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Photosynthesis

Photosynthesis. Light energy. CO 2. H 2 O. C 6 H 12 O 6. O 2. 6. +. 6. +. 6. Carbon dioxide. Water. Glucose. Oxygen gas. PHOTOSYNTHESIS. 0. Photosynthesis. 0. Human demand for energy Fossil fuel supplies? Energy plantations Biomass energy. Carbon and Energy.

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Photosynthesis

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  1. Photosynthesis

  2. Light energy CO2 H2O C6H12O6 O2 6 + 6 + 6 Carbon dioxide Water Glucose Oxygen gas PHOTOSYNTHESIS 0 Photosynthesis

  3. 0 • Human demand for energy • Fossil fuel supplies? • Energy plantations • Biomass energy

  4. Carbon and Energy • Photoautotrophs • C source? • Energy source? • Heterotrophs • C source? • Energy source?

  5. Figure 7.1A–D Photoautotrophs

  6. Mesophyll Cell Leaf Cross Section Leaf Mesophyll LM 2,600  Chloroplast Vein Stoma O2 CO2 Chloroplast Outer membrane TEM 9,750  Inner membrane Stroma Intermembrane space Stroma Grana Thylakoid Granum Thylakoid space Where does PS happen? • Green parts… • Chloroplasts (stroma and thylakoids) • Stomata

  7. Where does O2 come from? • By splitting water

  8. Reduction   6 O2 6 CO2 6 H2O C6H12O6 Oxidation Oxidation   6 H2O C6H12O6 6 CO2 6 O2 Reduction 0 Just like respiration? • Redox processes

  9. Photosynthesis Energy-storing Releases O2 Requires CO2 Aerobic Respiration Energy-releasing Requires O2 Releases CO2 Linked Processes

  10. H2O CO2 Chloroplast Light NADP+ ADP + P CALVIN CYCLE (in stroma) LIGHT REACTIONS (in thylakoids) ATP Electrons NADPH O Sugar 0 Overview 2 stages • The light reactions… • Energy capture • produce O2 • The Calvin cycle • Uses CO2 • Makes sugar • The Coenzymes • ATP • NADPH

  11. Increasing energy 1 nm 1 m 10–5 nm 10–3 nm 103 nm 106 nm 103 m Micro- waves Radio waves Gamma rays X-rays UV Infrared Light Reflected light Visible light 400 500 600 700 750 380 Wavelength (nm) Absorbed light Chloroplast 650 nm Transmitted light Visible Light

  12. Pigments Colors? • Wavelengths not absorbed • Chlorophylls a and b • Carotenoids

  13. Chlorophylls chlorophyll b chlorophyll a Wavelength absorption (%) Wavelength (nanometers)

  14. T.E. Englemann’s Experiment

  15. Photons • Packets of light energy • Shortest wavelength (blue-violet light) = highest energy

  16. Photosystem Reaction center Primary electron acceptor Light-harvesting complexes Photon Excited state To electron transport chain e– Heat Energy of electron e– Photon Thylakoid membrane Photon (fluorescence) Ground state Pigment molecules Chlorophyll molecule Transfer of energy Chlorophyll a molecule 0 Photons and Photosystems Strike chlorophyll in photosystem Excite an electron Figure 7.7B, C

  17. Photosystem Reaction center Primary electron acceptor Light-harvesting complexes Photon Excited state To electron transport chain e– Heat Energy of electron e– Photon Thylakoid membrane Photon (fluorescence) Ground state Pigment molecules Chlorophyll molecule Transfer of energy Chlorophyll a molecule • Photon energy transfer to reaction-center • Excites electron • Which is taken by the primary electron acceptor • Which leads to the ETC

  18. Photosystem: Harvester Pigments • When excited by light energy:

  19. Photon Photon Photosystem II Photosystem I + H+ NADPH NADP+ Stroma 1 6 e– 2 e– Thylakoid membrane 4 5 P700 1 P680 2 Thylakoid space 3 Electron transport chain Provides energy for synthesis of by chemiosmosis ATP H2O O2 + 2 H+ Electron Transfer Chain • Uses electrons from reaction center • Powers H+ pump to produce ATP • Produces NADPH

  20. e– ATP e– e– NADPH e– e– e– Mill makes ATP Photon e– Photon Figure 7.8B Photosystem II Photosystem I Electron Transfer Chain • Electrons move from photosystem II to I • Make ATP • Electrons from photosystem I • Reduce NADP+ to NADPH

  21. Chloroplast Stroma (low H+ concentration) H+ H+ Light Light ADP + P ATP H+ NADP+ H+ NADPH + H+ Thylakoid membrane H+ H+ H2O 1 H+ H+ H+ H+ + O2 H+ 2 H+ H+ 2 H+ Photosystem II Electron transport chain Photosystem I ATP synthase H+ Thylakoid space (high H+ concentration) ATP Production

  22. Light-Independent Reactions • They put the “synthesis” in photosynthesis • Calvin-Benson cycle • In stroma

  23. Overall reactants CO2 ATP NADPH Overall products Glucose ADP NADP+ Calvin-Benson Cycle Cyclic! RuBP is regenerated

  24. Figure 7.14_4

  25. C3 Plants • 1st stable molecule is 3C PGA • C3 plants: tomatoes, petunias, roses, daisies, avocados

  26. C3 Plants • Hot, dry days what happens? • Inside leaf? • O2 increases • CO2 drops • PS rate?

  27. C4 Pathway • CO2 miner • 4C oxaloacetate forms in bundle sheath cells • Grasses

  28. CAM Plants • Opens stomata at night • Forms 4C compound • Release CO2 • Succulents and cacti • Slow growing

  29. C4 and CAM

  30. Greenhouse Effect? • What is the role of PS in global warming?

  31. Some heat energy escapes into space Sunlight ATMOSPHERE Radiant heat trapped by CO2 and other gases Greenhouse Effect • Excess CO2 in the atmosphere

  32. Question of the Day Scientists at Stanford University conducted a study on California grasslands. They looked at the effects of increased levels of CO2 , soil nitrogen, and temperature (modeling our future) on plant growth. What did they find?

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