Photosynthetic products can be converted into carbohydrates, lipids, amino acids and other compounds needed for plant growth and storage, connecting the mechanism to observable photosynthesis evidence.
The Calvin cycle supplies carbon intermediates for carbohydrates, amino acids and other carbon compounds, while depending on ATP and reduced NADP from the light-dependent reactions.
All carbon in compounds made by a photosynthesizing organism is first fixed through the Calvin cycle. TP and other intermediates enter metabolic pathways; mineral nutrients supply elements such as nitrogen needed for amino acids and other products.
The light-dependent reactions supply ATP and reduced NADP; the Calvin cycle returns ADP, phosphate and NADP. Without light, ATP and reduced NADP production stops. Without CO₂, carbon fixation stops and the coupled recycling of electron acceptors is disrupted, eventually preventing photosystem II from functioning.
Some TP contributes to sucrose or starch, while carbon skeletons combined with mineral nitrogen can form amino acids. Most TP remains in the cycle to regenerate RuBP.
‘Light-independent’ means light is not absorbed directly by these reactions; it does not mean they can continue indefinitely without light-reaction products. Glucose is not formed in one Calvin-cycle step.
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.