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Photosynthesis

Photosynthesis. Photosynthesis in Nature Capturing the Energy in Light Light-dependent Reactions The Calvin Cycle Light-independent Reactions. Photosynthesis in Nature. Autotrophy & Heterotrophy Chloroplast Structure & Function Leaf Structure & Function. Trophic Processes. Autotroph

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Photosynthesis

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  1. Photosynthesis • Photosynthesis in Nature • Capturing the Energy in Light • Light-dependent Reactions • The Calvin Cycle • Light-independent Reactions

  2. Photosynthesisin Nature • Autotrophy & Heterotrophy • Chloroplast Structure & Function • Leaf Structure & Function

  3. Trophic Processes • Autotroph • auto = “self”; trophos = “feeding” • produce organic molecules from inorganic substrates obtained from the environment • Types: • chemoautotrophy (prokaryotic bacteria only) • photoautotrophy

  4. Trophic Processes • Photoautotroph • obtains inorganic molecules from environment • energy source – radiant energy of sunlight (photosynthesis) • examples: • cyanobacteria (prokaryotes) • all algae & many other protists • all plants (w/ exceptions)

  5. Prokaryotic Photoautotrophs Oscillatoria - filamentous cyanobacterium (blue-green alga)

  6. EukaryoticProtist Photoautotrophs Euglena – a unicellular mixotroph

  7. EukaryoticProtist Photoautotrophs Laminaria – a multicellular algal kelp

  8. EukaryoticPlantPhotoautotrophs flowering seed plant moss fern

  9. Trophic Processes • Heterotroph • hetero = “other”; trophos = “feeding” • obtain organic molecules from feeding on other organisms or their products • Types: • Photoheterotrophs (prokaryotic bacteria only) • chemoheterotrophs

  10. Trophic Processes • Chemoheterotroph • obtains organic molecules by ingestion of or absorption from other organisms • energy source – breakdown of organic molecules ingested or absorbed from other organisms • examples: • most bacteria • many protists • all fungi • all animals

  11. ProkayoticChemoheterotrophs Salmonella – a parasitic enteric bacterium

  12. Eukaryotic Protist Chemoheterotrophs ingestedParamecia Amoeba – a free-living, unicellular protist

  13. Eukaryotic Fungal Chemoheterotrophs Mycena – a club fungus

  14. Eukaryotic Animal Chemoheterotrophs Oh my!

  15. Plant LeafStructure & Function • Leaf • plant organ specialized for photosynthesis • Leaf tissues • epidermis – contains stomata (sing., stoma) to allow influx of CO2 • mesophyll – contains photosynthetic cells • vascular tissue: • xylem – carries H2O to leaf • phloem – carries photosynthetic products away to plant stems & roots

  16. Plant LeafStructure & Function

  17. Plant CellStructure & Function • Plastids • chloroplasts • plant organelles specialized for photosynthesis • contain chlorophyll a and accessory pigments in thylakoid membrane • amyloplasts – store starch • chromoplasts – store colorful pigments for animal attraction to flowers • Central vacuole • bounded by tonoplast • stores H2O, waste products, nutrients, protective toxins

  18. Plant ChloroplastStructure & Function • outer membrane • intermembrane space • inner membrane • stroma • site of light-independent reactions • thylakoid membrane • grana (sing., granum) • site of light-dependent reactions • thylakoid space • site of [H+] (light-dependent reactions) Chlorophyll molecule

  19. Capturing Light Energy Light-dependent Reactions • Energy for Life Processes • Light Absorption in Chloroplasts • Electron Transport • Chemiosmosis

  20. Learning Objectives • Describe the role of chlorophylls & other pigments in photosynthesis • Summarize the main events of electron transport • Explain how the structure of the chloroplast relates to its function

  21. Energy &Life Processes • Photosynthesis • The conversion of light energy into chemical energy stored in organic compounds • glucose  starch • amino acids  proteins • Biochemical Pathways • A series of linked chemical reactions • The products of one reaction are consumed by the following reaction

  22. Autotrophs & Heterotrophs Autotrophs Autotrophs & heterotrophs

  23. PhotosynthesisOverview Tracking Atoms Through Photosynthesis Chemical Equation: 6CO2 + 6H2O+LightEnergy C6H12O6+ 6O2

  24. Chloroplast Structure • Outer membrane • Intermembrane space • Inner membrane • Stroma • Thylakoid membrane • Arranged in stacks: grana (sing., granum) • Thylakoid space

  25. Chlorophyll Molecule – in Thylakoid • Chlorophyll a • primary photosynthetic pigment molecule – in thylakoid • absorbs light energy: peak λ • 420 nm (violet) • 680 nm (orange-red) • reflects blue-green

  26. Accessory Pigments – in Thylakoid • Chlorophyll b • passes absorbed light energy to chlorophyll a • absorbs light energy: peak λ • 480 nm (violet-blue) • 650 nm (orange) • reflects yellow-green

  27. Accessory Pigments – in Thylakoid • Carotenoids • absorbed light energy • passed to chlorophyll a • photoprotection – absorption & dissipation of harmful, excess light energy • absorbs light energy: peak λ • 470 nm (violet-blue) • 650 nm (orange) • reflects yellow-orange

  28. Photoexcitation:Chlorophyll in Thylakoid

  29. Electromagnetic Spectrum

  30. Absorption & Action Spectra of Chlorophyll Absorption spectrum – plots a pigment’s light absorption against the wavelength of light absorbed Action spectrum – plots the wavelength of light absorbed by a pigment against a measure of photosynthetic rate (like CO2 consumption or O2 release)

  31. Photosystems • light harvesting complexes of the thylakoidmembrane • Structure • antenna complex: • clusters of 100s of chl a, chl b, & carotenoid molecules • proteins • reaction center: • chl a near a protein primary electron acceptor

  32. Photosystems • Function • antenna complex: • captures photons from light • energy passed from pigment molecule to pigment molecule until it reaches a reaction center • reaction center: • chl a absorbs energy and boosts electron to higher energy level where it is captured by the primary electron acceptor

  33. Pathways of Photosynthesis • Equation for Photosynthesis • Light-dependent Reactions • Non-cyclic electron flow • Cyclic electron flow • Light-independent Reactions • Calvin cycle (C3) • C4 processes • CAM (crassulacean acid metabolism)

  34. PhotosynthesisOverview In thylakoid membrane & space In stroma

  35. Noncyclic Electron Flow

  36. Light-dependent Reaction: Requirements • requires radiant energy from sunlight • Involves 2 photosystems • photosystemI (P700) • photosystem II (P680) • requires H2O from environment as source of H+ & e- • utilizes electron transport chains (ETCs)

  37. Light-dependent Reaction Steps • Photoexcitation step: light energy forces a pair of e- to enter a higher energy level in two chlorophyll molecules of photosystem II • Electron capture step: excited e- leave chlorophylls & are captured by a primary e- acceptor

  38. Light-dependent Reaction Steps (3) Pq-Pc ETC step: photoexcited e- pass from primary e- acceptor to photosystem I via “Pq-Pc” ETC; e- lose energy which is used to pump protons (H+) into thylakoid space; Note - photosystem I has previously lost and e- by photoexcitation (4) Photoexcitation step: light energy forces a pair of e- to enter a higher energy level in two chlorophyll molecules of photosystem I; e- move to another primary e- acceptor

  39. Light-dependent Reaction Steps (5)NADPH formation step: primary electron acceptor of photosystem I passes photoexcited e- to “Fd” ETC; e- pass down ETC to enzyme; e- from chain & H+ are attached to NADP+ to produce NADPH. Note: NADPH will be used in the light-independent reactions of photosynthesis

  40. Light-dependent Reaction Steps (6)Restoration of photosystem II e-: 2 H2O are split by a water-splitting enzyme to produce: 2H2O  4H+ + 4e- + O2

  41. Chemiosmosis

  42. Mechanical Analogyfor Light Reactions

  43. Light-dependent Reaction: Products • produces O2 as byproduct • produces energy from e- moving down ETCs • used to pump H+ across a membrane • creates a proton motive force • produces ATP • from flow of H+ through ATP synthase • produces NADPH • as final electron acceptor

  44. Organization of the Thylakoid Membrane

  45. The “Light” Reactions • To View Video: • Move mouse cursor over slide title-link • When hand appears, click once • MOV Video plays about 1-1/2 min

  46. Light-dependent ReactionsThe Calvin Cycle • Carbon Fixation by the Calvin Cycle • Alternative Pathways • Rate of Photosynthesis

  47. LearningObjectives • Summarize the main events of the Calvin cycle • Describe what happens to the compounds made in the Calvin cycle • Distinguish btw/ C3, C4, & CAM plants • Explain how environmental factors influence photosynthesis

  48. Light-independent Reaction:The Calvin Cycle

  49. Light-independent Reaction: Requirements requires 6 CO2 from environment as C source requires 6 NADPH noncyclic e- flow of light-dep. Rx requires 9 ATP 6 from noncyclicphotophosphorylation 3 from cyclic photophosphorylation requires 3 RuBP molecules

  50. Calvin CycleReactions Carbon fixation incorporation of CO2 into RuBP – ribulosebiphosphate enzyme that fixes (attaches) CO2 to RuBP: rubisco– RuBPcarboxylase most abundant protein on earth Cycles 2 times using 3 CO2 @ time to make C6H12O6

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