PHOTOSYNTHESIS

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PHOTOSYNTHESIS

• Nancy G. Morris
• Volunteer State Community College

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PHOTOSYNTHESIS

• I. Overview
• II. The Light Reactions
• III. The Dark Reactions (Calvin Cycle)
• IV. Summary

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PHOTOSYNTHESIS

• Plants are the producers of the biosphere.
• Photoautotrophs use the energy of sunlight to
  synthesis organic molecules such as glucose from
  CO2 and H2O.
• Heterotrophs must ingest other organisms or their
  by-products to obtain energy.

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PHOTOSYNTHESIS

• Chloroplasts are the sites of photosynthesis.
• They contain a system of stacked membranes called
  thylakoids.
• The chloroplast uses light energy
  to make glucose.

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PHOTOSYNTHESES

• The Light reactions occur in the thylakoids of
  the chloroplast.
• The Dark reactions occur in the stroma.

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The Site of Photosynthesis
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What is light anyway?

• Visible light is electromagnetic energy also
  called solar radiation.
• Light travels in waves but sometimes behaves as
  through it consists of discrete particles called
  photons.
• Pigments are substances that absorb visible
  light. (Figure 7.1)
• Chlorophyll looks green because it absorbs all
  light except green.

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The Light Reactions

• use visible light (solar radiation)
• convert solar energy to chemical energy
• Photophosphorylation
• Photolysis

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Phosphorylation
is simply the addition of a phosphate, so

• Photophosphorylation
  is the addition of a phosphate to ADP using
  solar energy

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Photolysis

• Light is used to split water
• 2H2O ? 2H2 O2
• How is photolysis different from hydrolysis?

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The Light Reactions include these two important
reactions

• Photophosphorylation
• light powers the addition of a phosphate to ADP
• Photolysis
• Light is used to split water
• 2H2O ? 2H2 O2

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Chlorophyll
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Exciting the chlorophyll

• As energy is absorbed, electrons are excited and
  are elevated to a temporary high energy but
  unstable state.
• The fall back to the ground state releases heat
  and sometimes light. The afterglow is
  fluorescence.

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Noncyclic electron flow
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Cyclic electron flow
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The Calvin Cycle or The Dark Reactions

• Carbon Fixation
• incorporation of carbon into organic compounds
• The fixed carbon is reduced to carbohydrates by
  the addition of electrons transported by NADPH

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The Calvin Cycle or The Dark Reactions

• To convert CO2 to carbohydrate, chemical energy
  in the form of ATP is used.
• 6CO2 12 H2O light ? C6H12O6 6O2 6H2O

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A review of Photosynthesis