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Photosynthesis

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Photosynthesis

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  1. Photosynthesis How Plants Make Food from Sunlight and Low Energy Molecules

  2. Photoautotrophs

  3. 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

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

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

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

  7. 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

  8. T.E. Englemann’s Experiment

  9. 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

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

  11. Focusing in on the location of photosynthesis in a plant

  12. Location and structure of chlorophyll molecules in plants

  13. Photosynthesis Equation LIGHT ENERGY 6O2 + C6H12O6 + 6H2O 12H2O + 6CO2 oxygen glucose water carbon dioxide water

  14. Two Stages of Photosynthesis sunlight water uptake carbon dioxide uptake ATP ADP + Pi LIGHT DEPENDENT-REACTIONS LIGHT INDEPENDENT-REACTIONS NADPH NADP+ glucose P oxygen release new water

  15. Sunlight Energy • Continual input of solar energy into Earth’s atmosphere • Almost 1/3 is reflected back into space • Of the energy that reaches Earth’s surface, about 1% is intercepted by photoautotrophs

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

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

  18. 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)

  19. Pigments • Light-absorbing molecules • Absorb some wavelengths and transmit others • Color you see are the wavelengths NOT absorbed chlorophyll a chlorophyll b Wavelength (nanometers)

  20. 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 transport systems

  21. Pigments in a Photosystem reaction center (a specialized chlorophyll a molecule)

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

  23. 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

  24. 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

  25. Cyclic Electron Flow e– electron acceptor electron transport system e– e– ATP e–

  26. Electron Transport System • Adjacent to photosystem • Acceptor molecule donates electrons from reaction center • As electrons flow through system, energy they release is used to produce ATP and, in some cases, NADPH

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

  28. Energy Changes second transport system e– NADPH e– first transport system e– Potential to transfer energy (voids) e– (PHOTOSYSTEM I) (PHOTOSYSTEM II) 1/2 O2 + 2H+ H2O

  29. 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

  30. Figure 10.4 An overview of photosynthesis: cooperation of the light reactions and the Calvin cycle (Layer 1)

  31. Figure 10.4 An overview of photosynthesis: cooperation of the light reactions and the Calvin cycle (Layer 2)

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

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

  34. Melvin Calvin

  35. The Calvin cycle (Layer 1)

  36. The Calvin cycle (Layer 2)

  37. The Calvin cycle (Layer 3)

  38. 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

  39. 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

  40. 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

  41. 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

  42. Figure 10.18 C4 leaf anatomy and the C4 pathway

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

  44. Figure 10.19 C4 and CAM photosynthesis compared

  45. Figure 10.20 A review of photosynthesis