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. Noncyclic electron flow
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

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

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

11. 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

12. Cyclic electron flow

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

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

15. Seven easy steps
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

16. 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

17. ??? 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?

18. ?????? 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

19. 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

20. 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

21. 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

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

23. 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)

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

25. A review of photosynthesis