Chlorophyll a

Chlorophyll a is a magnesium-containing photosynthetic pigment that absorbs light and participates directly in the reaction centers of oxygenic photosynthesis.

Photosystem II: A membrane protein complex that uses light energy to extract electrons from water and begin oxygenic photosynthesis. Chlorophyll a molecules in its reaction center initiate charge separation.
Porphyrin: A family of large, conjugated macrocycles built from four nitrogen-containing rings. Chlorophyll a’s light-absorbing head is a modified porphyrin-like macrocycle.
Chlorophyll fluorescence imaging: A technique that maps emitted chlorophyll fluorescence to assess photosynthetic activity across samples or landscapes. It uses chlorophyll a emission patterns to locate variation in photosynthetic performance.
Cyanobacteria: A diverse phylum of bacteria that perform oxygenic photosynthesis. Cyanobacteria use chlorophyll a in the photosystems that release oxygen.
Photosystem I: A membrane protein complex that uses light energy to transfer electrons to ferredoxin. Its reaction-center chlorophyll a absorbs light to drive a second major charge separation.
Magnesium: A metallic chemical element whose ions serve as cofactors in many biological molecules. A magnesium ion sits at the center of chlorophyll a’s ring structure.
Pulse-amplitude-modulated fluorometry: A method that measures chlorophyll fluorescence under controlled light pulses to estimate photosystem performance. It estimates how effectively absorbed energy is used by chlorophyll a-containing photosystems.
Endosymbiotic theory: The theory that mitochondria and plastids originated from bacteria incorporated into ancestral eukaryotic cells. Chloroplasts inherited chlorophyll a-based photosynthesis from bacterial ancestors.
P680: The pair of reaction-center chlorophyll a molecules in Photosystem II, named for its absorption peak near 680 nanometers. It is a specialized chlorophyll a pair whose excited state powers water oxidation.
Phytol: A long, hydrophobic diterpene alcohol that forms the tail of chlorophyll molecules. Its tail helps anchor chlorophyll a within photosynthetic membranes and protein complexes.

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