Calvin Cycle and
Photorespiration
Calvin Cycle
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Where does the Calvin Cycle occur?
In the stroma
What goes into the Calvin Cycle?
ATP, NADPH, Carbon Dioxide
What comes out of the Calvin Cycle?
Sugar, ADP, NADP+
The G3P
made in the
Calvin Cycle
is involved
in the
biosynthesis
of other
organic
molecules
Rate of Photosynthesis
• What is a rate?
• It is the activity per unit time.
• What factors can affect the
photosynthetic rate?
Light Intensity
The Effect of Light Intensity on
Photosynthetic Rate
Temperature
The Effect of Temperature on
Photosynthetic Rate
The Effect of Light Intensity and
Temperature on Photosynthetic Rate
Which is
the
limiting
factor
here;
light
intensity
or
temp.?
Oxygen Concentration
What would a graph for increasing levels of CO2 look like?
Why Does Oxygen Effect
Photosynthetic Rate?
• What is the role of rubisco?
• Rubisco incorporates carbon dioxide
into the RuBP during the Calvin cycle.
• Rubisco, however, has an active site
that accommodates both oxygen and
carbon dioxide.
• What happens when rubisco
incorporates oxygen into the RuBP
molecule?
Photorespiration
• The overall rate of photosynthesis
decreases.
• Photorespiration and photosynthesis
occur at the same time
Conditions for Photorespiation
• What conditions will lead to a lot of
photorespiration?
• Hot
• Dry
• Sunny
• What happens to stomates under such
conditions?
• They close.
Evolution
• Why does rubisco bind both oxygen and
carbon dioxide?
• When Calvin Cycle evolved there was
little oxygen in the atmosphere.
Solutions
• What solutions have some plants found
for this problem?
• C4 Pathway.
• Sugarcane, corn, crabgrass have all
evolved a different structure that
minimizes photorespiration.
What is the new structure?
The bundle sheath
cells!
How do the bundle sheath cells minimize photorespiration?
Different between C3 vs. C4 plants
• Photorespiration?
• Leaf anatomy?
• Levels of tolerancy under the hot, dry, sunny
conditions that favor photorespiration?
• Light comp. point?
• CO2 comp. point?
CAM Plants
• At night, stomata open, take in CO2,
incorporate it into organic acids and
store those acids in vacuoles until
daylight
• during the day, stomates close
• The organic acids stored at night, break
down, release CO2 and rubisco
incorporates it into sugar.
Mesophyll cell
• C4 plants use a new structure to solve
the photorespiration problem.
• CAM plants use time to solve the
photorespiration problem.
Photorespiration cycle