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Photosynthesis: Life from Light

Photosynthesis: Life from Light. + water + energy  glucose + oxygen. carbon dioxide. glucose + oxygen  carbon + water + energy. . C 6 H 12 O 6. +. 6O 2. 6CO 2. +. 6H 2 O. +. ATP. dioxide. light energy. . 6CO 2. +. 6H 2 O. +. +. 6O 2. C 6 H 12 O 6.

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Photosynthesis: Life from Light

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  1. Photosynthesis:LifefromLight

  2. + water + energy  glucose + oxygen carbon dioxide glucose + oxygen  carbon + water + energy  C6H12O6 + 6O2 6CO2 + 6H2O + ATP dioxide light energy  6CO2 + 6H2O + + 6O2 C6H12O6 How are they connected? Heterotrophs and Autotrophs making energy & organic molecules from ingesting organic molecules exergonic Where’s the ATP? Autotrophs making energy & organic molecules from light energy endergonic

  3. Plant structure • Obtaining raw materials • sunlight • leaves= solar collectors • CO2 • stomates= gas exchange • Found under leaves • H2O • uptake from roots • Nutrients • N, P, K, S, Mg, Fe… • uptake from roots

  4. H+ H+ H+ H+ H+ H+ H+ H+ H+ H+ H+ Plant structure • Chloroplasts • double membrane • stroma • thylakoid sacs • grana stacks • Chlorophyll & ETC in thylakoid membrane • H+ gradient built up within thylakoid sac

  5. Pigments of photosynthesis • chlorophyll & accessory pigments • “photosystem” • embedded in thylakoid membrane • structure  function Why does this structure make sense?

  6. Light: absorption spectra • Photosynthesis gets energy by absorbing wavelengths of light • chlorophyll a (dominant pigment) • absorbs best in red & bluewavelengths & least in green • other pigments with different structures absorb light of different wavelengths Why areplants green?

  7. Photosynthesis • Light reactions • light-dependent reactions • energy production reactions • convert solar energy to chemical energy • ATP & NADPH • Calvin cycle • light-independent reactions • sugar production reactions • uses chemical energy (ATP & NADPH) to reduce CO2 & synthesize C6H12O6 It’s the Dark Reactions!

  8. Light reactions • Electron Transport Chain (like cell respiration!) • membrane-bound proteins in organelle • electron acceptor • NADPH • proton (H+) gradient across inner membrane • ATP synthase enzyme

  9. Photosystems • 2 photosystems in thylakoid membrane • act as light-gathering “antenna complex” • Photosystem II • chlorophyll a • P680 = absorbs 680nm wavelength red light • Photosystem I • chlorophyll b • P700 = absorbs 700nm wavelength red light reactioncenter

  10. ETC of Photosynthesis • ETC produces from light energy • ATP & NADPH • NADPH (stored energy)goes to Calvin cycle • PS II absorbs light • excited electron passes from chlorophyll to “primary electron acceptor” at the REACTION CENTER. • splits H2O (Photolysis!!) • O2released to atmosphere • ATP is produced for later use

  11. Photosystem II Photosystem I ETC of Photosynthesis

  12. Noncyclic Photophosphorylation • Light reactions elevate electrons in 2 steps (PS II & PS I) • PS IIgenerates energy as ATP • PS Igenerates reducing power as NADPH

  13. Cyclic photophosphorylation • If PS Ican’t pass electron to NADP, it cycles back to PS II& makes more ATP, but noNADPH • coordinates light reactions to Calvin cycle • Calvin cycle uses more ATP than NADPH X

  14. From Light reactions to Calvin cycle • Calvin cycle • Chloroplast stroma • Need products of light reactions to drive synthesis reactions • ATP • NADPH What is there left to do? Make sugar!

  15. From CO2 C6H12O6 • CO2 has very little chemical energy • fully oxidized • C6H12O6contains a lot of chemical energy • reduced • endergonic • Reduction of CO2C6H12O6proceeds in many small uphill steps • each catalyzed byspecific enzyme • using energy stored in ATP & NADPH

  16. 1C 3C CO2 RuBP 5C 6C 3 ATP PGAL to make glucose 3 ADP 3C PGA PGAL 2x x2 3C 6 ATP 6 NADPH 2x 6 NADP 6 ADP Calvin cycle ribulose bisphosphate 1. Carbon fixation 3. Regeneration of RuBP Rubisco -enzyme that Binds CO2 to RuBP sucrose cellulose etc. 2. Reduction

  17. Calvin cycle • PGAL  important intermediate • Six turns of Calvin Cycle = 1 glucose PGAL   glucose   carbohydrates   lipids   amino acids   nucleic acids

  18. NADP ADP Summary • Light reactions • produced ATP • produced NADPH • consumed H2O • produced O2 as by product • Calvin cycle • consumed CO2 • produced PGAL • regenerated ADP • regenerated NADP

  19. Factors that affect Photosynthesis • Enzymes are responsible for several photosynthetic processes, therefore, temperature and pH can affect the rate of photosynthesis. • The amount and type of light can affect the rate. • A shortage of any of the reactants,CO2 and/or H2O, can affect the rate.

  20. Supporting a biosphere • On global scale, photosynthesis is the most important process for the continuation of life on Earth • each year photosynthesis synthesizes 160 billion tons of carbohydrate • heterotrophs are dependent on plants as food source for fuel & raw materials

  21. sun CO2 H2O glucose O2 The Great Circleof Life! Where’s Mufasa? ATP Energy cycle Photosynthesis Cellular Respiration

  22. light energy  6CO2 + 6H2O + + 6O2 C6H12O6 Summary of photosynthesis • Where did the CO2 come from? • Where did the CO2 go? • Where did the H2O come from? • Where did the H2O go? • Where did the energy come from? • What’s the energy used for? • What will the C6H12O6be used for? • Where did the O2 come from? • Where will the O2 go? • What else is involved that is not listed in this equation?

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