Light Reactions and Calvin Cycle

Also called

light reactions · Calvin cycle · photosynthesis · thylakoid · photosystem II · photosystem I · Z scheme · electron transport chain · photolysis of water · chemiosmosis · proton gradient · ATP synthase · NADPH · Rubisco · carbon fixation · RuBP · C3 cycle · प्रकाश संश्लेषण · केल्विन चक्र · थाइलेकॉइड

Topics

• The light reactions run in the thylakoid membrane; the Calvin cycle runs in the stroma around it.
• Light absorbed by PS II (P680) excites an electron; the hole is filled by splitting water: 2H₂O → 4H⁺ + 4e⁻ + O₂.
• In the Z-scheme, electrons pass from PS II through plastoquinone, cytochrome b6f and plastocyanin to PS I.
• Light at PS I (P700) excites the electrons again; ferredoxin and NADP reductase use them to make NADPH.
• Water splitting and the cytochrome b6f pump build up protons in the lumen: a gradient across the membrane.
• Protons flow back out through ATP synthase, turning it to make ATP: this is chemiosmosis.
• In the Calvin cycle Rubisco fixes CO₂ onto RuBP (carboxylation), ATP and NADPH reduce it to triose sugar.
• Most triose regenerates RuBP; for every 3 CO₂ fixed, one triose leaves, and two trioses make a glucose.

About this model

A GLB file of about 615 KB, shown in Lably's 3D viewer and, on a phone, placed in your room with AR. Credit: Model, science and animation: Lably (built procedurally with three.js; no downloaded meshes). | CC BY 4.0. Original geometry and animation made for Lably.

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