LightReaction of photosynthesis z scheme2.pptx

light reaction in thylakoid

1. Overview of Light Reaction Occurs in the thylakoid membranes of chloroplasts Requires light energy Converts light energy into chemical energy (ATP & NADPH) Produces oxygen as a by-product by splitting water

2. Key Components Photosystem I (PSI) and Photosystem II (PSII) Chlorophyll a: Primary pigment Plastoquinone (PQ), Cytochrome b6f, Plastocyanin (PC) ATP synthase, Ferredoxin (Fd), NADP+ reductase

3. Photosystem II (PSII) Absorbs light at P680 Photolysis of water: 2H₂O → 4H⁺ + 4e⁻ + O₂ Electrons transferred to plastoquinone (PQ)

4. Non-Cyclic Photophosphorylation Involves both PSII and PSI Electron flow: PSII → PQ → Cyt b6f → PC → PSI → Fd → NADP⁺ Produces ATP, NADPH, and O₂ One-way electron flow

5. Cyclic Photophosphorylation Involves only PSI Electron flow: PSI → Fd → Cyt b6f → PC → back to PSI Produces ATP only No NADPH or O₂ formed

6. Photosynthetic Electron Transport Chain Series of redox reactions Electrons lose energy step-by-step Energy used to pump protons into thylakoid lumen Creates proton gradient for ATP synthesis

7. ATP and NADPH Formation ATP Synthase uses proton motive force NADP⁺ reductase forms NADPH ATP and NADPH used in Calvin Cycle

8. Comparison – Cyclic vs. Non-Cyclic Cyclic: PSI only, ATP only, no O₂, no NADPH Non-Cyclic: PSI & PSII, ATP + NADPH + O₂ Cyclic balances ATP/NADPH demand

9. Conclusion Light reaction converts light energy into chemical energy Produces ATP and NADPH for carbon fixation Crucial for maintaining energy flow in plants