1. Capturing Solar Energy The Light-Dependent Reactions
Chapter 4.1 & 4.2
McGraw-Hill Ryerson
Biology 12 (2011)

2. Water-splitting Z-protein splits H2O into: Where do each of these go?
2 protons (H+)
2 electrons (e-)
½O2.
Where do each of these go?
Oxygen _______________
Protons _______________
Electrons ______________ ???

3. Water-splitting 1 electron goes to PSII
Enters ground state
In your textbook it does say 2, but that’s because the whole electron flow occurs twice

4. Photoexcitation Chlorophyll Molecules Ground State
Excitation & Fluorescence
Reaction center (chlorophyll a)
P700 in PSI, P680 in PSII
Primary Electron Acceptor

5. Refer to page 156-157 of your textbook

6. Noncyclic Electron Flow
Primary electron acceptor (pheophytin)
Redox reactions
Electron carrier Plastiquinone takes excited electron

7. Noncyclic Electron Flow
Q cycle
Plastiquinone along with a protein b6-f cytochrome complex
Pumps 4 protons per 2 electrons
B6-f complex with plastoquinone create a complicated mechanism to introduce 4 protons into the lumen (you’ll learn this in university!)

8. Noncyclic Electron Flow
Q cycle
Plastocyanin takes excited electron
Transfer electron to PSI (back in ground state)

9. Noncyclic Electron Flow
Primary electron acceptor (pheophytin)
Redox reactions
Electron carrier ferredoxin takes excited electron

10. Noncyclic Electron Flow
NADPH production
Protein NADP Reductase uses 2 electrons to reduce NADP+ + H+  NADPH

11. Noncyclic Electron Flow
ATP production
Protons accumulate to create gradient
ATPase complex pumps proton out
Movement allows ADP + Pi  ATP

12. Noncyclic Electron Flow
NADPH production
Protein NADP Reductase uses 2 electrons to reduce NADP+ + H+  NADPH
ATP production
Protons accumulate to create gradient
ATPase complex pumps proton out
Movement allows ADP + Pi  ATP
The products formed, ATP and NADPH proceed to the Calvin Cycle
To review the entire process, review pg of your textbook

13. Noncyclic Electron Flow

14. Cyclic Electron Flow
Some cases where PSI does it’s own thing

15. Cyclic Electron Flow
Some cases where PSI does it’s own thing

16. Cyclic Electron Flow Why do you think this would happen?
What are its advantages and its disadvantages?

17. C3 vs C4 photosynthesis C3 photosynthesis Photorespiration
AKA: Calvin Cycle
Most plants go through this form
Optimal temperature: (15oC – 25oC)
Photorespiration
O2 bonds to Rubisco instead of CO2
Rubisco + O2  PGA (3 Cs) + glycolate (2 Cs)
2 glycolate  CO2 + G3P (returned to Calvin Cycle)
C3 plants continually do this and lose 20-50% of carbon

18. C3 vs C4 photosynthesis C4 photosynthesis AKA: “Hatch-slack pathway”
A CO2 delivery system,
More CO2 to outcompete O2 for rubisco in interior cells
Oxaloacetate and malate are the CO2 transporters

19. The upper half is the
C4 photosynthesis
Please refer to
Pg of
your textbook
The lower half is the
Calvin Cycle

20. C3 vs C4 vs CAM photosynthesis
C3 Photosynthesis
C4 Photosynthesis
Optimal Temperature
15oC-25oC
Energy Cost
Uses up 18 ATP
Examples of plants
Soybeans, Kentucky bluegrass, sunflowers, etc.
30oC-47oC
Uses up 30 ATP
Tropical plants; Sugar cane, maize, corn

21. CAM Plants CAM – Crassulacean Acid Metabolism
Stomata open at night to take in CO2
CO2 incorporated into C4 organic acids
Organic acids stored in vacuoles until morning
Organic acids release CO2 to enter Calvin Cycle
Please refer to pg of your textbook

22. C4 vs CAM Plants
C4 plants have carbon fixation and Calvin cycle in different compartments
Carbon fixation in mesophyll cells
Calvin cycle in bundle-sheath cell
CAM plants have processes occur in same compartment but different times
Carbon fixation into organic acids at night
Calvin Cycle during the day

23. Homework
4.1
Pg. 165 # 1 – 8, 11, 12
4.2
Pg. 171 #1,