Photosynthesis

Which of the following accurately describes the energetics of photosynthesis?

A. non-spontaneous

B. spontaneous

A

• photosynthesis has positive Gibbs free energy, so non-spontaneous and endergonic

• an input of energy is required for photosynthesis to occur

Where in the chloroplast do the light-dependent reactions occur?

A. intermembrane space

B. outer membrane

C. stroma

D. thylakoid membranes

D

What is another name for the reaction center in photosystem I?

A. P560

B. P680

C. P700

D. P770

C

• b/c it absorbs 700nm wavelengths the best

What is another name for the reaction center in photosystem II?

A. P560

B. P680

C. P700

D. P770

B

Which of the following is NOT true of the photolysis of water?

A. it occurs at photosystem I

B. protons are used to reduce NADP+

C. protons are used to synthesize ATP

D. the oxygen contributes to atmospheric oxygen

A

• photolysis of water occurs at photosystem II

How many electron transport chain(s) are there in non-cyclic photophosphorylation?

A. one

B. two

C. three

B

• e- will be passed from the first ETC to P700 at the reaction center of photosystem I

• photons excite the pigments contained in photosystem I, raising the e- to a higher energy level

  • when that happens, the e- will be passed to another e- acceptor (NADP+), and they will travel down a second ETC

Which of the following is NOT a product of light-dependent reactions?

A. ATP

B. glucose

C. NADPH

D. oxygen

B

• light dependent products

  • ATP

  • NADPH

  • a half molecule of oxygen that that will be released into the atmosphere

All of the following statements accurately describe cyclic photophosphorylation EXCEPT one. Which is the EXCEPTION?

A. electrons are used by NADP+ reductase to reduce NADP+ to NADPH

B. involves only photosystem I and the first ETC

C. more ATP is synthesized compared to the non-cyclic photophosphorylation

D. results in continuous pumping of protons into the thylakoid lumen

A

• cyclic photophosphorylation

  • involves only PS I and the first ETC

  • as e- are cycled thru PS I and the first ETC, protons are continuously pumped into the thylakoid lummen

    • results in an increased production of ATP when compared to non-cyclic photophosphorylation

• e- are NOT passed to NADP+ reductase, so NADP+ is not reduced to NADPH

In what direction does gas exchange occur when stomata are open?

A. carbon dioxide in; oxygen in

B. carbon dioxide in; oxygen out

C. carbon dioxide out; oxygen out

D. carbon dioxide out; oxygen in

B

• water is also able to escape via transpiration when stomata are open

What is the path of carbon dioxide from the atmosphere to chloroplasts? 

A. stomata to epidermis

B. stomata to mesophyll cells

C. stroma to epidermis

D. stroma to mesophyll cells

B

• the Calvin cycle fixes inorganic carbon dioxide into organic glucose

• photosynthetic leaves obtain CO2 from the atmosphere through their stomata, then the CO2 will diffuse into mesophyll cells and finally their chloroplasts

What is ATP from the light-dependent reactions used for?

A. Calvin cycle

B. cellular respiration

C. chemiosmosis

D. hydrolysis

A

• ATP from the light-dependent reactions is used to power the Calvin cycle, which makes glucose

• the glucose will undergo cellular respiration to produce the ATP that does power the cell

In the reduction stage of the Calvin cycle, what occurs after PGA has been phosphorylated?

A. NADP+ reduces the intermediate to make G3P

B. NADPH reduces the intermediate to make G3P

C. NADP+ reduces the intermediate to make PEP

D. NADPH reduces the intermediate to make PEP

B

• ATP from the light-dependent reactions phosphorylates the PGA made int he first stage to produce another three-carbon intermediate

• after this intermediate is made, NADPH from the light-dependent reactions reduces it to make G3P

• (NADP+ never reduces things)

After the Calvin cycle, where are NADP⁺ and ADP sent to for the light-dependent reactions?

A. intermembrane space

B. outer membrane

C. stroma

D. thylakoid membranes

D

• the Calvin cycle occurs in the stroma where NADP+ and ADP are by-products in step 2 (reduction)

• they are sent back to the thylakoid membranes for the light-dependent reactions b/c that is where the reactions occur

What is another name for photorespiration?

A. CAM photosynthesis

B. C2 photosynthesis

C. C3 photosynthesis

D. C4 photosynthesis

B

• photorespiration is a process that occurs in plants, where RuBisCO oxygenates RuBP, leading to the production of a two-carbon molecule called glycolate

  • this is generally less efficient for the plant b/c it uses oxygen instead of CO2 which can decrease photosynthesis efficiency

• C2 photosynthesis refers to this process b/c of the two-carbon molecule, glycolate, that is produced

In which environment does C₄ photosynthesis occur in a small number of plants?

A. aquatic

B. cold

C. hot

D. temperate

C

• C4 photosynthesis reduces photorespiration, which is a wasteful process that becomes more prevalent in hot conditions

• C4 plants can concentrate CO2 around RuBisCO, even when stomata are closed to conserve water

• so they can close their stomata more frequently to minimize water loss while still efficiently capturing CO2, which is achieved due to spatial separation

What is oxaloacetate quickly turned into at the mesophyll cell?

A. CO2

B. malate

C. PEP

D. PGA

B

• C4 photosynthesis uses PEP carboxylase which has no affinity to oxygen to fix inorganic CO2 into a three-carbon molecule called PEP

• this carboxylation reactions produces oxaloacetate, which quickly turns into malate in the mesophyll cell

Which of the following does NOT happen to CAM plants during the day?

A. carbon dioxide enters the leaf

B. close their stomata

C. prevent desiccation

D. prevent transpiration

A

• during the day, CAM plants close their stomata to prevent transpiration which prevents desiccation

Which of the following best describes the overall reaction of C₃ photosynthesis?

A. spontaneous

B. endergonic

C. exergonic

D. aerobic

E. anaerobic

B

• this reaction absorbs energy to create larger molecules, so it’s endergonic

Which pathway represents the movement of protons within the chloroplast to generate ATP?

A. intermembrane space → matrix

B. intermembrane space → stroma

C. stroma → intermembrane space

D. stroma → thylakoid lumen

E. thylakoid lumen → stroma

E

• within chloroplasts, chemiosmosis describes the movement of protons from the thylakoid lumen into the stroma to generate ATP

Which element is found at the center of the porphyrin ring structure in chlorophyll?

A. iron

B. magnesium

C. sulfur

D. mercury

B

Which of the following acts as a competitive inhibitor of the enzyme RuBisCo during photosynthesis?

A. carbon dioxide

B. glucose

C. nitrogen

D. oxygen

E. water

D

• when RuBisCo binds to oxygen instead of CO2, it causes photorespiration, a process that does not produce glucose and results in a net loss of fixed carbon

What are the products of the light-dependent reactions of photosynthesis?

A. C6H12O6, NADPH, and ATP

B. C6H12O6, NADP+, and ADP

C. CO2, NADPH, and ATP

D. O2, NADP+, and ADP

E. O2, NADPH, and ATP

E

What is the first intermediate produced in C₄ photosynthesis?

A. citrate

B. glyceraldehyde-3-phosphate

C. malate

D. oxaloacetate

E. pyruvate

D

Which of the following molecules is regenerated during the Calvin cycle?

A. G3P

B. glucose

C. pyruvate

D. RuBisCo

E. RuBP

E

• RuBP is regenerated and is available to join another molecule of CO2 in a RuBisCo-catalyzed reaction

Where do the light-dependent reactions of photosynthesis take place?

A. inner membrane

B. stroma

C. stroma lamellae

D. thylakoid lumen

E. thylakoid membrane

E.