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8 Photosynthesis
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Overview: The Process That Feeds the Biosphere
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Figure 8.1 Figure 8.1 How can sunlight, seen here as a spectrum of colors in a rainbow, power the synthesis of organic substances? 4
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(c) Unicellular eukaryotes
Figure 8.2 40 m (d) Cyanobacteria (a) Plants Figure 8.2 Photoautotrophs (b) Multicellular alga 1 m (e) Purple sulfur bacteria 10 m (c) Unicellular eukaryotes 5
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Concept 8.1: Photosynthesis converts light energy to the chemical energy of food
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Chloroplasts: The Sites of Photosynthesis in Plants
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Leaf cross section Chloroplasts Vein Mesophyll Stomata CO2 O2
Figure 8.3 Leaf cross section Chloroplasts Vein Mesophyll Stomata CO2 O2 Chloroplast Mesophyll cell Figure 8.3 Zooming in on the location of photosynthesis in a plant Outer membrane Thylakoid Granum Thylakoid space Intermembrane space Stroma 20 m Inner membrane 1 m 9
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Leaf cross section Chloroplasts Vein Mesophyll Stomata CO2 O2
Figure 8.3a Leaf cross section Chloroplasts Vein Mesophyll Figure 8.3a Zooming in on the location of photosynthesis in a plant (part 1: leaf cross section) Stomata CO2 O2 10
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Chloroplast Mesophyll cell Outer Thylakoid membrane Granum Thylakoid
Figure 8.3b Chloroplast Mesophyll cell Outer membrane Thylakoid Granum Thylakoid space Intermembrane space Stroma 20 m Inner membrane Figure 8.3b Zooming in on the location of photosynthesis in a plant (part 2: chloroplast) 1 m 11
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Tracking Atoms Through Photosynthesis: Scientific Inquiry
Photosynthesis equation _________________________________________ © 2014 Pearson Education, Inc. 12
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Reactants: 6 CO2 12 H2O Products: C6H12O6 6 H2O 6 O2 Figure 8.4
Figure 8.4 Tracking atoms through photosynthesis 13
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Photosynthesis as a Redox Process
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becomes reduced becomes oxidized Figure 8.UN01
Figure 8.UN01 In-text figure, photosynthesis equation, p. 158 15
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The Two Stages of Photosynthesis: A Preview
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Calvin Cycle Light Reactions [CH2O] (sugar)
Figure 8.5 H2O CO2 Light NADP ADP P i Calvin Cycle Light Reactions ATP Figure 8.5 An overview of photosynthesis: cooperation of the light reactions and the Calvin cycle NADPH Chloroplast [CH2O] (sugar) O2 17
![Calvin Cycle Light Reactions [CH2O] (sugar)](http://slideplayer.com./slide/12749964/77/images/17/Calvin+Cycle+Light+Reactions+%5BCH2O%5D+%28sugar%29.jpg "Figure 8.5. H2O. CO2. Light. NADP ADP. P i. Calvin. Cycle. Light. Reactions. ATP. Figure 8.5 An overview of photosynthesis: cooperation of the light reactions and the Calvin cycle. NADPH. Chloroplast. [CH2O] (sugar) O")
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H2O Light NADP ADP Light Reactions Chloroplast P i Figure 8.5-1
Figure An overview of photosynthesis: cooperation of the light reactions and the Calvin cycle (step 1) Chloroplast 18
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H2O Light NADP ADP Light Reactions Chloroplast O2 P i ATP NADPH
Figure 8.5-2 H2O Light NADP ADP P i Light Reactions ATP Figure An overview of photosynthesis: cooperation of the light reactions and the Calvin cycle (step 2) NADPH Chloroplast O2 19
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Calvin Cycle Light Reactions
Figure 8.5-3 H2O CO2 Light NADP ADP P i Calvin Cycle Light Reactions ATP Figure An overview of photosynthesis: cooperation of the light reactions and the Calvin cycle (step 3) NADPH Chloroplast O2 20
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Calvin Cycle Light Reactions [CH2O] (sugar)
Figure 8.5-4 H2O CO2 Light NADP ADP P i Calvin Cycle Light Reactions ATP Figure An overview of photosynthesis: cooperation of the light reactions and the Calvin cycle (step 4) NADPH Chloroplast [CH2O] (sugar) O2 21
![Calvin Cycle Light Reactions [CH2O] (sugar)](http://slideplayer.com./slide/12749964/77/images/21/Calvin+Cycle+Light+Reactions+%5BCH2O%5D+%28sugar%29.jpg "Figure H2O. CO2. Light. NADP ADP. P i. Calvin. Cycle. Light. Reactions. ATP. Figure An overview of photosynthesis: cooperation of the light reactions and the Calvin cycle (step 4) NADPH. Chloroplast. [CH2O] (sugar) O")
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1 m (109 nm) 10−5 nm 10−3 nm 1 nm 103 nm 106 nm 103 m Micro- waves
Figure 8.6 1 m (109 nm) 10−5 nm 10−3 nm 1 nm 103 nm 106 nm 103 m Micro- waves Gamma rays Radio waves X-rays UV Infrared Visible light Figure 8.6 The electromagnetic spectrum 380 450 500 550 600 650 700 750 nm Shorter wavelength Longer wavelength Higher energy Lower energy 22
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Photosynthetic Pigments: The Light Receptors
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Light Reflected light Chloroplast Absorbed Granum light Transmitted
Figure 8.7 Light Reflected light Chloroplast Figure 8.7 Why leaves are green: interaction of light with chloroplasts Absorbed light Granum Transmitted light 24
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Pigments in Photosynthesis
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T.E. Englemann’s Experiment
Background Information __________________________________________________________________________
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T.E. Englemann’s Experiment
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Chloro- phyll a Absorption of light by chloroplast pigments
Figure 8.9a Chloro- phyll a Chlorophyll b Absorption of light by chloroplast pigments Carotenoids 400 500 600 700 Figure 8.9a Inquiry: which wavelengths of light are most effective in driving photosynthesis? (part 1: absorption spectra) Wavelength of light (nm) (a) Absorption spectra 28
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Wavelength absorption (%) Wavelength (nanometers)
Chlorophylls Main pigments in most photoautotrophs Wavelength absorption (%) chlorophyll a chlorophyll b Wavelength (nanometers)
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Accessory Pigments Carotenoids, Phycobilins, Anthocyanins
beta-carotene phycoerythrin (a phycobilin) percent of wavelengths absorbed wavelengths (nanometers)
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Pigments Fig. 7-3a, p.109
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Pigments Fig. 7-3b, p.109
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Pigments Fig. 7-3d, p.109
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interacts with hydrophobic regions of proteins inside
Figure 8.10 CH3 in chlorophyll a CH3 CHO in chlorophyll b Porphyrin ring: light-absorbing “head” of molecule; note magnesium atom at center Figure 8.10 Structure of chlorophyll molecules in chloroplasts of plants Hydrocarbon tail: interacts with hydrophobic regions of proteins inside thylakoid membranes of chloroplasts; H atoms not shown 35
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Excitation of Chlorophyll by Light
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(a) Excitation of isolated chlorophyll molecule (b) Fluorescence
Figure 8.11 Excited state e− Heat Energy of electron Photon (fluorescence) Photon Figure 8.11 Excitation of isolated chlorophyll by light Ground state Chlorophyll molecule (a) Excitation of isolated chlorophyll molecule (b) Fluorescence 37
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A Photosystem: A Reaction-Center Complex Associated with Light-Harvesting Complexes
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(INTERIOR OF THYLAKOID) Protein subunits THYLAKOID SPACE
Figure 8.12 Photosystem STROMA Photon Light- harvesting complexes Reaction- center complex Primary electron acceptor e Chlorophyll STROMA Thylakoid membrane Thylakoid membrane Transfer of energy Figure 8.12 The structure and function of a photosystem Special pair of chlorophyll a molecules Pigment molecules THYLAKOID SPACE (INTERIOR OF THYLAKOID) Protein subunits THYLAKOID SPACE (a) How a photosystem harvests light (b) Structure of a photosystem 39
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(INTERIOR OF THYLAKOID)
Figure 8.12a Photosystem STROMA Photon Light- harvesting complexes Reaction- center complex Primary electron acceptor e− Thylakoid membrane Figure 8.12a The structure and function of a photosystem (part 1) Pigment molecules Transfer of energy Special pair of chlorophyll a molecules THYLAKOID SPACE (INTERIOR OF THYLAKOID) (a) How a photosystem harvests light 40
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Light-Dependent Reactions
photon Photosystem Light-Harvesting Complex Fig. 7-7, p.112
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Linear Electron Flow _________________________________________ __________________________________________________________________________________ © 2014 Pearson Education, Inc. 45
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cross-section through a disk-shaped fold in the thylakoid membrane
LIGHT- HARVESTING COMPLEX PHOTOSYSTEM II sunlight PHOTOSYSTEM I H+ NADPH e- e- e- e- e- e- NADP + + H+ e- H2O H+ H+ H+ H+ thylakoid compartment H+ H+ H+ H+ H+ H+ O2 H+ thylakoid membrane stroma ADP + Pi ATP cross-section through a disk-shaped fold in the thylakoid membrane H+ Fig. 7-8, p.113
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Linear Electron Flow 1. ________________________________________ _________________________________________ 2. ________________________________________ _________________________________________ 3. ________________________________________ _________________________________________ © 2014 Pearson Education, Inc. 47
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2 P680 1 Light Pigment molecules Photosystem II (PS II) Primary
Figure Primary acceptor 2 e− P680 1 Light Figure How linear electron flow during the light reactions generates ATP and NADPH (steps 1-2) Pigment molecules Photosystem II (PS II) 48
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2 2 H 3 P680 1 Light Pigment molecules Photosystem II (PS II) 1 2
Figure Primary acceptor 2 2 H H2O e− 2 1 3 O2 e− e− P680 1 Light Figure How linear electron flow during the light reactions generates ATP and NADPH (step 3) Pigment molecules Photosystem II (PS II) 49
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4 Electron transport chain 2 2 H 3 P680 1 5 Light Pigment
Figure 4 Electron transport chain Primary acceptor Pq 2 2 H H2O e− Cytochrome complex 2 1 3 O2 Pc e− P680 1 e− 5 Light ATP Figure How linear electron flow during the light reactions generates ATP and NADPH (steps 4-5) Pigment molecules Photosystem II (PS II) 50
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Photosystem I (PS I) Photosystem II (PS II)
Figure 4 Electron transport chain Primary acceptor Primary acceptor Pq e− 2 2 H H2O e− Cytochrome complex 2 1 3 O2 Pc e− P700 e− P680 1 5 Light Light 6 ATP Figure How linear electron flow during the light reactions generates ATP and NADPH (step 6) Pigment molecules Photosystem I (PS I) Photosystem II (PS II) 51
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Photosystem I (PS I) Photosystem II (PS II)
Figure 4 Electron transport chain 7 Electron transport chain Primary acceptor Primary acceptor Fd Pq e− 8 2 NADP e− 2 H H2O e− e− Cytochrome complex H NADP reductase 2 1 3 O2 NADPH Pc e− P700 P680 1 e− 5 Light Light 6 ATP Figure How linear electron flow during the light reactions generates ATP and NADPH (steps 7-8) Pigment molecules Photosystem I (PS I) Photosystem II (PS II) 52
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Mill makes ATP NADPH Photosystem II Photosystem I Photon Photon
Figure 8.14 Mill makes ATP NADPH Photon Figure 8.14 A mechanical analogy for linear electron flow during the light reactions Photon Photosystem II Photosystem I 55
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Light-Dependent Reactions
photon Photosystem Light-Harvesting Complex Fig. 7-7, p.112
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cross-section through a disk-shaped fold in the thylakoid membrane
LIGHT- HARVESTING COMPLEX PHOTOSYSTEM II sunlight PHOTOSYSTEM I H+ NADPH e- e- e- e- e- e- NADP + + H+ e- H2O H+ H+ H+ H+ thylakoid compartment H+ H+ H+ H+ H+ H+ O2 H+ thylakoid membrane stroma ADP + Pi ATP cross-section through a disk-shaped fold in the thylakoid membrane H+ Fig. 7-8, p.113
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Machinery of Noncyclic Electron Flow
H2O second electron transfer chain photolysis e– e– ATP SYNTHASE first electron transfer chain NADP+ NADPH ATP PHOTOSYSTEM II PHOTOSYSTEM I ADP + Pi
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Electron transport chain ATP synthase
Figure 8.15 MITOCHONDRION STRUCTURE CHLOROPLAST STRUCTURE Inter- membrane space H Diffusion Thylakoid space Electron transport chain Inner membrane Thylakoid membrane Figure 8.15 Comparison of chemiosmosis in mitochondria and chloroplasts ATP synthase Matrix Stroma Key ADP P i ATP Higher [H] H Lower [H] 59
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Electron transport chain
Figure 8.15a MITOCHONDRION STRUCTURE CHLOROPLAST STRUCTURE Inter- membrane space H Diffusion Thylakoid space Electron transport chain Inner membrane Thylakoid membrane ATP synthase Figure 8.15a Comparison of chemiosmosis in mitochondria and chloroplasts (detail) Matrix Stroma Key ADP P i ATP Higher [H] H Lower [H] 60
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Calvin Cycle Light Reactions
Figure 8.UN02 H2O CO2 Light NADP ADP Calvin Cycle Light Reactions ATP Figure 8.UN02 In-text figure, light reaction schematic, p. 164 NADPH O2 [CH2O] (sugar) 62
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Cytochrome complex NADP reductase To Calvin Cycle ATP synthase
Figure 8.16 Cytochrome complex NADP reductase Photosystem II Photosystem I Light 4 H 3 Light NADP H Fd Pq NADPH e− Pc e− 2 H2O 1 2 1 O2 THYLAKOID SPACE (high H concentration) 2 H 4 H To Calvin Cycle Figure 8.16 The light reactions and chemiosmosis: the organization of the thylakoid membrane Thylakoid membrane ATP synthase STROMA (low H concentration) ADP ATP P i H 63
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Cytochrome complex ATP synthase
Figure 8.16a Cytochrome complex Photosystem II Photosystem I Light 4 H Light Fd Pq Pc e− 2 e− H2O 1 2 1 O2 THYLAKOID SPACE (high H concentration) 2 H 4 H Figure 8.16a The light reactions and chemiosmosis: the organization of the thylakoid membrane (part 1) Thylakoid membrane ATP synthase STROMA (low H concentration) ADP ATP P i H 64
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Cytochrome complex NADP reductase To Calvin Cycle ATP synthase
Figure 8.16b Cytochrome complex NADP reductase Photosystem I Light 3 NADP H Fd NADPH Pc 2 THYLAKOID SPACE (high H concentration) 4 H To Calvin Cycle Figure 8.16b The light reactions and chemiosmosis: the organization of the thylakoid membrane (part 2) ATP synthase STROMA (low H concentration) ADP ATP P i H 65
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Concept 8.3: The Calvin cycle uses the chemical energy of ATP and NADPH to reduce CO2 to sugar
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Concept 8.3: The Calvin cycle
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(ribulose bisphosphate)________________________
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Calvin Cycle Light Reactions
Figure 8.UN03 H2O CO2 Light NADP ADP Calvin Cycle Light Reactions ATP Figure 8.UN03 In-text figure, Calvin cycle schematic, p. 168 NADPH O2 [CH2O] (sugar) 69
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Phase 1: Carbon fixation Rubisco
Figure Input 3 as 3 CO2 Phase 1: Carbon fixation Rubisco 3 P P 3 P P 6 P RuBP 3-Phosphoglycerate Calvin Cycle Figure The Calvin cycle (step 1) 70
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Phase 1: Carbon fixation Rubisco
Figure Input 3 as 3 CO2 Phase 1: Carbon fixation Rubisco 3 P P 3 P P 6 P RuBP 3-Phosphoglycerate 6 ATP 6 ADP Calvin Cycle 6 P P 1,3-Bisphosphoglycerate 6 NADPH 6 NADP 6 P i Figure The Calvin cycle (step 2) 6 P G3P Phase 2: Reduction Glucose and other organic compounds 1 P G3P Output 71
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Phase 1: Carbon fixation Rubisco
Figure Input 3 as 3 CO2 Phase 1: Carbon fixation Rubisco 3 P P 3 P P 6 P RuBP 3-Phosphoglycerate 6 ATP 6 ADP 3 ADP Calvin Cycle 6 P P 3 ATP 1,3-Bisphosphoglycerate 6 NADPH Phase 3: Regeneration of RuBP 6 NADP 6 P i 5 P Figure The Calvin cycle (step 3) G3P 6 P G3P Phase 2: Reduction Glucose and other organic compounds 1 P G3P Output 72
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Evolution of Alternative Mechanisms of Carbon Fixation in Hot, Arid Climates
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C3 Plants Fig. 7-11a1, p.116
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C3 Plants upper epidermis palisade mesophyll spongy mesophyll lower
stoma leaf vein air space Basswood leaf, cross-section. Fig. 7-11a2, p.116
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C4 Plants Fig. 7-11b1, p.117
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C4 Plants upper epidermis mesophyll cell bundle- sheath cell lower
Fig. 7-11b2, p.117
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Calvin Cycle Calvin Cycle
Figure 8.18 Sugarcane Pineapple 1 1 CO2 CO2 C4 CAM Mesophyll cell Organic acid Organic acid Night CO2 2 CO2 2 Figure 8.18 C4 and CAM photosynthesis compared Bundle- sheath cell Day Calvin Cycle Calvin Cycle Sugar Sugar (a) Spatial separation of steps (b) Temporal separation of steps 81
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Calvin Cycle Calvin Cycle
Figure 8.18c 1 1 CO2 CO2 C4 CAM Mesophyll cell Organic acid Organic acid Night CO2 2 CO2 2 Bundle- sheath cell Day Calvin Cycle Calvin Cycle Figure 8.18c C4 and CAM photosynthesis compared (part 3: detail) Sugar Sugar (a) Spatial separation of steps (b) Temporal separation of steps 82
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CAM Plants Fig. 7-11c1, p.117
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CAM Plants _________________________________________
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CAM Plants stoma epidermis with thick cuticle mesophyll cell air space
Fig. 7-11c2, p.117
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Photosynthesis overview sunlight Light- Dependent Reactions 12H2O 6O2
ADP + Pi ATP NADPH NADP+ 6CO2 Calvin-Benson cycle 6 RuBP 12 PGAL Light- Independent Reactions 6H2O phosphorylated glucose end products (e.g., sucrose, starch, cellulose) Fig. 7-14, p.120
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Electron transport chain Electron transport chain
Figure 8.19 H2O CO2 Light NADP ADP P i Light Reactions: RuBP 3-Phosphpglycerate Photosystem II Electron transport chain Calvin Cycle Photosystem I Electron transport chain ATP G3P Figure 8.19 A review of photosynthesis Starch (storage) NADPH Chloroplast O2 Sucrose (export) 87
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