Lecture 12Lecture 12
PHOTOSYNTHESIS ANDCARBOHYDRATE PRODUCTION
Photosynthesis andCarbohydrate ProductionPhotosynthesis andCarbohydrate Production
The Photosynthetic Process
Photosynthetic Reaction
Factors Affecting Photosynthesis
Source-Sink Relations
Metabolism
Carbohydrate Production
Photosynthesis andCarbohydrate ProductionPhotosynthesis andCarbohydrate Production
“It is the business of agriculture to harvest thelight energy that is used to produce food,fiber, and usable stuffs produced byagricultural plants and animals”
National Academy of Science, 1975
Question of the Day – How does a corn kernelweighing 0.15 g, become a mature plantweighing 6-7 Kg in 90 days?
The Photosynthetic ProcessThe 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
In Photosynthesis, always remember that light energy isbeing converted to chemical energy or food.In Photosynthesis, always remember that light energy isbeing converted to chemical energy or food.
The Plant Cell
Photosynthetic Reaction –GeneralizedPhotosynthetic Reaction –Generalized
6 CO2 + 12H2O C6H12O6 + 6H2O + 6O2
^
green tissue
^
light
CO2 from the atmosphere around the leaf,enters the stomate, travels to a photosyntheticcell where glucose is producedCO2 from the atmosphere around the leaf,enters the stomate, travels to a photosyntheticcell where glucose is produced
Photosynthetic Reaction –GeneralizedPhotosynthetic Reaction –Generalized
Resources used:
–Water, nutrients CO2, light energy
Energy provided:
–Chemical bond energy
Products produced:
–Sugars, lipids, amino acids (proteins) , manyothers
Amino acids are the components of proteins and thereare 20 in nature. Look carefully and you will see whynitrogen (N) is so important in plants and animals.Amino acids are the components of proteins and thereare 20 in nature. Look carefully and you will see whynitrogen (N) is so important in plants and animals.
Photosynthetic Reaction –GeneralizedPhotosynthetic 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
Photosynthetic Reaction –GeneralizedPhotosynthetic Reaction –Generalized
Photosynthesis: H2O + CO2 CH2O + O2
Respiration: CH2O + O2 H2O + CO2
Note! These are almost the exact opposite reaction
Factors Affecting PhotosynthesisFactors Affecting Photosynthesis
Light quality
–Action spectrum of photosynthesis and growth
–Function of chlorophyll in plant cells
Factors Affecting PhotosynthesisFactors 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
Continued from previous slideContinued from previous slide
Light Intensity -
Maximum photosynthetic rate
Determined by chloroplasts per leaf
Factors AffectingPhotosynthesisFactors AffectingPhotosynthesis
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
Factors Affecting PhotosynthesisFactors Affecting Photosynthesis
Water
–Water stress
guard cells become flaccid
stomates close
gas exchange stops
factors affect water flow through xylem
–Drought
incipient or prolonged
Factors Affecting PhotosynthesisFactors Affecting Photosynthesis
Source – Sink relationships
–Sources
Net exporters of photosynthetic products (leaves)
–Sinks
Net importers of photosynthetic products (roots,shoots)
Factors Affecting PhotosynthesisFactors 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
Factors Affecting PhotosynthesisFactors 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
Factors Affecting PhotosynthesisFactors Affecting Photosynthesis
Carbohydrate production viaphotosynthesis
–Light reaction
Splitting of H2O
Release of H, O2, e-, ATP
Factors AffectingPhotosynthesisFactors AffectingPhotosynthesis
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
The EndThe End
The Plant Cell