1. Photosynthesis Carbon dioxide + water glucose + oxygen sunlight
absorbed by chlorophyll
Plants use sunlight to turn water and carbon dioxide into glucose.

2. Plant leaves have many types of cells!

3. Typical Dicot Leaf Cross-Section
Cuticle
Epidermis
Palisade Parenchyma
Vascular bundles
Guard Cells
Spongy Parenchyma
Stoma

4. Plant Cells Chloroplasts

5. Plant Cells Chloroplasts

6. Visible light is only a small part of the electromagnetic spectrum (all forms of light).

7. Wavelength of Light (nm)
400
500
600
700
Short wave
Long wave
(more energy)
(less energy)

8. LIGHT behaves as if it were composed of "units" or "packets" of energy that travel in waves. These packets are photons.
The wavelength of light determines its color.

10. Different pigments absorb light differently

12. Chlorophyll: A Light Absorbing Pigment
The Solar Panel Chemical!

13. A. Cyclic Electron Flow SUN e- Photons Photosystem I ATP produced
Primary
Electron
Acceptor e-
ATP
produced
by ETC
Photosystem I
Accessory
Pigments
SUN
Photons

14. B. Noncyclic Electron Flow
P700
Photosystem I
P680
Photosystem II
Primary
Electron
Acceptor
ETC
Enzyme
Reaction
H2O
1/2O2 + 2H+
ATP
NADPH
Photon
2e-
SUN

15. PHOTOSYNTHESIS O2 as a byproduct of photosynthesis
Photolysis: replaces lost electrons by splitting water

16. At each step along the transport chain, the electrons lose energy.
Sun
Light energy transfers to chlorophyll.
At each step along the transport chain, the electrons lose energy.
Chlorophyll passes energy down through the electron transport chain.
Energized electrons provide energy that
to ADP
splits
H2O
bonds P
forming ATP H+
NADP+
oxygen
released
NADPH
for the use in light-independent reactions

19. Calvin cycle Incorporation of CO2 - carboxylation rxn
Ribulose bisphosphate carboxylase/oxygenase (Rubisco)
very abundant protein (40% leaf soluble protein)

21. Light-independent reactions. Notice where ATP and NADPH are used up.
1 Carbon
fixation
combines
CO2 with
RuBP.
6 CO2
2 G3P
synthesis
uses energy. 6 12
6 RuBP
C3 cycle
(Calvin-Benson cycle)
PGA
3 RuBP
synthesis
uses energy
and 10 G3P. 12
ATP 12
ADP 6
ADP 12
NADPH 12 6
ATP 12
G3P
NADP+
4 G3P available for synthesis of carbon compounds such as glucose.
glucose
(or other molecules)

22. Calvin Cycle (C3 fixation)
6CO2
6C-C-C-C-C-C
6C-C-C
6C-C-C-C-C
12PGA
RuBP
12G3P
(unstable)
6NADPH
6ATP
C-C-C-C-C-C
Glucose
(6C)
(36C)
(30C) C3
glucose

23. protects against light damage
Photorespiration
depends on light
“wastes” CO2
protects against light damage
favored by high O2, low CO2 and warm temperatures
9/12/07

25. C2 oxidative carbon cycle: Input 4C Output 3C 75% C recovery rate
2 x 5C
1 x 3C
2 x 2C
Chloroplast
1 x 3C
C2 oxidative carbon cycle:
Input 4C
Output 3C
75% C recovery rate
Peroxisome
2 x 2C
2 x 2C
1 x 3C
Mitochondrion

26. Leaf Anatomy In C3 Plants
In C3 plants (those that do C3 photosynthesis), all processes occur in the mesophyll cells.
Mesophyll cells
Bundle sheath cells
Image taken without permission from

27. C3 and C4 Leaf structure

28. C4 Pathway
Affinity of PEP Carboxylase for CO2 is much higher than its affinity for O2.
Image taken without permission from

29. C4 plants use the C4 pathway
CO2 is captured with
a highly specific enzyme.
CO2
PEP C4
Pathway
4-carbon
molecule
AMP
ATP
within mesophyll
chloropast
pyruvate
CO2 O2
PGA
rubisco
CO2
stoma C3
Cycle
bundle-
sheath
cells
RuBP
G3P
Almost no
photorespiration
occurs in hot, dry
conditions.
glucose
In a C4 plant, both mesophyll
and bundle-sheath cells contain
chloroplasts.
within bundle-sheath
chloropast
Lots of glucose is synthesized.
C4 plants essentially store carbon for hot times of the day. Guess what pathway many weeds use?

30. 9/12/07

31. C4 Photosynthesis
C4 plants need more light quanta than C3 plants to fix CO2

32. CAM vs C4 Syndrome

34. C4 Plants C3 CO2 C-C-C PEP C-C-C-C Malate ATP C-C-C Pyruvic Acid
Mesophyll Cell
CO2
C-C-C
PEP
C-C-C-C
Malate
ATP
Bundle Sheath Cell
C-C-C
Pyruvic Acid
C-C-C-C
CO2 C3
Malate
Transported
glucose
Vascular
Tissue

35. CAM Plants Night (Stomates Open) Day (Stomates Closed) Vacuole C-C-C-C
Malate
CO2 C3
C-C-C
Pyruvic acid
ATP
PEP
glucose

37. PHOTOSYNTHESIS What affects photosynthesis?
Light intensity: as light increases, rate of photosynthesis increases
CO2 uptake (mmol m-2 s-1)
Fluence rate (mmol m-2 s-1)

38. Light response curves
Light saturation point
Light saturation for an individual leaf is ~ 1/3 - 1/2 photon flux of full sunlight
BUT
At the whole plant level P/S is rarely saturated even in full sunlight
Slope = max. quantum yield for CO2 assimilation

39. CO2 response curve of photosynthesis:
Net Ps
Compensation point
CO2 diffusion
Biochem limits: light-harvesting, Rubisco (N), RuBP (P)
5.6

40. PHOTOSYNTHESIS What affects photosynthesis? Temperature:
Temperature Low = Rate of photosynthesis low
Temperature Increases = Rate of photosynthesis increases
If temperature too hot, rate drops

41.
Atmospheric CO2 (ppm) C4 C3
CO2 uptake rate
9/12/07

42. C3 versus C4 plants C3 C4 Photorespiration Yes Not detectable
CO2 compensation point (mL CO2 l-1)
20 – 100
0 – 5
Temperature optimum (oC)
20 – 25
30 – 45
Quantum yield as a function of temp.
Declining
Steady
Transpiration ratio
500 – 1000
200 – 350
Light saturation (mmole photons m-2 s-1)
400 – 500
Does not saturate
C3 plants are favoured in environments where water is plentiful, temperature and light levels are moderate (temperate climates)
C4 plants are favoured in environments where water is limiting and light and temperatures are high (tropical / subtropical habitats)