1. PHOTOSYNTHESIS AND CARBOHYDRATE PRODUCTION
Lecture 12
PHOTOSYNTHESIS AND CARBOHYDRATE PRODUCTION

2. Photosynthesis and Carbohydrate Production
The Photosynthetic Process
Photosynthetic Reaction
Factors Affecting Photosynthesis
Source-Sink Relations
Metabolism
Carbohydrate Production

3. Photosynthesis and Carbohydrate Production
“It is the business of agriculture to harvest the light energy that is used to produce food, fiber, and usable stuffs produced by agricultural plants and animals”
National Academy of Science, 1975
Question of the Day – How does a corn kernel weighing 0.15 g, become a mature plant weighing 6-7 Kg in 90 days?

4. The Photosynthetic Process
Occurs in tissues within chloroplasts in plant cells
Requirements are:
Green leafy tissue, healthy plants
Light, solar energy
CO2 & H2O
Net primary production from photosynthesis
1.41 x 1011 metric tons of carbon per year
3.9 billion metric tons of carbon per day
8 trillion pounds/day

5. In Photosynthesis, always remember that light energy is being converted to chemical energy or food.

6. The Plant Cell

7. Photosynthetic Reaction – Generalized
6 CO2 + 12H2O  C6H12O6 + 6H2O + 6O2 ^
green tissue
light

8. CO2 from the atmosphere around the leaf, enters the stomate, travels to a photosynthetic cell where glucose is produced

9. Photosynthetic Reaction – Generalized
Resources used:
Water, nutrients CO2, light energy
Energy provided:
Chemical bond energy
Products produced:
Sugars, lipids, amino acids (proteins) , many others

10. Amino acids are the components of proteins and there are 20 in nature
Amino acids are the components of proteins and there are 20 in nature. Look carefully and you will see why nitrogen (N) is so important in plants and animals.

11. Photosynthetic Reaction – Generalized
Endothermic reaction:
114 Kcal/mole CO2
Total photosynthesis:
Total CO2 uptake
Net photosynthesis:
(Measured CO2 uptake)-(respiration losses)
Photosynthesis beyond losses from respiration

12. Photosynthetic Reaction – Generalized
Photosynthesis: H2O + CO2  CH2O + O2
Respiration: CH2O + O2  H2O + CO2
Note! These are almost the exact opposite reaction

13. Factors Affecting Photosynthesis
Light quality
Action spectrum of photosynthesis and growth
Function of chlorophyll in plant cells

14. Factors Affecting Photosynthesis
Light intensity
Sun leaves vs. shade leaves
Photosynthetic light response curve(Fig 7.7, p. 151)
Dark respiration
Occurs at night, no photosynthesis
Compensation point
When respiration = photosynthesis
Saturation point
Light exists in surplus

15. Continued from previous slide
Light Intensity -
Maximum photosynthetic rate
Determined by chloroplasts per leaf

16. Factors Affecting Photosynthesis
Day length
Time of year – photo period
CO2 concentration
Hardly ever limiting
Temperature
Temperature response curve
Hot temps can be limiting
Extreme cold also be limiting

19. Factors Affecting Photosynthesis
Water
Water stress
guard cells become flaccid
stomates close
gas exchange stops
factors affect water flow through xylem
Drought
incipient or prolonged

20. Factors Affecting Photosynthesis
Source – Sink relationships
Sources
Net exporters of photosynthetic products (leaves)
Sinks
Net importers of photosynthetic products (roots, shoots)

22. Factors Affecting Photosynthesis
Stages of leaf development
Heterotrophs (sinks)
1 – 10% full size
Autotrophs (sources)
10 – 15% full size (unfolding)
Exporters (sources)
25% of full size (expanding)
Senescing (source/sink transition)
Aging, slowing down on photosynthesis

23. Factors Affecting Photosynthesis
Plant metabolism
Anabolism
Plant products (carbohydrates, oils, proteins) being produced or assembled
energy storage
Catabolism
Plant products (carbohydrates, oils, proteins) being broken down
Energy release

25. Factors Affecting Photosynthesis
Carbohydrate production via photosynthesis
Light reaction
Splitting of H2O
Release of H, O2, e-, ATP

26. Factors Affecting Photosynthesis
Carbohydrate production via photosynthesis
C3 vs. C4 photosynthetic pathways
Slightly different pathways
C4 experience less net respiration losses, they recycle
much of the respired CO-2
Examples:
C4 – corn, sorghum, bermudagrass
C3 – soybean, barley, rice, cotton

27. The End

29. The Plant Cell