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Photosynthesis Lecture


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  • 1. PHOTOSYNTHESISPhotosynthesis, importance of photosynthesis, structure and function of chloroplast, dark andlight reaction, CO2 fixation, C3,C4 and CAM, advantages of C4 pathway, photorespiration andits implications, Factors affecting photosynthesis.
  • 2. Energy can not be produce ordestroyed , it can only transformedfrom one form to anotherThe sun: main source of energy forlife on earth
  • 3. Light Energy Harvested by Plants &Other Photosynthetic Autotrophs
  • 4. Evolution of Photosynthesis
  • 5. Why are plants green? Transmitted light
  • 6. Structure of Leaf upper epidermis protect internal tissues from mechanical damage and bacterial and fungal invasion
  • 7. Structure of Leaf Cuticle • a waxy layer • prevent water loss from the leaf surface
  • 8. Structure of Leaf mesophyll
  • 9. Structure of Leaf palisade mesophyll contains many columnar cells chloroplasts closely packed together absorb light more efficiently
  • 10. Structure of Leaf irregular cells loosely packed together to leave numerous large air spaces allow rapid diffusion less chloroplasts for of gases throughout photosynthesis the leaf spongy mesophyll
  • 11. Structure of Leaf same as upper epidermis except the cuticle is thinner lower epidermis
  • 12. Structure of Leaf stoma opening which allows gases to pass through it to go into or out of the leaf
  • 13. Structure of Leaf guard cells control the size of stoma
  • 14. Structure of Leaf vascular bundle (vein)
  • 15. Structure of Leaf xylem • to transport water and mineral salts towards the leaf
  • 16. Structure of Leaf phloem • to transport organic substances away from the leaf
  • 17. Adaptation of leaf to photosynthesis Upper epidermis and cuticle is transparent Allows most light to pass to photosynthetic mesophyll tissues
  • 18. Adaptation of leaf to photosynthesis Palisade mesophyll cells are closely packed and contain many chloroplasts To carry out photosynthesis more efficiently
  • 19. Adaptation of leaf to photosynthesis Spongy mesophyll cells are loosely packed with numerous large air spaces To allow rapid diffusion of gases throughout the leaf
  • 20. Adaptation of leaf to photosynthesis Numerous stomata on lower epidermis To allow rapid gaseous exchange with the atmosphere
  • 21. Adaptation of leaf to photosynthesis Extensive vein system • Allow sufficient water to reach the cells in the leaf • To carry food away from them to other parts of the plant
  • 22. Function of chloroplast:PhotosynthesisThe chlorophyll molecules in the chloroplasts are essential in theprocess of photosynthesis.Protein SynthesisChloroplasts are capable of doing Protein Synthesis.Carriers of Heredity CharactersChloroplasts have a limited role in cytoplasmic inheritance sincethese contain traces of DNA.
  • 23. ChlorophyllChlorophyll is the molecule thattraps this most elusive of allpowers - photoreceptor.It is found in the chloroplasts ofgreen plants,The basic structure of achlorophyll molecule is aporphyrin ring, co-ordinated to acentral atom.This is very similar in structure tothe heme group found inhemoglobin,except that in heme the centralatom is iron, whereas inchlorophyll it is magnesium.
  • 24. Photosynthesis Mechanism:
  • 25. PHOTOSYNTHESIS Solar energy to Chemical energy Oxidation – Reduction processLight OxidationWater Protons + Electrons Pigments Assimilatory Powers Reduction CO2 Carbohydrate
  • 26. Evidence of Light and Dark reaction:Temperature coefficientIntermittent lightTracer technique
  • 27. Red dropsharp decrease in quantum yield at wavelength greater than 680nm, in the red part of the spectrum, the phenomenon was calledas red drop Emerson enhancement effect inefficient far-red light beyond 680 nm could be made fully efficient if supplemented with RED light
  • 28. LIGHT REACTIONProduction of Assimilatory Powers (ATP and NADPH)by light, water and pigments 1. Absorption of light energy by the pigments 2. Activation of Chlorophyll molecule 3. Photolysis of water 4. Electron Transport Chain 5. Synthesis of Assimilatory Powers
  • 29. Absorption of Light EnergyAll pigments – Absorb – Light Energy – Transfer to – Chlorophyll a Chlorophyll a – Absorb and Conversion – To Chemical Energy PHOTOSYSTEM Group of Pigments PS І (P 700) PS І (P 700) PS ІІ (P 680) More Chlorophyll Less Chlorophyll Less Accessory Pigments More Accessory Pigments
  • 30. Absorption of light energy by chloroplast pigmentsDifferent chloroplast pigments absorb light in different regions of the visiblepart of the spectrum
  • 31. Transfer of light energy from accessory pigments to chlorophyll a
  • 32. What happens when chlorophyll absorbs light? The chlorophyll molecule becomes excited (this takes only 10-15 sec = fempto sec) and anelectron moves to an outer energy level. CHL (ground state) → CHL* (excited state) Electrons don’t stay excited long (10-9 sec), because they either: return to the ground state and release their absorbed energy as heat (thermal deactivation); return to ground state and release their extra energy as light (fluorescence); transfer their energy to another molecule; kind of like hitting pool balls (resonance transfer); or be used in a photochemical reaction (photochemistry). Prepared By: KIRTI BARDHAN
  • 33. Activation of chlorophyll molecule by photon of light Chl a Excited second singlet state Excited second singlet state Heat loss Meta stableLight Triplet state fluorescen ce Chl a Ground state
  • 34. Photosystem :Two physically and chemically distinct photosystems (I and II), each with its ownantenna pigments and photochemical reaction center.The two photosystems arelinked by an electron transport chain
  • 35. PSI PSII Is located on the inner surface of Is located on the outer surface of non appressed parts of granaappressed parts of grana thylakoids. thylakoids. Comprises of about 200 - 400 Comprises of about 200chlorophylls, 50 carotenoids, one chlorophylls, 50 carotenoids, onemolecules of P700 molecules of P680Is light green in colour Is dark green in colour Is not directly involved with Is directly involved withphotooxidation of H2O and evolution of photooxidation of H2O andmolecules of O2 evolution of molecules of O2
  • 36. How the Light Reactions Generate ATP and NADPH Primary NADP electron acceptor Energy to make 3 Primary electron 2 acceptor Light Light Primary electron acceptor Reaction- 1 center NADPH-producing chlorophyll photosystem Water-splitting photosystem 2 H + 1/2
  • 37. Cyclic Photophosphorylation• Process for ATP generation associated with some Photosynthetic Bacteria• Reaction Center => 700 nm Prepared By: KIRTI BARDHAN
  • 38. Cyclic photophosphorylation Prepared By: KIRTI BARDHAN
  • 39. Prepared By: KIRTI BARDHAN
  • 40. Noncyclic Photophosphorylation• Photosystem II regains electrons by splitting water, leaving O2 gas as a by-product Primary electron acceptor Primary electron acceptor Photons Energy for synthesis of PHOTOSYSTEM I PHOTOSYSTEM II by chemiosmosis
  • 41. Noncyclic Photophosphorylation Prepared By: KIRTI BARDHAN
  • 42. • Two types of photosystems cooperate in the light reactions ATP mill Water-splitting NADPH-producing photosystem photosystem
  • 43. In the light reactions, electron transport chains generate ATP, NADPH, & O2• Two connected photosystems collect photons of light and transfer the energy to chlorophyll electrons• The excited electrons are passed from the primary electron acceptor to electron transport chains – Their energy ends up in ATP and NADPH
  • 44. Chemiosmosis powers ATP synthesis in the light reactions• The electron transport chains are arranged with the photosystems in the thylakoid membranes and pump H+ through that membrane – The flow of H+ back through the membrane is harnessed by ATP synthase to make ATP – In the stroma, the H+ ions combine with NADP+ to form NADPH
  • 45. The Light Reaction
  • 47. DARK REACTION Reduction of CO2 to Carbohydrate by utilizing Assimilatory Powers (ATP and NADPH2) Produced by Light Reaction DARK REACTIONC3 PATHWAYCALVIN CYCLE C4 PathwayREDUCTIVE PENTOSE CAM Hatch and Slack PathwayPHOSPHATE [RPP] CYCLE Cycle
  • 48. Calvin cycle or C3 cycleCalvin cycle was first observed by Melvin Calvin in chlorellaCalvin was awarded Nobel Prize for this work in 1961It is a cyclic reaction occurring in the dark phase of photosynthesisCO2 is converted into sugars and it is a process of carbon fixationFirst stable compound in Calvin cycle is a 3 carbon compound(3 phosphoglyceric acid)cycle is also called as C3 cycle
  • 49. Synthesis of carbohydrateRibulose 1,5 diphosphate + CO2+H2O  3 Phosphoglyceric acid (2 molecule) Rubisco 3 PGA + NADPH + H  3 Phosphoglyceral aldehyde ATP + Triose phosphate dehydrogenase3 Phosphoglyceral aldehyde  Dihydroxy acetone phosphate Triose phosphate isomerase 3 Phosphoglyceral aldehyde  Fructose 1,6 diphosphate + Dihydroxy acetone phosphate Aldolase
  • 50. Regeneration of Ribulose diphosphateFructose 6 phosphate + 3 Phosphoglyceraldehyde  Erythrose 4 phosphate + Xylose-5- phosphate TransketolasecErythrose 4 phosphate + Dihydroxy acetone phosphate Aldolase Sedoheptulose 1, 7 diphosphate PhosphataseSedoheptulose 7 diphosphate
  • 51. Sedoheptulose- 7- phosphate 3 Phosphoglyceraldehyde Transketolase Xylose 5 phosphate + Ribose 5 Phosphate Phosphopentose isomerase Ribulose 5 phosphate + ATP Phosphopentokinase Ribulose, 1, 5 diphosphate
  • 52. PhotorespirationHigh light intensityLow CO2, High O2 Prepared By: KIRTI BARDHAN
  • 53. Prepared By: KIRTI BARDHAN
  • 54. C4 cycle/ Hatch and Slack / C4 dicarboxylic acid pathwayIt is the alternate pathway of C3 cycle to fix CO2first formed stable compound 4 carbon oxaloacetic acidEnzyme - PEP corboxylasedifferent type of leaf anatomy- chloroplasts are dimorphic innaturevascular bundles are surrounded by bundle sheath of largerparenchymatous cells have chloroplastschloroplasts of bundle sheath are larger, lack granapeculiar anatomy of leaves of C4 plants is called Kranz anatomyEg : sugar cane, maize, sorghum and amaranthus
  • 55. C4 cycle consists of four stages1. Fixation of CO2 by the carboxylation of phosphoenolpyruvate in the mesophyll cells to form a C4 acid (malate and/or aspartate)2. Transportation of the C4 acids to the bundle sheath cells3. Decarboxylation of the C4 acids within the bundle sheath cells and generation of CO2, which is then reduced to carbohydrate via Calvin cycle4. Transport of the C3 acid (pyruvate or alanine) that is formed by the decarboxylation step back to the mesophyll cell and regeneration of the CO2 acceptor phosphoenolpyruvate
  • 56. C3 leaf C4 leaf
  • 57. Structural specification of C4 plants: Dimorphism of chloroplast Kranz anatomyDifferences b/w C3 and C4 Plants CO2 acceptor and stable product Efficiency of CO2 absorption (CO2 compensation point) Type of chloroplast Calvin cycle enzymes Light saturation point Photorespiration Optimum temp.
  • 58. Biological Significance of C4 plantsPhotosynthesis in low CO2 Xeric condition – partial stomatal closure Absence of photorespiration, higher fixation
  • 59. CAM(Crassulation acid metabolism) Fixation
  • 60. Prepared By: KIRTI BARDHAN
  • 61. CAM Photosynthesis
  • 62. C3 C4 CAM no distinct bundle Usually no palisadeLeaf anatomy Kranz anatomy sheath cells, large vacuolesInitial carboxylating enzyme rubisco PEPcase PEPcaseProduct of CO2 fixation PGA (C3) OAA (C4) OAA (C4)Chloroplasts one type dimorphic one typeTheoretical energy requirements 1: 3: 2 1: 5 : 2 1: 6.5: 2(CO2: ATP: NADPH)Transpiration ratio (g H2O/g dry wt) 450-950 250-350 18-125Photosynthesis rate (mg CO2 fixed 15 - 30 40 - 80 (low)dm-2 h-1)Carbon dioxide compensation 50 - 150 (Hi) 0-10 (low) 0-5 (in dark)point (ppm) Light saturation easilyResponse to light No light saturation - achievedPhotosynthesis inhibited by Yes No Yesoxygen?Temperature optimum for 15-25 30-47 35photosynthesis
  • 63. Factor affecting photosynthesis:Internal factor: Chlorophyll Leaf resistance Demand for photosynthates Genotype
  • 64. Fate of carbohydrate products in the plantcarbon dioxide and water photosynthesiscarbohydrates (e.g. glucose) mineral salts (e.g. NO3-, SO42-) fatty acids glycerol amino acids water
  • 65. Fate of carbohydrate products in the plant carbon dioxide and water photosynthesiscarbohydrates (e.g. glucose) mineral salts (e.g. NO3-, SO42-) fatty acids glycerol amino acids waterrelease energy by respiration
  • 66. Fate of carbohydrate products in the plant carbon dioxide and water photosynthesiscarbohydrates (e.g. glucose) mineral salts (e.g. NO3-, SO42-) fatty acids glycerol amino acids waterconvert into starch for storage
  • 67. Fate of carbohydrate products in the plant carbon dioxide and water photosynthesiscarbohydrates (e.g. glucose) mineral salts (e.g. NO3-, SO42-) fatty acids glycerol amino acids waterchange into sucrose and is transportedto other parts through phloem
  • 68. Fate of carbohydrate products in the plantcarbon dioxide and water photosynthesiscarbohydrates (e.g. glucose) mineral salts (e.g. NO3-, SO42-) fatty acids glycerol amino acids water combine to form fats and oils to form cell membranes and as a food store
  • 69. Fate of carbohydrate products in the plantcarbon dioxide and water photosynthesiscarbohydrates (e.g. glucose) mineral salts (e.g. NO3-, SO42-) fatty acids glycerol amino acids water join together to become protein molecules
  • 70. External Factor : CO2
  • 71. External Factor : Light
  • 72. External Factor: Temperature Water Nutrient
  • 73. Thank You