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Chapter 10

Chapter 10. Photosynthesis. What is the difference between an autotroph and heterotroph?. Autotrophs: biotic producers; obtains organic food without eating other organisms Heterotrophs: biotic consumers; obtains organic food by eating other organisms or their by-products.

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Chapter 10

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  1. Chapter 10 Photosynthesis

  2. What is the difference between an autotroph and heterotroph? • Autotrophs: biotic producers; obtains organic food without eating other organisms • Heterotrophs: biotic consumers; obtains organic food by eating other organisms or their by-products

  3. What is the equation for photosynthesis • 6CO2 + 6H2O  C6H12O6 + 6O2

  4. The chloroplast • Sites of photosynthesis • Pigment: chlorophyll • Draw and Label a chloroplast

  5. Photosynthesis: an overview • 2 major steps: • light reactions -light energy converted to cell energy (e- from chlorophyll used to make ATP & NADPH) (e- from water used to replace) • Dark reaction (Calvin Cycle) - organic compounds made from inorganic (sugar made from CO2)

  6. Photosystems • Light harvesting units of the thylakoid membrane • Composed mainly of protein and pigment antenna complexes • Antenna pigment molecules are struck by photons • Energy is passed to reaction centers (redox location) • Excited e- from chlorophyll is trapped by a primary e- acceptor

  7. Photosystem II (P680) and Photosystem I (P700) used Photosystem II (P680): photons excite chlorophyll e- e- are replaced by splitting of H2O e-’s travel to Photosystem I down an ETC (Pq~cytochromes~Pc) as e- fall, ADP ---> ATP (noncyclic) Photosystem I (P700): Fallen e- absorbed by chlorophyll e- in PI Photons boost e- in PI 2nd ETC ( Fd~NADP+ reductase) e- help form NADPH Noncyclic electron flow

  8. Primary e- Acceptor Primary e- Acceptor H2O Photosystem I P700 Photosystem II P680

  9. These photosystems produce equal amounts of ATP and NADPH which will be used in the Calvin cycle

  10. Cyclic electron flow – (P700 complex) • Alternative cycle • e- boosted by the light energy pass down the 1st ETC (Fd Pq cytochrome complex Pc) and H+ gradient that is produced ATP • e- return to the P700 complex • Why? The Calvin cycle consumes more ATP than NADPH

  11. Cyclic electron flow

  12. Primary e- Acceptor Primary e- Acceptor H2O Photosystem I P700 Photosystem II P680

  13. The Calvin cycle • 3 Phases: • 1) - Carbon fixation - 3 CO2 are added to the cycle • 2- Reduction - NADPH and ATP are used • 3- Regeneration – RuBP is regenerated

  14. 1) each CO2 is attached to RuBP (5C) and forms Rubisco 3CO2 + 3RuBP  3Rubisco - This is unstable so each Rubisco quickly splits in half to make 6 PGA (3C) 2) A Phosphate is added to each of the 6 PGA to form 6 DPGA 6 ATP are used 3) 6 DPGA are converted to 6 PGAL 6 NADPH are used Seven easy steps

  15. 4) 1 PGAL is released (2 will form a glucose) 5) 5 PGAL continue around the cycle 6) these molecules reorganize to form 3 RuP (5C) molecules 7) an ATP is added to each RuP to make RuBP 3 ATP are used The cycle starts over

  16. ??? Calvin Cycle ??? • How many NADH were used? • How many ATP were used? • Since non-cyclic electron flow makes equal amounts of ATP and NADPH What process help compensate for the additional ATP that are needed?

  17. ?????? Light Reaction ?????? • 2) In Cyclic electron flow where do the electrons come from to replace those that were boosted? What form of energy is made? • The original e- return the photosystem, ATP

  18. 3) In non-cyclic electron flow where do the electrons come from to replace those lost by PII? By PI? • PII – H2O; PI – ETC from PII

  19. 4) In non-cyclic electron flow what is the order of the electron acceptors on the 1st ETC? 2nd ETC? • 1st - Pq  cytochrome  Pc 2nd  Fd  NADP+ reductase

  20. 5) In non-cyclic electron flow what is the energy made by the electrons that flow down the first ETC? the 2nd ETC? • 1st ETC – ATP; 2nd ETC – NADPH

  21. 6) In cyclic electron flow what is the order of electron acceptors? • Fd  cytochrome complex  Pc

  22. The problem with photorespiration • On hot dry days the stomata close to avoid dehydration • A limited amount of CO2 and an increases amount of O2 • Rubiso prefers O2 • The • Two Solutions….. • 1- C4 plants: 2 photosynthetic cells, bundle-sheath & mesophyll; PEP carboxylase (instead of rubisco) fixes CO2 in mesophyll; new 4C molecule releases CO2 (grasses)

  23. Alternative carbon fixation methods, II • 2- CAM plants: open stomata during night, close during day (crassulacean acid metabolism); cacti, pineapples, etc.

  24. A review of photosynthesis

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