Photosynthesis

1. Photosynthesis Conversion of solar energy to chemical energy

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

3. 1.4 x 1014 Kg of CO2is 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! Photosynthate -- How Much?

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 + 6O2

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

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

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

13. Photosynthesisand 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