In a chloroplast, light-dependent reactions take place at thylakoid membranes. Chlorophyll captures light; electron transfer helps establish an electrochemical gradient across the thylakoid membrane, enabling formation of ATP. The oxygenic photosynthesis pathway also forms NADPH and releases molecular oxygen from water. ATP and NADPH become available in the chloroplast stroma for the Calvin cycle. See Alberts et al.: chloroplast light reactions.
Figure 1.
Thylakoid membranes and chloroplast stroma couple two stages of photosynthesis
. Original chloroplast schematic, not an experimental photograph or a scale drawing. Light-dependent reactions supply ATP and NADPH to the stromal Calvin cycle; depleted carriers return for reuse. The molecular oxygen arrow leaves the water-using stage, while carbon dioxide enters carbon fixation. Details.
An organized light-harvesting and reaction-center assembly supporting photosynthetic energy conversion.
Photosystem I is a light-driven reaction-centre complex in oxygenic photosynthesis. Excitation supports electron transfer to acceptors including ferredoxin; the balance between linear and cyclic routes affects reductant and ATP supply.
A photosystem involved in water oxidation during oxygenic photosynthesis. Its reaction-center components include D1 protein.
The manganese–calcium-containing catalytic machinery that extracts electrons from water in oxygenic photosynthesis. Four oxidizing equivalents permit formation of one oxygen molecule from two water molecules.
LHCII is a major light-harvesting antenna complex in plants. A regulated mobile fraction participates in photosynthetic state transitions; antenna redistribution is distinct from simply dissipating excitation.
PsbS participates in rapid proton-dependent regulation of photosynthetic antenna quenching in plants. Loss of PsbS-dependent quenching can be separated experimentally from loss of light-harvesting capacity.
Processes replacing damaged photosystem II components and restoring functional complexes. Regulated D1 protein synthesis is one part of this cycle.
A reaction-center protein of photosystem II, encoded by psbA messenger RNA in chloroplast expression systems. Damage creates demand for replacement during photosystem II repair.
Chlorophyll is a family of molecules that absorb light for photosynthesis. In chloroplasts, chlorophyll works with proteins in thylakoid membranes; absorbing light initiates energy capture rather than directly constructing a sugar. See OpenStax Biology 2e, 8.2: photosynthetic pigments.
A widespread photosynthetic pigment with prominent blue and red absorption bands. Its concentration is a useful index of phytoplankton biomass, but pigment per unit carbon varies with light acclimation and physiological condition.

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