Download - Photosynthesis: Using Light to Make Food
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Lectures by Chris C. Romero, updated by Edward J. Zalisko
PowerPoint® Lectures forCampbell Essential Biology, Fourth Edition – Eric Simon, Jane Reece, and Jean DickeyCampbell Essential Biology with Physiology, Third Edition – Eric Simon, Jane Reece, and Jean Dickey
Chapter 7Chapter 70
Photosynthesis: Using Light to Make Food
Biology and Society: Green Energy• Wood has historically been the main fuel used to:
– Cook
– Warm homes
– Provide light at night
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Figure 7.0
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• Industrialized societies replaced wood with fossil fuels.
• To limit the damaging effects of fossil fuels, researchers are investigating the use of biomass (living material) as efficient and renewable energy sources.
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• Fast-growing trees, such as willows:
– Can be cut every three years
– Do not need to be replanted
– Are a renewable energy source
– Produce fewer sulfur compounds
– Reduce erosion
– Provide habitat for wildlife
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THE BASICS OF PHOTOSYNTHESIS• Photosynthesis:
– Is used by plants, some protists, and some bacteria
– Transforms light energy into chemical energy
– Uses carbon dioxide and water as starting materials
• The chemical energy produced via photosynthesis is stored in the bonds of sugar molecules.
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• Organisms that use photosynthesis are:
– Photosynthetic autotrophs
– The producers for most ecosystems
Plants(mostly on land)
Photosynthetic Protists(aquatic)
PHOTOSYNTHETIC AUTOTROPHS
Photosynthetic Bacteria(aquatic)
Micrograph of cyanobacteriaKelp, a large algaForest plants
LM
Figure 7.1
Plants(mostly on land)
Forest plantsFigure 7.1a
Photosynthetic Protists(aquatic)
Kelp, a large algaFigure 7.1b
Photosynthetic Bacteria(aquatic)
Micrograph of cyanobacteria
LM
Figure 7.1c
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Chloroplasts: Sites of Photosynthesis• Chloroplasts are:
– The site of photosynthesis
– Found mostly in the interior cells of leaves
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• Inside chloroplasts are membranous sacs called thylakoids, which are suspended in a thick fluid, called stroma.
• Thylakoids are concentrated in stacks called grana.
• The green color of chloroplasts is from chlorophyll, a light-absorbing pigment.
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• Stomata are tiny pores in leaves where carbon dioxide enters and oxygen exits.
Leaf cross section
Stomata
Vein
CO2 O2
Figure 7.2-1
Leaf cross section
Stomata
Vein
CO2 O2
Interior cellLM
StromaGranum Thylakoid
Chloroplast Outermembrane
Innermembrane
TEM
Figure 7.2-2
Leaf cross section
Stomata
Vein
CO2 O2
Figure 7.2a
StromaGranum Thylakoid
Chloroplast Outermembrane
Innermembrane
TEM
Figure 7.2b
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The Overall Equation for Photosynthesis• In the overall equation for photosynthesis, notice that:
– The reactants of photosynthesis are the waste products of cellular respiration.
Carbon dioxide
6 O26 CO2 6 H2O C6H12O6
Water GlucosePhoto-synthesis Oxygen gas
Light energy
Figure 7.UN1
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• In photosynthesis:
– Sunlight provides the energy
– Electrons are boosted “uphill” and added to carbon dioxide
– Sugar is produced
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• During photosynthesis, water is split into:
– Hydrogen
– Oxygen
• Hydrogen is transferred along with electrons and added to carbon dioxide to produce sugar.
• Oxygen escapes through stomata into the atmosphere.
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A Photosynthesis Road Map• Photosynthesis occurs in two stages:
– The light reactions convert solar energy to chemical energy
– The Calvin cycle uses the products of the light reactions to make sugar from carbon dioxide
Blast Animation: Photosynthesis: Light-Independent Reaction
LightH2O
O2
Chloroplast
Lightreactions
NADPH
ATP
Figure 7.3-1
LightH2O
O2
Chloroplast
Lightreactions
NADPH
ATP
Calvincycle
CO2
NADP+
ADPP
Sugar(C6H12O6)
Figure 7.3-2
THE LIGHT REACTIONS: CONVERTING SOLAR ENERGY TO CHEMICAL ENERGY• Chloroplasts:
– Are chemical factories powered by the sun
– Convert solar energy into chemical energy
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The Nature of Sunlight• Sunlight is a type of energy called radiation, or electromagnetic
energy.
• The full range of radiation is called the electromagnetic spectrum.
Visible light
Wavelength (nm)
Radiowaves
380 400 500 600 750700
Wavelength = 580 nm
Micro-waves
Gammarays
InfraredUVX-rays
10–5 nm 10–3 nm 103 nm1 nm 106 nm 1 m 103 m
Increasing wavelength
Figure 7.4
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
– Used a prism to create a spectrum of light shining on the slide
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• Results: Bacteria:
– Mostly congregated around algae exposed to red-orange and blue-violet light
– Rarely moved to areas of green light
• Conclusion: Chloroplasts absorb light mainly in the blue-violet and red-orange part of the spectrum.
Animation: Light and Pigments
Bacterium
Wavelength of light (nm)400 500 600 700
Light
Num
ber o
f bac
teria
Algal cells
Prism
Microscope slide
Figure 7.5
Light
Chloroplast
Reflectedlight
Absorbedlight Transmitted
light
Figure 7.6
Light
Chloroplast
Reflectedlight
Absorbedlight
Transmittedlight
Figure 7.6a
Figure 7.6b
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Chloroplast Pigments• Chloroplasts contain several pigments:
– Chlorophyll a:
– Absorbs mostly blue-violet and red light
– Participates directly in the light reactions
– Chlorophyll b:
– Absorbs mostly blue and orange light
– Participates indirectly in the light reactions
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– Carotenoids:
– Absorb mainly blue-green light
– Participate indirectly in the light reactions
– 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.
Figure 7.7
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How Photosystems Harvest Light Energy• Light behaves as photons, discrete packets of energy.
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• 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.
Light
(b) Fluorescenceof a glow stick
Photon
HeatLight (fluorescence)
Ground stateChlorophyllmolecule
Excited statee–
(a) Absorptionof a photon
Figure 7.8
Light
Photon
Heat
Light (fluorescence)
Ground stateChlorophyllmolecule
Excited state
e–
(a) Absorption of a photonFigure 7.8a
(b) Fluorescence of a glow stickFigure 7.8b
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• A photosystem is a group of chlorophyll and other molecules that function as a light-gathering antenna.
Chloroplast
Figure 7.9-1
Chloroplast
Thylakoidmembrane
Pigment molecules
Figure 7.9-2
Chloroplast
Thylakoidmembrane
Pigment molecules
Antenna pigmentmolecules
PrimaryelectronacceptorReaction-centerchlorophyll a
Photon
Electrontransfer
Reactioncenter
PhotosystemTransfer of energy
Figure 7.9-3
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How the Light Reactions Generate ATP and NADPH
• Two types of photosystems cooperate in the light reactions:
– The water-splitting photosystem
– The NADPH-producing photosystem
Primaryelectronacceptor
Water-splittingphotosystem
Light
H2O
2 H
Reaction-centerchlorophyll
2e–
2e–
O2++ 12
Figure 7.10-1
Primaryelectronacceptor
Water-splittingphotosystem
Light
H2O
2 H
Reaction-centerchlorophyll
2e–
2e–
O2++
Electron transport chain
Energyto make ATP
12
Figure 7.10-2
Primaryelectronacceptor
Water-splittingphotosystem
Light
H2O
2 H
Reaction-centerchlorophyll
2e–
2e–
O2++
Electron transport chain
Energyto make ATP
Primaryelectronacceptor
2e–
Light
NADPH-producingphotosystem
Reaction-centerchlorophyll
2e–
NADPH
NADP+
12
Figure 7.10-3
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• The light reactions are located in the thylakoid membrane.
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• An electron transport chain:
– Connects the two photosystems
– Releases energy that the chloroplast uses to make ATP
Light
H2O
Thylakoidmembrane
2e–
O2
ATP
NADP+
Light
Stroma
Inside thylakoid
Photosystem PhotosystemElectron transport chain
NADPH
ADP + P
H+
ATPsynthase
To Calvin cycle
H+
Electron flow
H+H+
H+
H+
H+
12
Figure 7.11
Light
H2O
Thylakoidmembrane
2e–
O2
ATP
NADP+
Light
Stroma
Inside thylakoid
Photosystem PhotosystemElectron transport chain
NADPH
ADP + P
ATPsynthase
To Calvin cycle
Electron flow
H+
12
H+H+
H+
H+ H+
H+
Figure 7.11a
Water-splittingphotosystem
e–
Phot
on
ATP
NADPH
e–
e–
e–
e–e–
Phot
on
e–
NADPH-producingphotosystem
Figure 7.12
THE CALVIN CYCLE: MAKING SUGAR FROM CARBON DIOXIDE
• The Calvin cycle:
– Functions like a sugar factory within the stroma of a chloroplast
– Regenerates the starting material with each turn
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Calvincycle
P P
P
Three-carbon moleculeRuBP sugar
CO2 (from air)
Figure 7.13-1
ATP
NADPH
Calvincycle
ADP + P
NADP+
P
P P
P
G3P sugar
Three-carbon moleculeRuBP sugar
CO2 (from air)
Figure 7.13-2
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)
Figure 7.13-3
ATP
NADPH
Calvincycle
ADP + P
NADP+
P
P
P
P P
P
ADP + P
ATP
G3P sugar
Three-carbon molecule
G3P sugar
G3P sugar
RuBP sugar
CO2 (from air)
Glucose (and other organic compounds)
Figure 7.13-4
Evolution Connection:Solar-Driven Evolution• C3 plants:
– Use CO2 directly from the air
– Are very common and widely distributed
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• C4 plants:
– Close their stomata to save water during hot and dry weather
– Can still carry out photosynthesis
• CAM plants:
– Are adapted to very dry climates
– Open their stomata only at night to conserve water
Sugar
C4 Pathway(example: sugarcane)
C4 plant CAM plantSugar
Calvincycle
Calvincycle
Day
Celltype 1
Four-carboncompound
Night
Four-carboncompound
Celltype 2
CAM Pathway(example: pineapple)
ALTERNATIVE PHOTOSYNTHETIC PATHWAYS
CO2 CO2
CO2 CO2
Figure 7.14
Sugar
C4 Pathway(example: sugarcane)
C4 plant
Calvincycle
Celltype 1
Four-carboncompound
Celltype 2
CO2
CO2
Figure 7.14a
CAM plantSugar
Calvincycle
Day
Four-carboncompound
Night
CAM Pathway(example: pineapple)
CO2
CO2
Figure 7.14b
Carbon dioxide
6 O26 CO2 6 H2O C6H12O6
Water GlucosePhoto-synthesis Oxygen gas
Light energy
Figure 7.UN1
Light reactions
CO2
O2
H2O
(C6H12O6)
NADPH
Light
Sugar
ATP
ADPP
NADP+
Calvin cycle
Figure 7.UN2
Light reactions
CO2
O2
H2O
(C6H12O6)
NADPH
Light
Sugar
ATP
ADPP
NADP+
Calvin cycle
Figure 7.UN3
Carbon dioxide
6 O26 CO2 6 H2O C6H12O6
Water GlucosePhotosynthesis
Oxygen gas
Light energy
Figure 7.UN4
Light H2O
O2
Chloroplast
Lightreactions
NADPH
ATP
Calvincycle
CO2
NADP+
ADPP
Sugar
(C6H12O6)
Stack ofthylakoids Stroma
Figure 7.UN5
acceptor
Water-splittingphotosystem
Photon
H2O
2 H
Chlorophyll
2e–
O2++
Electron transport chain
ATP
NADPH-producingphotosystem
Chlorophyll
NADPH
NADP+
e–
2e–
2e–
2e–
e–acceptorADP
Photon
21
Figure 7.UN6
NADPH
Calvincycle
ADP P
NADP+
P
ATP
G3P
CO2
Glucose andother compounds
Figure 7.UN7