Pigment arrays improve photosynthesis by combining chlorophyll and accessory pigments so more wavelengths can be captured efficiently, connecting the mechanism to observable photosynthesis evidence.
A photosystem is a membrane-bound molecular array of chlorophyll and accessory pigments surrounding a special reaction-centre chlorophyll.
Different antenna pigments absorb different wavelengths and transfer excitation energy toward the reaction centre. The reaction-centre chlorophyll emits an excited electron to an electron acceptor, initiating electron flow.
Photosystems occur in chloroplast thylakoid membranes and photosynthetic membranes of cyanobacteria. The structured array broadens light capture and funnels energy efficiently to one reaction centre.
A wavelength weakly absorbed by the reaction-centre chlorophyll can still drive electron emission when an accessory pigment absorbs it and transfers the excitation energy through the array.
A single isolated chlorophyll or accessory-pigment molecule cannot perform any part of photosynthesis by itself; the organized pigment–protein membrane system is essential.
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.