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Phs 08 09


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Phs 08 09

  1. 1. PHOTOSYNTHESIS Light Energy to Chemical Energy
  2. 3. Importance of Photosynthesis <ul><li>Source of atmospheric oxygen </li></ul><ul><ul><li>Earth’s atmosphere </li></ul></ul><ul><ul><ul><li>78% N 2 , 21% O 2 , 0.035% CO 2 </li></ul></ul></ul><ul><li>Source of energy for food chain </li></ul><ul><ul><li>Photoautotrophs vs. Heterotrophs </li></ul></ul><ul><li>Direct/indirect involvement in all products </li></ul><ul><li>Maintain stable ecosystem </li></ul>
  3. 4. Photosynthesis and Transpiration Whole Plant Perspective <ul><li>CO 2 enters leaf through open stomata; water is lost </li></ul><ul><li>CO 2 is converted to carbohydrate in the leaf & transported as sucrose in phloem </li></ul><ul><li>Water is taken up by roots & transported via xylem </li></ul><ul><li>Loss of water from the leaf via stomata is evapotranspiration </li></ul>
  4. 5. Photosynthesis <ul><li>6 H 2 0 + 6 CO 2 + Light Energy  C 6 H 12 O 6 + 6 O 2 </li></ul>
  5. 7. Chloroplast Granum Thylakoid Stroma Outer Membrane Inner Membrane
  6. 8. Thylakoid Thylakoid Membrane Thylakoid Space Granum
  7. 9. Grana – Site of ‘Light Reactions’. Pigments Embedded in Thylakoid Membranes. Stroma – Site of ‘Light-Independent Reactions’. CO 2 Fixed into Sugar (Glucose). Membrane – Bounded by 2 smooth membranes
  8. 10. Visible light
  9. 11. <ul><li>Chlorophyll pigments harvest energy (photons) by absorbing certain wavelengths </li></ul><ul><ul><li>Blue (420 nm) </li></ul></ul><ul><ul><li>Red (660 nm) </li></ul></ul>
  10. 12. <ul><li>Plants are green because the green wavelength is reflected, not absorbed. </li></ul>
  11. 13. Photosynthetic Pigments <ul><li>Main photosynthetic pigment </li></ul><ul><ul><li>Chlorophyll a </li></ul></ul><ul><li>Accessory Pigments </li></ul><ul><ul><li>Absorb light & transfer energy to Chl a </li></ul></ul><ul><ul><li>Chlorophyll b </li></ul></ul><ul><ul><li>Carotenoids (Aids in photoprotection) </li></ul></ul><ul><ul><ul><li>Carotenes </li></ul></ul></ul><ul><ul><ul><li>Xanthophylls </li></ul></ul></ul>
  12. 14. Photosynthetic Unit <ul><li>Chlorophyll bound to proteins in PS </li></ul><ul><li>Light harvesting molecules pass their energy at a reaction center </li></ul><ul><li>Two photosystems </li></ul><ul><ul><li>PS I (P700) </li></ul></ul><ul><ul><li>PS II (P680) </li></ul></ul>
  13. 16. Processes in Photosynthesis (1) light O 2 CO 2 sugar starch H 2 O (2) Light Reactions (3) Dark Reactions NADPH ATP
  14. 17. 3 Processes in Photosynthesis <ul><li>Absorption of light energy </li></ul><ul><ul><li>Pigments in thylakoids </li></ul></ul><ul><li>Light Reactions </li></ul><ul><ul><li>Pigments & proteins in thylakoids </li></ul></ul><ul><ul><li>Generates ATP and NADPH </li></ul></ul><ul><li>“ Dark” Reactions </li></ul><ul><ul><li>Enzymes in stroma </li></ul></ul><ul><ul><li>Reduce CO 2 to carbohydrates using ATP & NADPH </li></ul></ul>
  15. 18. <ul><li>The light- dependent reactions of photosynthesis produce chemical energy in the form of ATP and NADPH. </li></ul>
  16. 19. Lab 4B <ul><li>Expose samples to red wavelength </li></ul><ul><ul><li>Why? </li></ul></ul><ul><li>Role of DPIP </li></ul><ul><ul><li>Electron acceptor </li></ul></ul><ul><ul><ul><li>Works in place of NADP+ </li></ul></ul></ul><ul><ul><li>When DPIP is reduced, resultant increases light transmittance </li></ul></ul>
  17. 20. Light Reaction <ul><li>Light Dependent Reaction </li></ul><ul><li>Captures Light Energy </li></ul><ul><ul><li>Electrons exited to higher energy state </li></ul></ul><ul><li>Produces energy from solar power (photons) in the form of ATP and NADPH </li></ul><ul><li>Splits H 2 O, Uses H+ & Electrons, Spits out O 2 as waste </li></ul><ul><li>Two possible routes for electron flow: </li></ul><ul><ul><li>Noncyclic Electron Flow </li></ul></ul><ul><ul><li>Cyclic Electron Flow </li></ul></ul>
  18. 21. Light Reaction Noncyclic Electron Flow <ul><li>Uses Photosystem II and Photosystem I </li></ul><ul><li>Uses Electron Transport Chain (ETC) </li></ul><ul><ul><li>Pq (Plastoquinone) </li></ul></ul><ul><ul><li>Cytochrome complex </li></ul></ul><ul><ul><li>Pc (Plastocyanin – Cu-containing proteins) </li></ul></ul><ul><li>Other proteins involved (P700) </li></ul><ul><ul><li>Fd (Ferredoxin – Fe-containing protein) </li></ul></ul><ul><ul><li>NADP+ reductase </li></ul></ul><ul><li>Generates O 2 , ATP, and NADPH </li></ul>
  19. 25. Light Reaction Cyclic Electron Flow <ul><li>Uses Photosystem I only </li></ul><ul><li>Uses Electron Transport Chain (ETC) </li></ul><ul><ul><li>Fd (Ferredoxin) </li></ul></ul><ul><ul><li>Cytochrome complex </li></ul></ul><ul><li>Generates ATP only </li></ul><ul><ul><li>No production of NADPH </li></ul></ul><ul><ul><li>No release of O 2 </li></ul></ul>
  20. 26. Cyclic Electron Flow
  21. 27. Why Cyclic Electron Flow? <ul><li>Calvin cycle consumes more ATP than NADPH </li></ul><ul><li>Makes up the difference needed for the Calvin cycle to function properly </li></ul>
  22. 28. Light Reactions Inputs Outputs Light H 2 O ADP NADP + O 2 ( Waste) ATP NADP H + H + Energy Carrier Molecules Take Converted ‘Light’ Energy to Stroma
  23. 29. Chemiosmosis <ul><li>Powers ATP synthesis </li></ul><ul><li>Located in the thylakoid membranes </li></ul><ul><li>Uses ETC and ATP synthase (enzyme) to make ATP </li></ul><ul><li>Photophosphorylation </li></ul><ul><ul><li>Addition of phosphate to ADP to make ATP </li></ul></ul>
  24. 34. Dark Reaction <ul><li>Light Independent Reaction, Calvin Cycle, Carbon Fixation </li></ul><ul><li>Occurs in the stroma </li></ul><ul><li>Uses energy (ATP and NADPH) from light reaction to make sugar (glucose) from CO 2 </li></ul><ul><li>Uses CO 2 </li></ul><ul><li>Regenerates ‘Empty’ Carrier Molecules (NADP+ & ADP) </li></ul><ul><li>To produce glucose </li></ul><ul><ul><li>It takes 6 turns and uses 18 ATP and 12 NADPH </li></ul></ul>
  25. 35. 3 Phases – Calvin Cycle <ul><li>Carbon fixation </li></ul><ul><li>Reduction </li></ul><ul><li>G3P routes </li></ul>
  26. 37. Photosynthesis H 2 O CO 2 O 2 C 6 H 12 O 6 Light Reaction Dark Reaction Light is Adsorbed By Chlorophyll Which splits water Chloroplast ATP and NADPH 2 ADP NADP Calvin Cycle Energy Used Energy and is recycled. + +
  27. 38. Types of plants Processes of Photosynthesis <ul><li>C3 plants </li></ul><ul><li>C4 plants </li></ul><ul><li>CAM plants </li></ul>
  28. 39. C3 photosynthesis <ul><li>Called ‘C3’ - 3-carbon acid (PGA) </li></ul><ul><li>Catalyzed by enzyme Rubisco </li></ul><ul><ul><li>Most abundant enzyme on Earth! </li></ul></ul><ul><li>C3 pathway used by 85% of plants </li></ul><ul><li>Most trees and many crops use C3 photosynthesis </li></ul>
  29. 40. Relatively high water loss
  30. 41. Photorespiration <ul><li>Occurs on hot, dry, bright days </li></ul><ul><li>Stomata close </li></ul><ul><li>Fixation of O 2 instead of CO 2 </li></ul><ul><li>Produces 2-C molecules instead of 3-C sugar molecules </li></ul><ul><li>Produces no sugar molecules or no ATP </li></ul><ul><li>Plants have special adaptations to limit the effect of photorespiration. </li></ul><ul><ul><li>C4 plants & CAM plants </li></ul></ul>
  31. 42. C4 Plants <ul><li>Hot, moist environments </li></ul><ul><li>15% of plants (grasses, corn, sugarcane) </li></ul><ul><li>Divides photosynthesis spatially </li></ul><ul><li>Light rxn - mesophyll cells </li></ul><ul><li>Calvin cycle - bundle sheath cells </li></ul>
  32. 43. C4 photosynthesis <ul><li>Four carbon molecule as 1 st intermediate </li></ul><ul><li>Catalyzed by phosphoenolpyruvate carboxylase (PEP carboxylase) </li></ul><ul><li>PEP carboxylase reacts effectively with CO 2 at low concentrations </li></ul><ul><li>C4 plants can achieve high photosynthesis with small stomatal opening, thereby saving water </li></ul><ul><li>Carbon Fixation & Calvin cycle occur in two types of cells </li></ul>
  33. 45. CAM Plants <ul><li>Crassulacean Acid Metabolism </li></ul><ul><li>Hot, dry environments </li></ul><ul><li>5% of plants (cactus and ice plants) </li></ul><ul><li>Stomates closed during day </li></ul><ul><li>Stomates open during the night </li></ul><ul><ul><li>Lower temperatures at night reduce water loss </li></ul></ul><ul><li>Light rxn - occurs during the day </li></ul><ul><li>Calvin Cycle - occurs when CO 2 is present </li></ul><ul><li>Carbon Fixation and Calvin cycle occur in the same cell but at different times </li></ul>