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Photosynthesis 2011 - 2012
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Photosynthesis 2011 - 2012


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  • 1. This presentation will focus on: The importance of autotrophs An overview of photosynthesis Leaf and chloroplast structure and function The electromagnetic spectrum Pigment function and variety The Light Reactions The Calvin Cycle
  • 2. All organisms require a source of energyAll organisms require a source of carbon compoundsProvides molecular oxygen for the atmosphere
  • 3. 2 Types of Autotrophs: Chemotrophs Photoautotrophs
  • 4. 6 CO2 + 6 H2O C6H12O6 + 6 O2
  • 5. Plants are composed of three major organ systems: The Root System anchors the plant in place stores excess sugars absorbs water and mineral nutrients The Shoot System supports the plant body provides passageway for nutrients and minerals Leaves site of photosynthesis (food production)
  • 6. Plant organs are made up of 3 types of tissues:• Dermal • cells for structure and protection • secretion of cutin to prevent water loss• Ground • photosynthesis • storage of food and water• Vascular • specialized for transport of water and nutrients
  • 7. • The ultimate source of energy is the sun• Solar energy is called electromagnetic radiation• Travels in waves of photons• The Electromagnetic spectrum describes the range ofenergy in solar radiation• The EM spectrum is measured by wavelength
  • 8. Pigments are organic molecules that absorb visible light Wavelengths not absorbed are reflected, creating the visible color of an object Wavelengths absorbed cause the excitations of electrons Plants contain a major pigment, chlorophyll a, and accessory pigments like carotenoids and anthocyanins
  • 9. Go to through the sections called “Overview” and “Strategy/Players”
  • 10. The Light Reactions•Light Dependent•“Photo” Division•Energy CapturingThe Calvin Cycle•Light Independent•“Synthesis” Division•Energy Storage
  • 11. •Occur on thylakoid membranes•Use 2 Photosystems•PSI (p700) and PSII (p680)
  • 12. Click image to see a membrane view of the light reactions
  • 13. •Sunlight strikes p680 boosting electron to excited state•High energy electrons passed from primary electronacceptor down electron transport system via oxidation-reduction. These reactions power the active transport ofH+ from the stroma into the thylakoid space•H+ diffuse back into stroma through ATP synthetaseconverting ADP + P into ATP•Electrons from p680 end up at p700. Hole at p680 filledby oxidation of H2O into O2
  • 14. •Sunlight hits p700 boosting electron to excited state•High energy electrons passed from primary electronacceptor down electron transport system via oxidation-reduction.•High energy electrons transferred by NADP+ reductaseto NADP+ to form NADPH•Hole at p700 filled by electrons from p680
  • 15. Click image for link to animated overview of noncyclic photophosphorylation
  • 16. Sunlight + H2O O2 + ATP + NADPH ADP, P, and NADP+ from Inorganic Nutrient Pool are raw materialsStudy the following tutorials:You control the light reactions!Biology Project Light RXNs TutorialPhotosynthesis Light RXNs Interactive
  • 17. Occurs in theStromaUses ATP andNADPH fromLight RxnsCO2 is RawMaterial
  • 18. .. .
  • 19. Phase 1: Carbon FixationCO2 comes into the stroma of the chloroplast viathe stomata of the leaves.Rubisco catalyzes the bonding of CO2 to RuBP tocreate an unstable 6-carbon molecule thatinstantly splits into two 3-carbon molecules of3-PGA. Back to diagram
  • 20. Phase 2: ReductionATP phosphorylates each 3-PGA molecule andcreates 1,3-bisphosphoglycerate (1,3 DPGA).NADPH reduces 1,3-bisphosphoglycerate whichcauses the molecule to become glyceraldehyde-3-phosphate (PGAL). NADPH is oxidized by this processand becomes NADP+. Back to diagram
  • 21. Phase 3: RegenerationFor every six molecules of PGAL created, fivemolecules continue on to phase 3 while one leavesto be used for organic compounds.ATP is once again needed. However, this time itphosphorylates G3P to regenerate RuBP after somerearrangement. Back to diagram
  • 22. Summary of Calvin Cycle CO2 + ATP + NADPH ADP + NADP+ + PGAL PGAL is rearranged to produce: •Glucose for cellular respiration •Fructose in Fruits •Sucrose for Transport Throughout Plant •Starch for StorageStudy the following tutorials:The 3 Phases AnimatedCalvin Cycle Tutorial at Biology ProjectPhotosynthesis Dark RXNs Interactive
  • 23. Plants fight water loss and dehydration • Close stoma to prevent water loss • Closed stoma mean no input of CO2 into leaf • Light reactions continue to produce O2Photorespiration • When O2 concentration increases, rubisco adds O2 to the Calvin Cycle instead of CO2
  • 24. Photorespiration • Occurs on bright, hot, dry days when stoma close • Consumes O2 • Releases CO2 • Unlike cellular respiration, generates no ATP • Unlike photosynthesis, generates no food • Actually decrease rate of photosynthetic output
  • 25. Mechanisms to fightphotorespiration: C4and CAM pathwaysIncorporate CO2 intoorganic acids first,then release it intothe Calvin Cycle
  • 26. •PEP Carboxylase accepts CO2 inmesophyll cells•A 4C intermediate carries the CO2 intothe bundle-sheath cells•This maintains a high concentrationof CO2 in the bundle sheath to avoidphotorespiration