now electrons themselves transfer between molecules. P700 uses the energy of the excited electrons to boost its own electrons to an energy level that enables an adjoining electron acceptor molecule to capture them [6]. The electrons are then passed down a chain of carrier molecules, called an electron transport chain. The electrons are passed from one carrier molecule to another in a downhill direction. Each electron carrier is at a lower energy level than the one before it, and the result is that electrons release energy as they move down the chain. At the end of the electron transport chain lies the molecule nicotine adenine dinucleotide (NADP+). Using the energy released by the flow of electrons, two electrons from the electron transport chain combine with a hydrogen ion and NADP+ to form NADPH. When P700 transfers its electrons to the electron acceptor, it becomes oxidized and loses electrons. Before it can function again, it must be replenished with new electrons. Photosystem II accomplishes this task. As in Photosystem I, light energy activates electrons of the Photosystem II pigments. These pigments transfer the energy of their excited electrons to a special Photosystem II chlorophyll molecule, P680, that absorbs light best in the red region at 680 nanometers [4]. Just as in Photosystem I, energy is transferred among pigment molecules and is then directed to the P680 chlorophyll, where the energy is used to transfer electrons from P680 to its adjoining electron acceptor molecule. From the Photosystem II electron acceptor, the electrons are passed through a different electron transport chain. As they pass along the movement of electron carrier molecules, the electrons give up some of their energy to fuel the production of ATP, which is formed by the addition of one phosphorous atom to adenosine diphosphate (ADP) [3]. Eventually, the electron transport carrier molecules deliver the Photosystem II electrons to Photosys...
