1. A2E Today:
1. Introduction to Photosynthesis 2. Lunch 3. Guest Speaker (noon; Green Room)

2. ? PHOTOSYNTHESIS! Brainstorm: 4 Things We Know About Photosynthesis
4 Questions About Photosynthesis
Why is Photosynthesis important?? ?

3. A Quick Introduction to the Carbon Cycle
What does it mean to be a carbon source? A carbon sink? Examples?

4. 6CO2 + 6H2O + Light Energy  C6H12O6 + 6O2
PHOTOSYNTHESIS
Photosynthesis is an enzyme-mediated, metabolic process performed by photoautotrophs
6CO2 + 6H2O + Light Energy  C6H12O6 + 6O2 or
CO2 + H2O  CH2O + O2

5. Overview of Leaf and Chloroplast
Anatomy
Note the interplay of
Form and Function!

6. Overview of Photosynthesis

7. The LIGHT Reactions

8. LIGHT used in Photosynthesis?

9. LIGHT used in Photosynthesis

10. Engelmann
figured
out the
ACTION SPECTRUM
in 1883!!

11. When PHOTONS hit a Chlorophyll Molecule they EXCITE ELECTRONS

12. When PHOTONS hit a Chlorophyll Molecule they EXCITE ELECTRONS

13. EXCITED ELECTRONS are passed from molecule to molecule until they reach the REACTION CENTER

14. Noncyclic electron flow generates
ATP and NADPH

15. What is NADPH?
I carry electrons!

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

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

18. CHEMIOSMOTIC synthesis of ATP

19. CHEMIOSMOTIC synthesis of ATP

20. Overview of Photosynthesis

21. The Light-Independent Reactions

22. RUBISCO

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

24. O2
H2O
CO2

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

26. The Pitfall…

27. Why is this enzyme so sloppy??
RUBISCO
Why is this enzyme so sloppy??

28. 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

29. 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

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

31. 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!)

32. C4 and CAM Strategies:

33. What Can You Do If You Understand Photosynthesis??
Feed a growing human population?? Maybe! Maybe not!