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PowerLecture:PowerLecture:Chapter 7Chapter 7
Where It Starts - PhotosynthesisWhere It Starts - Photosynthesis
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Section 7.0 : ASU Center for the Study of Early Events in Photosynthesis
Section 7.0 : When Did Photosynthesis Emerge on Earth?
David Des Marais, Science, Sept. 8, 2000.
How Would You Vote?How Would You Vote?The following is the question for this chapter. See The following is the question for this chapter. See
the "Polls and ArtJoinIn" for this chapter if your the "Polls and ArtJoinIn" for this chapter if your campus uses a Personal Response System,or campus uses a Personal Response System,or have your students vote online. See national have your students vote online. See national results below.results below.
Should public funds be used to find potentiShould public funds be used to find potentially life supporting planets too far away for ally life supporting planets too far away for us to visit?us to visit?
Plants are Plants are autotrophsautotrophs, or self-nourishing organisms, or self-nourishing organisms
The first autotrophs filled Earth’s atmosphere with oxygen, creating The first autotrophs filled Earth’s atmosphere with oxygen, creating an ozone (Oan ozone (O33) layer) layer
The ozone layer became a shield against deadly UV rays from the The ozone layer became a shield against deadly UV rays from the sun, allowing life to move out of the oceansun, allowing life to move out of the ocean
Impacts, Issues: Impacts, Issues: Sunlight and Sunlight and SurvivalSurvival
Fig. 7-1, p.106
Sunlight and SurvivalSunlight and Survival
p.107
Sunlight and SurvivalSunlight and Survival
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Section 7.1: Chemistry of Autumn Colors
Section 7.1: Molecule of the Month—Chlorophyll
Section 7.1: Foliage Afire: Why Leaves Change Colors. Esther McGuire. New York State Conservationist, Oct. 1998.
Section 7.1: Photochemistry of Chlorophyll. Bulletin of the South Carolina Academy of Science, 2002.
Electromagnetic Spectrum Electromagnetic Spectrum
Shortest Shortest Gamma raysGamma rays
wavelength wavelength X-raysX-rays
UV radiationUV radiation
Visible lightVisible light
Infrared radiationInfrared radiation
MicrowavesMicrowaves
LongestLongest Radio wavesRadio waves
wavelengthwavelength
PhotonsPhotons
Packets of light energyPackets of light energy
Each type of photon has fixed amount of Each type of photon has fixed amount of energyenergy
Photons having most energy travel as Photons having most energy travel as shortest wavelength (blue-violet light)shortest wavelength (blue-violet light)
Visible Light Visible Light
Wavelengths humans perceive as different Wavelengths humans perceive as different colorscolors
Violet (380 nm) to red (750 nm) Violet (380 nm) to red (750 nm) Longer wavelengths, lower energyLonger wavelengths, lower energy
Figure 7-2Page 108
shortest wavelengths
(most energetic)
range of most radiationreaching Earth’s surface
gamma rays
range of heat escapingfrom Earth’s surface
longest wavelengths
(lowest energy)x
raysultravioletradiation
near-infraredradiation
infraredradiation microwaves radio
waves
VISIBLE LIGHT
Wavelengths of light (nanometers)
Fig. 7-2, p.108
Visible Light Visible Light
400 450 500 550 600 650 700
Visible Light Visible Light
Wavelengths of light
PigmentsPigments
Color you see is the wavelengths not Color you see is the wavelengths not absorbed absorbed
Light-catching part of molecule often has Light-catching part of molecule often has alternating single and double bondsalternating single and double bonds
These bonds contain electrons that are These bonds contain electrons that are capable of being moved to higher energy capable of being moved to higher energy levels by absorbing light levels by absorbing light
Variety of Pigments Variety of Pigments
Chlorophylls Chlorophylls aa and and bb
CarotenoidsCarotenoids
AnthocyaninsAnthocyanins
PhycobilinsPhycobilins
ChlorophyllsChlorophyllsW
avel
eng
th a
bso
rpti
on
(%
)
Wavelength (nanometers)
chlorophyll b
chlorophyll a
Main pigments in most photoautotrophsMain pigments in most photoautotrophs
Accessory PigmentsAccessory Pigmentsp
erce
nt
of
wav
elen
gth
s ab
sorb
ed
wavelengths (nanometers)
beta-carotenephycoerythrin (a phycobilin)
Carotenoids, Phycobilins, Anthocyanins
Fig. 7-3a, p.109
PigmentsPigments
Fig. 7-3b, p.109
PigmentsPigments
Fig. 7-3c, p.109
PigmentsPigments
Fig. 7-3d, p.109
PigmentsPigments
Fig. 7-3e, p.109
PigmentsPigments
Pigments in PhotosynthesisPigments in Photosynthesis
BacteriaBacteria Pigments in plasma membranesPigments in plasma membranes
PlantsPlants Pigments and proteins organized into Pigments and proteins organized into
photosystems that are embedded in thylakoid photosystems that are embedded in thylakoid membrane systemmembrane system
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Section 7.2: Milestones in Photosynthesis Research
Section 7.2: Photosynthetic Pigments in Bacteria and Plants
Section 7.2: Sunlight at Southall Green. Norman & Elaine Beale. Perspectives in Biology and Medicine, Summer 2001.
Section 7.2: Photosynthesis and Respiration in a Jar. Joseph Buttner. Science Activities, Summer 2000.
T.E. Englemann’s Experiment T.E. Englemann’s Experiment
Background Background Certain bacterial cells will move Certain bacterial cells will move
toward places where oxygen concentration toward places where oxygen concentration is highis high
Photosynthesis produces oxygenPhotosynthesis produces oxygen
T.E. Englemann’s ExperimentT.E. Englemann’s Experiment
Fig. 7-4a, p.110
T.E. Englemann’s ExperimentT.E. Englemann’s Experiment
Fig. 7-4c, p.110
T.E. Englemann’s ExperimentT.E. Englemann’s Experiment
Fig. 7-5, p.110
T.E. Englemann’s ExperimentT.E. Englemann’s Experiment
Englemann’s Experiment
T.E. Englemann’s ExperimentT.E. Englemann’s Experiment
Linked ProcessesLinked Processes
PhotosynthesisPhotosynthesis
Energy-storing Energy-storing pathway pathway
Releases oxygenReleases oxygen
Requires carbon Requires carbon dioxidedioxide
Aerobic RespirationAerobic Respiration
Energy-releasing Energy-releasing pathwaypathway
Requires oxygenRequires oxygen
Releases carbon Releases carbon dioxidedioxide
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Section 7.3: MIT Biology Hypertextbook—Physics of Photosynthesis
Chloroplast StructureChloroplast Structure
two outer membranes
inner membrane system(thylakoids connected by channels)
stroma
Fig. 7-6, p.111
Photosynthesis EquationPhotosynthesis Equation
12H2O + 6CO2 6O2 + C2H12O6 + 6H2O
Water Carbon Dioxide
Oxygen Glucose Water
LIGHT ENERGY
In-text figurePage 111
Fig. 7-6a, p.111
PhotosynthesisPhotosynthesis
(see next slide)
leaf’s upper epidermis photosynthetic cells
Fig. 7-6a, p.111
vein stoma (gap) across lower leaf epidermis
PhotosynthesisPhotosynthesis
stroma
thylakoid compartment
thylakoid membrane system inside stroma
Fig. 7-6b, p.111
two outer membranes
PhotosynthesisPhotosynthesis
CO2H2O
SUNLIGHT
Fig. 7-6c, p.111
O2
light-dependant reactions
light-independant
reactions
sugars
CHLOROPLAST
NADPH, ATP
NADP+, ADP
PhotosynthesisPhotosynthesis
Sites of Photosynthesis
Photosynthesis EquationPhotosynthesis Equation
Where Atoms End UpWhere Atoms End Up
Products 6O2 C6H12O6 6H2O
Reactants 12H2O 6CO2
Two Stages of PhotosynthesisTwo Stages of Photosynthesis
sunlight water uptake carbon dioxide uptake
ATP
ADP + Pi
NADPH
NADP+
glucoseP
oxygen release
LIGHT-INDEPENDENT
REACTIONS
LIGHT-DEPENDENT REACTIONS
new water
Arrangement of PhotosystemsArrangement of Photosystems
water-splitting complex thylakoidcompartment
H2O 2H + 1/2O2
P680
acceptor
P700
acceptor
pool of electron carriers stromaPHOTOSYSTEM II
PHOTOSYSTEM I
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Section 7.4: Photosynthetic Antennas and Reaction Centers
Section 7.4: The Amazing All-Natural Light Machine (light-harvesting molecule LH2). Mark Caldwell.
scover, Dec. 1995.
Pigments absorb light energy, give up ePigments absorb light energy, give up e--, , which enter electron transfer chainswhich enter electron transfer chains
Water molecules split, ATP and NADH Water molecules split, ATP and NADH form, and oxygen is releasedform, and oxygen is released
Pigments that gave up electrons get Pigments that gave up electrons get replacementsreplacements
Light-Dependent ReactionsLight-Dependent Reactions
Fig. 7-7, p.112
photon
Light-Harvesting Complex
Photosystem
Light-Dependent ReactionsLight-Dependent Reactions
Noncyclic pathway of electron flow
Light-Dependent ReactionsLight-Dependent Reactions
NADPH
NADP + + H+
thylakoidcompartment
thylakoidmembrane
stroma
ATPADP + Pi
H+
H+
H+H+
H+
H+
H+
H+ H+
H+
H+
PHOTOSYSTEM IsunlightPHOTOSYSTEM II
LIGHT-HARVESTING
COMPLEX
Fig. 7-8, p.113
H+
e- e-e- e-e- e-
H+
e-
O2
H2O
cross-section through a disk-shaped fold in the
thylakoid membrane
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Photosystem Function: Photosystem Function: Harvester Pigments Harvester Pigments
Most pigments in photosystem are Most pigments in photosystem are harvester pigmentsharvester pigments
When excited by light energy, these When excited by light energy, these pigments transfer energy to adjacent pigments transfer energy to adjacent pigment moleculespigment molecules
Each transfer involves energy loss Each transfer involves energy loss
Pigments in a PhotosystemPigments in a Photosystem
reaction center
Photosystem Function: Photosystem Function: Reaction Center Reaction Center
Energy is reduced to level that can be Energy is reduced to level that can be captured by molecule of chlorophyll captured by molecule of chlorophyll aa
This molecule (P700 or P680) is the This molecule (P700 or P680) is the reaction center of a photosystemreaction center of a photosystem
Reaction center accepts energy and Reaction center accepts energy and donates electron to acceptor molecule donates electron to acceptor molecule
Harvesting photo energy
Photo EnergyPhoto Energy
Electron Transfer ChainElectron Transfer Chain
Adjacent to photosystem Adjacent to photosystem Acceptor molecule donates electrons from Acceptor molecule donates electrons from
reaction centerreaction center
As electrons pass along chain, energy As electrons pass along chain, energy they release is used to produce ATP they release is used to produce ATP
Cyclic Electron FlowCyclic Electron Flow
Electrons Electrons are donated by P700 in photosystem I to are donated by P700 in photosystem I to
acceptor moleculeacceptor molecule flow through electron transfer chain and back flow through electron transfer chain and back
to P700to P700
Electron flow drives ATP formationElectron flow drives ATP formation No NADPH is formedNo NADPH is formed
Cyclic Electron FlowCyclic Electron Flow
electron acceptor
electron transfer chain
e–
e–
e–
e–
ATP
Electron flow through transfer chain sets up
conditions for ATP formation at other membrane sites.
Noncyclic Electron FlowNoncyclic Electron Flow
Two-step pathway for light absorption and Two-step pathway for light absorption and
electron excitationelectron excitation
Uses two photosystems: type I and Uses two photosystems: type I and
type II type II
Produces ATP and NADPHProduces ATP and NADPH
Involves photolysis - splitting of waterInvolves photolysis - splitting of water
Machinery of Machinery of Noncyclic Electron FlowNoncyclic Electron Flow
photolysis
H2O
NADP+ NADPH
e–
ATP
ATP SYNTHASE
PHOTOSYSTEM IPHOTOSYSTEM II ADP + Pi
e–
first electron transfer chain
second electron transfer chain
Energy ChangesEnergy ChangesP
ote
nti
al t
o t
ran
sfer
en
erg
y (v
olt
s)
H2O 1/2O2 + 2H+
(Photosystem II)
(Photosystem I)
e– e–
e–e–
secondtransfer
chain
NADPHfirst
transferchain
PHOTOSYSTEM I
p700*
photon e-
H+
Cyclic Pathway of ATP Formation
Hig
her
en
erg
y p700
Fig. 7-9a, p.114
PHOTOSYSTEM I
e-
Noncyclic Pathway of ATP and NADPH Formation
2H2O
NADPH
NADH+
p700*
p700photon
PHOTOSYSTEM II
p680*
p680
4H+ + O2
Fig. 7-9b, p.114
Energy changes in photosynthesis.
Energy ChangesEnergy Changes
Chemiosmotic Model Chemiosmotic Model of ATP Formationof ATP Formation
Electrical and HElectrical and H++ concentration gradients concentration gradients are created between thylakoid are created between thylakoid compartment and stromacompartment and stroma
HH++ flows down gradients into stroma flows down gradients into stroma through ATP synthesisthrough ATP synthesis
Flow of ions drives formation of ATPFlow of ions drives formation of ATP
Chemiosmotic Model for ATP Chemiosmotic Model for ATP FormationFormation
ADP + Pi
ATP SYNTHASE
Gradients propel H+ through ATP synthases;ATP forms by phosphate-group transfer
ATP
H+ is shunted across membrane by some components of the first electron transfer chain
PHOTOSYSTEM II
H2Oe–
acceptor
Photolysis in the thylakoid compartment splits water
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Section 7.6: 1961 Nobel Prize—Melvin Calvin
Section 7.6: Biographical Memoirs—Melvin Calvin
Section 7.6: Robust Plants' Secret? Rubisco Activase! Marcia Wood. Agricultural Research, Nov. 2002.
Section 7.6: Revealing the Secrets of Old Sol's Sugar Factories. Wim Vermaas. World and I, Mar. 1998.
Synthesis part of Synthesis part of
photosynthesisphotosynthesis
Can proceed in the darkCan proceed in the dark
Take place in the stromaTake place in the stroma
Calvin-Benson cycleCalvin-Benson cycle
Light-Independent ReactionsLight-Independent Reactions
Calvin-Benson Cycle Calvin-Benson Cycle
Overall reactantsOverall reactants Carbon dioxideCarbon dioxide
ATPATP
NADPHNADPH
Overall productsOverall products GlucoseGlucose
ADPADP
NADPNADP++
Reaction pathway is cyclic and RuBP (ribulose bisphosphate) is regenerated
Calvin- Calvin- Benson Cycle Benson Cycle
CARBON FIXATION
6 CO2 (from the air)
6 6RuBP
PGA
unstable intermediate
6 ADP
6
12
12ATP
ATP
NADPH
10
12PGAL
glucoseP
PGAL2
Pi
12 ADP12 Pi
12 NADP+
12
4 Pi
PGAL
Fig. 7-10a, p.115
THESE REACTIONS PROCEED IN THE CHLOROPLAST’S
STROMA
Calvin- Benson Cycle Calvin- Benson Cycle
ATP
6 RuBP
phosphorylated glucose
10 PGAL
1 Pi
12 PGA
Calvin-Benson cycle
Fig. 7-10b, p.115
6 ADP
ATP
12 ADP +12 Pi
6CO2
NADPH
12 NADP+
12 PGAL
4 Pi
1
12
12
Calvin- Calvin- Benson Benson
Cycle Cycle
Calvin-Benson cycle
Calvin- Benson Cycle Calvin- Benson Cycle
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Section 7.7: Botany Online: Photosynthesis—C3, C4, and CAM
Section 7.7: International Society of Crassulacean Acid Metabolism Research
Section 7.7: CAM Photosynthesis: Not Just for Desert Plants. Elia Ben-Ari. BioScience, Dec. 1998.
Section 7.7: Evolution of CAM and C4 Carbon-Concentrating Mechanisms. Jon Keeley et al. International Journal of Plant Sciences, May 2003.
In Calvin-Benson cycle, the first stable In Calvin-Benson cycle, the first stable intermediate is a three-carbon PGAintermediate is a three-carbon PGA
Because the first intermediate has three Because the first intermediate has three carbons, the pathway is called the C3 carbons, the pathway is called the C3 pathwaypathway
The C3 PathwayThe C3 Pathway
Photorespiration in C3 PlantsPhotorespiration in C3 Plants
On hot, dry days stomata closeOn hot, dry days stomata close Inside leaf Inside leaf
Oxygen levels riseOxygen levels rise Carbon dioxide levels dropCarbon dioxide levels drop
Rubisco attaches RuBP to oxygen instead Rubisco attaches RuBP to oxygen instead of carbon dioxideof carbon dioxide
Only one PGAL forms instead of twoOnly one PGAL forms instead of two
Fig. 7-11a1, p.116
C3 PlantsC3 Plants
upperepidermis
palisademesophyll
spongymesophyll
lowerepidermis
stoma leaf vein air space
Basswood leaf, cross-section.
Fig. 7-11a2, p.116
C3 PlantsC3 Plants
6 PGA + 6 glycolate
6 PGAL
1 PGAL
Twelve turns of the cycle, not just six, to make one 6-carbon sugar
RuBP
Calvin-Benson Cycle
CO2
+ water
5 PGAL
Stomata closed: CO2 can’t get in; O2 can’t get out
Rubisco fixes oxygen, not carbon, in mesophyll cells in leaf
Fig. 7-11a3, p.117
C3 PlantsC3 Plants
C4 Plants C4 Plants
Carbon dioxide is fixed twiceCarbon dioxide is fixed twice In mesophyll cells, carbon dioxide is fixed to In mesophyll cells, carbon dioxide is fixed to
form four-carbon oxaloacetate form four-carbon oxaloacetate
Oxaloacetate is transferred to bundle-sheath Oxaloacetate is transferred to bundle-sheath
cellscells
Carbon dioxide is released and fixed again in Carbon dioxide is released and fixed again in
Calvin-Benson cycleCalvin-Benson cycle
Fig. 7-11b1, p.117
C4 PlantsC4 Plants
upperepidermis
mesophyllcell
bundle-sheath cell
lowerepidermis
Basswood leaf, cross-section.
Fig. 7-11b2, p.117
C4 PlantsC4 Plants
oxaloacetate
malateC4
cycle
pyruvate
CO2
12 PGAL
10 PGAL
2 PGAL
1 sugar
RuBP Calvin-Benson
Cycle
Carbon fixed in the mesophyll cell, malate diffuses into adjacent bundle-sheath cell
In bundle-sheath cell, malate gets converted to pyruvate with release of CO2,
which enters Calvin-Benson cycle
12 PGAL
PEP
Stomata closed: CO2 can’t get in; O2 can’t get out
Fig. 7-11b3, p.117
C4 C4 PlantsPlants
CAM PlantsCAM Plants
Carbon is fixed twice (in same cells)Carbon is fixed twice (in same cells) Night Night
Carbon dioxide is fixed to form organic acidsCarbon dioxide is fixed to form organic acids
DayDay Carbon dioxide is released and fixed in Carbon dioxide is released and fixed in
Calvin-Benson cycleCalvin-Benson cycle
Fig. 7-11c1, p.117
CAM PlantsCAM Plants
Fig. 7-11c2, p.117
epidermis with thick cuticle
mesophyll cell
air space
stoma
CAM CAM PlantsPlants
Stomata stay closed during day, open for CO2 uptake at night only.
C4 CYCLE
Calvin-Benson
Cycle
C4 cycle operates at night when CO2 from aerobic respiration fixed
1 sugar
CO2 that accumulated overnight used in C3 cycle during the day
Fig. 7-11c3, p.117
CAM PlantsCAM Plants
C3-C4 comparison
CAM PlantsCAM Plants
Summary of PhotosynthesisSummary of Photosynthesis
Figure 7-14Page 120
light6O2
12H2O
CALVIN-BENSON CYCLE
C6H12O6
(phosphorylated glucose)
NADPHNADP+ATPADP + Pi
PGA PGAL
RuBP
P
6CO2
end product (e.g., sucrose, starch, cellulose)
LIGHT-DEPENDENT REACTIONS
6H2O
LIGHT-INDEPENDENT REACTIONS
Summary of PhotosynthesisSummary of Photosynthesis
Photosynthesis overview
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Section 7.8: NASA’s Earth Observatory—Phytoplankton
Section 7.8: The Plankton Net
Section 7.8: A Model of Phytoplankton Blooms. Amit Huppert et al. The American Naturalist, Feb. 2002.
Section 7.8: Rust in the Wind (absence of phytoplankton in the ocean). Mary Beth Aberlin. The Sciences, March–April 1996.
Videos: CNNVideos: CNN
Ask your Thomson Sales Representative for Ask your Thomson Sales Representative for these volumes on CD or VHSthese volumes on CD or VHS
Biology, 2002, Vol. 6, Biology, 2002, Vol. 6, Algal FuelAlgal Fuel (2:00) (2:00)
PhotoautotrophsPhotoautotrophs
Carbon source is carbon dioxideCarbon source is carbon dioxide
Energy source is sunlightEnergy source is sunlight
HeterotrophsHeterotrophs
Get carbon and energy by eating autotrophs or one Get carbon and energy by eating autotrophs or one
anotheranother
Carbon and Energy SourcesCarbon and Energy Sources
Fig. 7-12, p.118
sunlight energy
Photosynthesis1. H2O is split by light energy. Its oxygen diffuses away; its electrons, hydrogen enter transfer chains with roles in ATP formation. Coenzymes pick up the electrons and hydrogen
2. ATP energy drives the synthesis of glucose from hydrogen and electrons (delivered by coenzymes), plus carbon and oxygen (from carbon dioxide).
glucose (stored energy, building blocks)
carbon dioxide,
water
oxygen
Aerobic Respiration1. Glucose is broken down completely to carbon dioxide and water. Coenzymes pick up the electrons, hydrogens.
2. The coenzymes give up the electrons and hydrogen atoms to oxygen-requiring transfer chains that have roles in forming many ATP molecules.
ATP available to drive nearly all cellular tasks
Carbon and Energy SourcesCarbon and Energy Sources
Photoautotrophs Photoautotrophs
Capture sunlight energy and use it to carry Capture sunlight energy and use it to carry out photosynthesisout photosynthesis
PlantsPlants
Some bacteriaSome bacteria
Many protistansMany protistans
NORTH AMERICA ATLANTIC OCEAN
AFRICA
SPAINWinter
Spring
Fig. 7-13, p.119
Photoautotrophs Photoautotrophs
Satellite Images Show Satellite Images Show PhotosynthesisPhotosynthesis
Photosynthetic activity in spring
Atlantic Ocean
Figure 7-13Page 119
p.120
12H2O + 6CO2 6O2 + C2H12O6 + 6H2O
Water Carbon Dioxide
Oxygen Glucose Water
light energy
enzymes
sunlight
Calvin-Benson
cycle
Light-DependentReactions
end products (e.g., sucrose, starch, cellulose)
ATP
12 PGAL
Light-Independent
Reactions
phosphorylated glucose
6H2O
6 RuBP
12H2O 6O2
NADPH NADP+
6CO2
ADP + Pi
Fig. 7-14, p.120
Fig. 7-15, p.121
Fig. 7-16a, p.121
Fig. 7-16b, p.121