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?

Where ‘dark’ reactionstake place

Where ‘light’ reactionstake place

Chloroplast

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

Photosynthesisand 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