8 Photosynthesis

(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 2

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 4

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 5

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

becomes reduced becomes oxidized Figure 8.UN01 Figure 8.UN01 In-text figure, photosynthesis equation, p. 158 7

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 8

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 9

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 10

The high transmittance (low absorption) reading indicates Figure 8.8 Technique White light Refracting prism Chlorophyll solution Photoelectric tube Galvanometer 2 3 1 4 The high transmittance (low absorption) reading indicates that chlorophyll absorbs very little green light. Slit moves to pass light of selected wavelength. Green light Figure 8.8 Research method: determining an absorption spectrum The low transmittance (high absorption) reading indicates that chlorophyll absorbs most blue light. Blue light 11

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 12

(measured by O2 photosynthesis Rate of release) Figure 8.9b (measured by O2 photosynthesis Rate of release) 400 500 600 700 Figure 8.9b Inquiry: which wavelengths of light are most effective in driving photosynthesis? (part 2: action spectrum) (b) Action spectrum 13

(a) Excitation of isolated chlorophyll molecule (b) Fluorescence Figure 8.11 Excited state e− Heat Energy of electron Photon (fluorescence) Photon Ground state Figure 8.11 Excitation of isolated chlorophyll by light Chlorophyll molecule (a) Excitation of isolated chlorophyll molecule (b) Fluorescence 14

(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 Special pair of chlorophyll a molecules Pigment molecules Figure 8.12 The structure and function of a photosystem THYLAKOID SPACE (INTERIOR OF THYLAKOID) Protein subunits THYLAKOID SPACE (a) How a photosystem harvests light (b) Structure of a photosystem 15

(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 16

(b) Structure of a photosystem Figure 8.12b Chlorophyll STROMA Thylakoid membrane Protein subunits THYLAKOID SPACE Figure 8.12b The structure and function of a photosystem (part 2) (b) Structure of a photosystem 17

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) 18

Primary acceptor Electron transport chain Primary acceptor Figure 8.UN05 Primary acceptor Electron transport chain Primary acceptor Electron transport chain Fd NADP H2O Pq NADP reductase  H O2 NADPH Cytochrome complex Pc Figure 8.UN05 Summary of key concepts: the light reactions Photosystem I ATP Photosystem II 19

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 20

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) 21

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] 22

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 Matrix Stroma Figure 8.15a Comparison of chemiosmosis in mitochondria and chloroplasts (detail) Key ADP  P i ATP Higher [H] H Lower [H] 23

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) 24

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 25

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) 26

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) 27

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 28

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 29

Calvin Cycle Regeneration of CO2 acceptor Figure 8.UN06 3 CO2 Carbon fixation 3  5C 6  3C Calvin Cycle Regeneration of CO2 acceptor 5  3C Figure 8.UN06 Summary of key concepts: the Calvin cycle Reduction 1 G3P (3C) 30

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 31

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) 32