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Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Sunlight
Cuticle
Epidermis
Mesophyll
Vascular bundle Stoma
Photosystem
H 2O
Thylakoid
Vacuole
O2
Cell wall
Light-Dependent
Reactions
1.58 µm
Inner membrane
Outer membrane
Chloroplast
ADP + Pi
CO2
ATP
NADP+
Calvin
Cycle
NADPH
Organic
molecules
Stroma
Courtesy Dr. Kenneth Miller, Brown University
1
2
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high
carotenoids
chlorophyll a
chlorophyll b
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Light
Absorbtion
Increasing energy
Increasing wavelength
0.001 nm
1 nm
Gamma rays
10 nm 1000 nm
UV
light
X-rays
0.01 cm
1 cm
Infrared
1m
100 m
Radio waves
Visible light
low
400 nm
430 nm
500 nm
560 nm
600 nm
650 nm
740 nm
400
450
500
550
600
Wavelength (nm)
650
3
700
4
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Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
H 2C
R
H
CH
H 3C
Porphyrin
head
Chlorophyll a: R =
CH3
Chlorophyll b: R =
CHO
CH2CH3
N
N
Mg
H
N
H 3C
H
O
Hydrocarbon
tail
H
N
CH3
H
H
CH2 CO2CH3 O
CH2
C
O
CH2
CH
CCH3
CH2
CH2
CH2
CHCH3
CH2
CH2
CH2
CHCH3
CH2
CH2
CH2
CHCH3
CH3
Oak leaf
in summer
Oak leaf
in autumn
5
© Eric Soder
6
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Excited
chlorophyll
molecule
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Light
Photosystem
Photon
Electron
acceptor
e– Electron
e–
donor
Electron
donor
Reaction center
chlorophyll
Chlorophyll
molecule
Electron
acceptor
e–
e–
e–
e–
Chlorophyll
reduced
Donor
oxidized
+
Chlorophyll
oxidized
Acceptor
reduced
–
e–
Thylakoid membrane
–
+
e–
e–
e–
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8
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Excited reaction center
2. The electrons pass through the b6-f
complex, which uses the energy
released to pump protons across
the thylakoid membrane. The proton
gradient is used to produce ATP by
Excited reaction center
chemiosmosis.
2
e–
2
e–
NADP
reductase
Energy of electrons
Photon
H+
Antenna
complex
Thylakoid
membrane
PC
ATP
ADP
H+ + NADP+
Fd
2e–
Reaction
center
Photon
2e–
2e–
PC
H 2O
3. A pair of chlorophylls in the reaction
center absorb two photons. This
excites two electrons that are passed to
NADP+, reducing it to NADPH. Electron
transport from photosystem II replaces
these electrons.
H 2O
PQ
2e–
Stroma
Proton gradient formed
for ATP synthesis
2H+ + 1/2O2
Photon
Photon
NADPH
Plastocyanin
H+
2
e–
NADP
Calvin
Cycle
NADPH
NADP+ + H+
2 e–
2 e–
ATP
NADPH
Plastoquinone
b6-f
complex
Light-Dependent
Reactions
ADP + Pi
Fd
PQ
Reaction
center
Ferredoxin
Thylakoid
space
1/ O
2 2
1. A pair of chlorophylls in the reaction center
absorb two photons of light. This excites two
electrons that are transferred to plastoquinone
(PQ). Loss of electrons from the reaction center
produces an oxidation potential capable of
oxidizing water.
Proton
gradient
H+
H+
H+
2H+
1. Photosystem II
absorbs photons,
exciting electrons
that are passed to
plastoquinone (PQ).
Electrons lost from
photosystem II are
replaced by the
oxidation of water,
producing O2
Photosystem II
Ferredoxin
H+
Photosystem II
Photosystem I
Plastocyanin
Plastoquinone
Water-splitting
enzyme
b6-f complex
2. The b6-f complex
receives electrons
from PQ and passes
them to plastocyanin
(PC). This provides
energy for the b6-f
complex to pump
protons into the
thylakoid.
NADP
reductase
Photosystem I
3. Photosystem I absorbs
photons, exciting
electrons that are
passed through a
carrier to reduce
NADP+ to NADPH.
These electrons are
replaced by electron
transport from
photosystem II.
ATP
synthase
4. ATP synthase uses
the proton gradient
to synthesize ATP
from ADP and Pi
enzyme acts as a
channel for protons
to diffuse back into
the stroma using this
energy to drive the
synthesis of ATP.
9
10
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ADP+ Pi
ATP
NADP+
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Stroma of chloroplast
6 molecules of
Light-Dependent
Reactions
Carbon
dioxide (CO2)
NADPH
Calvin
Cycle
12 molecules of
Rubisco
6 molecules of
3-phosphoglycerate (3C) (PGA)
Ribulose 1,5-bisphosphate (5C) (RuBP)
Heat
Sunlight
12 ATP
Photosystem
II
12 ADP
6 ADP
12 molecules of
Calvin Cycle
O2
Photosystem
I
H 2O
Electron
Transport
System
1,3-bisphosphoglycerate (3C)
6 ATP
ATP
ADP + Pi
12 NADPH
4
ADP + Pi
Pi
ATP
NADPi
NADPH
NAD+
NADH
12 NADP+
10 molecules of
12 Pi
Glyceraldehyde 3-phosphate (3C)
12 molecules of
Glyceraldehyde 3-phosphate (3C) (G3P)
Calvin
Cycle
CO2
2 molecules of
Glyceraldehyde 3-phosphate (3C) (G3P)
Pyruvate
Glucose
Glucose and
other sugars
Krebs
Cycle
ATP
ADP + Pi
ATP
11
12
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Leaf
epidermis
Heat
H 2O
H 2O
O2
CO2
Stomata
Under hot, arid conditions, leaves lose water by
evaporation through openings in the leaves
called stomata.
CO2
The stomata close to conserve water but as a
result, O2 builds up inside the leaves, and CO2
cannot enter the leaves.
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14
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CO2
Mesophyll cell Bundle-sheath cell
CO2
O2
Mesophyll
cell
Mesophyll
cell
RuBP
Phosphoenolpyruvate Oxaloacetate
(PEP)
Calvin
Cycle
AMP +
PPi
3PG
(C3)
ATP
G3P
Stoma
+ Pi
Vein
a. C4 pathway
Mesophyll cell
CO2
Pyruvate
Malate
Pyruvate
Malate
Bundlesheath cell
Mesophyll
cell
C4
Bundlesheath
cell
CO2
Bundle-sheath
cell
Calvin
Cycle
CO2
Calvin
Cycle
G3
Stoma
b. C4 pathway
a: © John Shaw/Photo Researchers, Inc. b: © Joseph Nettis/National Audubon Society Collection/Photo Researchers, Inc.
Vein
Glucose
15
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night
CO2
C4
day
CO2
Calvin
Cycle
G3P
© ClydeH. Smith/Peter Arnold Inc.
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