2. AP Biology Photosynthesis: Life from Light

3. AP Biology How are they connected? glucose + oxygen  carbon + water + energy dioxide C 6 H 12 O 6 6O 2 6CO 2 6H 2 OATP  +++ Heterotrophs and Autotrophs + water + energy  glucose + oxygen carbon dioxide 6CO 2 6H 2 O C 6 H 12 O 6 6O 2 light energy  +++ Autotrophs making energy & organic molecules from light energy making energy & organic molecules from ingesting organic molecules Where ’ s the ATP? exergonic endergonic

4. AP Biology 2005-2006 Plant structure  Obtaining raw materials  sunlight  leaves = solar collectors  CO 2  stomates = gas exchange  Found under leaves  H 2 O  uptake from roots  Nutrients  N, P, K, S, Mg, Fe…  uptake from roots

5. AP Biology  Chloroplasts  double membrane  stroma  thylakoid sacs  grana stacks  Chlorophyll & ETC in thylakoid membrane  H + gradient built up within thylakoid sac Plant structure H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+

6. AP Biology 2005-2006 Pigments of photosynthesis  chlorophyll & accessory pigments  “photosystem”  embedded in thylakoid membrane  structure  function Why does this structure make sense?

7. AP Biology Light: absorption spectra  Photosynthesis gets energy by absorbing wavelengths of light  chlorophyll a (dominant pigment)  absorbs best in red & blue wavelengths & least in green  other pigments with different structures absorb light of different wavelengths Why are plants green?

8. AP Biology 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 CO 2 & synthesize C 6 H 12 O 6 It ’ s the Dark Reactions!

9. AP Biology 2005-2006 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

10. AP Biology Photosystems  2 photosystems in thylakoid membrane  act as light-gathering “antenna complex”  Photosystem II  chlorophyll a  P 680 = absorbs 680nm wavelength red light  Photosystem I  chlorophyll b  P 700 = absorbs 700nm wavelength red light reaction center

11. AP Biology 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 H 2 O (Photolysis!!)  O 2 released to atmosphere  ATP is produced for later use

12. AP Biology ETC of Photosynthesis Photosystem IIPhotosystem I

13. AP Biology 2005-2006 Noncyclic Photophosphorylation  Light reactions elevate electrons in 2 steps (PS II & PS I)  PS II generates energy as ATP  PS I generates reducing power as NADPH

14. AP Biology 2005-2006 Cyclic photophosphorylation  If PS I can’t pass electron to NADP, it cycles back to PS II & makes more ATP, but no NADPH  coordinates light reactions to Calvin cycle  Calvin cycle uses more ATP than NADPH X

15. AP Biology 2005-2006 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!

16. AP Biology From CO 2  C 6 H 12 O 6  CO 2 has very little chemical energy  fully oxidized  C 6 H 12 O 6 contains a lot of chemical energy  reduced  endergonic  Reduction of CO 2  C 6 H 12 O 6 proceeds in many small uphill steps  each catalyzed by specific enzyme  using energy stored in ATP & NADPH

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

18. AP Biology Calvin cycle  PGAL   important intermediate  Six turns of Calvin Cycle = 1 glucose PGAL   glucose   carbohydrates   lipids   amino acids   nucleic acids

19. AP Biology Summary  Light reactions  produced ATP  produced NADPH  consumed H 2 O  produced O 2 as by product  Calvin cycle  consumed CO 2  produced PGAL  regenerated ADP  regenerated NADP ADPNADP

20. AP Biology 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,CO 2 and/or H 2 O, can affect the rate.

21. AP Biology 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

22. AP Biology Energy cycle Photosynthesis Cellular Respiration glucoseO2O2 H2OH2OCO 2 ATP sun The Great Circle of Life! Where ’ s Mufasa?

23. AP Biology 2005-2006 Summary of photosynthesis  Where did the CO 2 come from?  Where did the CO 2 go?  Where did the H 2 O come from?  Where did the H 2 O go?  Where did the energy come from?  What’s the energy used for?  What will the C 6 H 12 O 6 be used for?  Where did the O 2 come from?  Where will the O 2 go?  What else is involved that is not listed in this equation? 6CO 2 6H 2 O C 6 H 12 O 6 6O 2 light energy  +++