chapter 7 1 biology and society:...
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© 2013 Pearson Education, Inc.Lectures by Edward J. Zalisko
PowerPoint® Lectures forCampbell Essential Biology, Fifth Edition, and
Campbell Essential Biology with Physiology,
Fourth Edition– Eric J. Simon, Jean L. Dickey, and Jane B. Reece
Chapter 7Chapter 7Photosynthesis: Using Light
to Make Food
1 Biology and Society: Biofuels
• Wood has historically been the main fuel used to
produce
– heat and
– light.
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2
Figure 7.0 3
• Industrialized societies replaced wood with fossil
fuels including
– coal,
– gas, and
– oil.
• To limit the damaging effects of fossil fuels,
researchers are investigating the use of biomass
(living material) as efficient and renewable energy
sources.
Biology and Society: Biofuels
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• There are several types of biofuels.
– Bioethanol is a type of alcohol produced by the fermentation of glucose made from starches in crops such as grains, sugar beets, and sugar cane.
– Bioethanol may be used
– directly as a fuel source in specially designed
vehicles or
– as a gasoline additive.
Biology and Society: Biofuels
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5 THE BASICS OF PHOTOSYNTHESIS
• Photosynthesis
– is used by plants, algae (protists), and some bacteria,
– transforms light energy into chemical energy, and
– uses carbon dioxide and water as starting materials.
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• The chemical energy produced via photosynthesis
is stored in the bonds of sugar molecules.
• Organisms that use photosynthesis are
– photosynthetic autotrophs and
– the producers for most ecosystems.
THE BASICS OF PHOTOSYNTHESIS
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8 Figure 7.1
Plants(mostly on land)
Photosynthetic Protists(aquatic)
PHOTOSYNTHETIC AUTOTROPHS
Photosynthetic Bacteria(aquatic)
Micrograph of cyanobacteriaKelp, a large, multicellular algaForest plants
LM
9
Chloroplasts: Sites of Photosynthesis
• Chloroplasts are
– the site of photosynthesis and
– found mostly in the interior cells of leaves.
• Inside chloroplasts are interconnected,
membranous sacs called thylakoids, which are
suspended in a thick fluid called stroma.
• Thylakoids are concentrated in stacks called grana.
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• The green color of chloroplasts is from chlorophyll, a light-
absorbing pigment that plays a central role in converting
solar energy to chemical energy.
– The green light we see is the light that is not absorbed by
these pigments
• Stomata are tiny pores in leaves where
– carbon dioxide enters and
– oxygen exits.
– Stoma is the singular form. Do not confuse with
Stroma!!!
– Stoma is the greek root for mouth. Stomach has the same root.
Chloroplasts: Sites of Photosynthesis 11
Figure 7.2-1
Leaf cross section
Stomata
Vein
CO2O2
Photosyntheticcells
12 Figure 7.2-2
Interior cell
LM
Chloroplast
Leaf cross section
Stomata
Vein
CO2O2
Photosyntheticcells
13
Figure 7.2-3
Interior cell
LM
StromaGranum
Thylakoidspace
ChloroplastInner and outermembranes
Co
lori
zed
TE
MLeaf cross section
Stomata
Vein
CO2O2
Photosyntheticcells
14 The Simplified Equation for Photosynthesis
• In the overall equation for photosynthesis, notice
that the reactants of photosynthesis are the waste
products of cellular respiration.
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Carbon dioxide
6 O26 CO2 6 H2O C6H12O6
Water GlucosePhoto-
synthesis Oxygen gas
Light energy
The Simplified Equation for Photosynthesis 16
C6H12O6 CO2 ATPO2 H2O
Glucose Oxygen Carbondioxide
Water Energy
6 66
The Simplified Equation for Cellular Respiration
17
Figure 6.2
Sunlight energyenters ecosystem
Photosynthesis
Cellular respiration
C6H12O6 CO2
drives cellular work
Heat energy exits ecosystem
ATP
O2 H2O
18
• In photosynthesis,
– sunlight provides the energy,
– electrons are boosted “uphill” and added to carbon dioxide, and
– sugar is produced.
The Simplified Equation for Photosynthesis
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• During photosynthesis, water is split into
– hydrogen and
– oxygen.
• Hydrogen is transferred along with electrons and
added to carbon dioxide to produce sugar.
• Oxygen escapes through stomata into the
atmosphere.
The Simplified Equation for Photosynthesis
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20 A Photosynthesis Road Map
• Photosynthesis occurs in two multistep stages:
1. the light reactions convert solar energy to chemical energy and
– This occurs in the thylakoid membrane
2. the Calvin cycle uses the products of the light reactions to make sugar from carbon dioxide.
– This occurs in the stroma
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A Photosynthesis Road Map
• The initial incorporation of carbon from the
atmosphere into organic compounds is called
carbon fixation.
– This lowers the amount of carbon in the air.
– Deforestation reduces the ability of the biosphere to absorb carbon by reducing the amount of photosynthetic plant life.
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BioFlix Animation: Photosynthesis
23
Figure 7.3-1
Light
H2O
O2
Chloroplast
Lightreactions
NADPH
ATP
– –
24 Figure 7.3-2
Calvincycle
CO2
NADP+
ADPP
Sugar
Light
H2O
O2
Chloroplast
Lightreactions
NADPH
ATP
++++
– –
25
THE LIGHT REACTIONS: CONVERTING SOLAR ENERGY TO CHEMICAL ENERGY
• Chloroplasts
– are chemical factories powered by the sun and
– convert sunlight into chemical energy.
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26 Figure 7-UN02
Light reactions
CO2
O2
H2O
NADPH
Light
Sugar
ATP
ADP
P
NADP++++
Calvin cycle
– –
+
27
The Nature of Sunlight
• Sunlight is a type of energy called radiation, or
electromagnetic energy.
• The distance between the crests of two adjacent
waves is called a wavelength.
• The full range of radiation is called the
electromagnetic spectrum.
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28 Figure 7.4
Visible light
Wavelength (nm)
Radiowaves
400 500 600 750700
Wavelength ====580 nm
Micro-waves
Gamma
raysInfraredUVX-rays
10–5 nm 1 nm 1 m
Increasing wavelength
380
10–3 nm 103 nm 106 nm 103 m
29
Figure 7.5
Light
Chloroplast
Absorbedlight
Transmittedlight (detectedby your eye)
Reflectedlight
30 Figure 7.5a
Light
Chloroplast
Absorbedlight
Transmittedlight (detectedby your eye)
Reflectedlight
31
Figure 7.5b 32 The Process of Science: What Colors of Light Drive Photosynthesis?
• Observation: In 1883, German biologist Theodor
Engelmann saw that certain bacteria tend to
cluster in areas with higher oxygen concentrations.
• Question: Could this information determine which
wavelengths of light work best for photosynthesis?
• Hypothesis: Oxygen-seeking bacteria will
congregate near regions of algae performing the
most photosynthesis.
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• Experiment: Engelmann
– laid a string of freshwater algal cells in a drop of water on a microscope slide,
– added oxygen-sensitive bacteria to the drop, and
– used a prism to create a spectrum of light shining on the slide.
The Process of Science: What Colors of Light Drive Photosynthesis?
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• Results: Bacteria
– mostly congregated around algae exposed to red-orange and blue-violet light and
– rarely moved to areas of green light.
• Conclusion: Chloroplasts absorb light mainly in
the blue-violet and red-orange part of the
spectrum.
The Process of Science: What Colors of Light Drive Photosynthesis?
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35
© 2013 Pearson Education, Inc.
Animation: Light and Pigments
Right click slide / select “Play”
36 Figure 7.6Light
Microscope slide
Prism
Bacteria
Algal cells
Bacteria
Wavelength of light (nm)
400 500 600 700
Nu
mb
er
of
bacte
ria
37
Chloroplast Pigments
• Chloroplasts contain several pigments:
1. Chlorophyll a
– absorbs mainly blue-violet and red light and
– participates directly in the light reactions.
2. Chlorophyll b
– absorbs mainly blue and orange light and
– participates indirectly in the light reactions.
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• Carotenoids
– absorb mainly blue-green light,
– participate indirectly in the light reactions, and
– absorb and dissipate excessive light energy that might damage chlorophyll.
• The spectacular colors of fall foliage are due partly
to the yellow-orange light reflected from
carotenoids.
Chloroplast Pigments
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Figure 7.7 40 How Photosystems Harvest Light Energy
• Light behaves as photons, a fixed quantity of light
energy.
• Chlorophyll molecules absorb photons.
– Electrons in the pigment gain energy.
– As the electrons fall back to their ground state, energy is released as heat or light.
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Figure 7.8
Light
(b) Fluorescence of a glow stick
Photon
Heat
Light (fluorescence)
Ground stateChlorophyll
molecule
Excited state
e–
(a) Absorption of a photon
The electronfalls to itsground state.
Absorption of a photon excitesan electron.
42
• In the thylakoid membrane, chlorophyll molecules
are organized with other molecules into
photosystems.
• A photosystem is a cluster of a few hundred
pigment molecules that function as a light-
gathering antenna.
How Photosystems Harvest Light Energy
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• The reaction center of the photosystem consists of chlorophyll a molecules that sit next to another molecule called a primary electron acceptor, which traps the light-excited electron from chlorophyll a.
• Another team of molecules built into the thylakoid membrane then uses that trapped energy to make
– ATP and
– NADPH.
How Photosystems Harvest Light Energy
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44 Figure 7.9
Chloroplast
Thylakoid membrane
Cluster of pigment molecules
Pigmentmolecules
Primaryelectronacceptor
Reaction-center
chlorophyll a
Electrontransfer Reaction
center
Photosystem
Transferof energy
Photon
e–
45
How the Light Reactions Generate ATP and NADPH
• Two types of photosystems cooperate in the light
reactions:
1. the water-splitting photosystem and
2. the NADPH-producing photosystem.
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46 Figure 7.10-1
Primaryelectronacceptor
Water-splittingphotosystem
Light
H2O
2 H++++
Reaction-centerchlorophyll
O2++++1
2
2e–
2e–
1
47
Figure 7.10-2
Primaryelectronacceptor
Water-splittingphotosystem
Light
H2O
2 H++++
Reaction-centerchlorophyll
O2++++
Energyto make ATP
1
2
2e–
2e–
1
2
48 Figure 7.10-3
Primaryelectronacceptor
Water-splittingphotosystem
Light
H2O
2 H++++ O2++++
Energyto make ATP
Primaryelectronacceptor
2e–
Light
NADPH-producingphotosystem
Reaction-centerchlorophyll
2e–
NADPH
NADP++++
1
2
2e–
2e–
1
2
3
– –
Reaction-centerchlorophyll
49
• The light reactions are located in the thylakoid
membrane.
• An electron transport chain
– connects the two photosystems and
– releases energy that the chloroplast uses to make ATP.
How the Light Reactions Generate ATP and NADPH
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50 Figure 7.11
Light
H2O
Thylakoidmembrane
2e–
O2
ATP
NADP++++
Light
Stroma
Inside thylakoid
Photosystem Photosystem
Electron transport chain
NADPH
ADP ++++ P
H++++
ATPsynthase
To Calvin cycle
H++++
Electron flow
H++++
H++++
H++++
H++++
H++++
1
2
Thylakoidmembrane
– –
51
Figure 7.12
Water-splittingphotosystem
ATP
NADPH
e–
NADPH-producingphotosystem
– –e–
e–
e–
e–
e–
e–
52 THE CALVIN CYCLE: MAKING SUGAR FROM CARBON DIOXIDE
• The Calvin cycle
– functions like a sugar factory within a chloroplast and
– regenerates the starting material with each turn.
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53
© 2013 Pearson Education, Inc.
Blast Animation: Photosynthesis: Light-Independent Reactions
Select “Play”
54 Figure 7-UN03
Light reactions
CO2
O2
H2O
NADPH
Light
Sugar
ATP
ADPP
NADP++++
Calvin cycle
– –
+
55
Figure 7.13-1
P P
P
Three-carbon moleculeRuBP sugar
CO2 (from air)
Calvincycle
1
56 Figure 7.13-2
ATP
NADPH
ADP ++++ P
NADP++++
P
P P
P
G3P sugar
Three-carbon moleculeRuBP sugar
CO2 (from air)
Calvincycle – –
2
1
57
Figure 7.13-3
ATP
NADPH
ADP ++++ P
NADP++++
P
P
P
P P
P
G3P sugar
Three-carbon molecule
G3P sugar
G3P sugar
RuBP sugar
CO2 (from air)
Calvincycle
Glucose (and other
organic compounds)
– –
23
1
58 Figure 7.13-4
ATP
NADPH
ADP ++++ P
NADP++++
P
P
P
P P
P
G3P sugar
Three-carbon molecule
G3P sugar
G3P sugar
RuBP sugar
CO2 (from air)
Calvincycle
Glucose (and other
organic compounds)
– –
23
1
4
ATP
ADP ++++ P
59
Evolution Connection:Solar-Driven Evolution
• C3 plants
– use CO2 directly from the air and
– are very common and widely distributed.
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• C4 plants
– close their stomata to save water during hot and dry weather and
– can still carry out photosynthesis.
• CAM plants
– are adapted to very dry climates and
– open their stomata only at night to conserve water.
Evolution Connection:Solar-Driven Evolution
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Figure 7.14
Sugar
C4 Pathway(example: sugarcane)
C4 plant CAM plant
Sugar
Calvincycle
Calvincycle
Day
Celltype 1
Four-carboncompound
Night
Four-carboncompound
Celltype 2
CAM Pathway(example: pineapple)
ALTERNATIVE PHOTOSYNTHETIC PATHWAYS
CO2 CO2
CO2CO2
62 Figure 7.14a
Sugar
C4 Pathway(example: sugarcane)
C4 plant
Calvincycle
Celltype 1
Four-carboncompound
Celltype 2
CAM plant
Sugar
Calvincycle
Day
Four-carboncompound
Night
CO2
CO2
CAM Pathway(example: pineapple)
CO2
CO2
63
Figure 7.14b
C4 Pathway(example: sugarcane)
64
CAM Pathway(example: pineapple)
Figure 7.14c 65
Figure 7-UN04
Carbon dioxide
6 O26 CO2 6 H2O C6H12O6
Water GlucosePhotosynthesis
Oxygen gas
Light energy
66 Figure 7-UN05
Light H2O
O2
Chloroplast
Lightreactions
NADPH
ATP
Calvin
cycle
CO2
NADP++++
ADP
P
Sugar
Stack ofthylakoids Stroma
– –
Sugar used for• cellular respiration• cellulose• starch• other organic compounds
67
Figure 7-UN06
acceptor
Water-splittingphotosystem
Photon
H2O
2 H++++
Chlorophyll
2e–
O2+
ATP
NADPH-producingphotosystem
Chlorophyll
NADPH
NADP++++
e–
2e–
2e–e–
acceptorADP
Photon
21
– –
2e–
68 Figure 7-UN07
NADPH
Calvincycle
ADP P
NADP++++
P
ATP
G3P
CO2
Glucose andother compounds(such as celluloseand starch)
– –
69