Photosynthesis

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Chapter 10

• Photosynthesis

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Ch. 10 - Photosynthesis

• Photosynthesis in nature
• Pathways of photosynthesis
• Overview
• The light reactions
• The dark reactions

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Photosynthesis in Nature

• Plants and other autotrophs are the the producers
  of the biosphere.
• Chloroplasts are the site of photosynthesis in
  plants.

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Autotrophs Heterotrophs

• Autotrophs - obtain energy and carbon from the
  inorganic (nonliving) world.
• Photoautotrophs - Obtain energy from sunlight.
• Chemoautotrophs - Obtain energy by oxidizing
  inorganic molecules - Fe
• Carbon dioxide carbon source
• Heterotrophs - obtain energy (and carbon) from
  the living world.

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Chloroplasts are the site of photosynthesis in
plants.
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Leaf cross section
Mesophyll
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Plant Leaf Mesophyll Cell
Chloroplast
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Chloroplasts
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Overview of Photosynthetic Pathways

• Photosynthesis can be divided into light and dark
  reactions.
• Light splits water molecules.
• Photosynthesis is a redox reaction.
• The light and dark reactions (Calvin cycle)
  cooperate in converting light energy to the
  chemical energy of food.

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Photosynthesis requires energy
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Two Hypotheses

Hypothesis A
(1) CO2 light C O2
(2) C H2O CH2O
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Hypotheses B - Light splits water
(1) H2O light 2 H 1/2 O2
(2) CO2 2 H CH2O 1/2 O2
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Van Neil - Comparative Photosynthesis
Higher plants CO2 H2O light
CH2O O2
CO2 2 H2O light
CH2O O2 H2O
Photosynthetic bacteria
CO2 H2S light
CH2O 2S H2O
CO2 H2X light
CH2O 2X H2O
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O Experiments
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CO2 H2O light CH2O O2
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CO2 H2O light CH2O O2
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Photosynthesis is a redox process
H2O is oxidized.
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Light and Dark Reactions
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Carriers of Energy-rich Electrons
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The light and dark reactions cooperate.
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Tracking atoms through photosynthesis