1 / 49

Where It Starts – Photosynthesis

Where It Starts – Photosynthesis. Chapter 6. Sunlight as an Energy Source. Photosynthesis runs on a fraction of the electromagnetic spectrum, or the full range of energy radiating from the sun. Visible Light. Wavelengths humans perceive as different colors Violet (380 nm) to red (750 nm)

ranger
Download Presentation

Where It Starts – Photosynthesis

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  1. Where It Starts – Photosynthesis Chapter 6

  2. Sunlight as an Energy Source • Photosynthesis runs on a fraction of the electromagnetic spectrum, or the full range of energy radiating from the sun

  3. Visible Light • Wavelengths humans perceive as different colors • Violet (380 nm) to red (750 nm) • Longer wavelengths, lower energy

  4. Electromagnetic Spectrum Shortest Gamma rays wavelength X-rays UV radiation Visible light Infrared radiation Microwaves Longest Radio waves wavelength

  5. Photons • Packets of light energy • Each type of photon has fixed amount of energy • Photons having most energy travel as shortest wavelength (blue-green light)

  6. Pigments • Light-absorbing molecules • Absorb some wavelengths and transmit others • Color you see are the wavelengths not absorbed

  7. Pigment Structure • Light-catching part of molecule often has alternating single and double bonds • These bonds contain electrons that are capable of being moved to higher energy levels by absorbing light

  8. Variety of Pigments Chlorophylls a and b Carotenoids Xanthophylls Phycobilins Anthocyanins

  9. Chlorophylls Main pigments in most photoautotrophs chlorophyll a Wavelength absorption (%) chlorophyll b Wavelength (nanometers)

  10. Carotenoids • Found in all photoautotrophs • Absorb blue-violet and blue-green that chlorophylls miss • Reflect red, yellow, orange wavelengths • Two types • Carotenes - pure hydrocarbons • Xanthophylls - contain oxygen

  11. Yellow, brown, purple, or blue accessory pigments Xanthophylls

  12. Phycobilins & Anthocyanins Red to purple pigments • Phycobilins • Found in red algae and cyanobacteria • Anthocyanins • Give many flowers their colors

  13. T.E. Englemann’s Experiment Background • Certain bacterial cells will move toward places where oxygen concentration is high • Photosynthesis produces oxygen

  14. T.E. Englemann’s Experiment Hypothesis • Movement of bacteria can be used to determine optimal light wavelengths for photosynthesis

  15. T.E. Englemann’s Experiment Method • Algal strand placed on microscope slide and illuminated by light of varying wavelengths • Oxygen-requiring bacteria placed on same slide

  16. T.E. Englemann’s Experiment Results Bacteria congregated where red and violet wavelengths illuminated alga Conclusion Bacteria moved to where algal cells released more oxygen – areas illuminated by the most effective light for photosynthesis

  17. T.E. Englemann’s Experiment

  18. Light-Dependent Reactions • Pigments absorb light energy, give up e- which enter electron transfer chains • Water molecules are split, ATP and NADH are formed, and oxygen is released • Pigments that gave up electrons get replacements

  19. Light-Independent Reactions • Synthesis part of photosynthesis • Can proceed in the dark • Take place in the stroma • Calvin-Benson cycle

  20. Photosynthesis Equation

  21. Chloroplasts Organelles of photosynthesis

  22. Inside the Chloroplast • Two outer membranes enclose a semifluid interior, the stroma • Thylakoid membrane inside the stroma

  23. Inside the Chloroplast • Photosystems are embedded in thylakoids, containing 200 to 300 pigments and other molecules that trap sun’s energy • Two types of photosystems: I and II

  24. Carbon and Energy Sources • Photoautotrophs • Carbon source is carbon dioxide • Energy source is sunlight • Heterotrophs • Get carbon and energy by eating autotrophs or one another

  25. Photoautotrophs • Capture sunlight energy and use it to carry out photosynthesis • Plants • Some bacteria • Many protistans

  26. Photosynthesis Energy-storing pathway Releases oxygen Requires carbon dioxide Aerobic Respiration Energy-releasing pathway Requires oxygen Releases carbon dioxide Linked Processes

  27. Two Stages of Photosynthesis

  28. Excitation of Electrons • Excitation occurs only when the quantity of energy in an incoming photon matches the amount of energy necessary to boost the electrons of that specific pigment • Amount of energy needed varies among pigment molecules

  29. Pigments in Photosynthesis • Bacteria • Pigments in plasma membranes • Plants • Pigments embedded in thylakoid membrane system • Pigments and proteins organized into photosystems • Photosystems located next to electron transfer chains

  30. Photosystem Function: Harvester Pigments • Most pigments in photosystem are harvester pigments • When excited by light energy, these pigments transfer energy to adjacent pigment molecules • Each transfer involves energy loss

  31. Photosystem Function: Reaction Center • Energy is reduced to level that can be captured by molecule of chlorophyll a • This molecule (P700 or P680) is the reaction center of a photosystem • Reaction center accepts energy and donates electron to acceptor molecule

  32. Electron Transfer Chains • Adjacent to photosystem • Acceptor molecule donates electrons from reaction center • As electrons flow through chain, energy they release is used to produce ATP and, in some cases, NADPH

  33. Cyclic Electron Flow • Electrons • are donated by P700 in photosystem I to acceptor molecule • flow through electron transfer chain and back to P700 • Electron flow drives ATP formation • No NADPH is formed

  34. Noncyclic Electron Flow • Two-step pathway for light absorption and electron excitation • Uses two photosystems: type I and type II • Produces ATP and NADPH • Involves photolysis - splitting of water

  35. ATP and NADPH Formation

  36. ATP Formation • When water is split during photolysis, hydrogen ions are released into thylakoid compartment • More hydrogen ions are pumped into the thylakoid compartment when the electron transfer chain operates

  37. ATP Formation • Electrical and H+concentration gradient exists between thylakoid compartment and stroma • H+ flows down gradients into stroma through ATP synthesis • Flow of ions drives formation of ATP

  38. Energy Transfers

  39. Energy Transfers

  40. Overall reactants Carbon dioxide ATP NADPH Overall products Glucose ADP NADP+ Calvin-Benson Cycle Reaction pathway is cyclic and RuBP (ribulose bisphosphate) is regenerated

  41. Calvin-Benson Cycle

  42. Building Glucose • PGA accepts • phosphate from ATP • hydrogen and electrons from NADPH • PGAL (phosphoglyceraldehyde) forms • When 12 PGAL have formed • 10 are used to regenerate RuBP • 2 combine to form phosphorylated glucose

  43. Using the Products of Photosynthesis • Phosphorylated glucose is the building block for: • Sucrose • The most easily transported plant carbohydrate • Starch • The most common storage form

  44. The C3 Pathway • In Calvin-Benson cycle, the first stable intermediate is a three-carbon PGA • Because the first intermediate has three carbons, the pathway is called the C3 pathway

  45. Photorespiration in C3 Plants • On hot, dry days stomata close • Inside leaf • Oxygen levels rise • Carbon dioxide levels drop • Rubisco attaches RuBP to oxygen instead of carbon dioxide • Only one PGAL forms instead of two

  46. C4 Plants • Carbon dioxide is fixed twice • In mesophyll cells, carbon dioxide is fixed to form four-carbon oxaloacetate • Oxaloacetate is transferred to bundle-sheath cells • Carbon dioxide is released and fixed again in Calvin-Benson cycle

  47. C4 Plants

  48. CAM Plants • Carbon is fixed twice (in same cells) • Night • Carbon dioxideis fixed to form organic acids • Day • Carbon dioxide is released and fixed in Calvin-Benson cycle

  49. Summary of Photosynthesis

More Related