The Reactions of P/S SBI4U

1) The Light Reactions Occur in the thylakoid membranes/space Steps: Photon of light hits PS II Photon’s energy splits water which releases O2 gas into the atmosphere, electrons from water are donated to an ETC and H+ is released (will be used later)

Electrons (from the splitting of water) are boosted by the photons to a higher energy level where they fall down the ETC being passed from protein to protein. At each protein, the energy from the falling electrons is used to pump H+ from the stroma into the thylakoid. H+ diffuses back into the stroma through ATP synthase making ATP.

Low energy electrons for PSII pass to PSI Another photon of light (700 nm) re-energizes the electron.

Electrons jump to a higher energy level and again fall down the ETC being passed from protein to protein and pumping H+, H+ again goes through ATP synthase making ATP.

At the end of the ETC, low energy electrons are passed to NADP+ which then gains a H+ from the stroma and makes NADPH. The ATP and NADPH produced in the light reactions go to fuel the Calvin Cycle.

2) The Calvin Cycle occur in the stroma (of chloroplast) indirectly dependent on light because... ...the ATP and NADPH made during the light rxn fuel the dark reactions.

3 major steps of the Calvin Cycle Carbon fixation – CO2 from the atmosphere is fixed to a 5C compound called ribulose biphosphate (RuBP) 3C 3-phosphoglycerate CO2 RuBP unstable 6C ATP ADP

Reduction (G3P)

Regeneration of RuBP – a complex series of rxns rearranges the carbon skeletons of 5 G3P’s to make 3 RuBP’s. 5 G3P 3 RuBP 6 G3P 1 G3P carbohydrates *Triose sugars move out of chloroplast to make glucose, sucrose, and starch.

C4 Plants Many plants begin the Calvin Cycle with a 4 carbon compound instead of a 3 carbon compound. They include grasses (sugar can and corn). These plants live in areas that are very hot and semi-arid.