Let's focus on PSII first.
The primary
electron acceptor cannot keep these electrons for long.
It passes the
electrons down a series of carriers,
starting from plastoquinone, then to the
cytochrome complex and finally plastocyanin.
Plastocyanin transfer the 2 electrons to each of the P700+,
reducing them to become P700.
Now let’s take a look at the primary electron acceptor in PSI.
Just like in PSII, the primary electron acceptor cannot keep these electrons for long.
It passes the electrons to a protein carrier known as ferredoxin,
which then passes these electrons to an enzyme known as NADP+ reductase.
NADP+ reductase reduces NADP+ to NADPH,
the first main product of the light reaction.
The transfer of electrons from PSII to PSI through the electron carriers causes a force,
that drives the H+ ions from stroma into the thylakoid space.
In addition to the H+ ions that was produced by the photolysis,
this causes the accumulation of H+ ions in the thylakoid space,
resulting in a concentration gradient.
The high H+ ion concentration in the thylakoid space is forced to be removed
through an enzyme known as ATP synthase.
Removal of H+ ions through this ATP synthase results in the production of ATP,
from ADP and phosphate.
That completes the process of light reaction with the 2 main products -
NADPH as the first, followed by ATP as the second.
Both these products are going to used in the Calvin cycle, for the production of sugar molecule.
Depending on the demand of Calvin cycle, the electron flow in light reaction is divided into 2:
a linear electron flow and a cyclic electron flow.
The flow of electrons from PSII to PSI shown earlier is known as the linear flow.
