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Photosynthesis

Photosynthesis: Light and Dark Reaction

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Photosynthesis

  1. 1. Photosynthesis
  2. 2. • Almost all plants are photosynthetic autotrophs, as are some bacteria and protists – Autotrophs generate their own organic matter through photosynthesis – Sunlight is transformed to energy stored in the form of chemical bonds (a) Mosses, ferns, and flowering plants (b) Kelp (c) Euglena (d) Cyanobacteria THE BASICS OF PHOTOSYNTHESIS
  3. 3. Why is Photosynthesis important? Makes organic molecules (glucose) out of inorganic materials (carbon dioxide and water). It begins all food chains/webs. Thus all life is supported by this process. It also makes oxygen gas!!
  4. 4. Photosynthesis-starts to ecological food webs!
  5. 5. WHY ARE PLANTS GREEN? It's not that easy bein' green Having to spend each day the color of the leaves When I think it could be nicer being red or yellow or gold Or something much more colorful like that… Kermit the Frog
  6. 6. Electromagnetic Spectrum and Visible Light Gamma rays X-rays UV Infrared & Microwaves Radio waves Visible light Wavelength (nm)
  7. 7. Different wavelengths of visible light are seen by the human eye as different colors. WHY ARE PLANTS GREEN? Gamma rays X-rays UV Infrared Micro- waves Radio waves Visible light Wavelength (nm)
  8. 8. Sunlight minus absorbed wavelengths or colors equals the apparent color of an object. The feathers of male cardinals are loaded with carotenoid pigments. These pigments absorb some wavelengths of light and reflect others.
  9. 9. Why are plants green? Transmitted light
  10. 10. WHY ARE PLANTS GREEN? Plant Cells have Green Chloroplasts The thylakoid membrane of the chloroplast is impregnated with photosynthetic pigments (i.e., chlorophylls, carotenoids).
  11. 11. • Chloroplasts absorb light energy and convert it to chemical energy Light Reflected light Absorbed light Transmitted light Chloroplast THE COLOR OF LIGHT SEEN IS THE COLOR NOT ABSORBED
  12. 12. Plants use sunlight to turn water and carbon dioxide into glucose. Glucose is a kind of sugar. Plants use glucose as food for energy and as a building block for growing. Autotrophs make glucose and heterotrophs are consumers of it. Photo-synthesis means "putting together with light."
  13. 13. PHOTOSYNTHESIS • Absorbing Light Energy to make chemical energy: glucose! – Pigments: Absorb different colors of white light (ROY G BIV) •Main pigment: Chlorophyll a •Accessory pigments: Chlorophyll b and Carotenoids •These pigments absorb all wavelengths (light) BUT not green!
  14. 14. Chloroplasts: Sites of Photosynthesis • Photosynthesis – Occurs in chloroplasts, organelles in certain plants – All green plant parts have chloroplasts and carry out photosynthesis • The leaves have the most chloroplasts • The green color comes from chlorophyll in the chloroplasts • The pigments absorb light energy
  15. 15. • In most plants, photosynthesis occurs primarily in the leaves, in the chloroplasts • A chloroplast contains: – stroma, a fluid – grana, stacks of thylakoids • The thylakoids contain chlorophyll – Chlorophyll is the green pigment that captures light for photosynthesis Photosynthesis occurs in chloroplasts
  16. 16. • The location and structure of chloroplasts LEAF CROSS SECTION MESOPHYLL CELL LEAF Chloroplast Mesophyll CHLOROPLAST Intermembrane space Outer membrane Inner membrane Thylakoid compartmentThylakoidStroma Granum StromaGrana
  17. 17. • Chloroplasts contain several pigments Chloroplast Pigments – Chlorophyll a – Chlorophyll b – Carotenoids Figure 7.7
  18. 18. Chlorophyll a & b •Chl a has a methyl group •Chl b has a carbonyl group Porphyrin ring delocalized e- Phytol tail
  19. 19. Different pigments absorb light differently
  20. 20. Excited state e Heat Light Photon Light (fluorescence) Chlorophyll molecule Ground state 2 (a) Absorption of a photon (b) fluorescence of isolated chlorophyll in solution Excitation of chlorophyll in a chloroplast Loss of energy due to heat causes the photons of light to be less energetic. Less energy translates into longer wavelength. Energy = (Planck’s constant) x (velocity of light)/(wavelength of light) Transition toward the red end of the visible spectrum. e
  21. 21. Fall Colors • During the fall, the green chlorophyll pigments are greatly reduced revealing the other pigments. • Carotenoids are pigments that are either red or yellow.
  22. 22. Chlorophyll: A Light Absorbing Pigment The Solar Panel Chemical!
  23. 23. Photosynthesis Glucose provides the energy and carbon needed to make other plant materials like wax and proteins.
  24. 24. • Photosynthesis is the process by which autotrophic organisms use light energy to make sugar and oxygen gas from carbon dioxide and water AN OVERVIEW OF PHOTOSYNTHESIS Carbon dioxide Water Glucose Oxygen gas PHOTOSYNTHESIS
  25. 25. • The Calvin cycle makes sugar from carbon dioxide – ATP generated by the light reactions provides the energy for sugar synthesis – The NADPH produced by the light reactions provides the electrons for the reduction of carbon dioxide to glucose Light Chloroplast Light reactions Calvin cycle NADP ADP + P • The light reactions convert solar energy to chemical energy – Produce ATP & NADPH AN OVERVIEW OF PHOTOSYNTHESIS
  26. 26. Oxygen and Sugar!
  27. 27. • In plants and simple animals, waste products are removed by diffusion. Plants, for example, excrete O2, a product of photosynthesis.
  28. 28. EQUATION FOR PHOTOSYNTHESIS 6CO2 + 6H2O + ENERGY C6H12O6 + 6O2 CARBON DIOXIDE WATER GLUCOSE OXYGEN
  29. 29. Redox Reaction • The transfer of one or more electrons from one reactant to another. • Two types: 1. Oxidation 2. Reduction
  30. 30. Oxidation Reaction • The loss of electrons from a substance. • Or the gain of oxygen. glucose 6CO2 + 6H2O  C6H12O6 + 6O2 Oxidation
  31. 31. Reduction Reaction • The gain of electrons to a substance. • Or the loss of oxygen. glucose 6CO2 + 6H2O  C6H12O6 + 6O2 Reduction
  32. 32. PHOTOSYNTHESIS • 2 Phases – Light-dependent reaction – Light-independent reaction • Light-dependent: converts light energy into chemical energy; produces ATP and NADPH molecules to be used to fuel light- independent reaction • Light-independent: uses ATP produced to make simple sugars/ glucose
  33. 33. PHOTOSYNTHESIS • Light-dependent reaction (LIGHT Reaction) – Requires light – Occurs in chloroplast (in thylakoids) – Chlorophyll (thylakoid) traps energy from light – Light excites electron (e-) •Kicks e- out of chlorophyll to an electron transport chain •Electron transport chain: series of proteins in thylakoid membrane – Bucket brigade
  34. 34. PHOTOSYNTHESIS • Light-dependent reaction (LIGHT Reaction) – Energy lost along electron transport chain – Lost energy used to recharge ATP from ADP – NADPH produced from e- transport chain •Stores energy until transfer to stroma •Plays important role in light-independent reaction – Total byproducts: ATP, NADP, O2
  35. 35. 1. Light Reaction (Electron Flow) • During the light reaction, there are two possible routes for electron flow. A. Cyclic Electron Flow B. Noncyclic Electron Flow
  36. 36. Water-splitting photosystem NADPH-producing photosystem ATP mill • Two types of photosystems cooperate in the light reactions
  37. 37. A. Cyclic Electron Flow • Occurs in the thylakoid membrane. • Uses Photosystem I only • P700 reaction center- chlorophyll a • Uses Electron Transport Chain (ETC) • Generates ATP only ADP + ATPP
  38. 38. A. Cyclic Electron Flow P700 Primary Electron Acceptor e- e- e- e- ATP produced by ETC Photosystem I Accessory Pigments SUN Photons
  39. 39. 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
  40. 40. B. Noncyclic Electron Flow P700 Photosystem I P680 Photosystem II Primary Electron Acceptor Primary Electron Acceptor ETC Enzyme Reaction H2O 1/2O2 + 2H+ ATP NADPH Photon 2e- 2e- 2e- 2e- 2e- SUN Photon
  41. 41. B. Noncyclic Electron Flow • ADP +  ATP • NADP+ + H  NADPH • Oxygen comes from the splitting of H2O, not CO2 H2O  1/2 O2 + 2H+ (Reduced) P (Reduced) (Oxidized)
  42. 42. Primary electron acceptor Primary electron acceptor Photons PHOTOSYSTEM I PHOTOSYSTEM II Energy for synthesis of by chemiosmosis Noncyclic Photophosphorylation • Photosystem II regains electrons by splitting water, leaving O2 gas as a by-product
  43. 43. • The O2 liberated by photosynthesis is made from the oxygen in water (H+ and e-) Plants produce O2 gas by splitting H2O
  44. 44. 2 H + 1/2 Water-splitting photosystem Reaction- center chlorophyll Light Primary electron acceptor Energy to make Primary electron acceptor Primary electron acceptor NADPH-producing photosystem Light NADP 1 2 3 How the Light Reactions Generate ATP and NADPH
  45. 45. Chemiosmosis • Powers ATP synthesis. • Located in the thylakoid membranes. • Uses ETC and ATP synthase (enzyme) to make ATP. • Photophosphorylation: addition of phosphate to ADP to make ATP.
  46. 46. Chemiosmosis H+ H+ ATP Synthase H+ H+ H+ H+ H+ H+ high H+ concentration H+ ADP + P ATP PS II PS I E T C low H+ concentration H+ Thylakoid Space Thylakoid SUN (Proton Pumping)
  47. 47. • 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 Chemiosmosis powers ATP synthesis in the light reactions
  48. 48. • The production of ATP by chemiosmosis in photosynthesis Thylakoid compartment (high H+) Thylakoid membrane Stroma (low H+) Light Antenna molecules Light ELECTRON TRANSPORT CHAIN PHOTOSYSTEM II PHOTOSYSTEM I ATP SYNTHASE
  49. 49. PHOTOSYNTHESIS • Light-independent reaction (Dark Reaction) – Does not require light – Calvin Cycle •Occurs in stroma of chloroplast •Requires CO2 •Uses ATP and NADPH as fuel to run •Makes glucose sugar from CO2 and Hydrogen
  50. 50. 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.
  51. 51. Chloroplast GranumThylakoid Stroma Outer Membrane Inner Membrane
  52. 52. • A Photosynthesis Road Map Chloroplast Light Stack of thylakoids ADP + P NADP Stroma Light reactions Calvin cycle Sugar used for  Cellular respiration  Cellulose  Starch  Other organic compounds
  53. 53. PHOTOSYNTHESIS • What affects photosynthesis? – Light intensity: as light increases, rate of photosynthesis increases
  54. 54. PHOTOSYNTHESIS • What affects photosynthesis? – Carbon Dioxide: As CO2 increases, rate of photosynthesis increases
  55. 55. PHOTOSYNTHESIS • What affects photosynthesis? – Temperature: •Temperature Low = Rate of photosynthesis low •Temperature Increases = Rate of photosynthesis increases •If temperature too hot, rate drops
  56. 56. Photorespiration • Occurs on hot, dry, bright days. • Stomates close. • Fixation of O2 instead of CO2. • Produces 2-C molecules instead of 3-C sugar molecules. • Produces no sugar molecules or no ATP.
  57. 57. Photorespiration • Because of photorespiration: Plants have special adaptations to limit the effect of photorespiration. 1. C4 plants 2. CAM plants
  58. 58. C4 Plants • Hot, moist environments. • 15% of plants (grasses, corn, sugarcane). • Divides photosynthesis spatially. • Light rxn - mesophyll cells. • Calvin cycle - bundle sheath cells.
  59. 59. C4 Plants Mesophyll Cell CO2 C-C-C PEP C-C-C-C Malate ATP Bundle Sheath Cell C-C-C Pyruvic Acid C-C-C-C CO2 C3 Malate Transported glucose Vascular Tissue
  60. 60. CAM Plants • Hot, dry environments. • 5% of plants (cactus and ice plants). • Stomates closed during day. • Stomates open during the night. • Light rxn - occurs during the day. • Calvin Cycle - occurs when CO2 is present.
  61. 61. CAM Plants Night (Stomates Open) Day (Stomates Closed) Vacuole C-C-C-C Malate C-C-C-C Malate Malate C-C-C-C CO2 CO2 C3 C-C-C Pyruvic acid ATP C-C-C PEP glucose
  62. 62. Check it! 1. The process that uses the sun’s energy to make simple sugars is _____________. A. Cellular respiration B. Glycolysis C. Photosynthesis D. Photolysis
  63. 63. Check it! 2. The function accomplished by the light- dependent reactions is ______________. A. Energy storage B. Sugar production C. Carbon fixation D. Conversion of sugar

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