Page 80 - Medicinal Plants_PharmD general

Photosystem II

It contains P680 reaction center that maximally absorbs 680 nm
light. Photosystem II (Figure 23) is the first link in the chain of
photosynthesis.
1. When light is absorbed by one of the many pigments in PSII, energy is

passed inward from pigment to pigment. The energy excites an electron
to a higher state. The energized electrons are passed from the reaction
center to an electron transport chain.
2. The electrons lost by PSII are replaced by a process called Photolysis
which is the oxidation of water molecule producing free electrons in
addition to oxygen gas as a by-product.
3. The electrons pass through the electron transport chain where the
energy from the electrons is used to pump hydrogen ions across the
thylakoid membrane from the stroma creating a concentration gradient.
4. This gradient powers ATP synthase which phosphorylates ADP to form
ATP. (ATP synthesis)
5. Finally, low energy electrons leaving PSII are shuttled to PSI.

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