How do the High-Energy Electrons During Chemiosmosis Come from Water?
The light harvesting complexes use light energy to &quot;lift&quot; electrons to a higher energy state from which they can be used to reduce organic molecules (by way of an electron transport chain and NADPH), leaving a &quot;hole&quot; or cation behind in the LHC and thereby oxidizing it. If these complexes were not re-reduced by something, they would become non-functional after absorption of a single photon. So, they are re-reduced by removing electrons from water to generate molecular oxygen, which happens in photosystem II. So the photosystems I and II act as a series of &quot;pumps&quot; that make otherwise thermodynamically &quot;uphill&quot; (unfavorable) electron transfer from water to NADPH spontaneous, but they do not act as a net source of electrons--water does.