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  1. 2.                                    
  2. 5. Can you label the plant cell?
  3. 8. <ul><li>The location and structure of chloroplasts </li></ul>Figure 7.2 LEAF CROSS SECTION MESOPHYLL CELL LEAF Chloroplast Mesophyll CHLOROPLAST Intermembrane space Outer membrane Inner membrane Thylakoid compartment Thylakoid Stroma Granum Stroma Grana Stoma (pl. stomata)
  4. 12. © Pearson Education Ltd 2009 This document may have been altered from the original Week 10 A photosystem
  5. 13. <ul><li>Two photo systems named by time of discovery </li></ul><ul><ul><li>PS I and PS II </li></ul></ul><ul><ul><li>PSI has a light absorption peak of 700nm and appears mainly on inter-granal lamellae </li></ul></ul><ul><ul><li>PSII has a light absorption peak of 680nm and appears mainly on granal lamellae </li></ul></ul><ul><li>Capture solar power in form of photons </li></ul><ul><li>Act as light harvesters </li></ul><ul><li>Accessory pigments make up antenna complex which absorbs photons of light energy </li></ul><ul><li>This energy is channeled to the reaction centre of each photo system </li></ul>
  6. 15. <ul><li>Light-absorbing molecules </li></ul><ul><li>Absorb some wavelengths and reflect others </li></ul><ul><li>Color you see are the wavelengths NOT absorbed </li></ul>Wavelength (nanometers) chlorophyll b chlorophyll a Q: what wavelengths are NOT absorbed?
  8. 17. <ul><li>An overview of photosynthesis </li></ul>Figure 7.5 Light Chloroplast LIGHT REACTIONS (in grana) CALVIN CYCLE (in stroma) Electrons H 2 O O 2 CO 2 NADP + ADP + P Sugar ATP NADPH
  9. 18. <ul><li>Each of the many photosystems consists of: </li></ul><ul><ul><li>an “antenna” of chlorophyll and other pigment molecules that absorb light </li></ul></ul><ul><ul><li>a primary electron acceptor that receives excited electrons from the reaction-center chlorophyll </li></ul></ul><ul><ul><ul><li>P680 (in PS II) </li></ul></ul></ul><ul><ul><ul><li>P700 (in PS I) </li></ul></ul></ul>
  10. 19. Figure 7.7C Primary electron acceptor Photon Reaction center PHOTOSYSTEM Pigment molecules of antenna
  11. 20. <ul><li>Fluorescence of isolated chlorophyll in solution. Excited electrons have no place to go. </li></ul>Figure 7.7A Heat Photon (fluorescence) Photon Chlorophyll molecule
  12. 21. <ul><li>Excitation of chlorophyll in a chloroplast </li></ul><ul><li>The electrons are then passed to other molecules in an electron transport chain </li></ul>Figure 7.7B Primary electron acceptor Other compounds Chlorophyll molecule Photon
  13. 23. <ul><li>The energy changes of electrons as they flow through the light reactions are analogous to the cartoon. </li></ul><ul><li>As complicated as the scheme is, don’t lose track of its functions: </li></ul><ul><li>The light reactions use solar power to generate ATP and NADPH which provide chemical energy and reducing power to the sugar making reactions. </li></ul>
  14. 26. © Pearson Education Ltd 2009 This document may have been altered from the original Week 10 (a) The distribution of photosystems on granal and intergranal lamellae; (b) Formation of ATP during non-cyclic photophosphorylation (a) (b)
  15. 27. <ul><li>Light reactions </li></ul>Figure 7.8 Primary electron acceptor Primary electron acceptor Electron transport chain Electron transport Photons PHOTOSYSTEM I PHOTOSYSTEM II Energy for synthesis of by chemiosmosis
  16. 28. © Pearson Education Ltd 2009 This document may have been altered from the original Week 10 The Z-scheme
  17. 30. <ul><li>Light strikes photo system II and the energy is absorbed and passed along until it reaches P680 chlorophyll. </li></ul><ul><li>The excited electron is passed to the primary electron acceptor. Photolysis in the thylakoid takes the electrons from water and replaces the P680 electrons that were passed to the primary electron acceptor. ( O2 is released as a waste product) </li></ul><ul><li>The electrons are passed to photo system I via the electron transport chain (ETC) and in the process used to pump protons across the thylakoid membrane into the lumen . </li></ul><ul><li>The stored energy in the proton gradient is used to produce ATP which is used later in the Calvin-Benson Cycle . </li></ul>
  18. 31. <ul><li>P700 chlorophyll then uses light to excite the electron to its second primary acceptor. </li></ul><ul><li>The electron is sent down another ETC and used to reduce NADP+ to NADPH. </li></ul><ul><li>The NADPH is then used later in the Calvin-Benson Cycle. </li></ul>
  19. 32. <ul><li>Where do the electrons come from that keep the light reactions running? </li></ul><ul><li>Photosystem II regains electrons by splitting water molecules and releasing oxygen </li></ul><ul><ul><li>The reaction center pigment (P680) that gave up electrons gets replacement electrons </li></ul></ul><ul><li>Photosystem I receives electrons from the bottom of the cascade of the ETC from PS II and passes it to the P700 chlorophyll </li></ul>
  20. 33. Light dependent phase
  21. 35. © Pearson Education Ltd 2009 This document may have been altered from the original Week 10 The Calvin cycle