photosynthesis- conversion of light energy to chemical energy where does it occur
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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. Autotrophs require only CO 2 , water and light (Where does the CO 2 come from?) Terrestrial plants Algae Some protists (e.g., Euglena ) - PowerPoint PPT PresentationTRANSCRIPT
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Photosynthesis- conversion of light energy tochemical 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 plantsAlgaeSome protists (e.g., Euglena)CyanobacteriaPurple sulfur bacteria
Many kingdoms represented!
How does photosynthesis occur in plants?
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Primarily in leaves, in chloroplasts
Interior tissue of leaf: mesophylldozens of chloroplasts per cell
Stomata let CO2 in and O2 out
Veins provide transport throughout plantwater from roots to leavessugar 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-carbonproducts
The oxygen is produced from the splitting ofwater, 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 differentamounts of energy (photons)
Visible light ranges from approx. 380-750 nm
Pigments absorb some wavelengths of lightand 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 energyto chlorophyll a
chlorophyll bcarotenoids
May have a “dampening effect” (photoprotection)
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When photons are absorbed by pigmentstheir energy is transferred to an electron
Electron falls back to ground state, givingoff heat
Some pigments (such as chlorophyll) alsogive off light (fluorescence; chlorophyllfluoresces red)
Fluorescent “tags” have many applications
Photosystems are specialized to harvestenergy 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 itbecomes an oxidizing agent- oxidizes waterand replaces electrons
Electrons fall down the electron transport chainand energy is used to form ATP(photophosphorylation)
Light hits photosystem I and releases electronselectrons from photosystem II “replace themNADPH is generated
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Cyclic phosphorylation
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When is this pathway used?
When ATP is scarce (Calvin cycle uses moreATP than NADPH)
How are these reactions organized in thethylakoid membrane?
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