylate cycle enzymes

A) are active at night when sugar reserves are high and lipid synthesis is activated.
B) bypass the decarboxylation steps of the TCA cycle, resulting in the net synthesis of a sugar molecule from acetyl-CoA.
C) replace the mitochondrial TCA cycle enzymes.
D) require ATP and NADPH from the light reactions.

Question 72

In C₃ plants CO₂ is first incorporated into , whereas in C₄ and CAM plants the CO₂ is first incorporated into _.

A) 3-phosphoglycerate; oxaloacetate
B) dihydroxyacetone phosphate; malate
C) 3-phosphoglycerate; malate
D) glyceraldehyde-3- phosphate; erythrose-4-phosphate

Question 73

List the five steps of photosynthesis, whereby solar energy is converted into chemical energy.

Question 74

Heme and chlorophyll have the same porphyrin cofactor, yet they have largely different roles. Compare their color and the metal ions employed by each.

Question 75

Transketolase requires the coenzyme

A) cobalamin (vitamin B_{1 2}).
B) pyridoxal phosphate.
C) tetrahydrofolic acid.
D) thiamine pyrophosphate.

Question 76

Which species from the light reactions keeps thioredoxin reduced so that it can activate enzymes in the Calvin cycle?

A) ferredoxin
B) plastoquinone
C) P700
D) NADPH

Question 77

Which cell type in C₄ plants is isolated from O₂ exposure as they perform Calvin cycle reactions?

A) Hatch-Slack cells
B) bundle sheath cells
C) guard cells
D) mesophyll cells

Question 78

What is the process depicted below, where plants react with O₂?

A) photorespiration
B) photosynthesis
C) photogeneration
D) photoglycolate pathway

Question 79

The glyoxylate cycle reaction shown below is catalyzed by which enzyme class?

A) lyase
B) hydrolase
C) transferase
D) oxidoreductase

Question 80

Unlike plant cells, animal cells lack the glyoxylate enzymes

A) isocitrate lyase and malate synthase.
B) rubisco and transaldolase.
C) acetyl-CoA carboxylase and citrate synthase.
D) isocitrate dehydrogenase and $\alpha$ -ketoglutarate dehydrogenase.