The Light reactions

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The Light reactions

• Conversion of light to chemical energy.
• Chloroplast electron transport
• ATP formation - chemiosmosis

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Conversion of Light to Chemical Energy

• Absorption of light
• Transformation to chemical energy - redox
  reaction

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Light is a wave.
Wavelength
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Relationship Between Energy and Wavelength
Speed of light
Energy
E hc/l
Wavelength
Plancks constant
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Which has more energy?
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The Electromagnetic Spectrum
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Light is absorbed bychlorophyll molecules.
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Interaction of light with matter in a chloroplast.
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Photoexcitation of Chlorophyll
Transfers Electron
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Absorption Spectra
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Action Spectra
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Englemanns Experiment
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Photosystems

• Absorb light
• Electron transfer

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Photosystems

• Absorb light - Antenna
• Electron transfer - Reaction Center

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A Photosystem
Reaction center
Antenna
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A Reaction Center
Reaction Center Chlorophyll
Primary Electron Acceptor
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A Reaction Center
Electron Transfer
Reaction Center Chlorophyll
Primary Electron Acceptor
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Energetics of a Light Reaction
Electron transferred
Energy
Primary electron acceptor
Light
Reaction center chlorophyll
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Chloroplast Electron Transport -Z scheme

• Two light reactions
• act in series
• to evolve molecular oxygen,
• reduce NADP to NADPH
• And produce ATP

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Carriers of Energy-rich Electrons

• NADH
• FADH2
• NADPH

Respiration
---- Photosynthesis
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Reaction Centers
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Cyclic Electron Flow
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