Photosynthesis
Conversion of solar energy
to chemical energy
Photosynthesis – Source of
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Coal
Oil
Gas
Wood
Alcohol
Grains
Fruits
Veggies
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Meat
Eggs
Dairy foods
Medicines
Flavorings
Paper
Clothing
Plastics
Photosynthate -- How Much?
• 1.4 x 1014 Kg
of CO2 is
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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
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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
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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
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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
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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:
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Light Quality
• Temperature
Light Intensity • Water
Light Duration • Plant
development
Carbon Dioxide
and sourceConcentration
sink
relationships
Photosynthesis - Light Quality
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Pigments =
chlorophyll a,
chlorophyll b, and
carotenoids
Action Spectrum
Photosynthesis rate:
net photosynthesis,
total photosynthesis
Photosynthesis
and Light Intensity
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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
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The longer
leaves receive
light, the longer
they
photosynthesize,
and the faster
plants grow
Photosynthesis and Carbon
Dioxide
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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
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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
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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
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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
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C3 Plants
C4 Plants
Crassulacean Acid Metabolism (CAM)
Plants
Photosynthesis in C3 Plants
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Cereals, peanuts,
soybeans,
Most ornamental
plants
Bind CO2 with an
enzyme (RUBISCO)
that competes with
oxygen
Inefficient system
Photosynthesis in C4 Plants
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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
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CAM plants also fix
CO2 with organic
acids, but at night
Cactus, pineapple,
orchids
Highest water use
efficiency plants