Thylakoids produce ATP and reduced NADP in the light-dependent reactions, supplying the Calvin cycle with energy and reducing power, connecting the mechanism to observable photosynthesis evidence.
Coverage 2022–2022 · Updated 15 Jul 2026
The thylakoid is an integrated membrane system that positions photosystems, electron carriers and ATP synthase for the light-dependent reactions.
Electron transfer releases energy that pumps H⁺ from the stroma into the thylakoid lumen. H⁺ then moves down its electrochemical gradient through ATP synthase, coupling that flow to ADP + Pi → ATP in the stroma.
Photolysis occurs at photosystem II, ATP synthesis across the membrane, and NADP reduction at photosystem I on the stromal side. Non-cyclic electron flow begins with electrons from photosystem II and makes ATP plus reduced NADP; cyclic flow returns electrons from photosystem I and supports ATP production without reducing NADP.
The membrane separates the H⁺-rich lumen from the stroma, so electron-carrier proton pumping stores energy as a gradient and ATP synthase converts that gradient energy into chemical energy in ATP.
Electron carriers build the gradient; ATP synthase uses it. Chemiosmosis is proton movement through ATP synthase, not electron passage through the enzyme.
This objective is assessed through structured response, commonly using State.
State
Build the answer around this relationship: Thylakoids house the light-dependent reactions of photosynthesis.
Representative question
State two products that pass from the light-dependent to the light-independent stages of photosynthesis.
1.
2.
HL photosynthesis links light-dependent reactions to the Calvin cycle. Photosystems are pigment-protein arrays in thylakoid membranes; antenna pigments broaden absorption and pass energy to reaction-centre chlorophyll. PSII uses light to split water, supplying electrons, protons, and oxygen. Electron transport pumps protons into the thylakoid space, ATP synthase makes ATP by photophosphorylation, PSI re-excites electrons, and NADP is reduced. The Calvin cycle uses ATP and reduced NADP: Rubisco fixes CO2 to RuBP to form GP, GP is reduced to triose phosphate, most triose phosphate regenerates RuBP, and some becomes wider biomolecules.
