Leaf cross section
Vein
Mesophyll
Stomata
CO2
O2
(a) Plants
Chloroplast
Mesophyll cell
Outer
membrane
(c) Unicellular protist
Thylakoid
10 µm
Stroma
(e) Purple sulfur
bacteria
(b) Multicellular alga
(d) Cyanobacteria
Thylakoid
space
Granum
Intermembrane
space
5 µm
Inner
membrane
1.5 µm
40 µm
1 µm
1
2
CO2
H 2O
Light
NADP+
Reactants:
6 CO2
ADP
12 H2O
+ P i
Light
Reactions
Products:
6 H 2O
C6H12O6
Calvin
Cycle
ATP
6 O2
NADPH
Chloroplast
[CH2O]
(sugar)
O2
3
10–5 nm 10–3 nm
103 nm
1 nm
Gamma
X-rays
rays
UV
106 nm
Infrared
1m
(109 nm)
Microwaves
4
103 m
Light
Reflected
light
Radio
waves
Chloroplast
Visible light
380
450
500
Shorter wavelength
Higher energy
550
600
650
700
Absorbed
light
750 nm
Longer wavelength
Lower energy
Granum
Transmitted
light
5
6
Absorption of light by
chloroplast pigments
RESULTS
Chlorophyll a
CH3
Chlorophyll b
CHO
Porphyrin ring:
light-absorbing
“head” of molecule;
note magnesium
atom at center
Carotenoids
400
(a) Absorption spectra
500
600
in chlorophyll a
in chlorophyll b
700
Rate of photosynthesis
(measured by O2 release)
Wavelength of light (nm)
(b) Action spectrum
Hydrocarbon tail:
interacts with hydrophobic
regions of proteins inside
thylakoid membranes of
chloroplasts; H atoms not
shown
Aerobic bacteria
Filament
of alga
(c) Engelmann’s
experiment
400
600
500
700
7
8
Photosystem
STROMA
Light-harvesting Reaction-center
complex
complexes
Primary
electron
acceptor
Photon
Excited
state
Energy of electron
e–
Thylakoid membrane
Heat
Photon
(fluorescence)
Photon
Ground
state
Chlorophyll
molecule
e–
Transfer
of energy
(b) Fluorescence
(a) Excitation of isolated chlorophyll molecule
Pigment
molecules
Special pair of
chlorophyll a
molecules
THYLAKOID SPACE
(INTERIOR OF THYLAKOID)
9
H 2O
e–
Pq
Primary
acceptor
4
tran
spo
rt c
hain
e–
Cytochrome
complex
3
e–
e–
8
NADP+
reductase
Pc
e–
e–
e–
e–
7
Fd
NADP+
+ H+
e–
P700
5
P680
Mill
makes
ATP
6
ATP
Pigment
molecules
e–
Light
1
Light
Photosystem II
(PS II)
NADPH
e–
NADPH
e–
Photosystem I
(PS I)
Photon
2 H+
+
O2
1/
2
2
tro
n
e–
ATP
E
tra lect
n ro
ch spo n
ain rt
n
Photo
Ele
c
Primary
acceptor
10
11
Photosystem II
Photosystem I
12
Mitochondrion
Primary
acceptor
Chloroplast
Primary
acceptor
Fd
Fd
Pq
NADP+
+ H+
NADP+
reductase
Cytochrome
complex
MITOCHONDRION
STRUCTURE
NADPH
CHLOROPLAST
STRUCTURE
Pc
Thylakoid
space
Electron
transport
chain
Inner
membrane
Photosystem I
Thylakoid
membrane
ATP
synthase
ATP
Photosystem II
Diffusion
H+
Intermembrane
space
Stroma
Matrix
Key
ADP + P i
Higher [H+]
Lower [H+]
H+
ATP
13
14
Input
(Entering one
at a time)
3
CO2
Phase 1: Carbon fixation
STROMA
(low H+ concentration)
4 H+
Light
Rubisco
Cytochrome
Photosystem I
complex
Light
Photosystem II
Fd
NADP+
reductase
H 2O
THYLAKOID SPACE
(high H+ concentration)
e–
1
+
3 P
Short-lived
intermediate
H+
6
P
3-Phosphoglycerate
3P
P
Ribulose bisphosphate
(RuBP)
6
3 ADP
4 H+
3
To
Calvin
Cycle
Calvin
Cycle
ATP
synthase
STROMA
(low H+ concentration)
ADP
+
Pi
6 P
P
1,3-Bisphosphoglycerate
ATP
6 NADPH
Phase 3:
Regeneration of
the CO2 acceptor
(RuBP)
6 NADP+
6 Pi
P
5
G3P
Thylakoid
membrane
ATP
6 ADP
O2
+2 H+
P
Pc
2
1/
2
NADP+
NADPH
Pq
e–
3
6
P
Glyceraldehyde-3-phosphate
(G3P)
Phase 2:
Reduction
ATP
H+
1
Output
P
Glucose and
other organic
compounds
G3P
(a sugar)
15
The C4 pathway
C4 leaf anatomy
Mesophyll
cell
Mesophyll cell
Photosynthetic
cells of C4
Bundleplant leaf
sheath
cell
CO2
PEP carboxylase
PEP (3C)
ADP
Oxaloacetate (4C)
Vein
(vascular tissue)
Malate (4C)
Stoma
16
Bundlesheath
cell
ATP
Sugarcane
Pyruvate (3C)
Pineapple
C4
CAM
CO2
CO2
Mesophyll
cell
Organic acid
Calvin
Cycle
Bundlesheath
cell
Sugar
CO2
Calvin
Cycle
Vascular
tissue
17
CO2
1 CO2 incorporated
into four-carbon Organic acid
organic acids
(carbon fixation)
CO2
2 Organic acids
release CO2 to
Calvin cycle
Night
Day
Calvin
Cycle
Sugar
Sugar
(a) Spatial separation of steps
(b) Temporal separation of steps
18
H 2O
CO2
Light
NADP+
ADP
Pi
+
Light
Reactions:
Photosystem II
Electron transport chain
Photosystem I
Electron transport chain
RuBP
ATP
NADPH
3-Phosphoglycerate
Calvin
Cycle
G3P
Starch
(storage)
Chloroplast
O2
Sucrose (export)
19