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PHOTOSYNTHESIS Chapter 7

PHOTOSYNTHESIS Chapter 7. I. Introduction A. Energy—the capacity to do work 1. Potential—stored energy 2. Kinetic—energy at work. B. Laws of Thermodynamics 1. 1st Law—Energy is constant in the universe. It cannot be created or destroyed.

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PHOTOSYNTHESIS Chapter 7

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  1. PHOTOSYNTHESISChapter 7

  2. I. Introduction A. Energy—the capacity to do work 1. Potential—stored energy 2. Kinetic—energy at work

  3. B. Laws of Thermodynamics 1. 1st Law—Energy is constant in the universe. It cannot be created or destroyed. 2. 2nd Law—Energy can be converted from one form to another but in the conversion, most is wasted or lost as heat. a. There is a move toward entropy or disorganization. b. Heat is dispersed into the environment.

  4. C. Light 1. Defined—electromagnetic energy from sunlight. a. Travels in waves b. Distance between the crests is wavelength c. Measured in nanometers d. Plants use wavelengths between 380-750 nm.

  5. 2. How it is produced a. Result of nuclear fusion b. Temperature of the sun is hot enough to fuse two H atoms together toform Helium. c. This reaction results in photons of light.

  6. Solar Flares

  7. 3. Photons a. A unit or packet of light b. Measurement of light energy 4. Less than 1 % of all of the light produced by the sun is used in photosynthesis.

  8. II. Background A. Joseph Priestly, 1772 1. Proved plants affect air quality 2. Set up candle in a bell dome; burned out. 3. Added a plant with the candle and it burned until all of the wax was used up. 4. Concluded that plants in some way affected air quality.

  9. B. Role of H2O in photosynthesis 1. The energy of sunlight is used to split the water into H and O2. 2. This is called photolysis. 3. Source of O2 in the atmosphere. 4. H is used to make sugar in photosynthesis.

  10. C. Role of chlorophyll in photosynthesis 1. A green pigment that absorbs light of certain wavelengths. 2. Atoms that form it—C, H, O, N, Mg 3. Excited electrons—have absorbed light energy

  11. 4. K to L shell, back to K—excited electrons move to a higher energy shell, then return 5. Types a. Chlorophyll a is the most abundant. b. Table 7.1 lists other photosynthetic pigments.

  12. D. Summary Equation sunlight6CO2 + 12 H2O--------------> C6H12O6 + 6O2 + 6H2O chlorophyll

  13. III. Structure of the Chloroplast A. Doubled walled organelle B. Thylakoid membrane 1. Within the chloroplast 2. Made of stacks of hollow disks called grana (or granum)

  14. 3. Grana contain chlorophyll--site of light phases in clusters of molecules called photosystems 4. Matrix between grana is the stroma--site of dark phase 5. Lamella--interconnecting membranes

  15. IV. General Steps of C3 Photosynthesis A. Cyclic Photophosphorylation--Light B. Non-cyclic Photophosphorylation-- Light C. Carbohydrate synthesis—Light independent (Dark)

  16. V. Light Dependent Reactions (Light Phases) A. Cyclic Photophosphorylation-- occurs in the grana 1. Antennae molecules of chlorophyll a. Made of 200-300 molecules b. Group together to form antennae complex and reaction center. 2. Absorption of sunlight--700 nm. long

  17. 3. H electrons are excited 4. p700 reaction center-- Photosystem I donates electrons to ETS 5. ETS pathway—Redox reaction in membrane passes electrons 6. ATP formation a. H proton gradient created— drives ATP synthase b. a Proton driven generator that phosphorylates ADP to ATP 7. H electrons are returned

  18. Non-cyclic Photosynthesis

  19. B. Non-Cyclic Photophosphorylation--occurs in the grana 1. Antennae molecules—absorb photons of light 2. Energy is absorbed—electrons passed to 680 center 3. Water is split, O2 released-- photolysis 4. H electrons excited 5. p680 reaction center

  20. 6. H passed to ETS—creates a H ion gradient; drives ATP synthase to create ATP’s 7. Replaces H lost in p700 center a. Electrons are passed to protein called plastocyanin (PC) b. Donates electrons to Photosystem I c. Can shuttle over 1,000 electron per second

  21. 8. This is Photosystem II 9. Antennae molecules—absorb photon of light 10. H electrons excited 11. p700 reaction center—collects H electrons from Photosystem I &II 12. H electrons are passed to ETS 13. ETS)--->NADP + 2H+--- NADPH(2) (H bus) 14. H protons are bussed to dark phase 15. This is Photosystem I

  22. VI. Light Independent Reactions--Dark Phase--occurs in the stroma A. Calvin Cycle 1. RuBP--binds to CO2 (carbon fixation) 2. 6C unstable compound immediately splits 3. 2, PGA’s formed 4. NADPH2 from Non-cyclic light phase donates H2

  23. 5. ATP’s from light phase drive the process 6. 2 PGAL’s are formed--C3 photosynthesis 7. Occurs for 6 CO2--total of 12 PGAL’s made 8. 10 PGAL’s form 3 RuBP’s 9. 2 PGAL’s form fructose biphosphate, then glucose

  24. VII. C4 Photosynthesis A. Advantageous to hot climates with intense sunlight B. Forms 4C oxyloacetic acid and then 3C PGA C. Ex.: Corn and sugar cane

  25. VIII. CAM Photosynthesis A. Crassulacean Acid Metabolism, first found in members of the Crassulaceae family B. Found in cacti and other succulents C. Similar to C4 photosynthesis

  26. CAM plant (Jade Plant)

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