Nerve activates contraction

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PHOTOSYNTHESIS
WITHOUT WHICH EVERY OTHER BIOLOGICAL PROCESS
WOULD BE IRRELEVANT
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Light
6 CO2 6 H20 C6H12O6 6 O2
Into 1940s, source of liberated oxygen was
unknown
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van Niels experiment
6 CO2 6 H2S C6H12O6 2S
6 CO2 6 H2A C6H12O6 2A
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Why are plants green?
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Figure 10.5 The electromagnetic spectrum
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Halobacterium halobacter a type of Archaea that
inhabits hypersaline habitats
http//www.bio.ic.ac.uk/research/agold/goldsworthy
.htm
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Sites of photosynthesis
Palisade mesophyll
Spongy mesophyll
Green light particularly effective in spongy
mesophyll
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The Chloroplast
lumen
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Freeze-fracture of thylakoids showing
photosystems (bumps) embedded in membrane
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Photosystem II
Photosystem I
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Light-Harvesting Complex pigment absorbs a
photon possible fates of energy

• Excited electron simply returns to ground state,
  emitting light energy (as fluorescence) or heat
• Energy is transferred to neighboring pigment
  molecules (resonance transfer)
• Chlorophyll a reaction center pigment ejects
  electron, which goes to first acceptor in
  electron transport chain (initiating
  photosynthesisgood)
• Chlorophyll a transfers excess energy to O2,
  creating reactive oxygen species (leading to
  damage, photoinhibitionbad)

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Light Harvesting Complex
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• Chlorophyll athe reaction center pigment
• (P680, P700)
• Other antenna pigments in addition to chl a
• Chlorophyll b
• Carotenoids
• Phycobilins
• Xanthophylls (along with carotenoids, essential
  to protect against photoinhibition)

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Pheophytin
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How is water split in photolysis in Photosystem
II?
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Oxygen-Evolving Complex
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OEC manganese-calcium-oxide complex
http//www.chm.bris.ac.uk/motm/oec/motmc.htm
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Can artificial photosynthesis be used to harness
sunlight, split water, and provide tons of energy?
yes
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Summary light reactions
lumen
stroma
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Photophosphorylation
lumen
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Cyclic electron flow produces more ATP
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Two major problems for light reactions

• Too little light
• Too much light

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• Photoprotection via pigments acting as
  antioxidants

http//sciencenow.sciencemag.org/cgi/content/full/
2005/121/3