Electron transfer pathways in PSII and PSI

Chlorophyll is the dominant molecule for light harvesting in biology. Moreover, the special pair of chlorophyll molecules in the reaction centre not only harvests light energy but also provides the first step of energy transduction. At this centre the photon generates a biradical responsible for electron flow, which results in the first membrane potential [1], 

If the involvement of a pair of chlorophyll molecules as the reaction initiator signifies the fact that a large distance of charge separation is necessary for redox reactions to compete significantly with charge return, perhaps the role of Mg is to control the degree of association between the two molecules 

Bacteriochlorophylls (found in bacteria) are similar to chlorophylls, except for the reduction of an additional pyrrole ring and other minor differences that shift their absorption maxima to near infrared, up to wavelengths of about 900-1000 nm. 

Oxygen is produced during the light period of photosynthesis in the thylakoid membranes of green plant chloroplasts and the internal membranes of bacteria. PSII oxidoreductase oxidizes water, producing molecular oxygen on one side of the membrane  

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