Photosynthesis: Pathways, ETC, Pigments, and Calvin Cycle

What is the simplified photosynthesis reaction?

CO₂ + H₂O → C₆H₁₂O₆ + O₂.

What are the reactants and products of the light reactions?

Reactants: H₂O, light, NADP⁺, ADP+Pi.
Products: O₂, ATP, NADPH.

What are the reactants and products of the Calvin Cycle?

Reactants: CO₂, ATP, NADPH.
Products: G3P (sugar), ADP, NADP⁺.

What is the structure and function of Photosystem II (PSII)?

PSII contains an antenna complex and reaction center (P680). It splits water, releases O₂, and sends electrons to the ETC.

What is the function of the ETC in photosynthesis?

Moves electrons from PSII → PSI, pumps protons into the thylakoid lumen, and drives ATP synthesis.

Describe the flow of electrons in noncyclic electron transport.

H₂O → PSII → plastoquinone → cytochrome b6f → plastocyanin → PSI → ferredoxin → NADP⁺ reductase → NADPH.

How do cyclic and noncyclic electron transport differ?

Noncyclic: produces ATP, NADPH, O₂.
Cyclic: uses PSI only, returns electrons to cytochrome, produces ATP only.

What is photophosphorylation?

Light-driven formation of ATP as protons flow through ATP synthase.

What is the role of plastoquinone (PQ)?

Transfers electrons from PSII to cytochrome b6f and carries protons into the lumen.

What is the role of cytochrome b6f?

Accepts electrons from PQ, pumps protons into the lumen, and passes electrons to plastocyanin.

What does plastocyanin do?

Moves electrons from cytochrome b6f to PSI.

What does ferredoxin do?

Carries electrons from PSI to NADP⁺ reductase (or back to cytochrome in cyclic flow).

What is the function of NADP⁺ reductase?

Reduces NADP⁺ to NADPH using electrons from ferredoxin.

Where is ATP synthase located in chloroplasts?

In the thylakoid membrane, facing the stroma.

How do protons flow in chloroplasts vs mitochondria?

Chloroplasts: lumen → stroma through ATP synthase.
Mitochondria: intermembrane space → matrix.

How do plants capture CO₂?

CO₂ diffuses through stomata into leaf air spaces and dissolves into mesophyll cells.

What is the function of the cuticle?

Wax layer that prevents water loss.

What do stomata do?

Regulate gas exchange (CO₂ in, O₂ and H₂O out).

What are the 3 phases of the Calvin Cycle?

Carbon fixation → Reduction → Regeneration of RuBP.

What is the function of rubisco?

Catalyzes CO₂ fixation by attaching CO₂ to RuBP.

What was the experimental approach identifying the first Calvin Cycle product?

Pulse-chase experiments with radioactive ¹⁴C CO₂ showed 3PGA formed first.

What happens to G3P produced in the Calvin cycle?

Used to form glucose, starch, sucrose, amino acids, lipids.

How does light activate the Calvin Cycle?

Light produces ATP & NADPH and increases stromal pH, activating rubisco and cycle enzymes.