Photosynthesis Part 3Pages 114 to 115

The Light Reactions – part 1

Electron Flow

Pigments of PSII absorb energy Energy is passed to chlorophyll a (P680) of

the reaction center; P680 boosts e- to primary electron acceptor

Water is split to replace e- lost by P680; H+ accumulate in lumen (thylakoid space); O2 is formed and released

Excited e- from P680 pass from PSII to PSI via ETC; as e- pass thru ETC energy is released; energy used to pump H+ into lumen

Electron Flow continued

Light energy absorbed at PSI passed onto chlorophyll a (P700) of reaction center; e- lost at P700 are replaced by those from P680 via ETC

The e- form P700 passes thru a short ETC to a final acceptor NADP forming NADPH

Chemiosmosis

The production of ATP using the energy of H+ gradients across membranes to phosphorylate ADP forming ATP

H+ build up occurs in the lumen

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The process of ATP production in photosynthesis…•Light is absorbed at PSII and PSI•Energy used to transport electrons•As electrons are passed energy is released•Energy used to pump H+ into lumen•Lost electrons are released by splitting water•Oxygen is released as a by product•NADP is the final acceptor of electrons forming NADPH•Lumen becomes positively charged / stroma negatively charged•As H+ escapes thru ATP synthase (down the concentration gradient) ADP is phosphorylated producing ATP

Light Reactions

Products?› O2, ATP and NADPH

What is oxidized?› Water to Oxygen

What is reduced?› NADP to NADPH

How are electrons replaced at PSII?› Splitting water

How are electrons replaced at PSI?› From PSII