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Chapter 10: Photosynthesis

Chapter 10: Photosynthesis. What is photosynthesis & what organisms do photosynthesis? Photosynthesis – conversion of light energy to chemical energy Photoautotrophs. (a) Plants. (c) Unicellular protist. 10 m. (d) Pruple sulfur bacteria. 1.5 m. (c) Cyanobacteria.

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Chapter 10: Photosynthesis

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  1. Chapter 10: Photosynthesis • What is photosynthesis & what organisms do photosynthesis? • Photosynthesis – conversion of light energy to chemical energy • Photoautotrophs

  2. (a) Plants (c) Unicellular protist 10 m (d) Pruple sulfur bacteria 1.5 m (c) Cyanobacteria (b) Multicellular algae 40 m Figure 10.2 Photoautotrophs These organisms use light energy to drive the synthesis of organic molecules from carbon dioxide and (in most cases) water. They feed not only themselves, but the entire living world. (a) On land, plants are the predominant producers of food. In aquatic environments, photosynthetic organisms include (b) multicellular algae, such as this kelp; (c) some unicellular protists, such as Euglena; (d) the prokaryotes called cyanobacteria; and (e) other photosynthetic prokaryotes, such as these purple sulfur bacteria, which produce sulfur (spherical globules) (c, d, e: LMs).

  3. Chapter 10: Photosynthesis • What is photosynthesis & what organisms do photosynthesis? • Photosynthesis – conversion of light energy to chemical energy • Photoautotrophs • Where does photosynthesis occur? • Chloroplasts

  4. Leaf cross section Vein Mesophyll CO2 O2 Mesophyll cell Stomata Chloroplast 5 µm Outermembrane Granum Stroma Thylakoid ThylakoidSpace Intermembranespace Inner membrane 1 µm Fig. 10.3 Focusing in on the location of photosynthesis in a plant ½ million chloroplasts / mm2 of leaf 30 – 40 chloroplasts / mesophyll cell

  5. Reactants: 12 H2O 6 CO2 6 H2O 6 O2 C6H12O6 Products: Chapter 10: Photosynthesis • What is photosynthesis & what organisms do photosynthesis? • Where does photosynthesis occur? • How did chloroplasts evolve? • Endosymbiosis • Chemoheterotroph engulfed a photoautotroph (Ch 26) • What is the chemical equation for photosynthesis? • CO2 + H2O + light energy → C6H12O6 + O2 + H2O (+ energy) Let’s see where this occurs in the chloroplast…. The light reactions & the Calvin Cycle

  6. Figure 10.5 An overview of photosynthesis: cooperation of the light reactions and the Calvin cycle H2O Light LIGHT REACTIONS Chloroplast Light rxns require light – light-dependent

  7. Figure 10.5 An overview of photosynthesis: cooperation of the light reactions and the Calvin cycle H2O Light LIGHT REACTIONS ATP NADPH Chloroplast O2

  8. CO2 NADP ADP CALVIN CYCLE [CH2O] (sugar) O2 Figure 10.5 An overview of photosynthesis: cooperation of the light reactions and the Calvin cycle H2O Light + P i LIGHT REACTIONS ATP NADPH Chloroplast Calvin Cycle – light-independent rxns

  9. 1 m 106 nm 106 nm 10–5 nm 1 nm 10–3 nm 103 nm 103 m Micro- waves Radio waves Gamma rays X-rays UV Infrared Visible light 380 450 500 550 600 650 700 750 nm Shorter wavelength Longer wavelength Lower energy Higher energy Chapter 10: Photosynthesis • What is photosynthesis & what organisms do photosynthesis? • Where does photosynthesis occur? • How did chloroplasts evolve? • What is the chemical equation for photosynthesis? • What are the colors of the rainbow (in order)? • ROY G BIV

  10. Chapter 10: Photosynthesis • What is photosynthesis & what organisms do photosynthesis? • Where does photosynthesis occur? • How did chloroplasts evolve? • What is the chemical equation for photosynthesis? • What are the colors of the rainbow (in order)? • What 3 things can happen to light when it “hits” an object?

  11. Light Reflected Light Chloroplast Absorbed light Granum Transmitted light Figure 10.7 Why leaves are green: interaction of light with chloroplasts • What absorbs the light? • Photosynthetic pigments • chlorophyll a & b • carotenoids – broaden the spectrum of usable light

  12. Three different experiments helped reveal which wavelengths of light are photosynthetically important. The results are shown below. EXPERIMENT 400 500 700 600 Figure 10.9 Inquiry Which wavelengths of light are most effective in driving photosynthesis? RESULTS Chlorophyll a Chlorophyll b Absorption of light by chloroplast pigments Carotenoids Wavelength of light (nm) (a) Absorption spectra. The three curves show the wavelengths of light best absorbed by three types of chloroplast pigments.

  13. Rate of photosynthesis (measured by O2 release) (b) Action spectrum. This graph plots the rate of photosynthesis versus wavelength. The resulting action spectrum resembles the absorption spectrum for chlorophyll a but does not match exactly (see part a). This is partly due to the absorption of light by accessory pigments such as chlorophyll b and carotenoids.

  14. Aerobic bacteria Filament of alga 500 600 700 400 (c) Engelmann‘s experiment. In 1883, Theodor W. Engelmann illuminated a filamentous alga with light that had been passed through a prism, exposing different segments of the alga to different wavelengths. He used aerobic bacteria, which concentrate near an oxygen source, to determine which segments of the alga were releasing the most 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. Light in the violet-blue and red portions of the spectrum are most effective in driving photosynthesis. CONCLUSION

  15. Aerobic bacteria Filament of alga Rate of photosynthesis (measured by O2 release) 500 600 700 400 (b) Action spectrum. This graph plots the rate of photosynthesis versus wavelength. The resulting action spectrum resembles the absorption spectrum for chlorophyll a but does not match exactly (see part a). This is partly due to the absorption of light by accessory pigments such as chlorophyll b and carotenoids.

  16. Chapter 10: Photosynthesis • What is photosynthesis & what organisms do photosynthesis? • Where does photosynthesis occur? • How did chloroplasts evolve? • What is the chemical equation for photosynthesis? • What are the colors of the rainbow (in order)? • What 3 things can happen to light when it “hits” an object? • What is the structure of chlorophyll?

  17. CH3 in chlorophyll a in chlorophyll b CHO CH2 CH3 CH H C C C C Porphyrin ring: Light-absorbing “head” of molecule; note magnesium atom at center C CH3 C C H3C CH2 C C N N H C C Mg H N C C N H3C C C CH3 C C C C C H H CH2 H C C O CH2 O O C O O CH3 CH2 Hydrocarbon tail: interacts with hydrophobic regions of proteins inside thylakoid membranes of chloroplasts: H atoms not shown Fig. 10.10 Structure of chlorophyll molecules in chloroplasts of plants Amphipathic – both polar & non-polar

  18. Chapter 10: Photosynthesis • What is photosynthesis & what organisms do photosynthesis? • Where does photosynthesis occur? • How did chloroplasts evolve? • What is the chemical equation for photosynthesis? • What are the colors of the rainbow (in order)? • What 3 things can happen to light when it “hits” an object? • What is the structure of chlorophyll? • How do the photosystems harvest light energy?

  19. Excited state e– Heat Energy of election Photon (fluorescence) Ground state Photon Chlorophyll molecule (a) Excitation of isolated chlorophyll molecule (b) Fluorescence Figure 10.11 Excitation of isolated chlorophyll by light

  20. Thylakoid Photosystem STROMA Photon Reaction center Light-harvesting complexes Primary electron acceptor e– Thylakoid membrane Special chlorophyll a molecules Transfer of energy Pigment molecules THYLAKOID SPACE (INTERIOR OF THYLAKOID) Figure 10.12 How a photosystem harvests light

  21. 1 2 Figure 10.13 How noncyclic electron flow during the light reactions generates ATP and NADPH H2O CO2 Light NADP+ ADP CALVIN CYCLE LIGHT REACTIONS ATP NADPH O2 [CH2O] (sugar) Primary acceptor e Energy of electrons Light P680 Photosystem II (PS II)

  22. H2O CO2 Light NADP+ ADP CALVIN CYCLE LIGHT REACTIONS ATP NADPH O2 [CH2O] (sugar) Primary acceptor e H2O 2 H+ + 1⁄2 O2 e Energy of electrons e Light 1 3 2 Photosystem II (PS II) Figure 10.13 How noncyclic electron flow during the light reactions generates ATP and NADPH P680

  23. H2O CO2 Light NADP+ ADP CALVIN CYCLE LIGHT REACTIONS ATP NADPH O2 [CH2O] (sugar) Primary acceptor 4 Electron transport chain Pq 2 e H2O 2 H+ Cytochrome complex + 3 O2 1⁄2 Pc 5 Energy of electrons Light P680 1 ATP Photosystem II (PS II) Figure 10.13 How noncyclic electron flow during the light reactions generates ATP and NADPH e e

  24. H2O CO2 Light NADP+ ADP CALVIN CYCLE LIGHT REACTIONS ATP NADPH [CH2O] (sugar) O2 Primary acceptor Primary acceptor 4 Electron transport chain e Pq 2 H2O e Cytochrome complex 2 H+ O2 1⁄2 3 Pc 5 Energy of electrons Light P680 P700 Light 1 6 ATP Photosystem I (PS I) Photosystem II (PS II) Figure 10.13 How noncyclic electron flow during the light reactions generates ATP and NADPH + e e

  25. H2O CO2 Light NADP+ ADP CALVIN CYCLE LIGHT REACTIONS ATP NADPH Electron Transport chain [CH2O] (sugar) O2 Primary acceptor 7 Primary acceptor 4 Electron transport chain Fd e Pq e 8 e 2 e H2O NADP+ + 2 H+ Cytochrome complex 2 H+ NADP+ reductase + O2 NADPH 3 1⁄2 Pc e + H+ 5 P700 e Energy of electrons Light P680 Light 1 1 6 6 ATP Photosystem I (PS I) Photosystem II (PS II) Figure 10.13 How noncyclic electron flow during the light reactions generates ATP and NADPH

  26. Chapter 10: Photosynthesis • What is photosynthesis & what organisms do photosynthesis? • Where does photosynthesis occur? • How did chloroplasts evolve? • What is the chemical equation for photosynthesis? • What are the colors of the rainbow (in order)? • What 3 things can happen to light when it “hits” an object? • What is the structure of chlorophyll? • How do the photosystems harvest light energy? • What’s the difference re: chemiosmosis in mitochondria & chloroplasts?

  27. Key Higher [H+] Lower [H+] Chloroplast Mitochondrion CHLOROPLAST STRUCTURE MITOCHONDRION STRUCTURE H+ Diffusion Thylakoid space Intermembrance space Electron transport chain Membrance ATP Synthase Stroma Matrix ADP+ P ATP H+ Figure 10.16 Comparison of chemiosmosis in mitochondria and chloroplasts

  28. H2O CO2 LIGHT NADP+ ADP CALVIN CYCLE LIGHT REACTOR ATP NADPH STROMA (Low H+ concentration) O2 [CH2O] (sugar) Cytochrome complex Photosystem II Photosystem I NADP+ reductase Light 2 H+ 3 NADP+ + 2H+ Fd NADPH + H+ Pq Pc 2 H2O 1⁄2 O2 THYLAKOID SPACE (High H+ concentration) 1 2 H+ +2 H+ To Calvin cycle ATP synthase Thylakoid membrane STROMA (Low H+ concentration) ADP ATP P H+ Figure 10.17 The light reactions and chemiosmosis: the organization of the thylakoid membrane

  29. Chapter 10: Photosynthesis • What is photosynthesis & what organisms do photosynthesis? • Where does photosynthesis occur? • How did chloroplasts evolve? • What is the chemical equation for photosynthesis? • What are the colors of the rainbow (in order)? • What 3 things can happen to light when it “hits” an object? • What is the structure of chlorophyll? • How do the photosystems harvest light energy? • What’s the difference chemiosmosis in mitochondria & chloroplasts? • How do plants make “sugar?” • Calvin Cycle

  30. H2O CO2 Input Light 3 (Entering one at a time) NADP+ CO2 ADP CALVINCYCLE LIGHTREACTIONS ATP Phase 1: Carbon fixation NADPH Rubisco [CH2O] (sugar) 3 P P Short-livedintermediate P 3 P P Ribulose bisphosphate(RuBP) 3-Phosphoglycerate 6 ATP 6 ADP Figure 10.18 The Calvin cycle O2 6 CALVIN CYCLE

  31. H2O CO2 Input Light 3 (Entering one at a time) NADP+ CO2 ADP CALVINCYCLE LIGHTREACTIONS ATP Phase 1: Carbon fixation NADPH Rubisco [CH2O] (sugar) 3 P P Short-livedintermediate P 3 P P Ribulose bisphosphate(RuBP) 3-Phosphoglycerate 6 ATP 6 ADP CALVIN CYCLE 6 P P 1,3-Bisphosphoglycerate 6 NADPH 6 NADP+ 6 P i 6 P Glyceraldehyde-3-phosphate (G3P) Phase 2:Reduction P 1 G3P(a sugar)Output Glucose and other organic compounds Figure 10.18 The Calvin cycle O2 6

  32. H2O CO2 Input Light 3 (Entering one at a time) NADP+ CO2 ADP CALVINCYCLE LIGHTREACTIONS ATP Phase 1: Carbon fixation NADPH Rubisco [CH2O] (sugar) 3 P P Short-livedintermediate P 3 P P Ribulose bisphosphate(RuBP) 3-Phosphoglycerate 6 ATP 6 ADP CALVIN CYCLE 3 ADP P 6 P 3 ATP 1,3-Bisphosphoglycerate 6 NADPH Phase 3:Regeneration ofthe CO2 acceptor(RuBP) 6 NADP+ 6 P i 5 P G3P 6 P Glyceraldehyde-3-phosphate (G3P) Phase 2:Reduction 1 P G3P(a sugar)Output Glucose and other organic compounds Figure 10.18 The Calvin cycle O2 6

  33. Chapter 10: Photosynthesis • What is photosynthesis & what organisms do photosynthesis? • Where does photosynthesis occur? • How did chloroplasts evolve? • What is the chemical equation for photosynthesis? • What are the colors of the rainbow (in order)? • What 3 things can happen to light when it “hits” an object? • What is the structure of chlorophyll? • How do the photosystems harvest light energy? • What’s the difference chemiosmosis in mitochondria & chloroplasts? • How do plants make “sugar?” • How do plants get out of ATP debt? • - Cyclic electron flow

  34. Primary acceptor Primary acceptor Fd Fd Pq NADP+ reductase Cytochrome complex NADPH Pc ATP Figure 10.15 Cyclic electron flow NADP+ Photosystem I (PS I) Photosystem II (PS II)

  35. Chapter 10: Photosynthesis • What is photosynthesis & what organisms do photosynthesis? • Where does photosynthesis occur? • How did chloroplasts evolve? • What is the chemical equation for photosynthesis? • What are the colors of the rainbow (in order)? • What 3 things can happen to light when it “hits” an object? • What is the structure of chlorophyll? • How do the photosystems harvest light energy? • What’s the difference chemiosmosis in mitochondria & chloroplasts? • How do plants make “sugar?” • How do plants get out of ATP debt? • What is the difference between C3 & C4 photosynthesis?

  36. Mesophyll cell Mesophyll cell Photosynthetic cells of C4 plant leaf CO2 PEP carboxylase CO2 Bundle- sheath cell PEP (3 C) Oxaloacetate (4 C) ADP Vein (vascular tissue) Malate (4 C) ATP C4 leaf anatomy Pyruate (3 C) Bundle- Sheath cell CO2 Stoma CALVIN CYCLE Sugar Vascular tissue Figure 10.19 C4 leaf anatomy and the C4 pathway

  37. Chapter 10: Photosynthesis • What is photosynthesis & what organisms do photosynthesis? • Where does photosynthesis occur? • How did chloroplasts evolve? • What is the chemical equation for photosynthesis? • What are the colors of the rainbow (in order)? • What 3 things can happen to light when it “hits” an object? • What is the structure of chlorophyll? • How do the photosystems harvest light energy? • What’s the difference chemiosmosis in mitochondria & chloroplasts? • How do plants make “sugar?” • How do plants get out of ATP debt? • What is the difference between C3 & C4 photosynthesis? • How do CAM plants differ from C4 plants? • -Crassulacean Acid Metabolism

  38. 2 1 Pineapple Sugarcane C4 CAM CO2 CO2 Mesophyll Cell Night CO2 incorporated into four-carbon organic acids (carbon fixation) Organic acid Organic acid Bundle- sheath cell (b) Temporal separation of steps. In CAM plants, carbon fixation and the Calvin cycle occur in the same cellsat different times. Day (a) Spatial separation of steps. In C4 plants, carbon fixation and the Calvin cycle occur in different types of cells. CALVINCYCLE CALVINCYCLE Sugar Sugar Figure 10.20 C4 and CAM photosynthesis compared CO2 Organic acids release CO2 to Calvin cycle Organic acids release CO2 to Calvin cycle

  39. Light reactions Calvin cycle H2O CO2 Light NADP+ ADP + P1 RuBP 3-Phosphoglycerate Photosystem II Electron transport chain Photosystem I ATP G3P NADPH Starch (storage) Amino acids Fatty acids Chloroplast O2 Sucrose (export) 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 Figure 10.21 A review of photosynthesis

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