Cue Column | Note-Taking Area

Q: Where does each stage of photosynthesis occur? Light reactions occur on thylakoid membranes (grana). The Calvin cycle occurs in the stroma (fluid matrix). Cyclic photophosphorylation localises to stroma lamellae (unstacked membranes).

Q: What are thylakoid grana vs. stroma lamellae? Grana = stacks of thylakoid discs, enriched in PS II, site of non-cyclic photophosphorylation and photolysis. Stroma lamellae = inter-granal unstacked membranes, enriched in PS I, site of cyclic photophosphorylation.

Q: What is inside the thylakoid lumen? Thylakoid lumen = internal space within thylakoid sac. $H^{+}$ (protons) accumulate here during light reactions (from photolysis at PS II + PQ shuttle), creating the proton gradient for ATP synthesis by $CF_{0}$-$CF_{1}$.

Diagram Reference

Wikimedia Commons: Chloroplast_scheme.svg — Shows outer/inner envelope, thylakoid grana, stroma, and lamellae.

Summary Box

• Outer + inner envelope membranes → selectively permeable
• Stroma: Calvin cycle enzymes (RuBisCO), ribosomes, DNA
• Thylakoid membranes: photosystems, ETC, ATP synthase
• Lumen: $H^{+}$ reservoir for chemiosmosis
• Grana: non-cyclic; Stroma lamellae: cyclic photophosphorylation