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
Top Related