Light-Dependent Reaction

NCP Step One:

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The excited electrons from PSII must be replaced.
Light energy splits a water molecule (photolysis) into protons (H+ ions), electrons and O2. This is where the O2 in photosynthesis comes from.
The reaction is H2O -------> 2H+ + 1/2O2

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The excited electrons lose energy as they move along the electron transport chain.
This energy is used to transport protons INTO the thylakoid membrane so that the thylakoid has a higher concentration than the stroma.
This forms a proton concentration gradient (pH gradient) across the membrane.
Protons move down their concentration gradient through an enzyme known as ATP synthase. (CHEMIOSMOSIS)
The proton motive force causes the ATP synthase to rotate, and the active site to become accessable.
ADP and inorganic phosphate (P) are then combined to make ATP.

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Light energy is absorbed by PSI, which excites the electrons to a higher energy level.
The electrons are transferred to NADP along with a proton from the stroma (moved during chemiosmosis) to form reduced NADP (NADPH)

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Only uses PSI.
Electrons from chlorophyll do not reduce NADP but return to the photosystem via electron carriers.
Electrons are recycled and flow repeatedly through PSI.
Does not produce NADPH or O2.
Produces ATP.
Used in guard cells to open/close stomata.

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Chemicals that accept electrons from another compound. They are reduced while acting as an oxidising agent.

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