Question 1

Light Reactions

Accepted Answer

The stage of photosynthesis that converts solar energy (sun) into chemical energy (ATP and NADPH); occurs in the thylakoids and involve photosystems with pigment molecules in light-harvesting complexes.

Question 2

Linear Electron Flow

Accepted Answer

The primary pathway of electrons during the light reactions that uses Photosystem II and I to produce ATP and NADPH in one way (Z-shaped) route.

Question 3

Photosystem II (PSII / P680)

Accepted Answer

The first protein complex in the light reactions where photons excite pigments, energize P680 moving up to the higher level of energy (P.E.A) and begin electron flow after splitting water (photolysis) to replace lost electrons in the void.

Question 4

Photolysis of Water

Accepted Answer

A light-driven process in PSII that splits water into electrons (to refill P680), protons (into thylakoid lumen), and oxygen gas.

Question 5

Electron Transport Chain (ETC)

Accepted Answer

A series of redox reactions that pass electrons from PSII to PSI, releasing energy that pumps protons into the thylakoid lumen to build a proton gradient and create ATP.

Question 6

Proton Gradient

Accepted Answer

A buildup of hydrogen ions in the thylakoid lumen formed by ETC pumping, storing potential energy used to power ATP synthase.

Question 7

Chemiosmosis

Accepted Answer

The process in which the proton gradient generated by the ETC powers ATP synthase to produce ATP.

Question 8

ATP Synthase

Accepted Answer

A spinning enzyme in the thylakoid membrane that allows protons to diffuse down their gradient and synthesizes ATP from ADP and Pi (photophosphorylation).

Question 9

Photophosphorylation

Accepted Answer

The production of ATP powered by light energy during the light reactions using ATP synthase.

Question 10

Photosystem I (PSI / P700)

Accepted Answer

The photosystem that re-excites electrons using light; accepts electrons from the PSII ETC and transfers photoexcited electrons to NADP⁺ to form NADPH.

Question 11

NADP⁺ Reductase

Accepted Answer

The enzyme at the end of PSI’s ETC that transfers electrons and hydrogen to NADP⁺, forming NADPH.

Question 12

Cyclic Electron Flow

Accepted Answer

n alternative pathway that uses only PSI to create extra ATP (no NADPH produced and no oxygen released) by cycling electrons back to the cytochrome complex.

Question 13

Purpose of Cyclic Electron Flow

Accepted Answer

To produce additional ATP because the Calvin Cycle requires more ATP than NADPH, balancing the energy budget of photosynthesis.

Question 14

Calvin Cycle

Accepted Answer

The light-independent reactions in the stroma that use ATP and NADPH to convert CO₂ into G3P, ultimately forming glucose while regenerating RuBP.

Question 15

Carbon Fixation (Calvin Cycle Phase 1)

Accepted Answer

The Rubisco-catalyzed reaction that attaches CO₂ to RuBP, turning inorganic carbon into an organic molecule.

Question 16

Reduction (Calvin Cycle Phase 2)

Accepted Answer

The phase where ATP and NADPH are used to convert intermediate molecules into the high-energy sugar G3P.

Question 17

Regeneration of RuBP (Calvin Cycle Phase 3)

Accepted Answer

The stage where ATP is used to regenerate RuBP, the CO₂ acceptor, allowing the Calvin Cycle to continue.

Question 18

G3P (Glyceraldehyde-3-Phosphate)

Accepted Answer

A 3-carbon sugar produced in the Calvin Cycle; requires 3 turns of the cycle (and 3 CO₂ molecules) to generate one G3P.

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AP Biology Photosyn