Photosynthesis conversion of light energy to

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Photosynthesis- conversion of light energy
to chemical energy Where does it occur What
are the pathways What are the adaptations to
hot, dry climates
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Autotrophs require only CO2, water and
light (Where does the CO2 come
from?) Terrestrial plants Algae Some protists
(e.g., Euglena) Cyanobacteria Purple sulfur
bacteria Many kingdoms represented! How does
photosynthesis occur in plants?
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Primarily in leaves, in chloroplasts Interior
tissue of leaf mesophyll dozens of chloroplasts
per cell Stomata let CO2 in and O2 out Veins
provide transport throughout plant water from
roots to leaves sugar from leaves to other
structures
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How does photosynthesis happen? 6CO2 12H2O
light ? C6H12O6 6O2 6H2O Glucose is
eventually formed from 3-carbon products The
oxygen is produced from the splitting of water,
not carbon dioxide Confirmed using heavy oxygen
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Water is oxidized, CO2 is reduced
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Localization of photosynthesis reactions
What does NADPH do? ATP?
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How is light energy captured? Different
wavelengths of light contain different amounts
of energy (photons) Visible light ranges from
approx. 380-750 nm Pigments absorb some
wavelengths of light and reflect others (refer
to pp. 183-4 in anticipation of lab!)
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Chlorophyll a directly initiates light
reactions Other pigments absorb light, transfer
energy to chlorophyll a chlorophyll
b carotenoids May have a dampening effect
(photoprotection)
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When photons are absorbed by pigments their
energy is transferred to an electron Electron
falls back to ground state, giving off heat Some
pigments (such as chlorophyll) also give off
light (fluorescence chlorophyll fluoresces
red) Fluorescent tags have many
applications Photosystems are specialized to
harvest energy from light
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Two types of photosystems Photosystem I-
P700 Photosystem II- P680 Electron flow cyclic
or (predominantly) non-cyclic
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Summary when photosystem II absorbs light
it becomes an oxidizing agent- oxidizes
water and replaces electrons Electrons fall
down the electron transport chain and energy is
used to form ATP (photophosphorylation) Light
hits photosystem I and releases
electrons electrons from photosystem II replace
them NADPH is generated
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Cyclic phosphorylation
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When is this pathway used? When ATP is scarce
(Calvin cycle uses more ATP than NADPH) How are
these reactions organized in the thylakoid
membrane?
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