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PHOTOSYNTHESIS

PHOTOSYNTHESIS. Chapter 6. Photosynthesis. Capturing the energy in Light. The Calvin Cycle. Photosynthesis : Big Picture. Energy Transfer: Light  organic compound (food) Overall: 6CO 2 + 6H 2 O + sunlight  C 6 H 12 O 6 + 6O 2 Biochemical Pathway :

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PHOTOSYNTHESIS

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  1. PHOTOSYNTHESIS Chapter 6

  2. Photosynthesis Capturing the energy in Light The Calvin Cycle

  3. Photosynthesis: Big Picture • Energy Transfer: • Light  organic compound (food) • Overall: 6CO2 + 6H2O + sunlight  C6H12O6 + 6O2 • Biochemical Pathway: • product of one rxn consumed in 2nd rxn • 2 steps: • Light reactions: • Light  ATP + NADPH (energy-storing compounds) • Calvin Cycle= Dark Reactions • CO2 + ATP + NADPH  carbohydrate + ADP + NADP+

  4. Photosynthesis Overview

  5. Autotroph: manufacturer their own food • Heterotrophs: eat autotrophs or heterotrophs • Energy for Life Processes

  6. Light & Light Absorption in Plants • White Sunlight • Visible spectrum: ROY G. BIV • Travels in waves • Can be transmitted, absorbed, or reflected • Pigments • Organic compound that absorbs certain colors and reflects/ transmits others • Example: Chlorophyll in chloroplasts • Chloroplast Pigments: located in thylakoid membrane • Chlorophyll a • Chlorophyll b: accessory pigment • Carotenoids: accessory pigments, reflects yellow/ orange Most abundant, Reflects green

  7. Chloroplast Structure • Chloroplast: location for photosynthesis • 2 membranes: inner & outer • Thylakoids stacked= Grana • Stroma • Photosystems (PS I & PS II) • Located in thylakoid membrane • Cluster of pigment molecules that absorb light energy • Primary Electron Acceptor • Molecule in thylakoid membrane that accepts excited e- and passes them to electron transport chain • Electron Transport Chain (ETC) • Chain of molecules in thylakoid membrane that can release energy by carrying excited e-

  8. Chloroplast

  9. Thylakoid Membrane

  10. Light Reaction Steps @ PS II Step 1 PS II Absorbs Light Energy in Pigment Molecules exciting the electrons (e-) in the chlorophyll a Step 2 Excited e- leave PS II (oxidation)  received at primary e- acceptor (reduction) Step 3 Primary e- acceptor donates e- to 1st ETC • e- lose energy passing down the ETC • Lost energy is used to pump protons (H+) into thylakoid Step 4 These e- replace the e- lost in PS I

  11. Light Reaction Steps @ PS I Step 1 PS I Absorbs Light Energy in Pigment Molecules exciting the e- in the chlorophyll a • These events @ PS I are happening simultaneously as PS II Step 2 Excited e- leave PS I (oxidation)  received at primary e- acceptor (reduction) Step 3 Primary e- Aceptor donates e- to a 2nd ETC • e- lose energy passing down the ETC • Lost energy is used to combine e- with a proton (H+) and an e- acceptor molecule NADP+ to form NADPH in stroma

  12. Restoring PS II • Lost e- at PS II replaced by H2O • Enzyme splits H2O • 2H2O  4H+ + 4e- + O2 Left inside thylakoid Replace PS II Diffuses out of plant

  13. Chemiosmosis • Generates ATP • Relies onH+ conc. gradient: Creates PE • Maintained by: • Breakdown of H2O • Released energy from PS II e- transport chain pumps H+into thylakoid • ATP synthase: multifunctional protein • Channel • Enzyme

  14. Chemiosmosis

  15. **Summary of Light Reaction**

  16. Calvin Cycle= Light Independent Rxn Carbon Fixation • CO2 organic cmpds Can’t Run Without • NADPH • ATP G3P PGAL/G3P Converted to: • Organic Compounds • RuBP start cycle

  17. Calvin Cycle PGA G3P

  18. PHOTOSYNTHESIS SUMMARY

  19. Alternative Pathways • Regular Pathway: • C3 Pathway • Calvin Cycle: 3-C compound (PGA) • Alternative Pathways: adaptation to hot, dry climate • C4 Pathway • Fix Carbon into 4-C compound Calvin Cycle • Lose less H2O for same carbohydrate made • Sugar cane, corn, crabgrass • CAM Pathway • Fix Carbon into compounds at night Calvin Cycle by day • Grow slowly, but lose less H2O than C3 & C4 • Cacti, pineapples

  20. C4 and CAM Plants

  21. Influences on Rate of Photosynthesis • Light Intensity Increases • Increases photosynthesis until reach plateau • CO2 Increases • Increases photosynthesis until reach plateau • Temperature Increases • Increases photosynthesis until enzymes denatured & stomata close decreases photosynthesis

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