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Chapter 10
Photosynthesis
PowerPoint TextEdit Art Slides for
Biology, Seventh Edition
Neil Campbell and Jane Reece
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Figure 10.1 Sunlight consists of a spectrum of colors,
visible here in a rainbow
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Figure 10.2 Photoautotrophs
These organisms use light energy to drive the
synthesis of organic molecules from carbon dioxide
and (in most cases) water. They feed not only
themselves, but the entire living world. (a) On
land, plants are the predominant producers of
food. In aquatic environments, photosynthetic
organisms include (b) multicellular algae, such
as this kelp; (c) some unicellular protists, such
as Euglena; (d) the prokaryotes called
cyanobacteria; and (e) other photosynthetic
prokaryotes, such as these purple sulfur
bacteria, which produce sulfur (spherical
globules) (c, d, e: LMs).
(a) Plants
(c) Unicellular protist
10 m
(d) Pruple sulfur
bacteria
(b) Multicellular algae
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(c) Cyanobacteria
40 m
1.5 m
Figure 10.3 Focusing in on the location of
photosynthesis in a plant
Leaf cross section
Vein
Mesophyll
CO2 O2
Mesophyll cell
Stomata
Chloroplast
5 µm
Outer
membrane
Granum
Storma
Thylakoid Thylakoid
Space
Intermembrane
space
Inner membrane
1 µm
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Figure 10.4 Tracking atoms through photosynthesis
Reactants:
Products:
12 H2O
6 CO2
C6H12O6
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6
H2O
6
O2
Figure 10.5 An overview of photosynthesis: cooperation
of the light reactions and the Calvin cycle
H2O
Light
LIGHT
REACTIONS
Chloroplast
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Figure 10.5 An overview of photosynthesis: cooperation
of the light reactions and the Calvin cycle
H2O
Light
LIGHT
REACTIONS
ATP
NADPH
Chloroplast
O2
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Figure 10.5 An overview of photosynthesis: cooperation
of the light reactions and the Calvin cycle
H2O
CO2
Light
NADP
ADP
+ Pi
CALVIN
CYCLE
LIGHT
REACTIONS
ATP
NADPH
Chloroplast
O2
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[CH2O]
(sugar)
Figure 10.6 The electromagnetic spectrum
10–5
nm
10–3
Gamma
rays
103
1 nm
nm
X-rays
UV
106
nm
Infrared
1m
106 nm
nm
Microwaves
103 m
Radio
waves
Visible light
380
450
500
550
Shorter wavelength
Higher energy
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600
650
700
750 nm
Longer wavelength
Lower energy
Figure 10.7 Why leaves are green: interaction of
light with chloroplasts
Light
Reflected
Light
Chloroplast
Absorbed
light
Granum
Transmitted
light
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Figure 10.8 Research Method Determining an
Absorption Spectrum
APPLICATION An absorption spectrum is a visual
representation of how well a particular pigment absorbs different
wavelengths of visible light. Absorption spectra of various chloroplast
pigments help scientists decipher each pigment’s role in a plant.
TECNIQUE A spectrophotometer measures the relative
amounts of light of different wavelengths absorbed and
transmitted by a pigment solution.
1
White light is separated into colors (wavelengths) by a prism.
2
One by one, the different colors of light are passed through the
sample (chlorophyll in this example). Green light and blue light
are shown here.
3
The transmitted light strikes a photoelectric tube, which
converts the light energy to electricity.
4
The electrical current is measured by a galvanometer. The meter
indicates the fraction of light transmitted through the sample,
from which we can determine the amount of light absorbed.
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Refracting Chlorophyll
solution
prism
White
light
Photoelectric
tube
Galvanometer
2
1
3
4
Slit moves to
pass light
of selected
wavelength
Green
light
0
The high transmittance
(low absorption)
reading indicates that
chlorophyll absorbs
very little green light.
0
Blue
light
Result
100
100
The low transmittance
(high absorption) reading indicates that
chlorophyll absorbs most blue light.
See Figure 10.9a for absorption spectra of three types of chloroplast pigments.
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Figure 10.9 Inquiry Which wavelengths of light are
most effective in driving photosynthesis?
EXPERIMENT Three different experiments helped reveal which wavelengths of light are photosynthetically
important. The results are shown below.
RESULTS
Chlorophyll a
Absorption of light by
chloroplast pigments
Chlorophyll b
Carotenoids
400
500
600
700
Wavelength of light (nm)
(a) Absorption spectra. The three curves show the wavelengths of light best absorbed by
three types of chloroplast pigments.
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Rate of photosynthesis
(measured by O2 release)
(b) Action spectrum. This graph plots the rate of photosynthesis versus wavelength.
The resulting action spectrum resembles the absorption spectrum for chlorophyll
a but does not match exactly (see part a). This is partly due to the absorption of light
by accessory pigments such as chlorophyll b and carotenoids.
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Aerobic bacteria
Filament
of alga
400
500
600
700
(c) Engelmann‘s experiment. In 1883, Theodor W. Engelmann illuminated a filamentous alga with
light that had been passed through a prism, exposing different segments of the alga to different
wavelengths. He used aerobic bacteria, which concentrate near an oxygen source, to determine
which segments of the alga were releasing the most O2 and thus photosynthesizing most.
Bacteria congregated in greatest numbers around the parts of the alga illuminated with violet-blue
or red light. Notice the close match of the bacterial distribution to the action spectrum in part b.
Light in the violet-blue and red portions of the spectrum are most effective in
driving photosynthesis.
CONCLUSION
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Figure 10.10 Structure of chlorophyll molecules in
chloroplasts of plants
CH3
in chlorophyll a
CHO
in chlorophyll b
CH2
CH
C
H3C
C
C
C
H
C
C
N
C
C
C
CH2
H
H
C
O
C
H
C
CH3
Porphyrin ring:
Light-absorbing
“head” of molecule;
note magnesium
atom at center
C
O
O
C
CH3
C
C
CH2
CH2
C
N
C
C
C
N
Mg
C
H
C
N
C
H3C
CH3
H
O
O
CH3
CH2
Hydrocarbon tail:
interacts with hydrophobic
regions of proteins inside
thylakoid membranes of
chloroplasts: H atoms not
shown
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Figure 10.11 Excitation of isolated chlorophyll by light
e–
Excited
state
Heat
Photon
(fluorescence)
Photon
Chlorophyll
molecule
Ground
state
(a) Excitation of isolated chlorophyll molecule
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(b) Fluorescence
Figure 10.21 A review of photosynthesis
Light reactions
Calvin cycle
H2O
CO2
Light
NADP+
ADP
+P1
RuBP
3-Phosphoglycerate
Photosystem II
Electron transport chain
Photosystem I
ATP
NADPH
G3P
Starch
(storage)
Amino acids
Fatty acids
Chloroplast
O2
Light reactions:
• Are carried out by molecules in the
thylakoid membranes
• Convert light energy to the chemical
energy of ATP and NADPH
• Split H2O and release O2 to the
atmosphere
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Sucrose (export)
Calvin cycle reactions:
• Take place in the stroma
• Use ATP and NADPH to convert
CO2 to the sugar G3P
• Return ADP, inorganic phosphate, and
NADP+ to the light reactions
Figure 10.12 How a photosystem harvests light
Thylakoid
Photosystem
Photon
Reaction
Primary election
center
acceptor
Light-harvesting
complexes
Thylakoid membrane
STROMA
e–
Transfer
of energy
Special
chlorophyll a
molecules
Pigment
molecules
THYLAKOID SPACE
(INTERIOR OF THYLAKOID)
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Figure 10.13 How noncyclic electron flow during
the light reactions generates ATP and NADPH
H2O
CO2
Light
NADP+
ADP
CALVIN
CYCLE
LIGHT
REACTIONS
ATP
NADPH
O2
[CH2O] (sugar)
Primary
acceptor
Energy of electrons
e
Light
1
2
P680
Photosystem II
(PS II)
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Figure 10.13 How noncyclic electron flow during
the light reactions generates ATP and NADPH
H2O
CO2
Light
NADP+
ADP
CALVIN
CYCLE
LIGHT
REACTIONS
ATP
NADPH
O2
[CH2O] (sugar)
Primary
acceptor
Energy of electrons
2
H+
H2O
e
2
+
1⁄
2
Light
O2
3
e
e
P680
1
Photosystem II
(PS II)
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Figure 10.13 How noncyclic electron flow during
the light reactions generates ATP and NADPH
H2O
CO2
Light
NADP+
ADP
CALVIN
CYCLE
LIGHT
REACTIONS
ATP
NADPH
O2
[CH2O] (sugar)
Primary
acceptor
Energy of electrons
2
1⁄
Light
1
2
H+
+
O2
H2O
e
2
4
Pq
Cytochrome
complex
3
e
e
5
P680
ATP
Photosystem II
(PS II)
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Pc
Figure 10.13 How noncyclic electron flow during
the light reactions generates ATP and NADPH
H2O
CO2
Light
NADP+
ADP
CALVIN
CYCLE
LIGHT
REACTIONS
ATP
NADPH
[CH2O] (sugar)
O2
Primary
acceptor
Primary
acceptor
4
e
Energy of electrons
Pq
2 H+
+
1⁄ O2
2
Light
H2O
3
e
2
Cytochrome
complex
Pc
e
e
5
P700
P680
Light
1
6
ATP
Photosystem II
(PS II)
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Photosystem I
(PS I)
Figure 10.13 How noncyclic electron flow during
the light reactions generates ATP and NADPH
H2O
CO2
Light
NADP+
ADP
CALVIN
CYCLE
LIGHT
REACTIONS
ATP
NADPH
[CH2O] (sugar)
O2
Primary
acceptor
Primary
acceptor
4
e
Energy of electrons
Pq
1⁄
Light
2 H+
+
O2
2
H2O
e
2
7
Fd
e
8
e
Cytochrome
complex
NADP+
NADP+
+ 2 H+
reductase
NADPH
3
e
e
5
Pc
+ H+
P700
P680
Light
1 1
6
6
ATP
Photosystem II
(PS II)
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Photosystem I
(PS I)
Figure 10.14 A mechanical analogy for the light reactions
e–
ATP
e–
e–
NADPH
e–
e–
e–
Mill
makes
ATP
e–
Photosystem II
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Photosystem I
Figure 10.15 Cyclic electron flow
Primary
acceptor
Primary
acceptor
Fd
Fd
NADP+
Pq
NADP+
reductase
Cytochrome
complex
NADPH
Pc
Photosystem II
(PS II)
ATP
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Photosystem I
(PS I)
Figure 10.16 Comparison of chemiosmosis in
mitochondria and chloroplasts
Key
Higher [H+]
Lower [H+]
Chloroplast
Mitochondrion
CHLOROPLAST
STRUCTURE
MITOCHONDRION
STRUCTURE
H+
Diffusion
Thylakoid
space
Intermembrance
space
Membrance
Electron
transport
chain
ATP
Synthase
Matrix
Stroma
ADP+ P
H+
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ATP
Figure 10.17 The light reactions and chemiosmosis:
the organization of the thylakoid membrane
H2O
CO2
LIGHT
NADP+
ADP
CALVIN
CYCLE
LIGHT
REACTOR
ATP
NADPH
STROMA
(Low H+ concentration)
O2
[CH2O] (sugar)
Photosystem II
Cytochrome
complex
Photosystem I
NADP+
reductase
Light
2 H+
3
NADP+ + 2H+
Fd
NADPH
+ H+
Pq
Pc
2
H2O
THYLAKOID SPACE
(High H+ concentration)
1⁄
2
1
O2
+2 H+
2 H+
To
Calvin
cycle
STROMA
(Low H+ concentration)
Thylakoid
membrane
ATP
synthase
ADP
ATP
P
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H+
Figure 10.18 The Calvin cycle
H2 O
CO2
Input
3 (Entering one
CO2 at a time)
Light
NADP+
ADP
CALVIN
CYCLE
LIGHT
REACTIONS
ATP
Phase 1: Carbon fixation
NADPH
Rubisco
O2
[CH2O] (sugar)
3 P
P
Short-lived
intermediate
3 P
6
P
Ribulose bisphosphate
(RuBP)
P
3-Phosphoglycerate
6
6 ADP
CALVIN
CYCLE
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ATP
Figure 10.18 The Calvin cycle
H2 O
CO2
Light
Input
3 (Entering one
CO2 at a time)
NADP+
ADP
CALVIN
CYCLE
LIGHT
REACTIONS
ATP
Phase 1: Carbon fixation
NADPH
O2
Rubisco
[CH2O] (sugar)
3 P
P
Short-lived
intermediate
3 P
P
Ribulose bisphosphate
(RuBP)
P
6
3-Phosphoglycerate
6
ATP
6 ADP
CALVIN
CYCLE
6 P
P
1,3-Bisphosphoglycerate
6 NADPH
6 NADP+
6 P
6
P
Glyceraldehyde-3-phosphate
(G3P)
P
1
G3P
(a sugar)
Output
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i
Glucose and
other organic
compounds
Phase 2:
Reduction
Figure 10.18 The Calvin cycle
CO2
H2 O
Input
3 (Entering one
CO2 at a time)
Light
NADP+
ADP
CALVIN
CYCLE
LIGHT
REACTIONS
ATP
Phase 1: Carbon fixation
NADPH
Rubisco
O2
[CH2O] (sugar)
3 P
P
Short-lived
intermediate
3 P
P
6
P
Ribulose bisphosphate
(RuBP)
3-Phosphoglycerate
6
ATP
6 ADP
CALVIN
CYCLE
3 ADP
3
6 P
ATP
P
1,3-Bisphosphoglycerate
6 NADPH
Phase 3:
Regeneration of
the CO2 acceptor
(RuBP)
6 NADP+
6 P
5
i
P
G3P
6
P
Glyceraldehyde-3-phosphate
(G3P)
1
P
G3P
(a sugar)
Output
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Glucose and
other organic
compounds
Phase 2:
Reduction
Figure 10.19 C4 leaf anatomy and the C4 pathway
Mesophyll
cell
Mesophyll cell
Photosynthetic
cells of C4 plant
leaf
CO
CO
2 2
PEP carboxylase
Bundlesheath
cell
PEP (3 C)
ADP
Oxaloacetate (4 C)
Vein
(vascular tissue)
Malate (4 C)
ATP
C4 leaf anatomy
BundleSheath
cell
Pyruate (3 C)
CO2
Stoma
CALVIN
CYCLE
Sugar
Vascular
tissue
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Figure 10.20 C4 and CAM photosynthesis
compared
Pineapple
Sugarcane
C4
Mesophyll Cell
Organic acid
Bundlesheath
cell
(a) Spatial separation
of steps. In C4
plants, carbon fixation
and the Calvin cycle
occur in different
types of cells.
CAM
CO2
CO2
CALVIN
CYCLE
CO2
1 CO2 incorporated Organic acid
into four-carbon
organic acids
(carbon fixation)
2 Organic acids
release CO2 to
Calvin cycle
Sugar
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CALVIN
CYCLE
Sugar
Night
Day
(b) Temporal separation
of steps. In CAM
plants, carbon fixation
and the Calvin cycle
occur in the same cells
at different times.
Figure 10.21 A review of photosynthesis
Light reactions
Calvin cycle
H2O
CO2
Light
NADP+
ADP
+P1
RuBP
3-Phosphoglycerate
Photosystem II
Electron transport chain
Photosystem I
ATP
NADPH
G3P
Starch
(storage)
Amino acids
Fatty acids
Chloroplast
O2
Light reactions:
• Are carried out by molecules in the
thylakoid membranes
• Convert light energy to the chemical
energy of ATP and NADPH
• Split H2O and release O2 to the
atmosphere
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Sucrose (export)
Calvin cycle reactions:
• Take place in the stroma
• Use ATP and NADPH to convert
CO2 to the sugar G3P
• Return ADP, inorganic phosphate, and
NADP+ to the light reactions