Chlorophyll A Plant

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Absorption of light by photosynthetic pigments converts photons into chemical energy. Light energy radiating onto the chloroplast strikes the pigments in the thylakoid membrane and excites their electrons. Since the chlorophyll a molecules only capture certain wavelengths, organisms may use accessory pigments to capture a wider range of light energy shown as the yellow circles. It then transfers captured light from one pigment to the next as resonance energy, passing energy one pigment to the other until reaching the special chlorophyll a molecules in the reaction center. These special chlorophyll a molecules are located in both photosystem II and photosystem I. They are known as P680 for Photosystem II and P700 for Photosystem I. P680 and P700 are the primary electron donors to the electron transport chain. These two systems are different in their redox potentials for one-electron oxidation. The Em for P700 is approximately 500mV, while the Em for P680 is approximately 1,100-1,200 mV.