Calvin Cycle and Photorespiration

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Calvin Cycle and Photorespiration
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Calvin Cycle

• 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

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The G3P made in the Calvin Cycle is involved in
the biosynthesis of other organic molecules
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Rate of Photosynthesis

• What is a rate?
• It is the activity per unit time.
• What factors can affect the photosynthetic rate?

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Light Intensity
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The Effect of Light Intensity on Photosynthetic
Rate
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Temperature
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The Effect of Temperature on Photosynthetic Rate
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The Effect of Light Intensity and Temperature on
Photosynthetic Rate
Which is the limiting factor here light
intensity or temp.?
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Oxygen Concentration
What would a graph for increasing levels of CO2
look like?
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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?

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Photorespiration

• The overall rate of photosynthesis decreases.
• Photorespiration and photosynthesis occur at the
  same time

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Conditions for Photorespiation

• What conditions will lead to a lot of
  photorespiration?
• Hot
• Dry
• Sunny
• What happens to stomates under such conditions?
• They close.

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Evolution

• Why does rubisco bind both oxygen and carbon
  dioxide?
• When Calvin Cycle evolved there was little oxygen
  in the atmosphere.

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Solutions

• What solutions have some plants found for this
  problem?
• C4 Pathway.
• Sugarcane, corn, crabgrass have all evolved a
  different structure that minimizes
  photorespiration.

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What is the new structure?
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The bundle sheath cells!
How do the bundle sheath cells minimize
photorespiration?
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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?

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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.

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Mesophyll cell
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• C4 plants use a new structure to solve the
  photorespiration problem.
• CAM plants use time to solve the photorespiration
  problem.

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Photorespiration cycle