The Light Dependent Stage and the Calvin Cycle

Light Dependent Stage of Photosynthesis: Light Dependent Stage of
Photosynthesis:
An enzyme in the thylakoid is activated by light
& splits water (photolysis):
H2O  2H+ + 2e- + ½ O2
The 2 electrons produced replace those lost by
PSII.
In PSII in the thylakoid membrane, 2 electrons
absorb the energy from photons.
They become excited & are picked up by an
electron carrier.
The electron carrier carries them down the
electron carrier chain.
The electron loses energy as it passes down
the chain & this energy causes H+ ions to be
actively transported into the thylakoid.
These 2 electrons replace those lost at PSI.
A steep H+ gradient is now created (more H+
inside the thylakoid than in the stroma).
This causes them to diffuse out of the thylakoid
through protein channels associated with ATP
synthase.
The energy provided by this is used to:
ADP + Pi  ATP
(This happens each time 3H+ move through ATP
synthase).
2 electrons in PSI (in the thylakoid membrane)
absorb energy from photons.
They become excited & are picked up by an
electron carrier.
The electron carrier carries them down the
electron carrier chain.
The electron loses energy as it is passed down
the chain.
This energy is used with these electrons & the
H+ from photolysis (step 1) to produce reduced
NADP.
So the products are ATP, reduced NADP & ½ O2.