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Photosynthesis Stage 1: Light Phase
Electron Transport Chain
H+
ion
ch
ann
el
ATP
mak
ing
en
zym
e
H+
H+
H+
H+ H+
H+
H+
H+
H+ H+ H+
H+
and
H+ ion Reservoir
Stro
ma
Electron Transport Chain
H+
ion
ch
ann
el
ATP
mak
ing
en
zym
e
H+
H+
H+
H+ H+
H+
H+
H+
H+ H+ H+
H+
and
H+ ion Reservoir
and
Photosystem II Photosystem I
Thyl
ako
id m
em
bra
ne
St
rom
a
Occur at same time
Chlorophyll molecules
1. Light hits chlorophyll and “excites” an electron so that it jumps out of the chlorophyll molecule. This happens in both Photosystems II and I.
Excited
state
Heat
Photon
(fluorescence)
Ground
state Chlorophyll
molecule
Photon
Excitation of isolated chlorophyll molecule Fluorescence
e–
Electron Transport Chain
H+
ion
ch
ann
el
ATP
mak
ing
en
zym
e
H+
H+
H+
H+ H+
H+
H+
H+
H+ H+ H+
H+
and
H+ ion Reservoir
Light Energy 1
2. This “excited” electron moves down an electron transport chain, releasing Energy.
Electron Transport Chain
H+
ion
ch
ann
el
ATP
mak
ing
en
zym
e
H+
H+
H+
H+ H+
H+
H+
H+
H+ H+ H+
H+
and
H+ ion Reservoir
Light Energy 1
e- e- 2 e-
e-
3. A chlorophyll molecule is now missing an electron. It gets this electron replaced from a water molecule. The water molecule gets is split by an enzyme as follows:
Oxygen (waste gas, diffuses out of leaf through stomata)
enzyme splits H2O 2 H+ ions for the H+ ion Reservoir
2 e- for replacing lost e- in chlorophyll
Electron Transport Chain
H+
ion
ch
ann
el
ATP
mak
ing
en
zym
e
H+
H+
H+
H+ H+
H+
H+
H+
H+ H+ H+
H+
and
H+ ion Reservoir
Light Energy 1
e- e- 2
H2O splits
3
Oxygen
2H+
Diffuse out to stomata air
2e-
4. The Energy released from the ETC is used to actively transport (pump) H+ ions against their concentration gradient from the stroma (outside the thylakoid) into the H+ ion reservoir (inside the thylakoid).
Electron Transport Chain
H+
ion
ch
ann
el
ATP
mak
ing
en
zym
e
H+
H+
H+
H+ H+
H+
H+
H+
H+ H+ H+
H+
and
H+ ion Reservoir
Light Energy 1
e- e- 2
H2O splits
3
Oxygen
H+
Diffuse out to stomata air
4
E Released from e- passing (pumps H+) 2e-
5. H+ ions collect in the Hydrogen Ion Reservoir. Their concentration builds and they repel each other due to like charges.
Electron Transport Chain
H+
ion
ch
ann
el
ATP
mak
ing
en
zym
e
H+
H+
H+
H+ H+
H+
H+
H+
H+ H+ H+
H+
and
H+ ion Reservoir
Light Energy 1
e- e- 2
H2O splits
3
Oxygen
H+
Diffuse out to stomata air
4 E Released from e- passing (pumps H+)
5
(H+ collecting and repelling)
2e-
6. H+ ions rush back into the stroma (from high to low concentration) through the ATP Synthase enzyme, which uses this energy (rushing) to join ADP and P (make ATP).
Electron Transport Chain
H+
ion
ch
ann
el
ATP
mak
ing
en
zym
e
H+
H+
H+
H+ H+
H+
H+
H+
H+ H+ H+
H+
and
H+ ion Reservoir
Light Energy 1
e- e- 2
H2O splits
3
Oxygen
H+
Diffuse out to stomata air
4 E Released from e- passing (pumps H+)
6
(H+ collecting and repelling)
ADP + P
ATP 2e-
7. H+ ions join with the electrons coming off the ETC and form Hydrogen atoms. Hydrogen atoms get picked up by NADP.
2e- + 2H+ + NADP NADPH2.
Electron Transport Chain
H+
ion
ch
ann
el
ATP
mak
ing
en
zym
e
H+
H+
H+
H+ H+
H+
H+
H+
H+ H+ H+
H+
and
H+ ion Reservoir
Light Energy 1
e-
e- 2
H2O splits
3
Oxygen
H+
Diffuse out to stomata air
4 E Released from e- passing (pumps H+)
5
(H+ collecting and repelling)
2H+
NADP+ 2e-
NADPH2
ADP + P
ATP
Go to stage 2
6
7
e-
e-
2e-
ATP
Photosystem II
e–
e–
e–
e–
Mill
makes
ATP
e–
e–
e–
Photosystem I
NADPH
Light Phase Summary
• Only happens if light hits chlorophyll
• Requires H2O, which gets split
• Produces:
– NADPH2
– ATP
– Oxygen Gas
Go to stage 2
Released into the air
