Photosynthesis Using Light to Make Food

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PhotosynthesisUsing Light to Make Food
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Photosynthesis Why Study It?

• Most Important biological process on earth
• Fills food requirements needs for fiber
  building material
• Petroleum, natural gas, coal, firewood

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Photosynthesis

• Three major events
• Absorption of light energy
• Conversion of light energy into chemical energy
  (ATP and NADPH)
• Storage of potential energy in carbohydrates

• Photo
• Means Light
• Synthesis
• Means to Make

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Spectrum of Light Energy
Spectrum of light energy - Photosynthesis uses
only a small portion of this spectrum of light
energy.
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Where does it happen?

• Green tissues of plants
• Mostly in the leaves, but not always
• Cells of green tissues have chloroplasts which
  contain
• Thylakoids (pan-cake)
• Chlorophyll found here
• Grana (stacks)
• Light reactions occur here
• Stroma (thick fluid)
• Carbon Fixation
• Uses carbon from CO2 to make carbohydrates
• Dark reactions occur here

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Two Stages

• Light-Dependent Reactions
• Temperature independent
• (Light Reactions)
• Temperature-Dependent Reactions
• Light independent
• (Dark Reactions)

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Light Reactions

• Requires direct energy of light to make carrier
  molecule needed for Stage 2
• Occurs in the Grana
• Absorption of light by pigments
• Light energy is converted into chemical energy

• Three products formed
• Oxygen gas
• ATP
• NADPH (hydrogen carrier)

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Dark Reactions

• Occurs in Stroma
• Requires energy carriers from light reactions
  (ATP, NADPH)
• Calvin Cycle
• Incorporates carbons into carbohydrates

Carbon Fixation
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The Equation
6CO2 6H20 Light energy
----gt
C6H12O6 6 02
How does this equation compare to cellular
respiration?