Photosynthesis 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 CO 2 is • converted to carbohydrate yearly (3. 1 x 1014 lb) The total weight of humanity (5 B x 125 lb) = 6. 25 x 1011 lb, or 1/1000 th 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 • CO 2 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 n. CO 2 + n. H 2 O ---------> (CH 2 O)n + n. O 2 Conditions = green plant and light 6 CO 2 + 12 H 2 O ----> C 6 H 12 O 6 + 6 H 2 O + 6 O 2

Photosynthesis Supplies O 2 • 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 • Temperature Light Intensity • Water Light Duration • Plant development Carbon Dioxide and source. Concentration 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 CO 2 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 • • CO 2 in air = 0. 03% < CO 2 in air to 0. 10% doubles photosynthesis rate Greenhouses are often CO 2 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 CO 2 and O 2 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. CO 2 increase - Increases PS 4. High light /short time - Increases PS 5. Senescence - Vegetative to reproductive

Photosynthesis Types • • • C 3 Plants C 4 Plants Crassulacean Acid Metabolism (CAM) Plants

Photosynthesis in C 3 Plants • • Cereals, peanuts, soybeans, Most ornamental plants Bind CO 2 with an enzyme (RUBISCO) that competes with oxygen Inefficient system

Photosynthesis in C 4 Plants • • C 4 Plants grab CO 2 by using a special acid This acid releases CO 2 alone with enzyme so no competition with oxygen Efficient CO 2 users, better water-use efficiency than C 3 plants Corn, sugarcane, millet, crab grass, pigweed

Photosynthesis and CAM Plants • • • CAM plants also fix CO 2 with organic acids, but at night Cactus, pineapple, orchids Highest water use efficiency plants