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Vascular bundle Stoma
Cuticle Epidermis Mesophyll
Chloroplast Inner membrane Outer membrane
Cell wall
1.58 µm
Vacuole
Courtesy Dr. Kenneth Miller, Brown University
1
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O2
Stroma
Photosystem
Thylakoid
NADP+
ADP + Pi
CO2
Sunlight
Photosystem
Light-Dependent Reactions
Calvin Cycle
Organic molecules
O2
ATP NADPH
H2O
2
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400 nm
Visible light
430 nm 500 nm 560 nm 600 nm 650 nm 740 nm
1 nm 0.001 nm 10 nm 1000 nm Increasing wavelength
Increasing energy
0.01 cm 1 cm 1 m
Radio waves Infrared X-rays Gamma rays
100 m
UV light
3
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Wavelength (nm) 400 450 500 550 600 650 700
Lig
ht
Ab
sorb
tio
n
low
high carotenoids chlorophyll a chlorophyll b
4
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H2C CH
CH2CH3
H
H H
C O CH CCH3
CHCH3 CH2 CH2 CH2 CHCH3 CH2 CH2 CH2 CHCH3 CH3
O CO2CH3
O
N N
N N Mg
H
H Chlorophyll a: = CH3 Chlorophyll b: = CHO
R R
R
H Porphyrin head
H3C
H3C CH3
CH2 CH2
CH2
CH2 CH2 CH2
Hydrocarbon tail
5
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Oak leaf in summer
Oak leaf in autumn
© Eric Soder 6
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e– Photon
Photosystem
Thylakoid membrane
Chlorophyll molecule
Electron acceptor
Reaction center chlorophyll
Thylakoid membrane
Electron donor e–
7
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Light
e–
– + – +
Excited chlorophyll molecule
Electron donor
Electron acceptor
Chlorophyll reduced
Chlorophyll oxidized
Donor oxidized
Acceptor reduced
e– e– e–
e– e–
e–
e–
8
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En
erg
y o
f el
ectr
on
s
e–
Photon
Excited reaction center
Excited reaction center
Plastoquinone
Plastocyanin
Ferredoxin
Photosystem II
Photosystem I
Photon
b6-f complex
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 chemiosmosis.
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.
H2O
H+ PC
Fd
2H+ + 1/2O2
NADP+ + H+ NADPH
2
2
2
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.
Reaction center
Proton gradient formed for ATP synthesis
Reaction center
NADP reductase
e–
e–
e–
e–
PQ
9
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Photosystem II Photosystem I b6-f complex
Stroma
Plastoquinone Proton gradient Plastocyanin Ferredoxin
H+
H+ H+
H+
NADPH ATP
ADP + NADP+
NADPH NADP ATP ADP + Pi
Calvin Cycle
Photon Photon
H2O 2e–
2e–
2e– Fd
PC PQ
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
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.
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.
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.
NADP reductase
ATP synthase
1/2O2 2H+
Water-splitting enzyme
Thylakoid space
Antenna complex Thylakoid
membrane
Light-Dependent Reactions
H+
H+
2e–
10
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4 Pi 12 NADP+
12
12 ADP
NADPH NADP+
A T P ADP + Pi
Glucose and other sugars
Light-Dependent Reactions
Calvin Cycle
6 molecules of 12 molecules of
12 molecules of 1,3-bisphosphoglycerate (3C)
12 molecules of Glyceraldehyde 3-phosphate (3C) (G3P)
10 molecules of
Glyceraldehyde 3-phosphate (3C) (G3P)
Stroma of chloroplast 6 molecules of
Carbon dioxide (CO2)
12 NADPH
12 ATP
6 ADP
6 ATP
Rubisco
Calvin Cycle
Pi
Ribulose 1,5-bisphosphate (5C) (RuBP) 3-phosphoglycerate (3C) (PGA)
Glyceraldehyde 3-phosphate (3C)
2 molecules of
11
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O2
Heat
ATP NADPH NADH
ATP
Sunlight
Pyruvate
CO2
Glucose
ADP + Pi NAD+ NADPi
H2O Photo- system
II
Photo- system
I
Electron Transport
System ADP + Pi
ADP + Pi
ATP
ATP
Calvin Cycle
Krebs Cycle
12
13
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Heat
Stomata
O2 O2
CO2 CO2
Under hot, arid conditions, leaves lose water by evaporation through openings in the leaves called stomata.
The stomata close to conserve water but as a result, O2 builds up inside the leaves, and CO2
cannot enter the leaves.
Leaf epidermis
H2O H2O
14
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CO2
RuBP
3PG (C3)
a. C4 pathway
Bundle-sheath cell Mesophyll cell
Stoma Vein
G3P
b. C4 pathway Stoma Vein
Mesophyll cell
G3
CO2
CO2
C4
Bundle- sheath cell
Mesophyll cell
Bundle- sheath cell
Calvin Cycle
Mesophyll cell
Calvin Cycle
a: © John Shaw/Photo Researchers, Inc. b: © Joseph Nettis/National Audubon Society Collection/Photo Researchers, Inc.
15
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Oxaloacetate
Pyruvate Malate
Glucose
Malate Pyruvate
+ Pi
Mesophyll cell
Phosphoenolpyruvate (PEP)
Bundle-sheath cell
Calvin Cycle
AMP + PPi
ATP
CO2
CO2
16
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night
day
CO2
CO2
C4
G3P
Calvin Cycle
© ClydeH. Smith/Peter Arnold Inc.
17
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