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Photosynthesis

Photosynthesis. Chapter 10. Energy source. Autotrophs: Producers Make own organic molecules Heterotrophs: Consumers. Photosynthesis. Photosynthesis. Organisms capture energy from sunlight Build food molecules Rich in chemical energy 6CO 2 + 12H 2 O ⇨

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Photosynthesis

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  1. Photosynthesis Chapter 10

  2. Energy source • Autotrophs: • Producers • Make own organic molecules • Heterotrophs: • Consumers

  3. Photosynthesis

  4. Photosynthesis • Organisms capture energy from sunlight • Build food molecules • Rich in chemical energy • 6CO2 + 12H2O ⇨ C6H12O6 + 6H2O + 6O2

  5. Photosynthesis • Captures only 1% of sun’s energy • Provides energy for life

  6. Photosynthesis

  7. Leaf structure • Stoma (Stomata) opening on leaf • Exchange of gases. • Chloroplasts • Mesophyll layer of leaf

  8. Chloroplasts • Thylakoids: • Internal membranes of chloroplasts • Grana: • Stacks of thylakoids • Chlorophyll: • Green pigment • Captures light for photosynthesis • Membranes of thylakoids

  9. Chloroplasts • Stroma: • Semi-liquid substance • Surrounds thylakoids • Contain enzymes • Make organic molecules from carbon dioxide

  10. Chloroplasts

  11. Chloroplast Fig. 10-3b Outer membrane Thylakoid Intermembrane space Stroma Granum Thylakoid space Inner membrane 1 µm

  12. Chloroplasts • Photosystem: • Cluster of photosynthetic pigments • Membrane of thylakoids • Each pigment captures energy • Photosystem then gathers energy • Energy makes ATP, NADPH & organic molecules

  13. NADP+ • Nicotinamide Adenine Dinucleotide Phosphate • Coenzyme • Electron carrier • Reduced during light-dependent reactions • Used later to reduce carbon • Carbon dioxide forms organic molecules • Photosynthesis is a redox reaction

  14. Photophosphorylation • Addition of phosphate group to ADP • Light energy

  15. Photosynthesis • Occurs in 3 stages • 1. Capturing energy from sun • 2. Energy makes ATP • Reducing power in NADPH • 3. ATP & NADPH • Power synthesis of organic molecules

  16. Photosynthesis • Light dependent reactions • First 2 steps of photosynthesis • Presence of light • Light-independent reactions • Formation of organic molecules • Calvin cycle • Can occur +/- light

  17. Experimental history • Jan Baptista van Helmont • Plants made their own food • Joseph Priestly • Plants “restored” the air

  18. Experimental history • Jan Ingenhousz • Sun’s energy split CO2 • Carbon & Oxygen • Oxygen was released into air • Carbon combined with water • Make carbohydrates

  19. Experimental history • Fredrick Forest Blackman • 1. Initial “light” reactions are independent of temperature • 2. Second set of “dark” reactions are independent of light • Dependent on CO2 concentrations & temperature • Enzymes involved in light-independent reactions

  20. Experimental history • C.B. van Neil • Looked at light in photosynthesis • Studied photosynthesis in Bacteria

  21. C.B. van Neil CO2 + 2H2S (CH2O) + H2O + 2S CO2 + 2H2A (CH2O) + H2O + A2 CO2 + 2H2O (CH2O) + H2O + O2

  22. C.B. van Neil • O2 produce from plant photosynthesis comes from splitting water • Not carbon dioxide • Carbon Fixation: • Uses electrons & H+ from splitting water • Reduces carbon dioxide into organic molecules (simple sugars). • Light-independent reaction

  23. CO2 + 2H2O (CH2O) + H2O + O2 CO2 + 2H2O  (CH2O) + H2O + O2

  24. Photosynthesis • 1. Chloroplasts • 2. Light-dependent reactions • Sun’s energy makes NADPH & ATP • 3. Light-independent reactions • ATP & NADPH • CO2 into organic molecules

  25. CO2 H2O Light NADP+ Fig. 10-5-4 ADP + P i Calvin Cycle Light Reactions ATP NADPH Chloroplast [CH2O] (sugar) O2

  26. Sunlight • UV light from sun • Source of energy when life began • UV light can cause mutations in DNA • Lead to skin cancer

  27. Light • Photon: • Packets of energy • UV light photons have greater energy than visible light • UV light has shorter wavelengths

  28. Light • Visible light • Purple shorter wavelengths • More energetic photons • Red longer wavelengths • Less energetic photons

  29. Spectrum

  30. Spectrum

  31. Absorption Spectrums • Photon of energy strikes a molecule • Absorbed by the molecule or lost as heat • Depends on energy in photon (wavelength) • Depends on atom’s available energy levels • Specific for each molecule

  32. Pigments • Molecules • Absorb energy in visible range • Chlorophylls & Carotenoids • Chlorophyll a & b • Absorb photons in the blue-violet & red light

  33. Pigments • Chlorophyll a main pigment of photosynthesis • Converts light energy to chemical energy • Chlorophyll b & carotenoids are accessory pigments • Capture light energy at different wavelengths

  34. Pigments

  35. Pigments Chlorophyll b Chlorophyll a Carotenoids

  36. Chlorophyll structure • Located in thylakoid membranes • A porphyrin ring with a Mg in center • Hydrocarbon tail • Photons are absorbed by the ring • Absorbs photons very effectively • Excites electrons in the ring

  37. Chlorophyll structure

  38. Light & pigments

  39. Carotenoids • Two carbon rings attached by a carbon chain • Not as efficient as the Chlorophylls • Beta carotene (helps eyes) • Found in carrots and yellow veggies

  40. Photosystems • Captures the light • Located on surface of the photosynthetic membrane • Chlorophyll a molecules • Accessory pigments (chlorophyll b& carotenoids) • Associated proteins

  41. Photosystems • Consists of 2 components • 1. Antenna (light gathering) complex • 2. Reaction center

  42. Photosystem • 1. Antenna complex • Gathers photons from sun • Web of Chlorophyll a molecules • Held by proteins in membrane • Accessory pigments carotenoids • Energy is passed along the pigments to reaction center

  43. Photosystems • 2. Reaction centers • 2 special chlorophyll a molecules • Accept the energy • Chlorophyll a than passes the energized electron to an acceptor • Acceptor is reduced (quinone)

  44. Photosystem

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

  46. 2 photosystems • Photosystem I (older) • Absorbs energy at 700 nm wavelength • Generates NADPH • Photosystem II (newer) • Absorbs energy at 680 nm wavelength • Splits water (releases oxygen) • Generates ATP • 2 systems work together to absorb more energy

  47. Photosynthesis (Process) • Light dependent reactions • Linear electron flow • Energy transfer • Thylakoid membranes

  48. Light dependent reactions • Photosystem II (680 nm) • Light is captured by pigments • Excites an electron (unstable) • Energy is transferred to reaction center (special chlorophyll) • Passes excited electron to an acceptor molecule

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