Photosynthesis

AP Biology· difficulty 4/5

The schematic shows the linear (Z-scheme) electron flow in the thylakoid membrane.

PSII Cyt b6f PSI NADPH H2O light light

What is the immediate source of electrons that re-fill PSII after they are excited by light?

  • A

    ATP hydrolysis in the stroma

  • B

    Splitting of water (photolysis), which also releases O2

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  • C

    NADPH oxidation

  • D

    CO2 fixation in the Calvin cycle

Explanation

PSII replaces electrons by photolyzing water, producing O2, protons, and electrons. These electrons enter PSII's reaction center.

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