steps of photosynthesis

• excitation of chlorophyll or photoexcitation occur
• PSII gets oxidized and lose 2e , it under goes photolysis where H2O is broken down into 2h ,2e and and O atom released into the environment
• results photolysis : supplies electrons to PSII pigments to reform broken double bonds of pigments(2e per H2O molecule ) , releases O2 into atmosphere ( requires 2H2O molecules ) H+ ions retain in thylakoid interior increases H+ concentrations
• step 3. PQB is is a hydrogen carrier therefor it picks up 2H from stroma and joins with 2 e
• The cytochrome B6f then gains electrons from PQB 


  Sends the 2 H to the thylakoid lumen
• The next electron carrier, plastocyanon picks up the Electrons from cytochrome B6F

  the B6F gains 2H+ from the stroma then sends 2H+ to the last carrier ferredoxin , (Ferridoxin is reduce )
• Light energy is absorbed by internos pigments and choco

  1. Sends 2 for photosystem L

  2. Each photon of light results in the beating of a double bond within the photosystem I pigments

  3. The distros died by the plastecñan to photosystem I are used to reform the bratan double bonds of photosqiten L
• The slectrons from the broken double bends of the photosystem I pigments are en transferred to the last electron cater fedesin

  1. Ferredoxin is ded sports the electrons tedenis NADP Reductase

  2. At Ferredosin NADP- Reductase, lectrons join with AOP and bath from the stroma) form NADPH
• Due to this electron transport chain action during the light reactions

  CONCENTRATION GRADIENT has been created whereby the laid anterior (ame) as WIGHER calcation of H (protons) than in the stroms
• At the ATP Synthase pump


  1. Protons pass from the lunes through the ATP Spethase pomp (ets of proton pump) to the stroma

  2. This ATP (produced in the stroma) is now galy for the does reaction of photosynthesis
• Photosystem I (PS 1) or P700

  Contains a form of chlorophyll a called P700 that absorbs maximum light at approximately 680 mm (long red wavelengths)
• Photosystem II (PS II) or P680

  Contains a form of chlorophyll a called P680 that absorbs maximum light at approximately 680 nm (shorter red wavelengths)
• A combination of a Photosystem II (PS II) and Photosystem I (PS I) is called a PHOTOSYNTHETIC UNIT
• Each thylakoid membrane contains thousands of photosynthetic units
• The reason that the photosystems are numbered "backwards is because photosystem I was discovered first and photosystem II was discovered second
• Photosystem II (PSII)


  1. Absorption of light energy by chlorophyll molecules

  2. Excitation of electrons in chlorophyll

  3. Electrons passed along electron carriers in thylakoid membrane

  4. Water molecules split into oxygen, protons, and electrons

  5. Oxygen released as byproduct, protons released into thylakoid lumen
• Cytochrome b6f complex


  1. Excited electrons from PSII transferred

  2. Protons pumped from stroma into thylakoid lumen

  3. Contributes to proton gradient formation
• Plastoquinone (PQ)


  Electron carrier in electron transport chain
• Plastocyanin (PC)


  Electron carrier in electron transport chain
• Photosystem I (PSI)


  1. Light energy absorbed by chlorophyll molecules

  2. Electrons from Photosystem II replaced

  3. Excited electrons transferred to ferredoxin (Fd)
• Ferredoxin-NADP+ reductase (FNR)


  1. Electrons transferred from ferredoxin to NADP+

  2. NADPH produced
• ATP synthase


  1. Proton gradient drives ATP synthesis

  2. Process called chemiosmosis