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Do Now:. Structure of Leaves Worksheet Section 29-4, p. 599. Chapter 6: Photosynthesis. Section 1: Capturing the Energy in Light. Q.O.D:. Briefly describe the two reactions of photosynthesis. Energy and Life Processes. Autotrophs Photosynthesis Chemosynthesis Heterotrophs

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  1. Do Now: Structure of Leaves Worksheet Section 29-4, p. 599

  2. Chapter 6: Photosynthesis Section 1: Capturing the Energy in Light

  3. Q.O.D: Briefly describe the two reactions of photosynthesis

  4. Energy and Life Processes • Autotrophs • Photosynthesis • Chemosynthesis • Heterotrophs • Biochemical pathway • Photosynthesis • Cellular respiration

  5. The Chloroplast • Structure: • Double-membrane • Thylakoid discs • Thylakoid space • Grana • Stroma • Chlorophyll and other pigments

  6. The Process • 6CO2 + 6H2O + energy  C6H12O6 + 6O2 • Overview: 2 reactions • Light Reactions • Light energy  Chemical energy • Creates ATP and NADPH (an energy carrier) • Calvin Cycle or Dark Reaction • Takes in CO2 and produces sugars • Uses energy produced in light reaction

  7. Light and Pigments • Light • Visible spectrum of colors • Travels as waves of energy • Wavelengths – shorter = more energy • Colors can be reflected, transmitted or absorbed • Pigments • Compound that absorbs light

  8. 1 m (109 nm) 10–3 nm 103 nm 106 nm 10–5 nm 103 m 1 nm LE 10-6 Gamma rays Micro- waves Radio waves X-rays Infrared UV Visible light 650 750 nm 500 550 600 700 450 380 Shorter wavelength Longer wavelength Higher energy Lower energy

  9. Chloroplast Pigments • Primary pigment: Chlorophyll a • Accessory pigments: • Chlorophyll b • Carotenoids • Carotenes • Xanthophylls

  10. Chlorophyll a LE 10-9a Chlorophyll b Carotenoids Absorption of light by chloroplast pigments 400 700 500 600 Wavelength of light (nm) Absorption spectra

  11. The Light Reaction • Occurs in the thylakoid membranes • In: • Light energy • H2O • Out: • O2 • ATP • NADPH • Stages: Electron transport and Chemiosmosis

  12. Electron Transport Chain • Photosystems • Cluster of pigments + proteins imbedded in membrane of thylakoid • Contain light harvesting complex and reaction center • Transfers energy from light to electrons • Electrons move down electron transport chain • Energy is used to produce ATP and NADPH

  13. Thylakoid Photosystem STROMA Photon LE 10-12 Light-harvesting complexes Reaction center Primary electron acceptor e– Thylakoid membrane Special chlorophyll a molecules Pigment molecules Transfer of energy THYLAKOID SPACE (INTERIOR OF THYLAKOID)

  14. Section 1 The Light Reactions Chapter 6 Light Reactions in Photosynthesis

  15. Steps of Electron Transport • 1: Light energy excites a pair of electrons in 2 chlorophyll a molecules in photosystem II • 2: These electrons leave chlorophyll a (oxidation) and is picked up by the primary electron acceptor (reduction) • 3: Electron transport chain – energy from electrons used to move H+ from stroma into the thylakoid

  16. 4: Light is absorbed by photosystem I, exciting a pair of electrons in chlorophyll a • Electrons are replaced by electrons from photosystem II • 5: These electrons move down another ETC and are picked up by NADP+ to form NADPH • Restoring Photosystem II – replacing lost electrons • Photolysis: Light breaks up water into 4H+, O2 and electrons

  17. Section 1 The Light Reactions Chapter 6 Converting Light Energy To Chemical Energy

  18. Section 1 The Light Reactions Chapter 6 Light Reactions in Photosynthesis

  19. Q.O.D: What is chemiosmosis? What drives this process?

  20. Section 1 The Light Reactions Chapter 6 Converting Light Energy To Chemical Energy

  21. Chemiosmosis • Concentration gradient of H+ ions created by ETC and photolysis • More H+ in thylakoid than in stroma • Creates a potential energy • ATP synthase embedded in thylakoid membrane • As H+ diffuse back into stroma, they flow through the ATP synthase • Movement spins the enzyme, driving the production of ATP from ADP

  22. Light Reaction Reviewed • Reactants: • H2O • Light • Products: • O2 • ATP and NADPH • Looking forward: • ATP and NADPH provide energy for Calvin cycle

  23. Section 1 The Light Reactions Chapter 6 Summary of Processes in Light Reactions

  24. Chapter 6: Photosynthesis Section 2: The Calvin Cycle

  25. Calvin Cycle: An Overview • Light-independent • Location: The stroma • In: • CO2 • ATP • NADPH • Out: • C6H12O6 • ADP + P • NADP+

  26. Steps of the Calvin Cycle • 1: Carbon fixation: CO2 is added to RuBP, a 5-Carbon compound • Enzyme: Rubisco • Intermediate 6-C compound immediately breaks down into 2 3-C compounds (PGA) • 2: PGA is converted to PGAL • a: ATP gives a P to each PGA • b: NADPH gives a proton and energy  PGAL

  27. 3: RuBP is replenished • Most of the PGAL is converted back to RuBP • Allows cycle to continue • One PGAL for every 3 CO2 exits cycle to be incorporated into sugar • Results: • For every 3CO2 entering cycle, we get 6 PGAL. • 1 PGAL exits • 5 PGAL converted back to RuBP • Need 6CO2 for 2 PGAL  sugar

  28. Calvin Cycle To return to the chapter summary click escape or close this document.

  29. Section 2 The Calvin Cycle Chapter 6 The Calvin Cycle

  30. Section 2 The Calvin Cycle Chapter 6 Ongoing Cycle of Photosynthesis

  31. Alternative Pathways • C3 plants • Typical • Alternative pathways • Role of climate • Stomata • Gas exchange • Gas levels

  32. C4 Plants • C4 Pathway • Carbon fixation  4-Carbon compound • Source CO2 for Calvin cycle • Sugar cane, corn, crab grass

  33. LE 10-19 Mesophyll cell Mesophyll cell CO2 PEP carboxylase Photosynthetic cells of C4 plant leaf Bundle- sheath cell The C4 pathway Oxaloacetate (4 C) PEP (3 C) Vein (vascular tissue) ADP Malate (4 C) ATP C4 leaf anatomy Pyruvate (3 C) Bundle-sheath cell CO2 Stoma CALVIN CYCLE Sugar Vascular tissue

  34. CAM Plants • CAM Pathway • Stomata open at night • Fix carbon at night  organic compounds • Day, organic compounds release CO2 to Calvin cycle • Cacti, Pineapple – slower growth

  35. LE 10-20 Sugarcane Pineapple CAM C4 CO2 CO2 Night Mesophyll cell CO2 incorporated into four-carbon organic acids (carbon fixation) Organic acid Organic acid Bundle- sheath cell Day CO2 CO2 Organic acids release CO2 to Calvin cycle CALVIN CYCLE CALVIN CYCLE Sugar Sugar Spatial separation of steps Temporal separation of steps

  36. Rate of Photosynthesis • How it’s measured • O2 • Mass • CO2 • Influenced by: • Light intensity • CO2 • Temperature

  37. Section 1 The Light Reactions Chapter 6 Overview of Photosynthesis

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