8 Photosynthesis

Overview: The Process That Feeds the Biosphere _________________________________________ _________________________________________ © 2014 Pearson Education, Inc. 2

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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

(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

Concept 8.1: Photosynthesis converts light energy to the chemical energy of food _________________________________________ _________________________________________ © 2014 Pearson Education, Inc. 6

Chloroplasts: The Sites of Photosynthesis in Plants _________________________________________ _________________________________________ © 2014 Pearson Education, Inc. 7

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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

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

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

Tracking Atoms Through Photosynthesis: Scientific Inquiry Photosynthesis equation _________________________________________ © 2014 Pearson Education, Inc. 12

Reactants: 6 CO2 12 H2O Products: C6H12O6 6 H2O 6 O2 Figure 8.4 Figure 8.4 Tracking atoms through photosynthesis 13

Photosynthesis as a Redox Process _________________________________________ _________________________________________ © 2014 Pearson Education, Inc. 14

becomes reduced becomes oxidized Figure 8.UN01 Figure 8.UN01 In-text figure, photosynthesis equation, p. 158 15

The Two Stages of Photosynthesis: A Preview ___________________________(the photo part) ___________________________(the synthesis part) _________________________________________ ________ _________ __________________________________ _____________________________________________________________________________________ © 2014 Pearson Education, Inc. 16

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

H2O Light NADP ADP  Light Reactions Chloroplast P i Figure 8.5-1 Figure 8.5-1 An overview of photosynthesis: cooperation of the light reactions and the Calvin cycle (step 1) Chloroplast 18

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 8.5-2 An overview of photosynthesis: cooperation of the light reactions and the Calvin cycle (step 2) NADPH Chloroplast O2 19

Calvin Cycle Light Reactions Figure 8.5-3 H2O CO2 Light NADP ADP  P i Calvin Cycle Light Reactions ATP Figure 8.5-3 An overview of photosynthesis: cooperation of the light reactions and the Calvin cycle (step 3) NADPH Chloroplast O2 20

Calvin Cycle Light Reactions [CH2O] (sugar) Figure 8.5-4 H2O CO2 Light NADP ADP  P i Calvin Cycle Light Reactions ATP Figure 8.5-4 An overview of photosynthesis: cooperation of the light reactions and the Calvin cycle (step 4) NADPH Chloroplast [CH2O] (sugar) O2 21

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

Photosynthetic Pigments: The Light Receptors __________________________________ Animation: Light and Pigments © 2014 Pearson Education, Inc. 23

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

Pigments in Photosynthesis _________________ __________________________________________________________________________________

T.E. Englemann’s Experiment Background Information __________________________________________________________________________

T.E. Englemann’s Experiment

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)

Accessory Pigments Carotenoids, Phycobilins, Anthocyanins beta-carotene phycoerythrin (a phycobilin) percent of wavelengths absorbed wavelengths (nanometers)

Pigments Fig. 7-3a, p.109

Pigments Fig. 7-3b, p.109

Pigments Fig. 7-3d, p.109

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

Excitation of Chlorophyll by Light _________________________________________ _________________________________________ © 2014 Pearson Education, Inc. 36

(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

A Photosystem: A Reaction-Center Complex Associated with Light-Harvesting Complexes _________________________________________ _________________________________________ © 2014 Pearson Education, Inc. 38

(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

(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

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

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

Linear Electron Flow 1. ________________________________________ _________________________________________ 2. ________________________________________ _________________________________________ 3. ________________________________________ _________________________________________ © 2014 Pearson Education, Inc. 47

2 P680 1 Light Pigment molecules Photosystem II (PS II) Primary Figure 8.13-1 Primary acceptor 2 e− P680 1 Light Figure 8.13-1 How linear electron flow during the light reactions generates ATP and NADPH (steps 1-2) Pigment molecules Photosystem II (PS II) 48

2 2 H  3  P680 1 Light Pigment molecules Photosystem II (PS II) 1 2 Figure 8.13-2 Primary acceptor 2 2 H H2O e−   2 1 3 O2 e− e− P680 1 Light Figure 8.13-2 How linear electron flow during the light reactions generates ATP and NADPH (step 3) Pigment molecules Photosystem II (PS II) 49

4 Electron transport chain 2 2 H  3  P680 1 5 Light Pigment Figure 8.13-3 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 8.13-3 How linear electron flow during the light reactions generates ATP and NADPH (steps 4-5) Pigment molecules Photosystem II (PS II) 50

Photosystem I (PS I) Photosystem II (PS II) Figure 8.13-4 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 8.13-4 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

Photosystem I (PS I) Photosystem II (PS II) Figure 8.13-5 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 8.13-5 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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7. _________________________________________ 8. _________________________________________ 9. _______________________________________ _________________________________________ 10. _______________________________________ _________________________________________ _________________________________________ 54

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

Light-Dependent Reactions photon Photosystem Light-Harvesting Complex Fig. 7-7, p.112

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

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

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

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

_________________________________________ __________________________________where the Calvin cycle takes place © 2014 Pearson Education, Inc. 61

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

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

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

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

Concept 8.3: The Calvin cycle uses the chemical energy of ATP and NADPH to reduce CO2 to sugar _________________________________________ _________________________________________ © 2014 Pearson Education, Inc. 66

Concept 8.3: The Calvin cycle _________________________________________ ____________________________________(2 are then bonded to form the glucose) _________________________________________ __________________ _______________ © 2014 Pearson Education, Inc. 67

(ribulose bisphosphate)________________________ _________________________________________ _________________________________________ (ribulose bisphosphate)________________________ ___________________________________________ © 2014 Pearson Education, Inc. 68

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

Phase 1: Carbon fixation Rubisco Figure 8.17-1 Input 3 as 3 CO2 Phase 1: Carbon fixation Rubisco 3 P P 3 P P 6 P RuBP 3-Phosphoglycerate Calvin Cycle Figure 8.17-1 The Calvin cycle (step 1) 70

Phase 1: Carbon fixation Rubisco Figure 8.17-2 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 8.17-2 The Calvin cycle (step 2) 6 P G3P Phase 2: Reduction Glucose and other organic compounds 1 P G3P Output 71

Phase 1: Carbon fixation Rubisco Figure 8.17-3 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 8.17-3 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 _________________________________________ _________________________________________ ________________________________________… …________________________________________ _________________________________________ © 2014 Pearson Education, Inc. 75

C3 Plants Fig. 7-11a1, p.116

C3 Plants upper epidermis palisade mesophyll spongy mesophyll lower stoma leaf vein air space Basswood leaf, cross-section. Fig. 7-11a2, p.116

C4 Plants Fig. 7-11b1, p.117

C4 Plants _________________________________________ _________________________________________ _________________________________________ © 2014 Pearson Education, Inc. 79

C4 Plants upper epidermis mesophyll cell bundle- sheath cell lower Fig. 7-11b2, p.117

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

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

CAM Plants Fig. 7-11c1, p.117

CAM Plants _________________________________________ __________________________________________________________________________________ © 2014 Pearson Education, Inc. 84

CAM Plants stoma epidermis with thick cuticle mesophyll cell air space Fig. 7-11c2, p.117

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

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