Photosynthesis Energy Conversion 2 — Questions and Answers
Question 1: What is the primary role of the antenna complex in the light-harvesting stage of photosynthesis?
- To split water molecules
- To absorb photons and funnel energy to the reaction center (Correct answer)
- To synthesize ATP directly
- To reduce NADP+ to NADPH
Correct answer: To absorb photons and funnel energy to the reaction center
Antenna complexes contain pigment molecules that absorb light and transfer the excitation energy to the reaction center via resonance energy transfer.
Question 2: During the light-dependent reactions, which molecule acts as the final electron acceptor in the electron transport chain?
- ADP
- Oxygen
- NADP+ (Correct answer)
- CO2
Correct answer: NADP+
NADP+ accepts two electrons and one proton at the end of the electron transport chain to become NADPH, which carries reducing power to the Calvin cycle.
Question 3: How does cyclic electron flow differ from non-cyclic electron flow in terms of products?
- Cyclic produces O2; non-cyclic does not
- Cyclic produces only ATP; non-cyclic produces both ATP and NADPH (Correct answer)
- Cyclic produces only NADPH; non-cyclic produces both ATP and NADPH
- Cyclic produces glucose; non-cyclic produces ATP
Correct answer: Cyclic produces only ATP; non-cyclic produces both ATP and NADPH
Cyclic electron flow recycles electrons through PSI back to the electron transport chain, generating ATP without producing NADPH or releasing O2.
Question 4: What is the approximate energy (in eV) of a visible-light photon that drives Photosystem II?
- 0.01 eV
- 1.8 eV (Correct answer)
- 100 eV
- 1000 eV
Correct answer: 1.8 eV
Visible photons carry roughly 1.8–3.1 eV, and P680 in PSII is excited by red photons near 680 nm, corresponding to about 1.8 eV.
Question 5: Which process directly uses the proton gradient across the thylakoid membrane to synthesize ATP?
- Substrate-level phosphorylation
- Chemiosmosis through ATP synthase (Correct answer)
- Photophosphorylation via ferredoxin
- Oxidative decarboxylation
Correct answer: Chemiosmosis through ATP synthase
Chemiosmosis drives H+ ions through ATP synthase (a.k.a. CF0-CF1 complex) down their concentration gradient, powering ATP synthesis in the chloroplast.
Question 6: When a chlorophyll molecule absorbs a photon, what immediately happens to one of its electrons?
- It is destroyed and replaced
- It drops to a lower energy orbital
- It is excited to a higher energy state (Correct answer)
- It splits a water molecule
Correct answer: It is excited to a higher energy state
Photon absorption promotes an electron to a higher (excited) energy level, making the chlorophyll molecule a strong electron donor.
Question 7: Which wavelengths of light are most efficiently absorbed by chlorophyll a for driving photosynthesis?
- Green and yellow
- Red (~680 nm) and blue-violet (~430 nm) (Correct answer)
- Infrared and ultraviolet
- Orange and cyan
Correct answer: Red (~680 nm) and blue-violet (~430 nm)
Chlorophyll a has absorption peaks in the red (~680 nm) and blue-violet (~430 nm) regions; green light is mostly reflected, giving leaves their color.
Photosynthesis Energy Conversion 2
What is the primary role of the antenna complex in the light-harvesting stage of photosynthesis?