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  1. 1. PHOTOSYNTHESIS QBA Miguel A. Castro Ramírez
  2. 2. Photosynthesis• An anabolic, endergonic, carbon dioxide (CO2) requiring process that uses light energy (photons) and water (H2O) to produce organic macromolecules (glucose). SUN photons 6CO2 + 6H2O → C6H12O6 + 6O2 glucose
  3. 3. Question:• Where does photosynthesis take place?
  4. 4. Plants • Autotrophs: self-producers. • Location: 1. Leaves a. stoma b. mesophyll cellsMesophyll ChloroplastCell Stoma
  5. 5. Stomata (stoma) • Pores in a plant’s cuticle through which water and gases are exchanged between the plant and the atmosphere. Oxygen (O2)Carbon Dioxide (CO2) Guard Guard Cell Cell
  6. 6. Mesophyll Cell Nucleus Cell Wall ChloroplastCentral Vacuole
  7. 7. Chloroplast• Organelle where photosynthesis takes place. Stroma Outer Membrane Thylakoid GranumInner Membrane
  8. 8. Thylakoid Thylakoid Membrane Thylakoid SpaceGranum
  9. 9. Question:• Why are plants green?
  10. 10. Chlorophyll Molecules• Located in the thylakoid membranes. membranes• Chlorophyll have Mg+ in the center.• Chlorophyll pigments harvest energy (photons) by absorbing certain wavelengths (blue-420 nm and red-660 nm are most important).• Plants are green because the green wavelength is reflected, not absorbed. reflected absorbed
  11. 11. Wavelength of Light (nm) 400 500 600 700Short wave Long wave(more energy) (less energy)
  12. 12. Absorption of ChlorophyllAbsorption violet blue green yellow orange red wavelength
  13. 13. Question:• During the fall, what causes the leaves to change colors?
  14. 14. Fall Colors• In addition to the chlorophyll pigments, there are other pigments present.• During the fall, the green chlorophyll pigments are greatly reduced revealing the other pigments. pigments• Carotenoids are pigments that are either red or yellow. yellow
  15. 15. Redox Reaction• The transfer of one or more electrons from one reactant to another. another• Two types: 1. Oxidation 2. Reduction
  16. 16. Oxidation Reaction• The loss of electrons from a substance.• Or the gain of oxygen. oxygen Oxidation6CO2 + 6H2O → C6H12O6 + 6O2 glucose
  17. 17. Reduction Reaction• The gain of electrons to a substance.• Or the loss of oxygen. oxygen Reduction6CO2 + 6H2O → C6H12O6 + 6O2 glucose
  18. 18. Breakdown of Photosynthesis• Two main parts (reactions).1. Light Reaction or Light Dependent Reaction Produces energy from solar power (photons) in the form of ATP and NADPH. NADPH
  19. 19. Breakdown of Photosynthesis2. Calvin Cycle or Light Independent Reaction or Carbon Fixation or C3 Fixation Uses energy (ATP and NADPH) from light rxn to make sugar (glucose).
  20. 20. 1. Light Reaction (Electron Flow)• Occurs in the Thylakoid membranes• During the light reaction, there are two reaction possible routes for electron flow. flow A. Cyclic Electron Flow B. Noncyclic Electron Flow
  21. 21. A. Cyclic Electron Flow• Occurs in the thylakoid membrane. membrane• Uses Photosystem I only• P700 reaction center- chlorophyll a• Uses Electron Transport Chain (ETC)• Generates ATP only ADP + P ATP
  22. 22. A. Cyclic Electron Flow Primary e-SUN Electron Acceptor e- e- ATP produced Photons by ETC P700 e- Accessory Pigments Photosystem I
  23. 23. B. Noncyclic Electron Flow• Occurs in the thylakoid membrane• Uses PS II and PS I• P680 rxn center (PSII) - chlorophyll a• P700 rxn center (PS I) - chlorophyll a• Uses Electron Transport Chain (ETC)• Generates O2, ATP and NADPH
  24. 24. B. Noncyclic Electron Flow Primary Electron Acceptor 2e- Enzyme Primary Reaction Electron 2e- Acceptor 2e- ETC SUN 2e- 2e- P700 NADPHPhoton ATP P680 PhotonH2O Photosystem I Photosystem II1/2O2 + 2H+
  25. 25. B. Noncyclic Electron Flow• ADP + P → ATP (Reduced)• NADP+ + H → NADPH (Reduced)• Oxygen comes from the splitting of H2O, not CO2 H 2O → (Oxidized) 1/2 O2 + 2H+
  26. 26. Chemiosmosis• Powers ATP synthesis. synthesis• Located in the thylakoid membranes. membranes• Uses ETC and ATP synthase (enzyme) to make ATP.• Photophosphorylation: addition of phosphate to ADP to make ATP. ATP
  27. 27. Chemiosmosis SUN H+ H + (Proton Pumping)Thylakoid E PS II T PS I C high H+ H H + + concentration H+ H + H+ H + Thylakoid H + ATP Synthase Space low H+ ADP + P H+ ATP concentration
  28. 28. Calvin Cycle• Carbon Fixation (light independent rxn).• C3 plants (80% of plants on earth).• Occurs in the stroma.• Uses ATP and NADPH from light rxn.• Uses CO2.• To produce glucose: it takes 6 turns and uses 18 ATP and 12 NADPH.
  29. 29. Chloroplast Stroma Outer Membrane Thylakoid GranumInner Membrane
  30. 30. Calvin Cycle (C3 fixation) (36C)(6C) 6C-C-C-C-C-C6CO2 (unstable) 6C-C-C 6C-C-C 12PGA (36C) 6ATP 6ATP (30C) 6C-C-C-C-C 6NADPH 6NADPHRuBP (36C) 6ATP 6C-C-C 6C-C-C 12G3P C3 (30C) (6C) glucose C-C-C-C-C-C Glucose
  31. 31. Calvin Cycle• Remember: C3 = Calvin Cycle C3 Glucose
  32. 32. Photorespiration• Occurs on hot, dry, bright days. days• Stomates close.• Fixation of O2 instead of CO2.• Produces 2-C molecules instead of 3-C sugar molecules. molecules• Produces no sugar molecules or no ATP.
  33. 33. Photorespiration• Because of photorespiration: Plants have photorespiration special adaptations to limit the effect of photorespiration. photorespiration 1. C4 plants 2. CAM plants
  34. 34. C4 Plants• Hot, moist environments. environments• 15% of plants (grasses, corn, sugarcane).• Divides photosynthesis spatially.• Light rxn - mesophyll cells.• Calvin cycle - bundle sheath cells.
  35. 35. C4 Plants Malate Malate C-C-C-C C-C-C-C Transported CO2CO2 C3 Vascular Tissue glucoseC-C-CPEP ATP C-C-C Pyruvic AcidMesophyll Cell Bundle Sheath Cell
  36. 36. CAM Plants• Hot, dry environments. environments• 5% of plants (cactus and ice plants).• Stomates closed during day.• Stomates open during the night. night• Light rxn - occurs during the day.• Calvin Cycle - occurs when CO2 is present.
  37. 37. CAM Plants Night (Stomates Open) Day (Stomates Closed) Vacuole C-C-C-C C-C-C-C C-C-C-CCO2 Malate Malate Malate CO2 C3C-C-C PEP ATP C-C-C glucose Pyruvic acid
  38. 38. Question:• Why would CAM plants close their stomates during the day?
  39. 39. PhotosynthesisPhotosynthesis is a process which light energy is used in the synthesis of organic molecules.
  40. 40. What is the equation for photosynthesis? Water + carbon dioxide +light energy = Oxygen + glucose
  41. 41. The role of chloroplasts in Photosynthesis.
  42. 42. • Chloroplast is an organelle in the leaf of a plant that contain the thylakoid cells and the stroma. These are shown on the following diagram.• Here 2 important reactions take place. The light dependant reactions take place in the thylakoid cells and the light independent in the stroma.
  43. 43. Chloroplasts
  44. 44. What happens in the light dependent reactions.
  45. 45. • Electrons in the chloroplast gain energy from sunlight , this energy is used to add a phosphate group to ADP making ATP.• The energy is used also used in the photolysis of water to split it into oxygen and hydrogen molecules
  46. 46. • The electrons, protons and energy for the light dependent reactions are used to make NaDPH2.• The ATP/NADPH2 from the Light Dependent reactions enter the light independent reactions.
  47. 47. What happens in the light independent reactions.
  48. 48. The light independent reactions occur at night for only a fewseconds due to limited amounts of ATP and supply of NADPH2.
  49. 49. Role of NADPH2 and ATP Energy from ATP and electronsfrom NADPH2 are used to reduce carbon dioxide and build it to sugars
  50. 50. The following cycle is called the Calvin cycle.
  51. 51. • This is called Fixing the carbon dioxide. The carbohydrates(sugars) are in a form of RuBP.
  52. 52. • The following cycle is called the Calvin cycle.• What happens in the Calvin cycle?
  53. 53. • RuBP with the addition of carbon dioxide splits into 2 moles of GP. For GP to be turned to Carbohydrates it requires ATP and NADPH2. The NADPH2 give up its electrons which enter the GP molecules making GALP.
  54. 54. GALPGALP is converted to a wholeseries of mostly sugars, some lipids and some Proteins.
  55. 55. • Also some GALP is regenerated back to RUBP if sufficient amounts of NADPH2 and ATP are provided.
  56. 56. Photosynthesis H 2O + CO 2 Energy ATP and Which splits NADPH2 waterLight is Adsorbed C3 By Chlorophyll ADP Calvin Cycle NADP Chloroplast Used Energy and is recycled. O2 + C 6 H 12 O 6 Light Reaction Dark Reaction