1. Modified by Georgia Agricultural Education Curriculum Office
Photosynthesis
Modified by Georgia Agricultural Education Curriculum Office
July, 2002

2. 3 carbon sugars produced What is the transport sugar in plants?
Photosynthesis - Basics
3CO2 + 6H2O
C3H6O3 + 3O2 + 3H2O
3 carbon sugars produced
What is the transport sugar in plants?
O2 is liberated from the H2O

3. Energy and wavelength energy as wavelength Photosynthesis - Light

4. Color Wavelength Energy Violet short high Blue Green Yellow Red
Photosynthesis - Visible Spectrum
Color Wavelength Energy
Violet short high
Blue
Green
Yellow
Red
Far-Red long low

5. Color Wavelength Energy Violet short high Blue Green Yellow Red
Photosynthesis - PS Action Spectrum
Color Wavelength Energy
Violet short high
Blue
Green
Yellow
Red
Far-Red long low
Peak between nm
Peak at about 680 nm

6. Electrons kicked up to higher energy level Absorbed light has 3 fates:
Photosynthesis - Role of Pigments
Electrons kicked up to higher energy level
Absorbed light has 3 fates:
1. Fluorescence
2. Transfer energy
3. Transfer electrons

7. yellow pigments are carotenoids
Photosynthesis - Pigments
Chlorophyll a
required pigment, “the hanger”
Chlorophyll b
accessory pigment, “the tin foil”
Carotenoids
anti-oxidants, protect the chlorophyll
Figure 7-13 in text
yellow pigments are carotenoids

8. Energy Transduction Rxns light dependent Carbon Fixation
Photosynthesis - The Reactions
Energy Transduction Rxns
light dependent
harvesting energy from the sun
Carbon Fixation
either light or dark
requires energy from 1st rxns
fixes CO2 into sugars
Both occur in chloroplast

9. note similarities to figure 6-16
Photosynthesis - Energy Transduction Rxns
Light dependent
2 photosystems, linkage pumps protons
“purpose”: to generate ATP & NADPH
Figure 7-15 in text
note similarities to figure 6-16

10. Dependent on energy Calvin Cycle C3 pathway
Photosynthesis - Carbon Fixation Rxns
Dependent on energy
“purpose”: to fix carbon, storing energy
in bonds
Calvin Cycle
C3 pathway
1st product contains 3 carbons
occurs in most plants

11. Rubisco affinity Photosynthesis - Photorespiration
binds with both O2 and CO2
when it binds with O2, carbon
is bound into other products
energy must be used to salvage the C
rubisco contains nitrogen which is
commonly the limiting nutrient

12. “Warm season” plants Photosynthesis - C4 Pathway
many native prairie grasses
1st product contains 4 carbons
use BOTH C3 and C4 pathways
C fixed by PEP carboxylase in mesophyll
prefers CO2 over O2
handles photorespiration problems
product is shipped to bundle sheath cells
Kranz anatomy
the key to the C4 pathway:
spatial separation

13. C4 - Kranz Anatomy C3 C4 and C3 Pathways - Differences in Anatomy CO2
H2O
CO2
H2O
H2O and CO2 pass through stomatal openings

14. Succulent plants (like cacti)
Photosynthesis - CAM Pathway
Succulent plants (like cacti)
Crassulacean acid metabolism (CAM)
use BOTH C3 and C4 pathways
C fixed by PEP carboxylase in DARK
allows plants to close stomata
product is used in same cells
must have HUGE vacuoles to store C
the key to the CAM pathway:
temporal separation
allows internal cycling during drought
pineapple is CAM

15. C4 - Kranz Anatomy C3 C4 and C3 Pathways - Differences in Anatomy CO2
H2O
CO2
H2O
H2O and CO2 pass through stomatal openings

16. Photosynthesis - C4 and C3 Pathways10 20 30 40 50
14.0
For a given growth
rate, C3 species use
almost twice as much
water as C4 species.
(i.e., they have
lower water use
efficiencies (WUE)
Transpiration
both types
11.2 C4 C3
8.4
Net Photosynthesis (µmol m-2 s-1)
Transpiration (mmol m-2 s-1)
5.6
2.8
160
320
480
640
Leaf Conductance (mmol m-2 s-1)

17. C4 and C3 Pathways - Light Saturation
C3 species become
light saturated
more quickly
provides advantage
in low light
environments C4 C3
Carbon Gain
Light

18. C4 and C3 Pathways - Effect of Temperature60
330 ppm
1000 ppm 50 C4 40
Net Photosynthesis (µmol m-2 s-1) 30 C3 20 C3 C4 10 20 30 40 50 20 30 40 50
Leaf Temperature (°C)

19. C4 and C3 Pathways - Photorespiration60
C3, Low [O2]
Conflict between CO2 and
O2 places C3 species at a
disadvantage
C4 species are able to
concentrate CO2 providing
an advantage under low
CO2 conditions C3
Ambient [O2] 50 40
C4, Ambient [O2]
Net Photosynthesis (µmol m-2 s-1) 30 20 10
-10
100
200
300
400
500
600
Intercellular [CO2] (ppm)

20. Global Change - CO2, N and Diversity
Global N Fixation
CO2 Concentration
“Natural”
Anthropogenic
1920
1980
2000
Year
Year
Diversity
Time

21. C4 and C3 Pathways - Effect of CO2 concentration
Competitive advantage
between C3 and C4 switches
along CO2 gradient
Low CO2: C4 advantage
due to concentrating of CO2
Ambient CO2: net growth
about equal but water use
is greater in C3
High CO2: C3 advantage
due to C4’s low CO2
saturation point and reduction
of CO2 / O2 conflict in C3 C3 60 50 C4 40
700 ppm CO2 30
Net Photosynthesis (µmol m-2 s-1)
350 ppm CO2
200 ppm CO2 20 10
-10
100
200
300
400
500
600
Intercellular CO2 (ppm)

22. PS Pathways - Further Reading
Polley, H.W Implications of rising atmospheric carbon dioxide concentration for rangelands. Journal of Range Management. 50:
Pearcy, R.W., and J Ehleringer Comparative ecophysiology of C3 and C4 plants. Plant. Cell and Environment. 7:1-13.
Data presented in this slide set were adopted from these 2 sources. They are both excellent resources.