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Photosynthesis

"Discover the essential process of photosynthesis where organisms harness sunlight to create food molecules rich in energy. Learn the stages, leaf structure, chloroplast components, pigments, and light reactions involved. Dive into the historical experiments that unlocked the secrets of photosynthesis and understand the critical role of photons and pigments. Explore the dynamics of chlorophyll, carotenoids, and their functionalities within the intricate photosystems. Delve into the Calvin Cycle, light reactions, and the transformation of CO2 into organic molecules through this intricate energy-generating process that sustains life."

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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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