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Topic 7 Photosynthesis

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Compilation of various notes

Define what is photosynthesis
Explain the light dependent reactions
Explain the Calvin cycle
Define what is photorespiration
Compare the photorespiration in C3, C4 and CAM plants

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Topic 7 Photosynthesis

  1. 1. Topic  7:  Photosynthesis  
  2. 2. h0ps://   During  photosynthesis,  plants  emit   what  is  called  fluorescence  –  light   invisible  to  the  naked  eye  but   detectable  by  satellites  orbiHng   hundreds  of  miles  above  Earth.  NASA   scienHsts  have  now  established  a   method  to  turn  this  satellite  data  into   global  maps  of  the  subtle   phenomenon  in  more  detail  than  ever   before.  
  3. 3. Learning  Outcomes   1.  Define  what  is  photosynthesis   2.  Explain  the  light  dependent  reacHons   3.  Explain  the  Calvin  cycle   4.  Define  what  is  photorespiraHon   5.  Compare  the  photorespiraHon  in  C3,  C4   and  CAM  plants   h0ps://­‐in-­‐plants  
  4. 4. h0ps://  
  5. 5. 1.  Define  what  is  photosynthesis   2.  Explain  the  light  dependent  reacHons   3.  Explain  the  Calvin  cycle   4.  Define  what  is  photorespiraHon   5.  Compare  the  photorespiraHon  in  C3,  C4   and  CAM  plants  
  6. 6. Group  tasks   1.  Write  your  definiHon  of  photosynthesis   2.  Find  an  animaHon  or  video  on  photosynthesis   that  you  will  recommend   3.  Prepare  an  infographic  on  photosynthesis   process  
  7. 7. Flowering  Plants  as  Photosynthesis  Reactor   1.  The  green  porHons  of   plants,  such  as  leaves,   carry  out   photosynthesis,  using   carbon  dioxide  and   water  as  substrates.   2.  Carbon  dioxide  enters   leaves  through   stomata.   3.  The  carbon  dioxide   and  water  diffuse  to   the  chloroplast,  the   site  of  photosynthesis.      
  8. 8. Chloroplasts   1.  The  chloroplast  has  a   double  membrane  that   surrounds  the  liquid   stroma.   2.  The  stroma  contains   numerous  flat  thylakoid   disc  arranged  in  stacks   called  grana.   3.  The  chlorophyll  pigments   imbedded  in  the  thylakoid   membranes  absorb  solar   energy  during   photosynthesis.  
  9. 9. The  Photosynthesis  Process   CO2    +    H2O   (CH2O)  +  O2   oxida>on   reduc>on   gain  of  hydrogen  atoms   loss  of  hydrogen  atoms   Solar  energy   Produce/genera>ng   glucose   Release/waste   product  
  10. 10. Two  Sets  of  Reac>ons   1.  The  light  reacHons   2.  The  Calvin  cycle  reacHons  /  light  independent  reacHon  
  11. 11. Light  Reac>ons   Occur  in  granum     1.  Chlorophyll  absorbs  solar   energy,  which  energizes   electrons.   2.  ATP  is  produced  using  an   electron  transport  chain.   3.  NADP+,  a  coenzyme,   accepts  electrons  to   become  NADPH.   4.  ATP  &  NADPH  produced  in   thylakoid  membrane  are   used  by  the  Calvin  cycle    in   the  stroma  to  reduce  CO2   to  a  carbohydrate  
  12. 12. Calvin  cycle   Occur  in  the  stroma   1.  CO2  is  taken  up  by  one  of   the   substrates   in   the   cycle.       2.  ATP  and  NADPH  from  the   light   reacHons   reduce   CO2  to  a  carbohydrate.      
  13. 13. Calvin Cycle/Light Independent Reaction/Dark reaction
  14. 14. 1.  Define  what  is  photosynthesis   2.  Explain  the  light  dependent  reacHons   3.  Explain  the  Calvin  cycle   4.  Define  what  is  photorespiraHon   5.  Compare  the  photorespiraHon  in  C3,  C4   and  CAM  plants  
  15. 15. LIGHT  REACTIONS  
  16. 16. The  light  reac>ons  
  17. 17. The  electron  pathway  of  the  light  reac>ons   •  The  light  reacHons  consist  of  an  electron  pathway  that  produces   ATP  and  NADPH.   •  The  pathway  uses  2  photosystems  to  complete  the  light  reacHons.     –  Photosystem  I  (PS  I)   –  Photosystem  II  (PS  II)  
  18. 18. A  photosystem  (PS  I  &  PS  II)   consists  of  3  major  parts.   1.   Pigment  complex,  as  an   antenna  /light  harvesHng   antenna:     ConsisHng  300  chlorophyll   molecules  and  40  beta   carotenes  and  other   accessory  pigments  acHng   as  a  light  harvesHng   antenna   2.  Reac>on  center;  a  special   chlorophyll  pigment   *  Pigment  complex  (light   antenna)  gathering  solar   energy  and  passed  photon   from  one  pigment  to  the  other   un9l  in  a  reac9on  center   (chlorophyll  a)  
  19. 19. 3.  Electron  acceptor   molecules:   Photon  is  absorbed  by  one  of   the  pigment  molecules  and,   !  transfers  that  energy  to   neighboring  molecules,   !  unHl  it  reaches  the  acHon   center  where,   !  the  energy  is  used  to   transfer  an  energeHc  electron   to  an  electron  acceptor.  
  20. 20. Photosystem  II  contains  the  same  kind  of  chlorophyll  a  as  Photosystem  I   but  in  a  different  protein  environment  with  an  absorpHon  peak  at  680  nm.   (It  is  designated  P680).   Light  reac>ons:  PS  II  &  PS  I  
  21. 21. Light  reac>ons:  PS  II   1.  When  PS  II  absorbs  solar  energy,  electron  in  reacHon  center  of  PS  II  become   energized  electrons   2.  Energized  electron  are  passed  to  electron  acceptors.   3.  PS  II  splits  a  water  molecule  to  recover  the  electrons  passed  to  the  electron   acceptors  (at  electron  transport  chain),  releasing  O2  +  H2O     4.  The   electron   acceptors   send   the   energized   electrons   down   an   electron   transport  chain.   5.  Energy  is  released  and  stored  in  the  form  of  H+  gradient  in  thylakoid  lumen   6.  Electron  transport  chain  establishes  an  energy  gradient.   7.  Electron   transport   chain   carries   electron,   pass   electron   from   one   to   the   other     8.  As   the   electrons   are   passed   down   an   electron   transport   chain,   energy   is   released  and  stored  in  the  form  of  a  hydrogen  ion  (H+)  gradient.   9.  This  H+  gradient  is  used  later  in  photosynthesis  to  produce  ATP  
  22. 22. ATP  Produc>on   1.  During   photosynthesis,   the   thylakoid   space   becomes   an   H+   reservoir.   2.  The  H+  ions  that  fill  this  reservoir  come  from  two  sources.     1.  The  oxidaHon  of  water  by  PS  II  adds  H+.   2.  The   flow   of   electrons   through   the   electron   transport   chain   releases  energy  that  pumps  H+  into  the  thylakoid  space.     3.  As  the  H+  are  released  through  an  ATP  synthase,  the  H+  flow  down   their  concentraHon  gradient  and  release  energy.   4.  The   ATP   synthase   couples   that   release   of   energy   to   the   producHon  of  ATP  (ADP  +  Pi  "  ATP).  
  23. 23. Light  reac>ons:  PS  I   1.  When  PS  I  absorbs  solar  energy,  energized  electrons  are  passed  to   different  electron  acceptors.   2.  Electrons  from  the  end  of  the  electron  transport  chain  (from  PS  II)   replace  the  electrons  from  PS  I.   3.  The   electron   acceptors   pass   the   electrons   to   NADP+   to   form   NADPH.   4.  Electron  from  PS  II  replace  those  lost  by  PS  I   5.  When  PSI  absorbs  solar  energy,  electron  are  energized   6.  Electron  energized  are  passed  to  electron  acceptor.   7.  Electron  acceptor  pass  the  electron  to  series  of  electron  transport   chain,  then  final  electron  acceptor  (enzyme  that  accepts  H+)  ;   NADP   8.  NADP+  to  form  NADPH  
  24. 24. 1.  Define  what  is  photosynthesis   2.  Explain  the  light  dependent  reacHons   3.  Explain  the  Calvin  cycle   4.  Define  what  is  photorespiraHon   5.  Compare  the  photorespiraHon  in  C3,  C4   and  CAM  plants  
  25. 25. CALVIN  CYCLE  
  26. 26. •  The   Calvin   cycle   is   a   series   of   reacHons   that   conHnually   produce  a  carbohydrate  (glucose)  from  carbon  dioxide  during   photosynthesis.  
  27. 27. Calvin  Cycle  Reac>ons   The  Calvin  cycle  has  3  steps.   1.  Carbon  dioxide  fixaHon   2.  Carbon  dioxide  reducHon   3.  RegeneraHon   of   ribulose-­‐1,5-­‐ bisphosphate  (RuBP)  
  28. 28. Step  1:  Fixa>on  of  Carbon  Dioxide   1.  During  the  first  step  of   the   Calvin   cycle,   CO2   from   the   air   is   a0ached   (fixed)   to   RuBP.   2.  The   enzyme   for   this   reacHon   is   RuBP   carboxylase  oxygenase   (rubisco).   3.  Rubisco   splits   the   resulHng   6-­‐carbon   molecule   to   form   two   3-­‐carbon   molecules   (PGA).      
  29. 29. Step  2:  Reduc>on  of  Carbon  Dioxide   4.  ReducHon   of   CO2   is   a   series   of   reacHons  that  uses   NADPH   and   ATP   from   the   light   reacHons   to   form   the  carbohydrate.   –  NADPH   provides   electrons   for   the   reducHon.   –  ATP   provides   the   energy.      
  30. 30. Step  3:  Regenera>on  of  RuBP   5.  The   product   of   the   Calvin   cycle   is   glyceraldehyde-­‐3-­‐ phosphate  (G3P).   6.  About  1/6  of  the  G3P  is   used  to  make  glucose.   7.  About   5/6   of   the   glucose   is   used   to   regenerate   the   RuBP   required  for  the  fixaHon   of  carbon  dioxide.  
  31. 31. The  Importance  of  the  Calvin  Cycle   •  The  G3P  molecules   produced  by  plants   can  be  used  to  make   a  wide  variety  of   chemicals  :   Eg  :      glucose,  fructose,   sucrose,  starch,   alkaloid  
  32. 32. 1.  Define  what  is  photosynthesis   2.  Explain  the  light  dependent  reacHons   3.  Explain  the  Calvin  cycle   4.  Define  what  is  photorespiraHon   5.  Compare  the  photorespiraHon  in  C3,  C4   and  CAM  plants  
  33. 33. Photorespira>on  (also  known  as  the  oxidaHve   photosyntheHc  carbon  cycle,  or  C2  photosynthesis)     ! a  process  in  plant  metabolism  where  the  enzyme   RuBisCO  oxygenates  RuBP,  causing  some  of  the  energy   produced  by  photosynthesis  to  be  wasted.   ! Consumes  O2  and  organic  fuel  and  releases  CO2   ! Uses  ATP  but  not  making  ATP   ! Doesn’t  make  sugar   ! Decreases  photosynthesis  output  
  34. 34. Types  of  Photosynthesis  :  Carbon  metabolism   •  Plants   are   physically   adapted   to   their   environment   •  Plants   have   metabolically   adapted   photosynthesis  to  different  climates.   1.  C3  plants   2.  C4  plants   3.  CAM  plants  
  35. 35. 1.  C3  Photosynthesis     •  In  areas  with  moderate  temperature     •  plants  carry  out  C3  photosynthesis,     •  the  first  detectable  molecule  from  the  Calvin  cycle  is  a  3-­‐carbon   compound.   •  FixaHon  by  RuBP  carboxylase  (RUBISCO)  in  C3  plants:  with  CO2  &   O2.     •  The   process   of   RuBP   binding   with   O2   is   known   as   photorespiraHon.     •  PhotorespiraHon   reduce   photosynthesis   product  yield  
  36. 36. If  the  weather  is  hot  &  dry,  C3  plant:   o   stomata  closed   o   PrevenHng  the  loss  of  H2O   o   Also  prevents  CO2  from  entering    the  leaf   o      Traps   O2   (by-­‐product   of   photosynthesis   within   the   leaf   space  in  between  spongy  mesophyll)   o C3   photosynthesis   are   necessary   adapta>on   to   minimize   photorespira>on   effect   (O2   competes   with   CO2   for   the   binding   site   on   Rubisco,   decreasing   the   efficiency   of   photosynthesis/yield  decrease)   C3  
  37. 37. •  C4  have  an  adapta>on  that  allow  them  to  be  successful  in  hot   dry  climates     •  These  plants  carry  out/perform  C4  photosynthesis     2.    C4  Photosynthesis    
  38. 38. The  anatomy  of  a  C4  plant  is  different  from  that  of  a  C3  plant.       General  leaf/C3  leaf     C4  leaf   Keong BP Cross  sec>on  of  leaf  :  General  Versus  C4  Leaf   C4  
  39. 39. •  C4  photosynthesis  forming  a  4-­‐ carbon  compound.   •  PEP  carboxylase  fix  PEP  (3C)   with  CO2    in  bundle  sheath  cell.   •  the  first  detectable  molecule   from  the  Calvin  cycle  is  a  4-­‐ carbon  compound  (OAA)   •  C4  are  able  to  avoid  the  uptake   of  O2  by  Rubisco   C4  
  40. 40. •  The   anatomy   of   a   C4   plant   is   different  from  a  C3  plant.       •  Although   chloroplasts   are   found   in   both   the   mesophyll   and   bundle   sheath   cells,   the   Calvin  cycle  occurs  primarily  in   the  bundle  sheath  cells.   •  CO2  taken  in  by  the  mesophyll   cells   is   combined   with   a   3-­‐ carbon   compound   (PEP   @   phosphoenol   phyruvate)   to   form   a   4-­‐carbon   compound   (oxaloacetate).       C4  
  41. 41. The  C4  pathway   CO2   is   fixed   by   enzyme   PEP  carboxylase,  forming   a   four-­‐carbon   product   oxaloacetate  (4C)      
  42. 42. The  C4  pathway   CO2   is   transported   into   bundle   sheath,   released   and  fixed  by  rubisco  (RuBP)   to   allowing   Calvin   cycle   to   proceed.   Therefore   rubisco   have   to   react   with   CO2   instead   of   O2  because  O2  is  absent.  So   no  photorespira>on  occurs  
  43. 43. •  Crassulacean   Acid   Metabolism   (CAM),   found   commonly   in   desert  plants,  in  warm,  arid  regions.       3.  CAM  Photosynthesis  
  44. 44. CAM   •  Similar  to  C4  photosynthesis,  CAM  plants  separate  CO2  fixaHon  from   the  Calvin  cycle  reacHon  to  minimize  compeHHon  from  O2.   •  However  CAM  plants  separate  these  events  by  Hme.   •  CO2  is  fixed  during  the  night.   •  The  Calvin  cycle  reacHons  occur  during  the  day.      
  45. 45. The  advantage  of  CAM  photosynthesis  involves  the  conserva>on   of  water.   • When   CAM   plants   open   their   stomata   at   night   to   obtain   CO2,   water  loss  is  minimized.     • Calvin  cycle  reacHon  occur  during  the  day     *  H2O  is  conserve,  but  CO2    cannot  enter  the  plant   CAM  
  46. 46. 1.  Define  what  is  photosynthesis   2.  Explain  the  light  dependent  reacHons   3.  Explain  the  Calvin  cycle   4.  Define  what  is  photorespiraHon   5.  Compare  the  photorespiraHon  in  C3,  C4   and  CAM  plants  
  47. 47. Evolu>onary  Trends   •  C4   plants   most   likely   involved   in   areas   with   high  light,  high  temperature,  and  low  rainfall.   •  C3   plants   survive   be0er   than   C4   plants   in   temperatures  less  than  25˚C.   •  CAM  plants  compete  well  with  both  C3  and  C4   plants,  parHcularly  in  arid  environments.    
  48. 48. PEP  carboxylase   PEP  carboxylase  
  49. 49. Summary  of  C3,  C4,  And  CAM  Reac>on