Chapter 8: Photosynthesis: Energy from the Sun
CHAPTER 8Photosynthesis: Energy
from the Sun
Chapter 8: Photosynthesis: Energy from the Sun
Chapter 8: Photosynthesis: Energy from the SunPhotosynthesisPhotosynthesis
Identifying Photosynthetic Reactants andIdentifying Photosynthetic Reactants and Products Products
The Two Pathways of Photosynthesis: AnThe Two Pathways of Photosynthesis: An Overview Overview
Properties of Light and PigmentsProperties of Light and Pigments
Chapter 8: Photosynthesis: Energy from the Sun
Chapter 8: Photosynthesis: Energy from the SunLight Reactions: Light AbsorptionLight Reactions: Light Absorption
Making Sugar from COMaking Sugar from CO22: The Calvin–Benson Cycle: The Calvin–Benson Cycle
Photorespiration and Its Evolutionary CoPhotorespiration and Its Evolutionary Consequencesnsequences
Metabolic Pathways in PlantsMetabolic Pathways in Plants
Chapter 8: Photosynthesis: Energy from the Sun
Photosynthesis
• Life on Earth depends on the Life on Earth depends on the absorption of light energy from the absorption of light energy from the sun.sun.
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Chapter 8: Photosynthesis: Energy from the Sun
Photosynthesis
• In plants, photosynthesis takes place In plants, photosynthesis takes place in chloroplasts.in chloroplasts.
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Chapter 8: Photosynthesis: Energy from the Sun
Identifying Photosynthetic Reactants and Products• Photosynthesizing plants take in COPhotosynthesizing plants take in CO22, ,
water, and light energy, producing Owater, and light energy, producing O22 and carbohydrate. The overall reaction and carbohydrate. The overall reaction isis
6 CO6 CO22 + 12 H + 12 H22O + light O + light C C66HH1212OO66 + 6 O + 6 O22 + + 6 H6 H22OO
The oxygen atoms in OThe oxygen atoms in O22 come from water, come from water, not from COnot from CO22. Review Figures 8.1, 8.2. Review Figures 8.1, 8.2
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Chapter 8: Photosynthesis: Energy from the Sun
Figure 8.1
Figure 8.1Figure 8.1
figure 08-01.jpg
Chapter 8: Photosynthesis: Energy from the Sun
Figure 8.2
Figure 8.2Figure 8.2
figure 08-02.jpg
Chapter 8: Photosynthesis: Energy from the Sun
The Two Pathways of Photosynthesis: An Overview• In the light reactions of In the light reactions of
photosynthesis, electron flow and photosynthesis, electron flow and photophosphorylation produce ATP photophosphorylation produce ATP and reduce NADPand reduce NADP++ to NADPH + H to NADPH + H++. .
Review Figure 8.3Review Figure 8.3
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Chapter 8: Photosynthesis: Energy from the Sun
Figure 8.3
Figure 8.3Figure 8.3
figure 08-03.jpg
Chapter 8: Photosynthesis: Energy from the Sun
The Two Pathways of Photosynthesis: An Overview • ATP and NADPH + HATP and NADPH + H++ are needed for are needed for
the reactions that fix and reduce COthe reactions that fix and reduce CO22 in the Calvin–Benson cycle, forming in the Calvin–Benson cycle, forming sugars. sugars.
Review Figure 8.3Review Figure 8.3
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Chapter 8: Photosynthesis: Energy from the Sun
Figure 8.3
Figure 8.3Figure 8.3
figure 08-03.jpg
Chapter 8: Photosynthesis: Energy from the Sun
Properties of Light and Pigments
• Light energy comes in packets called Light energy comes in packets called photons, but it also has wavelike photons, but it also has wavelike properties. properties.
Review Figure 8.4Review Figure 8.4
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Chapter 8: Photosynthesis: Energy from the Sun
Figure 8.4
Figure 8.4Figure 8.4
figure 08-04.jpg
Chapter 8: Photosynthesis: Energy from the Sun
Properties of Light and Pigments
• Pigments absorb light in the visible Pigments absorb light in the visible spectrum. spectrum.
Review Figure 8.5Review Figure 8.5
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Chapter 8: Photosynthesis: Energy from the Sun
Figure 8.5
Figure 8.5Figure 8.5
figure 08-05.jpg
Chapter 8: Photosynthesis: Energy from the Sun
Properties of Light and Pigments
• Absorption of a photon puts a pigment Absorption of a photon puts a pigment molecule in an excited state with more molecule in an excited state with more energy than its ground state. energy than its ground state.
Review Figure 8.6Review Figure 8.6
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Chapter 8: Photosynthesis: Energy from the Sun
Figure 8.6
Figure 8.6Figure 8.6
figure 08-06.jpg
Chapter 8: Photosynthesis: Energy from the Sun
Properties of Light and Pigments
• Each compound has a characteristic Each compound has a characteristic absorption spectrum which reveals the absorption spectrum which reveals the biological effectiveness of different biological effectiveness of different wavelengths of light. wavelengths of light.
Review Figures 8.7, 8.8Review Figures 8.7, 8.8
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Chapter 8: Photosynthesis: Energy from the Sun
Figure 8.7
Figure 8.7Figure 8.7
figure 08-07.jpg
Chapter 8: Photosynthesis: Energy from the Sun
Figure 8.8
Figure 8.8Figure 8.8
figure 08-08.jpg
Chapter 8: Photosynthesis: Energy from the Sun
Properties of Light and Pigments
• Chlorophylls and accessory pigments Chlorophylls and accessory pigments form antenna systems for absorption form antenna systems for absorption of light energy. of light energy.
Review Figures 8.7, 8.9, 8.11Review Figures 8.7, 8.9, 8.11
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Chapter 8: Photosynthesis: Energy from the Sun
Figure 8.9
Figure 8.9Figure 8.9
figure 08-09.jpg
Chapter 8: Photosynthesis: Energy from the Sun
Light Reactions: Light Absorption
• An excited pigment molecule may lose An excited pigment molecule may lose its energy by fluorescence, or by its energy by fluorescence, or by transferring it to another pigment transferring it to another pigment molecule. molecule.
Review Figures 8.10, 8.11Review Figures 8.10, 8.11
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Chapter 8: Photosynthesis: Energy from the Sun
Figure 8.10
Figure 8.10Figure 8.10
figure 08-10.jpg
Chapter 8: Photosynthesis: Energy from the Sun
Figure 8.11
Figure 8.11Figure 8.11
figure 08-11.jpg
Chapter 8: Photosynthesis: Energy from the Sun
Electron Flow, Photophos-phorylation, and Reductions• Noncyclic electron flow uses two photosystems: Noncyclic electron flow uses two photosystems:
• Photosystem II uses PPhotosystem II uses P680680 chlorophyll, from chlorophyll, from which light-excited electrons pass to a redox which light-excited electrons pass to a redox chain that drives chemiosmotic ATP production. chain that drives chemiosmotic ATP production. Light-driven water oxidation releases OLight-driven water oxidation releases O2,2, passing electrons to Ppassing electrons to P680680 chlorophyll. chlorophyll.
• Photosystem I passes electrons from PPhotosystem I passes electrons from P700700 chlorophyll to another redox chain and then to chlorophyll to another redox chain and then to NADPNADP++, forming NADPH + H, forming NADPH + H++. Review Figure . Review Figure 8.128.12
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Chapter 8: Photosynthesis: Energy from the Sun
Figure 8.12 – Part 1
Figure 8.12 – Part 1Figure 8.12 – Part 1
figure 08-12a.jpg
Chapter 8: Photosynthesis: Energy from the Sun
Figure 8.12 – Part 2
Figure 8.12 – Part 2Figure 8.12 – Part 2
figure 08-12b.jpg
Chapter 8: Photosynthesis: Energy from the Sun
Electron Flow, Photophos-phorylation, and Reductions • Cyclic electron flow uses PCyclic electron flow uses P700700
chlorophyll producing only ATP. chlorophyll producing only ATP.
• Its operation maintains the proper Its operation maintains the proper balance of ATP and NADPH + Hbalance of ATP and NADPH + H++ in the in the chloroplast. chloroplast.
Review Figure 8.13Review Figure 8.13
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Chapter 8: Photosynthesis: Energy from the Sun
Figure 8.13
Figure 8.13Figure 8.13
figure 08-13.jpg
Chapter 8: Photosynthesis: Energy from the Sun
Electron Flow, Photophos-phorylation, and Reductions • Chemiosmosis is the source of ATP in Chemiosmosis is the source of ATP in
photophosphorylation. photophosphorylation. • Electron transport pumps protons from Electron transport pumps protons from
stroma into thylakoids, establishing a proton-stroma into thylakoids, establishing a proton-motive force. motive force.
• Proton diffusion to stroma via ATP synthase Proton diffusion to stroma via ATP synthase channels drives ATP formation from ADP and channels drives ATP formation from ADP and PPii. .
Review Figure 8.14Review Figure 8.14
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Chapter 8: Photosynthesis: Energy from the Sun
Figure 8.14
Figure 8.14Figure 8.14
figure 08-14.jpg
Chapter 8: Photosynthesis: Energy from the Sun
Electron Flow, Photophos-phorylation, and Reductions • Photosynthesis probably originated in Photosynthesis probably originated in
anaerobic bacteria that used Hanaerobic bacteria that used H22S as a S as a source of electrons instead of Hsource of electrons instead of H22O. O.
• Oxygen production by bacteria was Oxygen production by bacteria was important in eukaryote evolution.important in eukaryote evolution.
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Chapter 8: Photosynthesis: Energy from the Sun
Light-Dependent Reactions
Chapter 8: Photosynthesis: Energy from the Sun
Photosystem II
Photosynthesis begins when Photosynthesis begins when pigments in photosystem II absorb pigments in photosystem II absorb light, increasing their energy level.light, increasing their energy level.
Chapter 8: Photosynthesis: Energy from the Sun
Photosystem II
These high-energy electrons are These high-energy electrons are passed on to the electron transport passed on to the electron transport chain.chain.
Electroncarriers
High-energy electron
Chapter 8: Photosynthesis: Energy from the Sun
Photosystem II
2H2O
Enzymes on the thylakoid Enzymes on the thylakoid membrane break water molecules membrane break water molecules into:into:
Electroncarriers
High-energy electron
Chapter 8: Photosynthesis: Energy from the Sun
Photosystem II
2H2O
hydrogen ionshydrogen ions
oxygen atomsoxygen atoms
energized electronsenergized electrons
+ O2
Electroncarriers
High-energy electron
Chapter 8: Photosynthesis: Energy from the Sun
Photosystem II
2H2O
+ O2
The energized electrons from water The energized electrons from water replace the high-energy electrons replace the high-energy electrons that chlorophyll lost to the electron that chlorophyll lost to the electron transport chain.transport chain.
High-energy electron
Chapter 8: Photosynthesis: Energy from the Sun
Photosystem II
2H2O
As plants remove electrons from As plants remove electrons from water, oxygen is left behind and is water, oxygen is left behind and is released into the air.released into the air.
+ O2
High-energy electron
Chapter 8: Photosynthesis: Energy from the Sun
Photosystem II
2H2O
The hydrogen ions left behind The hydrogen ions left behind when water is broken apart are when water is broken apart are released inside the thylakoid released inside the thylakoid membrane.membrane.
+ O2
High-energy electron
Chapter 8: Photosynthesis: Energy from the Sun
Photosystem II
2H2O
Energy from the electrons is used Energy from the electrons is used to transport Hto transport H++ ions from the ions from the stroma into the inner thylakoid stroma into the inner thylakoid space.space.
+ O2
Chapter 8: Photosynthesis: Energy from the Sun
Photosystem II
2H2O
High-energy electrons move High-energy electrons move through the electron transport through the electron transport chain from photosystem II to chain from photosystem II to photosystem I.photosystem I.
+ O2
Photosystem I
Chapter 8: Photosynthesis: Energy from the Sun
2H2O
Pigments in photosystem I use Pigments in photosystem I use energy from light to re-energize energy from light to re-energize the electrons.the electrons.
+ O2
Photosystem I
Chapter 8: Photosynthesis: Energy from the Sun
2H2O
NADPNADP++ then picks up these high- then picks up these high-energy electrons, along with Henergy electrons, along with H++ ions, and becomes NADPH.ions, and becomes NADPH.
•
+ O2
2 NADP+
2 NADPH2
Chapter 8: Photosynthesis: Energy from the Sun
2H2O
As electrons are passed from As electrons are passed from chlorophyll to NADPchlorophyll to NADP++, more H, more H++ ions are pumped across the ions are pumped across the membrane.membrane.
+ O2
2 NADP+
2 NADPH2
Chapter 8: Photosynthesis: Energy from the Sun
2H2O
Soon, the inside of the membrane fills up with Soon, the inside of the membrane fills up with positively charged hydrogen ions, which makes positively charged hydrogen ions, which makes the outside of the membrane negatively the outside of the membrane negatively charged.charged.
+ O2
2 NADP+
2 NADPH2
Chapter 8: Photosynthesis: Energy from the Sun
2H2O
The difference in charges across The difference in charges across the membrane provides the the membrane provides the energy to make ATPenergy to make ATP
+ O2
2 NADP+
2 NADPH2
Chapter 8: Photosynthesis: Energy from the Sun
2H2O
HH++ ions cannot cross the membrane ions cannot cross the membrane directly.directly.
+ O2
ATP synthase
2 NADP+
2 NADPH2
Chapter 8: Photosynthesis: Energy from the Sun
2H2O
The cell membrane contains a protein The cell membrane contains a protein called called ATP synthaseATP synthase that allows H that allows H++ ions to pass through itions to pass through it
+ O2
ATP synthase
2 NADP+
2 NADPH2
Chapter 8: Photosynthesis: Energy from the Sun
2H2O
As HAs H++ ions pass through ATP ions pass through ATP synthase, the protein rotates.synthase, the protein rotates.
+ O2
ATP synthase
2 NADP+
2 NADPH2
Chapter 8: Photosynthesis: Energy from the Sun
2H2O
As it rotates, ATP synthase binds ADP As it rotates, ATP synthase binds ADP and a phosphate group together to and a phosphate group together to produce ATP.produce ATP.
+ O2
2 NADP+
2 NADPH2
ATP synthase
ADP
Chapter 8: Photosynthesis: Energy from the Sun
2H2O
Because of this system, light-dependent Because of this system, light-dependent electron transport produces not only high-electron transport produces not only high-energy electrons but ATP as well.energy electrons but ATP as well.
+ O2
ATP synthase
ADP2 NADP+
2 NADPH2
Chapter 8: Photosynthesis: Energy from the Sun
Making Sugar from CO2: The Calvin–Benson Cycle• The Calvin–Benson cycle makes sugar The Calvin–Benson cycle makes sugar
from COfrom CO22. .
• This pathway was elucidated through This pathway was elucidated through use of radioactive tracers. use of radioactive tracers. Review Figure 8.15 Review Figure 8.15
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Chapter 8: Photosynthesis: Energy from the Sun
Figure 8.15
Figure 8.15Figure 8.15
figure 08-15.jpg
Chapter 8: Photosynthesis: Energy from the Sun
Making Sugar from CO2: The Calvin–Benson Cycle • The Calvin–Benson cycle has three The Calvin–Benson cycle has three
phases: fixation of COphases: fixation of CO22, reduction and , reduction and carbohydrate production, and carbohydrate production, and regeneration of RuBP. regeneration of RuBP.
• RuBP is the initial CORuBP is the initial CO22 acceptor, 3PG is acceptor, 3PG is the first stable product of COthe first stable product of CO22 fixation. fixation.
• Rubisco catalyzes the reaction of CORubisco catalyzes the reaction of CO22 and RuBP to form 3PG. and RuBP to form 3PG.
Review Figures 8.16, 8.17Review Figures 8.16, 8.17
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Chapter 8: Photosynthesis: Energy from the Sun
Figure 8.16
Figure 8.16Figure 8.16
figure 08-16.jpg
Chapter 8: Photosynthesis: Energy from the Sun
Figure 8.17
Figure 8.17Figure 8.17
figure 08-17.jpg
Chapter 8: Photosynthesis: Energy from the Sun
Photorespiration and Its Evolutionary Consequences• Rubisco catalyzes a reaction between Rubisco catalyzes a reaction between
OO22 and RuBP in addition to that of CO and RuBP in addition to that of CO2 2
and RuBP. and RuBP. • Photorespiration significantly reduces Photorespiration significantly reduces
photosynthesis efficiency. photosynthesis efficiency. • Reactions that constitute Reactions that constitute
photorespiration are distributed over photorespiration are distributed over chloroplast, peroxisome, and chloroplast, peroxisome, and mitochondria organelles.mitochondria organelles.
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Chapter 8: Photosynthesis: Energy from the Sun
Photorespiration and Its Evolutionary Consequences • At high temperatures and low COAt high temperatures and low CO22
concentrations, the oxygenase concentrations, the oxygenase function of rubisco is favored.function of rubisco is favored.
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Chapter 8: Photosynthesis: Energy from the Sun
Photorespiration and Its Evolutionary Consequences • CC44 plants bypass photorespiration. plants bypass photorespiration.
• PEP carboxylase in mesophyll PEP carboxylase in mesophyll chloroplasts initially fixes COchloroplasts initially fixes CO22 in four- in four-carbon acids, which diffuse into bundle carbon acids, which diffuse into bundle sheath cells, where their sheath cells, where their decarboxylation produces locally high decarboxylation produces locally high concentrations of COconcentrations of CO22. .
Review Figures 8.19Review Figures 8.19
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Chapter 8: Photosynthesis: Energy from the Sun
Figure 8.19
Figure 8.19Figure 8.19
figure 08-19.jpg
Chapter 8: Photosynthesis: Energy from the Sun
Photorespiration and Its Evolutionary Consequences • CAM plants operate much like CCAM plants operate much like C44
plants, but their initial COplants, but their initial CO22 fixation by fixation by PEP carboxylase is temporally PEP carboxylase is temporally separated from the Calvin–Benson separated from the Calvin–Benson cycle, rather than spatially separated. cycle, rather than spatially separated.
Review Figure 8.21Review Figure 8.21
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Chapter 8: Photosynthesis: Energy from the Sun
Figure 8.21
Figure 8.21Figure 8.21
figure 08-21.jpg
Chapter 8: Photosynthesis: Energy from the Sun
Metabolic Pathways in Plants• Plants respire in light and darkness, Plants respire in light and darkness,
but photosynthesize only in light. but photosynthesize only in light.
• A plant must photosynthesize more A plant must photosynthesize more than it respires, giving it a net gain of than it respires, giving it a net gain of reduced energy-rich compounds.reduced energy-rich compounds.
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Chapter 8: Photosynthesis: Energy from the Sun
Metabolic Pathways in Plants • Photosynthesis and respiration are Photosynthesis and respiration are
linked through the Calvin–Benson linked through the Calvin–Benson cycle, the citric acid cycle, and cycle, the citric acid cycle, and glycolysis. glycolysis.
Review Figure 8.22Review Figure 8.22
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Chapter 8: Photosynthesis: Energy from the Sun
Figure 8.22 – Part 1
Figure 8.22 – Part 1Figure 8.22 – Part 1
figure 08-22a.jpg
Chapter 8: Photosynthesis: Energy from the Sun
Figure 8.22 – Part 2
Figure 8.22 – Part 2Figure 8.22 – Part 2
figure 08-22b.jpg
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