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Photosynthesis in plants.pptx

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Photosynthesis in plants.pptx

  1. 1. photosynthesis
  2. 2. note:  oxygen evolved comes from the water not from the co2
  6. 6. Joseph Priestley  He revealed the essential role of air in the growth of green plants.  He discovered oxygen
  7. 7. 3.JAN INGENHOUSZ  He showed that sunlight is essential for the plants
  8. 8. 4.JULIUS VON SACHS  Found that glucose is made in the green plants.
  9. 9. 5.T.W.ENGELMANN  Described the first action spectrum of photosynthesis by using cladophora.
  10. 10. 6.CORNELIUS VAN NIEL  Inferred that oxygen evolved by the green plants comes from the water and not from the co2.
  11. 11. 7.RUBEN, KAMEN ET AL  Proved that oxygen evolve during light reaction comes from the H2O not from CO2.
  12. 12. chloroplast
  13. 13.  Photosynthesis takes place in chloroplasts.  Pigments are substances that have an ability to abborb light , at specific wavelengths.
  14. 14. Chlorophyll pigments Many types of chlorophylls are :  Chlorophyll a  Chlorophyll b  Chlorophyll c  Chlorophyll d  Chlorophyll e  Bacteriochlorophyll a and b etc…..
  15. 15.  But the chromatographic separation of the leaf pigments shows that the color of leaves is due to four pigments:  Chlorophyll a bright or blue green  Chlorophyll b yellow green  Xanthophylls yellow  Carotene yellow orange
  16. 16.  Chlorophyll a is the primary photosynthetic pigment.
  17. 17.  chlor
  20. 20. Emerson effect  Rate of photosynthesis depends directly on two main factors  Wavelength of light  Quantum yield  Quantum yield = amount of O2 release amount of light absorbed
  21. 21. Quantum yield = amount of O2 release amount of light absorbed
  22. 22. RED DROP OR EMERSON’S FIRST EFFECT  Emerson conducted experiment in chorella using only one wavelength of light (monochromatic light) at a time and he measured quantum yield.
  23. 23.  He plotted a graph of the quantum yield in terms of O2 evolution at various wavelengths of light.
  24. 24.  His focus was to determine at which wavelengths of light the photochemical yield of oxygen was maximum.
  25. 25. Observations:  He found that in the wavelength of 600 to 680 the yield was constant  But suddenly dropped in the region above 680 nm (red region)
  26. 26. Inference  The fall in the photosynthetic yield beyond red region of the spectrum is referred as red drop or Emerson’s first effect.
  27. 27. Emerson’s enhancement effect
  28. 28. PS I  Location :  Stromal lamella + thylakoid membrane
  29. 29. PS I  700 nm
  30. 30. In vivo In vitro
  31. 31. Chemiosmotic hypothesis  Was first explained by Peter Mitchell.  This mechanism explains how ATP is synthesised in the chloroplast.  In respiration it is called oxidative phosphorylation  In photosynthesis it is called photophosphorylation .
  32. 32. ATP SYNTHESIS  ATP synthesis is linked to the development of a proton gradient across the membrane of the thylakoid  the proton accumulation is towards the inside of the membrane ie,. the lumen.
  33. 33. Processes involved in chemiosmotic hypothesis  Photolysis of water towards thylakoid lumen  Transfer of H+ from stroma to lumen as electrons move through photosystem  NADPH reductase reaction occur towards stroma.
  36. 36. 2.TRANSFER OF H+ FROM STROMA TO LUMEN AS THE ELECTRONS MOVE THROUGH PHOTOSYTEMS  The primary acceptor of electron located towards the outer side of the membrane transfers its electron to a H+ carrier and this molecule then removes a proton from the stroma while transporting an electron.
  37. 37.  When this H+ carrier molecule passes on its electron to an electron carrier present on the innner side of the membrane , the H+ is released into the lumen of the membrane.
  38. 38. 3.NADPH reductase reaction occurs towards stroma  The NADP reductase enzyme is located on the stroma side of the membrane.  Protons are necessary for the reduction of NADP+ to NADPH + H+ and protons are removed from the stroma.
  39. 39.  So, within the chloroplasts, protons in the stroma decrease while in lumen there is increase in H+.  This causes a decrease in PH in the lumen and creates a gradient across the thylakoid membrane.
  40. 40.  The gradient is important because the breakdown of the gradient leads to synthesis of ATP.
  41. 41.  The gradient is broken down by the movement of protons across the membrane to the stroma through the transmembrane channel of the F0 of the ATP synthetase.
  42. 42. The ATP synthetase consists of two parts:  CF0 is embedded in the membrane and forms the transmembrane channel that carries out facilitated diffusion of protons across the membrane.  CF1 protudes on the
  43. 43. Melvin Calvin used radioactive C14 in algal photosynthesis studies.
  44. 44.  This led to the discovery that the first CO2 fixation product was a three carbon organic acid.  He also helped to mark the complete biosynthetic pathway.  Hence it is called calvin cycle.  The first stable product identified was 3-phosphoglyceric acid.(PGA)
  45. 45.  Calvin cycle occurs in all photosynthetic plants whether they are C3 or C4 pathway.
  46. 46. 1.The primary acceptor molecule during the C3 cycle is a 5 C ketose sugar RuBP (ribulose bisphosphate) 2.The enzyme for CO2 FIXATION IS RuBisCO (Ribulose bisphosphate carboxylase oxygenase)
  47. 47.  Before this discovery it was believed that since the first product was a C3 acid ,the primary acceptor would be a 2C compound.
  48. 48.  It is the most abundant enzyme on earth.  It is characterised by the fact that its active site can bind both CO2 and O2.
  49. 49.  RuBisCO has a much greater affinity for CO2 than O2 and the binding is competitive.  It is the relative concentration that of O2 and CO2 that determines which of the two will bind to the enzyme.
  50. 50. 1Q  The assimilatory powers produced in cyclic photophosphorylation is/are 1. ATP only 2. NADPH only 3. Both ATP and NADPH 4. ATP and NADH
  51. 51. 1Q  The assimilatory powers produced in cyclic photophosphorylation is/are 1. ATP only 2. NADPH only 3. Both ATP and NADPH 4. ATP and NADH
  52. 52. Stages of calvin cycle  1.carboxylation.  2.reduction  3.regeneration
  53. 53. 1.Carboxylation or carbon fixation  It is the fixation of CO2 into a stable organic intermediate.  In this,CO2 is utilised for carboxylation of RuBP.
  54. 54.  This reaction is catalysed by RuBisCO  RESULTS :  Formation of 2 molecules of 3-PGA (3- phosphoglyceric acid).
  55. 55. 2.Reduction  This reaction leads to the formation of glucose.  The steps involve utilization of two molecules of ATP for phosphorylation and two of NADPH for reduction, per molecule of CO2 fixed .
  56. 56.  The fixation of six molecules of co2 and six turns of cycle are required for the removal of 1 molecule of glucose from the pathway.
  57. 57. 3.Regeneration  For the cycle to continue uninterrupted, regeneration of the CO2 acceptor molecule is crucial.  This step requires one ATP for phosphorylation to form RuBP.
  58. 58.  To make 1 molecule of glucose six turns of the cycle is required.  18 ATP and12 NADPH molecules are required to make a glucose.
  59. 59.  It is to meet this differrence in number of ATP and NADPH that the cyclic phosphorylation takes place.  RuBisCO and many other enzymes of calvin cycle are regulated by light.
  60. 60. IN OUT 6 CO2 I GLUCOSE 18 ATP 18 ADP 12 NADPH 12 NADP
  61. 61. C4 PATHWAY (HATCH AND SLACK PATHWAY)  Most of the plants adapted to dry tropical regions have the C4 pathway. TRICK : SAMS
  62. 62. Eg., sugarcane
  63. 63. AMARANTUS
  64. 64. MAIZE
  65. 65. SORGHUM
  66. 66.  In these plants double fixation of CO2 occurs.
  67. 67.  The initial or the first product of this pathway is a 4C compound OAA (oxaloacetic acid) and hence the name.
  68. 68.  Two Australian botanists HATCH AND SLACK discovered that tropical plants are more efficient in CO2 utilization.
  69. 69. C4 PLANTS  C4 plants have a special type of leaf anatomy , they can tolerate higher temperature.  They show a higher response to high intensities of light.  They lack a wasteful process called photorespiration.  Hence, they show a greater productivity and higher yield compared to C3 plants.
  70. 70.  C4 pathway requires two types of cells :  Mesophyll cells  Bundle sheath cells
  71. 71. C3PLANT
  72. 72.  The particularly large cells around the vascular bundles of C4 plants are called bundle sheath cells.
  73. 73.  These cells form several layers around the vascular bundles.  They are characterised by :  Large no of chloroplasts  Grana are absent  Thick walls impervious to gaseous exchange.  No intercellular spaces.
  74. 74.  Q) In C4 plants the bundle sheath cells a. Have thin walls to facilitate gaseous exchange . b. Have large intercellular spaces c. Are rich in PEP carboxylase. d. Have a high density of chloroplasts.
  75. 75.  Q) In C4 plants the bundle sheath cells a. Have thin walls to facilitate gaseous exchange . b. Have large intercellular spaces c. Are rich in PEP carboxylase. d. Have a high density of chloroplasts.
  76. 76. KRANZ ANATOMY  This special anatomy of leaves of the C4 plants is called KRANZ ANATOMY.  KRANZ means wreath and is a reflection of the arrangement of cells.
  77. 77. C4 PATHWAY (HATCH AND SLACK PATHWAY)  The primary CO2 acceptor is a 3C compound PEP ( phosphoenol pyruvate)  It is present in mesophyll cells.
  78. 78. PEP carboxylase or PEPcase  The enzyme that catalyses this CO2 fixation is PEP carboxylase or PEPcase.  The mesophyll cells of C4 plants lack RuBisCO.  So the 4C compound OAA is formed in the mesophyll cells.
  79. 79.  It is then converted into other 4C compounds like maleic acid and aspartic acid in the mesophyll cells itself and then transferred into bundle sheath cells.
  80. 80. Bundle sheath cells  In the bundle sheath cells these C4 acids are broken down into CO2 and 3C compounds.  The CO2 released enters C3 cycle .
  81. 81. Bundle sheath cells  The bundle sheath cells are rich in the enzymes RuBisCO , but lacks PEPcase.
  82. 82. MESOPHYLL CELLS  The 3C molecule is transported back into the mesophyll cells and converted into PEP again with the help of cold sensitive enzyme PEP synthetase.  Thus completing the cycle.
  83. 83.  Thus the basic pathway that results in the formation of the sugars , calvin pathway is common in both C3 and C4 plants.
  84. 84. Regeneration 1.Regeneration of PEP from C3 acid requires 2 ATP equivalent. 2.However there is no net gain or loss in NADPH in C4 cycle.
  85. 85. C4 PLANTS  Has both C3 and C4 cycle.  ATP consumed in C4 plants :  C4 cycle = 2 ATP per CO2 fixed.  C3 cycle = 3 ATP per CO2 fixed.  Total = 5 ATP per CO2 fixed.
  86. 86. C3 CYCLE C4 CYCLE It is a slower process of CO2 fixation. It is a faster process of CO2 fixation.
  87. 87. Importance of C4 plants  They can tolerate saline conditions due to abundant occurrence of organic acids (maleic and OAA) which lowers their water potential than that of soil.
  88. 88.  Can perform photosynthesis even when their stomata are closed due to the presence of strong CO2 fixing enzyme PEPcase.
  89. 89.  Concentric arrangement of cells in leaf produces smaller area in relation to volume for better water utilization.
  91. 91.  This metabolism was first of all reported in BRYOPHYLLUM a member of family Crassulaceae and hence it is called Crassulacean acid metabolism.
  92. 92. CAM (CRASSULACEAN ACID METABOLISM) OR DIURNAL ACID CYCLE  Certain plants have scotoactive stomata are called CAM plants.
  93. 93.  These plants fix CO2 during night but form sugars only during day ( when RuBisCO is active.
  94. 94. Eg ., TRICK  PICAASO
  95. 95. PINEAPPLE
  96. 96. KALANCHOE
  97. 97. SEDUM
  98. 98. OPUNTIA
  99. 99. CAM  CO2 is fixed during night (dark) to OAA using PEPcase.  Step1 :
  100. 100.  This CO2 comes from respiration (breakdown of starch) also from the atmosphere.
  101. 101. Maleic acid gets stored in the vacuole.
  102. 102.  The CAM also contains enzymes of calvin cycle.  During day time maleic acid breakdowns to form pyruvate and CO2.
  103. 103. PYRUVATE  Pyruvate is used up to regenerate PEP.
  104. 104. CO2  CO2 enters the calvin cycle.
  105. 105.  The succulents , therefore synthesise :  Plenty of organic acid (maleic acid) during night (when stomata are open)
  106. 106.  Plenty of carbohydrates during the day (when stomata are closed).
  107. 107. Important note  Like calvin cycle ,CAM cycle also operates in the mesophyll cells only.  None of these has shown chloroplast dimorphism as is found in C4 plants.
  108. 108.  It should be remembered slow growing desert succulents exhibiting CAM have the slowest photosynthetic rate while C4 plants show highest rates.
  109. 109.  Thus CAM plants are although not efficient as C4 plants , they definitely better suited to adverse conditions ( ie,. Conditions of extreme desiccation)
  111. 111. PHOTORESPIRATION OR C2 CYCLE  It is a process which involves loss of fixed CO2 in plants in the presence of light.  It is initiated in chloroplasts.  This process does not produce ATP or NADPH and is wasteful process.
  112. 112. CONDITIONS  Photorespiration usually occurs when there is high concentration of O2.
  113. 113.  Under such circumstances RuBisCO functions as an oxygenase.  Some O2 binds to the RuBisCO and hence CO2 fixation is reduced.
  114. 114.  The RuBP binds with O2 to form 1 molecule of PGA and phosphoglycolate.
  115. 115. WHY IT IS A WASTEFUL PROCESS ?  There is neither synthesis of sugar nor ATP.  Rather, it results in the release of CO2, with the utilization of ATP.
  116. 116. LOSS  It leads to a 25 % loss of the fixed CO2.  O2 is first utilised in chloroplats and then in peroxisomes.
  117. 117. ORGANELLES INVOLVED:  Chloroplast  Peroxisomes  Mitochondria (loss of CO2 occurs here)
  118. 118. NOTE:  In C4 plants , photorespiration does not occur.  Becoz they have a mechanism that increases the concentration of CO2 at the enzyme site.
  119. 119. Mechanism  During the C4 pathway, when the C4 acid ( maleic acid ) in the mesophyll cells is broken down in the bundle sheath cells it releases CO2.
  120. 120. Bundle sheath cells  In the bundle sheath cells these C4 acids are broken down into CO2 and 3C compounds.  The CO2 released enters C3 cycle .
  121. 121.  Thus increasing the intercellular conc. of CO2.  Thus ensures that RuBisBP functions as a carboxylase minimising the oxygenase activity.
  122. 122. WHY C4 PLANTS ARE MORE EFFICIENT? Thus the productivity and yields are better in C4 plants compared to C3 plants. In addition , C4 plants show tolerance to higher temperature also.
  123. 123. FACTORS AFFECTING PHOTOSYNTHESIS  External factors  Plant factors or internal factors
  124. 124. EXTERNAL FACTORS  Availability of sunlight  Temperature  CO2 concentration  Water
  125. 125. PLANT FACTORS  LEAVES (NASO) 1. Number 2. Age 3. Size 4. Orientation  Mesophyll cells  Chloroplasts  INTERNAL CO2 CONCENTRATION  AMOUNT OF CHLOROPHYLL
  126. 126.  The plant factors are dependent on the :  Genetic predisposition  Growth of the plant
  128. 128.  When several factors affect any biochemical process then this law comes into effect
  129. 129. Law of limiting factors  “If a chemical process is affected by more than one factor , then its rate will be determined by the factor which directly affects the process if its quantity is changed”
  130. 130. SOLARISATION  The intensity beyond light saturation point causes chlorophyll destruction and decrease in photosynthetic rate, this is called solarisation.
  131. 131.  Q) Very strong light has a direct inhibiting effect on photosynthesis which is known as a. Solarisation . b. Etiolation c. Chlorosis . d. Defoliation .
  132. 132.  Q) Very strong light has a direct inhibiting effect on photosynthesis which is known as a. Solarisation . b. Etiolation c. Chlorosis . d. Defoliation .
  133. 133. Oxygen  Small quantity of oxygen is essential for photosynthesis except in some anaerobic bacteria.
  134. 134. WARBURG EFFECT  At a very high oxygen concentration , the rate of photosynthesis declines in all green plants. This phenomenon is called warburg effect.