Photosynthesis Photosynthesis Electron Transport Chain 1 — Questions and Answers
Question 1: Which photosystem in the thylakoid membrane is responsible for splitting water molecules to release oxygen?
- Photosystem II (PSII) (Correct answer)
- Photosystem I (PSI)
- ATP synthase
- The cytochrome b6f complex
Correct answer: Photosystem II (PSII)
Photosystem II contains the oxygen-evolving complex that catalyzes the splitting of water into protons, electrons, and molecular oxygen as a byproduct.
Question 2: What molecule accepts electrons from the iron-sulfur centers of Photosystem I during the light reactions?
- Ferredoxin (Correct answer)
- Plastocyanin
- Plastoquinone
- NADP+ reductase
Correct answer: Ferredoxin
Ferredoxin is a small iron-sulfur protein that accepts electrons from PSI and transfers them to NADP+ reductase (FNR) for NADPH production.
Question 3: Which manganese-containing protein complex carries out the oxidation of water in Photosystem II?
- Oxygen-evolving complex (OEC) (Correct answer)
- Cytochrome b6f complex
- ATP synthase (CF0-CF1)
- Ferredoxin-NADP+ reductase
Correct answer: Oxygen-evolving complex (OEC)
The oxygen-evolving complex contains a cluster of four manganese ions that catalyze the oxidation of two water molecules, releasing four electrons, four protons, and one O2.
Question 4: What is the primary role of plastoquinone (PQ) in the photosynthetic electron transport chain?
- Shuttle electrons and protons from PSII to the cytochrome b6f complex (Correct answer)
- Split water molecules to release O2
- Reduce NADP+ to NADPH
- Synthesize ATP using a proton gradient
Correct answer: Shuttle electrons and protons from PSII to the cytochrome b6f complex
Plastoquinone is a mobile lipid-soluble carrier that picks up electrons and protons from PSII and delivers them to the cytochrome b6f complex, contributing to the proton gradient.
Question 5: Which metal ion is absolutely required for the function of the oxygen-evolving complex in Photosystem II?
- Manganese (Mn) (Correct answer)
- Iron (Fe)
- Copper (Cu)
- Zinc (Zn)
Correct answer: Manganese (Mn)
The oxygen-evolving complex requires a cluster of four manganese ions to catalyze the stepwise removal of electrons from water, accumulating oxidizing equivalents until O2 is released.
Question 6: In noncyclic photophosphorylation, what is the ultimate electron acceptor at the end of the linear electron transport chain?
- NADP+ (Correct answer)
- Oxygen (O2)
- Ferredoxin
- Plastocyanin
Correct answer: NADP+
NADP+ is the final electron acceptor in noncyclic electron flow; it is reduced to NADPH by ferredoxin-NADP+ reductase using electrons from PSI.
Photosynthesis Photosynthesis Electron Transport Chain 1
Which photosystem in the thylakoid membrane is responsible for splitting water molecules to release oxygen?