1. Today:
-Photosynthesis!
-Lunch
-Lab 3

2. Setting the Stage…

3. An Overview of Photosynthesis

4. LIGHT used in Photosynthesis?

5. LIGHT used in Photosynthesis

6. Check Out the Structure of Chlorophyll:

7. When PHOTONS hit a Chlorophyll Molecule they EXCITE ELECTRONS

8. ELECTRON TRANSPORT CHAINS
The Gain and Loss of Electrons through REDOX reactions allows for
ELECTRON TRANSPORT CHAINS

9. Noncyclic electron flow generates
ATP and NADPH

10. of NONCYCLIC ELECTRON FLOW
Cartoon Schematic
of NONCYCLIC ELECTRON FLOW
in the
LIGHT
REACTIONS

11. ELECTRON FLOW may also by CYCLIC
Cyclic Electron Flow allows cells to “catch up” on the production of ATP!

12. CHEMIOSMOTIC synthesis of ATP

13. What Should We Do With the ATP and Electrons (NADPH)??

14. The Light-Independent Reactions
The Calvin Cycle
The Light-Independent Reactions

15. Uh Oh… RUBISCO

16. THE DOWNSIDE: Plants must open their
STOMATA to acquire CO2 and release O2.
Open Stomata allow for Transpiration
(the evaporative loss of water)!

17. How could plants minimize this evaporative loss of water (transpiration)??

18. Why is this enzyme so sloppy??
The Pitfall…
Why is this enzyme so sloppy??

19. Photorespiration generates no ATP, NADPH, or glucose!
Photorespiration is a major limiting factor in the production levels of
C3 PLANTS
Photorespiration generates no ATP, NADPH, or glucose!
Rice
Up to 50% of the yield of many important agricultural crops like rice, soybeans, and wheat may be lost to photorespiration.
Soybeans

20. Alternate Strategy #1: the C4 PATHWAY
Carbon fixation and the Calvin Cycle
are separated. Fixation occurs in the
MESOPHYLL CELLS
while the Calvin Cycle occurs in the
BUNDLE-SHEATH CELLS.
corn
This separation allows the plants to minimize photorespiration and
maximize sugar production.
sugarcane

21. Results in a SPATIAL SEPARATION of CO2 acquisition and fixation!
An Overview of the C4 Pathway:
Results in a SPATIAL SEPARATION of CO2 acquisition and fixation!

22. Alternate Strategy #2: CAM
CAM plants open their STOMATA at night to acquire CO2. This CO2 is used during the day for fixation in the Calvin Cycle. (Temporal separation!)

23. C4 and CAM Strategies Summarized:

24. Final Key Point: Metabolic Processes are Connected!
During periods of light, which cycle must be faster, the Calvin Cycle or the Citric Acid Cycle? Why??