Copyright 2005 Pearson Education, Inc. publishing as Benjamin Cummings
PowerPoint Lectures forBiology, Seventh Edition
Neil Campbell and Jane Reece
Lectures by Chris Romero
Chapter 10Chapter 10
Photosynthesis
Copyright 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Photosynthesis
Occurs in plants, algae, certain other protists,and some prokaryotes
These organisms use light energy to drive thesynthesis of organic molecules from carbon dioxideand (in most cases) water. They feed not onlythemselves, but the entire living world. (a) Onland, plants are the predominant producers offood. In aquatic environments, photosyntheticorganisms include (b) multicellular algae, suchas this kelp; (c) some unicellular protists, suchas Euglena; (d) the prokaryotes calledcyanobacteria; and (e) other photosyntheticprokaryotes, such as these purple sulfurbacteria, which produce sulfur (sphericalglobules) (c, d, e: LMs).
(a) Plants
(b) Multicellular algae
(c) Unicellular protist 10 m
40 m(d) Cyanobacteria
1.5 m(e) Pruple sulfurbacteria
Figure 10.2
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Chloroplasts: The Sites of Photosynthesis in Plants
Vein
Leaf cross section
Figure 10.3
Mesophyll
CO2 O2Stomata
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Chloroplast
Mesophyll
5 m
Outermembrane
Intermembranespace
Innermembrane
Thylakoidspace
ThylakoidGranumStroma
1 m
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Tracking Atoms Through Photosynthesis:Scientific Inquiry Photosynthesis is summarized as
6 CO2 + 6 H2O + Light energy C6H12O6 + 6 O2
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The Splitting of Water Chloroplasts split water into
Hydrogen and oxygen, incorporating theelectrons of hydrogen into sugar molecules
6 CO2 12 H2OReactants:
Products: C6H12O66
H2O6
O2
Figure 10.4
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The Two Stages of Photosynthesis: A Preview Photosynthesis consists of two processes
The light reactions
The Calvin cycle
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An overview of photosynthesis
H2O CO2
Light
LIGHTREACTIONS
CALVINCYCLE
Chloroplast
[CH2O](sugar)
NADPH
NADP
ADP+ P
O2Figure 10.5
ATP
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Concept 10.2: The light reactions convert solarenergy to the chemical energy of ATP andNADPH
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The electromagnetic spectrum
Is the entire range of electromagnetic energy, orradiation
Gammarays X-rays UV Infrared
Micro-waves
Radiowaves
105 nm 103 nm 1 nm 103 nm 106 nm1 m
106 nm 103 m
380 450 500 550 600 650 700 750 nm
Visible light
Shorter wavelength
Higher energy
Longer wavelength
Lower energyFigure 10.6
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Reflect light, which include the colors we see
Light
ReflectedLight
Chloroplast
Absorbedlight
Granum
Transmittedlight
Figure 10.7
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The absorption spectra of three types of pigmentsin chloroplasts
Three different experiments helped reveal which wavelengths of light are photosyntheticallyimportant. The results are shown below.
EXPERIMENT
RESULTS
Abs
orpt
ion
of li
ght b
ych
loro
plas
t pig
men
tsChlorophyll a
(a) Absorption spectra. The three curves show the wavelengths of light best absorbed bythree types of chloroplast pigments.
Wavelength of light (nm)
Chlorophyll b
Carotenoids
Figure 10.9
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The action spectrum for photosynthesis
Was first demonstrated by Theodor W. Engelmann
400 500 600 700
Aerobic bacteria
Filamentof alga
Engelmanns experiment. In 1883, Theodor W. Engelmann illuminated a filamentous alga with light that hadbeen passed through a prism, exposing different segments of the alga to different wavelengths. He used aerobicbacteria, which concentrate near an oxygen source, to determine which segments of the alga were releasing themost 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.
(c)
Light in the violet-blue and red portions of the spectrum are most effective in drivingphotosynthesis.CONCLUSION
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Excitation of Chlorophyll by Light When a pigment absorbs light
It goes from a ground state to an excited state,which is unstable
Excitedstate
Heat
Photon(fluorescence)
Chlorophyllmolecule
GroundstatePhoton
e
Figure 10.11 A
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A photosystem
Primary electionacceptor
Photon
Thylakoid
Light-harvestingcomplexes
Reactioncenter
Photosystem
STROMATh
ylak
oid
mem
bran
e
Transferof energy
Specialchlorophyll amolecules
Pigmentmolecules
THYLAKOID SPACE(INTERIOR OF THYLAKOID)Figure 10.12
e
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Produces NADPH, ATP, and oxygen
Figure 10.13 Photosystem II(PS II)Photosystem-I
(PS I)
ATP
NADPH
NADP+
ADPCALVINCYCLE
CO2H2O
O2 [CH2O] (sugar)
LIGHTREACTIONS
Light
Primaryacceptor
Pq
Cytochromecomplex
PC
e
P680
e
e
O2+
H2O2 H+
Light
ATP
Primaryacceptor
Fd
ee
NADP+reductase
P700
Light
NADPH
NADP++ 2 H+
+ H+
1
5
7
2
3
4
6
8
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A mechanical analogy for the light reactions
MillmakesATP
ATP
e
ee
e
e
Photosystem II Photosystem I
e
e
NADPH
Figure 10.14
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The light reactions and chemiosmosis: theorganization of the thylakoid membrane
LIGHTREACTOR
NADP+ADP
ATP
NADPH
CALVINCYCLE
[CH2O] (sugar)STROMA(Low H+ concentration) Photosystem II
LIGHTH2O CO2
Cytochromecomplex
O2
H2O O21
12
2
Photosystem ILight
THYLAKOID SPACE(High H+ concentration)
STROMA(Low H+ concentration)
Thylakoidmembrane
ATPsynthase
PqPc
Fd
NADP+reductase
NADPH + H+
NADP+ + 2H+
ToCalvincycle
ADP
PATP
3
H+
2 H++2 H+
2 H+
Figure 10.17
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Key
Higher [H+]Lower [H+]
Mitochondrion Chloroplast
MITOCHONDRIONSTRUCTURE
Intermembrancespace
Membrance
Matrix
Electrontransport
chain
H+ DiffusionThylakoidspace
Stroma
ATPH+
PADP+
ATPSynthase
CHLOROPLASTSTRUCTURE
Figure 10.16
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Cyclic Electron Flow Under certain conditions
Photoexcited electrons take an alternative path
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In cyclic electron flow
Only photosystem I is used
Only ATP is produced
Primaryacceptor
Pq
Fd
Cytochromecomplex
Pc
Primaryacceptor
Fd
NADP+reductase
NADPH
ATPFigure 10.15 Photosystem II
Photosystem I
NADP+
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Objective: You will be able to discuss how theenergy from the light reactions helps build acarbohydrate in the Calvin cycle.
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The Calvin cycle has three phases
Carbon fixation
Reduction
Regeneration of the CO2 acceptor
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The Calvin cycle
(G3P)
Input(Entering one
at a time)CO23
Rubisco
Short-livedintermediate
3 P P
3 P PRibulose bisphosphate
(RuBP)
P
3-Phosphoglycerate
P6 P
6
1,3-Bisphoglycerate6 NADPH
6 NADPH+
6 P
P6
Glyceraldehyde-3-phosphate(G3P)
6 ATP
3 ATP
3 ADP CALVINCYCLE
P5
P1G3P
(a sugar)Output
LightH2O CO2
LIGHTREACTION
ATP
NADPH
NADP+ADP
[CH2O] (sugar)
CALVINCYCLE
Figure 10.18
O2
6 ADP
Glucose andother organiccompounds
Phase 1: Carbon fixation
Phase 2:Reduction
Phase 3:Regeneration ofthe CO2 acceptor(RuBP)
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Objective: You will be able to differentiatebetween photorespiration adaptations.
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Photorespiration: An Evolutionary Relic? In photorespiration
O2 substitutes for CO2 in the active site of theenzyme rubisco
The photosynthetic rate is reduced
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C4 leaf anatomy and the C4 pathway
CO2Mesophyll cell
Bundle-sheathcell
Vein(vascular tissue)
Photosyntheticcells of C4 plantleaf
Stoma
Mesophyllcell
C4 leaf anatomy
PEP carboxylase
Oxaloacetate (4 C) PEP (3 C)
Malate (4 C)
ADP
ATP
Bundle-Sheathcell CO2
Pyruate (3 C)
CALVINCYCLE
Sugar
Vasculartissue
Figure 10.19
CO2
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The CAM pathway
Spatial separationof steps. In C4plants, carbon fixationand the Calvin cycleoccur in differenttypes of cells.
(a) Temporal separationof steps. In CAMplants, carbon fixationand the Calvin cycleoccur in the same cellsat different times.
(b)
PineappleSugarcane
Bundle-sheathcell
Mesophyll Cell
Organic acid
CALVINCYCLE
Sugar
CO2 CO2
Organic acid
CALVINCYCLE
Sugar
C4 CAM
CO2 incorporatedinto four-carbonorganic acids(carbon fixation)
Night
Day
1
2 Organic acidsrelease CO2 toCalvin cycle
Figure 10.20
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The Importance of Photosynthesis: A Review A review of photosynthesis
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
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
O2
CO2H2O
Light
Light reaction Calvin cycle
NADP+ADP
ATP
NADPH
+ P 1RuBP 3-Phosphoglycerate
Amino acidsFatty acids
Starch(storage)
Sucrose (export)
G3P
Photosystem IIElectron transport chain
Photosystem I
Chloroplast
Figure 10.21