Everything you wanted to know about photosynthesis but were afraid to ask!

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Everything you wanted to know about
photosynthesis but were afraid to ask!

• AGRO 1033 Unit 5
• Photosynthesis, Photorespiration,
• Respiration.

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Photosynthesis Essential for high crop yields.
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Aristotle Plants Sun Soil
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1577 Famous willow tree study by Van Helmut.
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By 1850, it was known that plants reduce
atmospheric carbon by 6CO2 6H20 ? C6H12O6
6O2
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1941 Nuclear technology comes of age.
Non-lethal uses develop.
S. Ruben and M. D. Kamen discover
C16O2 H218O ? (CH218O) 16,18O2
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Their work discovered that the water molecule was
being split in a process later known as
photolysis.
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1945 Dr. Melvin Calvin discovers the Calvin
Cycle.
HOW? By tracking radioactive C in CO2
through time as it reacted with chloroplasts in
algae. This gave snap shots of products
formed and allowed the pieces of the puzzle to
be put together.
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Key players in the Calvin Cycle

• RuBP-carboxylase/oxygenase enzyme.

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Key players in the Calvin Cycle

• RuBP-carboxylase/oxygenase enzyme.
• ATPs, NADPH from light energy.

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Key players in the Calvin Cycle

• RuBP-carboxylase/oxygenase enzyme.
• ATPs, NADPH from light energy.
• CO2, O2

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Key players in the Calvin Cycle

• RuBP-carboxylase/oxygenase enzyme.
• ATPs, NADPH from light energy.
• CO2, O2
• RuBP (a 5 carbon compound)

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Key players in the Calvin Cycle

• RuBP-carboxylase/oxygenase enzyme.
• ATPs, NADPH from light energy.
• CO2, O2
• RuBP (a 5 carbon compound)
• 3-PGA (a 3 carbon compound)
• Chloroplasts

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Photosynthesis is basically the capture of
sunlight energy and conversion to chemical energy.
This occurs in basically two processes 1. Light
dependent reactions. 2. Light independent
reactions (this is what Calvin figured out).
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The Light Reactions convert sun ? chemical
energy.
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Light independent uses the energy to convert C
from CO2 in air to organic C (glucose).
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This occurs mostly in leaves!
C
C
C
80 of a crops weight is carbon from the air!
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But wait! Theres more!
Researchers soon discovered that not all plants
assimilate carbon the same. The initial carbon
compound formed from CO2 assimilation was
different, AND there was another enzyme
involved. Also, the leaf morphology was
different.
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These became known as C4 plants, because the
initial product was a 4 carbon compound called
OAA.
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These became known as C4 plants, because the
initial product was a 4 carbon compound called
OAA.
Most of these species evolved in more tropical
environments.
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These became known as C4 plants, because the
initial product was a 4 carbon compound called
OAA.
Most of these species evolved in more tropical
environments.
The other plants that Calvin had initially
studied were labeled C3 plants since the first
product was a 3 carbon compound called PGA.
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Major players in C4 plants

• PEP carboxylase

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Major players in C4 plants

• PEP carboxylase
• OAA (4 carbon initial product)

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Major players in C4 plants

• PEP carboxylase
• OAA (4 carbon initial product)
• bundle sheath cells

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Major players in C4 plants

• PEP carboxylase
• OAA (4 carbon initial product)
• bundle sheath cells
• Calvin cycle

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Examples of photosythesis path

• C4 Crops
• corn
• grain sorghum
• sugarcane

• C3 Crops
• soybeans
• cotton
• rice
• wheat
• oats
• peanut

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But wait! Theres more!
Researchers found out that desert succulent
species do it different!
These plants actually capture C at night! They
became known as CAM plants with regard to
photosynthesis.
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The major players were similar to C4 plants
PEP carboxylase OAA malate acid vacuoles
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So far, only 3 types of plants

• C3 plants
• C4 plants
• CAM plants

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Photorespiration
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Unfortunately, there is a leak in the C gas tank
its called photorespiration.
Photorespiration is the loss of potential C from
carbon dioxide due to the affinity of the RuBP
enzyme for oxygen.
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Photorespiration losses are very high in C3
plants.
WHY you say?

• Mostly due to morphology.
• RuBP carboxylase/oxygenase enzyme has
• more oxygen around it in C3 plants.
• Photorespiration losses can be as high as
• 30!
• - Compare that to lt5 for C4 crops.

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Observe the location of the chloroplast density
between the two.
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Understanding how plants grow is essential for
producing higher yielding crops. The knowledge
is helpful in variety development and crop
management programs (water, nutrients,
sunlight interception, pest control, use of
hormones, and many more).
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Knowledge is an
IDEA GENERATOR!
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This helps the farmer increase their yields and
hopefully, the bottom line!
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