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Chapter 4

Chapter 4. Photosynthesis. Light energy. CO 2. H 2 O. C 6 H 12 O 6. O 2. 6. +. 6. +. 6. Carbon dioxide. Water. Glucose. Oxygen gas. PHOTOSYNTHESIS. 0. Photosynthesis is the process by which certain organisms use light energy

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Chapter 4

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  1. Chapter 4 • Photosynthesis

  2. Light energy CO2 H2O C6H12O6 O2 6 + 6 + 6 Carbon dioxide Water Glucose Oxygen gas PHOTOSYNTHESIS 0 • Photosynthesis is the process by which certain organisms use light energy • To make sugar and oxygen gas from carbon dioxide and water • What does it need? (Input) • What does it make? (Output)

  3. Trophic Roles • Autotrophs Producers of the biosphere: • produce organic molecules from CO2 & inorganic raw materials • Heterotrophs consumers

  4. Learning Target 1. Describe Oxidation & Reduction reactions

  5. REDOX Reactions LEO the Lion Says GER

  6. REDOX Reactions • Oxidation • When a compound loses electrons • Reduction • When a compound gains electrons • CO2 + H2O + energy → C6H12O6 + O2 • CO2 is reduced to form glucose • Water is oxidized to form O2

  7. Reduction   6 O2 6 CO2 6 H2O C6H12O6 Oxidation Oxidation   6 H2O C6H12O6 6 CO2 6 O2 Reduction 0 • Photosynthesis is a redox process, as is cellular respiration • In photosynthesis • H2O is oxidized and CO2 is reduced Figure 7.4A, B

  8. Learning Check • If H2O is losing electrons than it is being reduced/oxidized • Co2 is being reduced/oxidized, which means it is gaining/losing electrons.

  9. Photosynthesis Overview • Light reactions • Depend on light • Occur in Thylakoid Membrane • Light Independent (“Dark”) reactions • Does NOT need light • Occurs in the Stroma

  10. Learning Target • Compare & contrast the structure & function of mitochondria & chloroplast 15. Determine what factors affect the process of photosynthesis & cellular respiration

  11. Location, location, location Where does the Light Dependent Reaction occur? The Light Independent reaction?

  12. Chloroplast Structure • Found in mesophyll • 1 mesophyll cell may have 30 chloroplasts • Stomata regulate passage of CO2, O2 and H2O

  13. Learning Check Where does the Light Dependent Reaction occur? The Light Independent reaction? • What factors could affect the process of photosynthesis?

  14. Learning Targets 11. Describe the purpose of Chlorophyll & Accessory pigments.

  15. Pigments • Pigments • Absorb light energy • Boost e-become unstable! • Chlorophyll • Chlorophyll a  main pigment  blue-green • Chlorophyll b  accessory pigment  yellow-green • Other accessory pigments  absorb different wavelengths of light • Carotenoids  yellow-orange • Xanthophyll yellow • Rhodophyll  red • Fucoxanthin  brown Why are plants green? Why are plants changing color?

  16. Photosystems • Pass energy  reaction center (chlorophyll a molecule)  transfers energy to primaryelectron acceptor • antenna pigments are primarily chlorophyll b, carotenoids & xanthophyll

  17. Learning Check • What is the purpose/function of pigments?

  18. Photosynthesis Overview • Light reactions • light energy  chemical energy (ATP and NADPH) and produce O2 • Light Independent (“Dark”) reactions • Using ATP and NADPH from the light reactions form sugar from CO2

  19. Learning Target 7. Contrast Chemiosmosis in Cellular Respiration and Photosynthesis 6. Explain how electron transport chains (ETC) establish an electrochemical gradient across membranes.

  20. ETC, Chemiosmosis & ATP Synthase • Powers ATP synthesis in light reactions • electrons (e-) are passed along a chain of proteins (called the ETC) in the membrane  H+ pumped into Thylakoid space (chemiosmosis) • H+ diffuse back across the membrane through ATP synthase  powers the phosphorylation of ADP to produce ATP (photophosphorylation)

  21. Photophosphorylation http://vcell.ndsu.nodak.edu/animations/atpgradient/movie.htm

  22. Learning Check! • ETC uses the energy of e- being passed along to pump _______ from the ________ into the thylakoid _______ • Chemiosmosis is the movement of ______ to create a ________concentration.

  23. Learning Target 3. Identify the inputs and outputs and location of the light reactions and Calvin Cycle. 4. Explain the role of NADH, FADH2, and NADPH. 14. Summarize how energy is transferred during photosynthesis and cellular respiration.

  24. Electron Carriers • NAD+ • Reacts with C-H bonds to become NADH • NADP+ • Reacts with free e- and H+ ions • ADP  ATP • diffusion of H+ through ATP Synthase

  25. LDR • Inputs? • Outputs? • Two types: • Noncyclic Photophosphorylation • Cyclic Photophosphorylation

  26. Non-cyclic photophosphorylation

  27. Learning Target 12. Describe the connection between PS2 & PS1

  28. H2O CO2 LIGHT NADP+ ADP CALVIN CYCLE LIGHT REACTOR ATP NADPH STROMA (Low H+ concentration) O2 [CH2O] (sugar) Cytochrome complex Photosystem II Photosystem I NADP+ reductase Light 2 H+ 3 NADP+ + 2H+ Fd NADPH + H+ Pq Pc 2 H2O 1⁄2 O2 THYLAKOID SPACE (High H+ concentration) 1 2 H+ +2 H+ To Calvin cycle ATP synthase Thylakoid membrane STROMA (Low H+ concentration) ADP ATP P H+

  29. Light Dependent RXN animation • http://www.science.smith.edu/departments/Biology/Bio231/ltrxn.html • http://vcell.ndsu.nodak.edu/animations/photosynthesis/movie-flash.htm

  30. Cyclic Photophosphorylation • Primitive  used by bacteria • Electron boosted out of P1  ETC  returned to P1 • Electron drives proton pumpschemiosmosis ATP

  31. Learning Targets 3. Identify the inputs and outputs and location of the light reactions and Calvin Cycle. 4. Explain the role of NADH, FADH2, and NADPH. 15. Summarize how energy is transferred during photosynthesis and cellular respiration.

  32. Calvin Cycle/Light Independent Reactions • Occur in the dark or the light • Light independent reactions • 3 steps • Carbon fixation • Reduction • Regeneration of RuBP

  33. Step 1:Carbon Fixation • RuBP (ribulose bisphosphate) • 5 C sugar • Catalyzed by Rubisco (RuBP carboxylase) • Adds CO2 • Creates an unstable 6 C molecule that splits • Creates PGA (3 C moleucle

  34. Step 2:Reduction • PGA gets phosphorylated by ATP (gets it’s energy) • Reduced by NADPH (gets it’s e-) • Produces G3P (PGAL) • some G3P  glucose • most G3P  regenerate RuBP

  35. Step 3:Regeneration of RuBP • 1 G3P moves out to eventually become glucose • G3P  rearranged into RuBP • Requires input of 3 ATP • Takes 6 turns of cycle  1 glucose

  36. http://www.science.smith.edu/departments/Biology/Bio231/calvin.htmlhttp://www.science.smith.edu/departments/Biology/Bio231/calvin.html

  37. Alternative mechanisms:Photorespiration • C3 plants  rice, wheat, soybeans • Uses Co2 directly to make PGA • On hot, dry days they close their stomata • no CO2 taken in and O2 builds up • rubisco substitutes O2 for CO2 • Creates a 2 C compound • 2 C compound gets broken down  releases CO2 & water • Called photorespiration • Uses light, releases CO2 and water • Doesn’t make glucose

  38. Alternative mechanisms:C4 Plants • Sunny ecosystems • C is fixed into 4 C molecule • Carbon fixed outside cells (in bundle sheath cellsvery efficient  requires extra ATP • Only fixes C, not oxygen • Donates the carbon to Calvin Cycle • Balances out photorespiration & saves water • Corn and sugarcane are a C4 plants

  39. Alternative mechanisms:CAM Plants • Crassulacean acid metabolism Hot/dry climates • Orchids, cacti, pineapple etc. • Stomates open at night to reduce water loss  evaporation • CO2 is fixed into a 4 C compound, used later

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