1. Two Reactions of Photosynthesis
Light Reaction
aka light dependent
rxn
Calvin Cycle aka light independent reaction
Transforming light photons into ATP and the electron carrier NADPH
Use ATP/NADPH to make glucose

2. The Light Reaction Occurs in the thylakoid membrane
2 Photosystems: I and II
2 Electron Transport Chains (ETC)
Consumes H2O for protons, e-
Generates O2 ATP and NADPH

3. e- of cholorphyll a is energized
ETC donates e-, reduces NADP+ to NADPH
ETC
Photosystem II pigments direct energy to chlorophyll a
which becomes oxidized
P680/P700 refers to the wavelength of cholorphyll each best absorbs
P680/p700 refer to the wavelength of chlorophyll each best absorbs.
Photosystem I is energized

4. • H+ builds up in thylakoid
Concurrently to ETC:
• H+ builds up in thylakoid
From H2O, proton pump
• H+ diffuse from high to low concentration
through ATP synthase
generating ATP

5. Creating high proton concentration in the thylakoid
Proton pump
driven by e-
ETC H+
Creating high proton concentration in the thylakoid
P680/P700 refers to the wavelength of cholorphyll each best absorbs
P680/p700 refer to the wavelength of chlorophyll each best absorbs.
2H2O
oxidized
4H+ + O (+ e-)

7. Inputs & Products Radiant energy (visible wavelengths)
2H2O O2 + 4H (+ e-)
At second ETC:
• NADP+ + H NADPH
Via chemiosmosis
• ADP ATP P

8. Chemiosmosis ADP + P ATP PS II PS I E T C Thylakoid Space
H+ H+
ATP Synthase
high H+
concentration H+
ADP + P
ATP
PS II
PS I E T C
low H+
Thylakoid
Space
SUN
(Proton Pumping)
H2O

10. Cyclic Electron Flow
P700
Primary
Electron
Acceptor e-
ATP
produced
by ETC
Photosystem I
Accessory
Pigments
SUN
Photons
Pigments absorb light energy & excite e- of Chlorophyll a to produce ATP

11. Light Reaction (Electron Flow)
During the light reaction, there are two possible routes for electron flow:
A. Cyclic Electron Flow
B. Noncyclic Electron Flow