Photosynthesis

Light Dependent Reaction

• In Grana
• PSII absorbs light energy
• 2 electrons in chlorophyll are excited to a higher energy level and move along the electron transport chain
• These are replaced by photolysis of water to produce electrons, protons and oxygen
• As the electrons move along the chain, they lose energy
• This energy is used to pump protons into the thylakoid membrane to create a concentration gradient of protons
• Protons move from stroma into the thylakoid via ATP Synthase
• ATP is also synthesised
• PSI absorbs light energy so electrons are boosted to even higher energy level
• Eventually NADP accepts the electrons so is reduced to NADPH

Light Independent Reaction

• In the stroma
• Carbon dioxide diffuses in through the stomata
• Combines with RuBP (5C) to form unstable 6C compound
• This breaks down into 2 x GP (3C)
• GP is broken down into TP, so there are now 2 x TP (3C)
• In breaking down GP to TP, ATP from LDR is broken down into ADP+Pi and NADPH is oxidised to NADP.
• TP can be used to make useful organic molecules
• But five out of six TP molecules generated are used to regenerate RuBP