1. Conversion of solar energy to chemical energy
Photosynthesis
Conversion of solar energy to chemical energy

2. Photosynthesis – Source of
Coal
Oil
Gas
Wood
Alcohol
Grains
Fruits
Veggies
Meat
Eggs
Dairy foods
Medicines
Flavorings
Paper
Clothing
Plastics

3. Photosynthate -- How Much?
1.4 x 1014 Kg of CO2 is converted to carbohydrate yearly (3.1 x 1014 lb)
The total weight of humanity (5B x 125lb) = 6.25 x 1011 lb, or 1/1000th the amount
The amount of carbon fixed would yield enough coal to fill 97 railroad cars every second of every hour of every day all year long!

4. Solar Energy Conversion Efficiency
Solar energy > Chemical energy
0.1% for poor growing conditions with clouds
3% for intensive cropping
25% for plants grown in controlled laboratory conditions

5. Photosynthesis Green leaves CO2 from air Water from soil
Light from the sun

6. Photosynthetic light:

7. Photosynthesis Products
Sucrose
6 C Sugar Phosphates
5 C Sugar Phosphates
Water
Oxygen

8. Photosynthesis Equation
nCO2 + nH2O > (CH2O)n + nO2
Conditions = green plant and light
6CO2 + 12H2O ----> C6H12O6 + 6H2O O2

9. Photosynthesis Supplies O2
C. B. Van Neil’s work in 1930 showed that water is the source of oxygen given off in photosynthesis

10. Photosynthesis: Where in the cell?
Chloroplast
Where ‘dark’ reactions
take place
Where ‘light’ reactions
take place

11. Photosynthetic Rate Factors:
Light Quality
Light Intensity
Light Duration
Carbon Dioxide Concentration
Temperature
Water
Plant development and source-sink relationships

12. Photosynthesis - Light Quality
Pigments = chlorophyll a, chlorophyll b, and carotenoids
Action Spectrum
Photosynthesis rate: net photosynthesis, total photosynthesis

13. Photosynthesis and Light Intensity
Sun plants
Shade plants
Moderate light plants
Foot candles
Lux
PPF (umol•m-2•s-1 )

14. Photosynthesis -- Light Saturation
Photosynthesis is limited by CO2 concentration and by light intensity

15. Photosynthesis and Photoperiod
The longer leaves receive light, the longer they photosynthesize, and the faster plants grow

16. Photosynthesis and Carbon Dioxide
CO2 in air = 0.03%
< CO2 in air to 0.10% doubles photosynthesis rate
Greenhouses are often CO2 enhanced
Crops may benefit from wind machines

17. Photosynthesis and Temperature
When light is not limiting, photosynthesis doubles for each 10 °C temperature increase
> Photosynthesis and < respiration at very high temps = low plant sugar storage

18. Photosynthesis and Water
When plants lose water faster than they can replace it, water deficits cause stomates to close, leaves to wilt, and CO2 and O2 exchange to stop, resulting in > photosynthesis

19. Source/Sink Relationships
Source = Photosynthesis (PS)
Sink = Growth and development
1. Growth Sink - Growth creates demand
2. Nitrogen - N applications energize PS
3. CO2 increase - Increases PS
4. High light /short time - Increases PS
5. Senescence - Vegetative to reproductive

20. Photosynthesis Types C3 Plants C4 Plants
Crassulacean Acid Metabolism (CAM) Plants

21. Photosynthesis in C3 Plants
Cereals, peanuts, soybeans,
Most ornamental plants
Bind CO2 with an enzyme (RUBISCO) that competes with oxygen
Inefficient system

22. Photosynthesis in C4 Plants
C4 Plants grab CO2 by using a special acid
This acid releases CO2 alone with enzyme so no competition with oxygen
Efficient CO2 users, better water-use efficiency than C3 plants
Corn, sugarcane, millet, crab grass, pigweed

23. Photosynthesis and CAM Plants
CAM plants also fix CO2 with organic acids, but at night
Cactus, pineapple, orchids
Highest water use efficiency plants