Conversion of solar energy to chemical energy Photosynthesis Conversion of solar energy to chemical energy

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

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!

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

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

Photosynthetic light:

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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