1. Chapter 10 Photosynthesis
Crosby High School
AP Biology

2. Pathways of Photosynthesis
Chemical equation:
6CO2 + 6H2O + Light Energy  C6H O2
Splitting of Water
Originally thought that oxygen released came from carbon dioxide
C.B. van Niel challenged in 1930’s
Used bacteria that used H2S
Radioactive O in carbon dioxide and water

3. Light Reactions Takes place in Thylakoids
Drives e- from water to NADP+
H2O splits
NADP+ reduced by electrons to NADPH
Adds P to ADP generating ATP

4. Calvin Cycle Named for Melvin Calvin Begins with Carbon Fixation
Reduces C to Carbohydrates by adding electrons
Reducing power from NADPH
ATP required to convert CO2  Carb.
Dark Reactions (Light Independent Reactions)
Takes place in Stroma

5. Absorbing Sunlight Photons act as particles of Light
Photosynthetic Pigments
Spectrophotometer: measures absorbtion
Chlorophyll a
Blue-green and participates directly in L.R.
Cholorphyll b
Yellow-green and transfers E to Chlorophyll a
Carotenoids
Red and Yellow Hydrocarbons
Photoprotection: Absord and dissipate excessive light energy
Excitation of Chlorophyll

6. Absorption and Transmittance

7. Excitation of Chlorophyll
Photon absorbed and e- excited
Must be same E as E dif. btwn. Ground and Excited state
Fluorescence: When an e- drops from excited to ground state it emits a photon

8. Noncyclic Electron Flow
Photosystem II (P680)
H2O donates e-
ETC
Noncyclic Photophosphorylation
Photosystem I (P700)
Fd to NADP+ reductase

9. Noncyclic Electron Flow

10. Cyclic Electron Flow Ferrodoxin to Cytochrome, back to P700
No O or NADPH
Cyclic Photophosphorylation
Usefullness
There is more ATP required in the Calvin Cycle than NADPH

11. Chemiosmosis: Mitochondria vs. Chloroplast
Uses chemical energy
Ion pump creates proton-motive force
Hydrogen ion gradient formed in intermembrane space
Chloroplast
Uses light energy
Ion pump creates proton-motive force
Hydrogen ion gradient formed in Thylakoid space (Lumen)

12. Spatial organization

13. Calvin Cycle (Dark Reactions)
Makes Glyceraldehyde-3-phosphate
Requires three cycles to make one G3P
Net synthesis
Uses 9 ATP
Uses 6 NADPH
Makes 1 G3P
G3P is used to make other compounds for the plant

14. Phases of Calvin Cycle Phase 1: Carbon Fixation Phase 2: Reduction
Each CO2 attaches to Ribulose biphosphate
RuBP carboxylase (Rubisco)
Results in 6-Carbon molecule
Unstable
Splits to form 3-phosphoglycerate
Phase 2: Reduction
Each 3-phosphoglycerate receives Pi
1,3-biphosphate formed and reduced to G3P by NADPH

15. Phases (cont.) Phase 3: Regeneration of CO2 acceptor (RuBP)
One molecule of G3P exits cycle for use
Five molecules of G3P are used to form 3 molecules of RuBP
Requires the use of 3 ATP

16. Calvin Cycle

17. Photorespiration Carbon is normally fixed by Rubisco (C3 plants)
On hot days Stomata close and prevent CO2 uptake
Rubisco will take up O2 instead producing a 2-C compound
Mitochondria and Peroxisomes convert to CO2
No food or E produced

18. C4 Plants Anatomy Bundle-Sheath cells: Mesophyll Cells:
Tightly packed around the veins
Location of Calvin Cycle
Mesophyll Cells:
Loosely packed between B-S and leaf surface
Location of Carbon fixation

19. C4 Plant (cont.) Fixation CO2 forms 4-C Oxaloacetate in the Mesophyll
Phosphoenolpyruvate Carboxylase combines PEP with CO2
4-C product enters B-S through Plasmodesmata
4-C releases CO2 for Calvin Cycle

20. CAM Plants Crassulacean Acid Metabolism Open Stomata at night
Take in CO2
Convert CO2 to organic acids
Organic acids stored in vacuoles
Organic acids released when L.R. begin
Separated by time of day

21. Products of Photosynthesis
50% of products used for fuel
Carbs. Transported as Sucrose
Large amounts of products used to form cellulose
Extra stored as Starch