biology lecture photosynthesis.pptx
DESCRIPTION
college biology lecture on photosynthesis,LIFE: The Science of Biology, Sadava, Purves.TRANSCRIPT
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PhotosynthesisMuhammad Tariq
Readings:Life Chapter 8
CO2 + H2O + Light energy Sugar + Oxygen
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The food Chain
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Autotrophs and Heterotrophs
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Sun as god in cultures
• The Egyptian peoples honored the sun god
• For people in ancient Egypt, the sun was a source of life
• It was power and energy, light and warmth
• It was what made the crops grow each season
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• 1/3rd of all the carbon fixed is used by humans• Law of conservation of energy
Photosynthesis
CO2 + H2O Carbohydates
• Conversion of energy from light to chemical bond in reduced electron carriers & ATP
• Sources of chemical energy in step 1 used to drive synthesis of carbohydrates from CO21/3rd of all the carbon fixed is used by humans
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Photosynthetic reactants & Products• 3 principal ingredients: Water, CO2, Light• Not only produces CHO but also O2
CO2 + H2O + Light energy Sugar + Oxygen
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Oxygen production
CO2 + H2O + Light energy Sugar + Oxygen
• What role does light play in this reaction???
• How carbon becomes linked to form sugar???
• O2 gas comes from CO2 or H2O???
6CO2 + 6H2O C6H12O6 + 6O2
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Source of the Oxygen
6CO2 + 12H2O C6H12O6 + 6H2O + 6O2
http://bcs.whfreeman.com/thelifewire/content/chp08/0802001.html
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Light as source of Energy
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Visible spectrum
• Photon must be absorbed by receptive molecule
• Must have sufficient energy to perform chemical work
Light as source of Energy: Photon mediated activation
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Receptivity of photon: pigments in photosynthesis
• Molecules that absorb wavelength in visible wavelength are called pigments
• Photon scattered• Photon transmitted• Photon absorbed, photon disappears but energy doesn’t
• Scattered and transmitted wavelengths make pigments appear to us colored
• Photosynthesis uses energy absorbed by several pigments• Several pigments, several absorbtion spectra• Chlorophyll, carotenoids, phycobillins• Chlorophyll a and b predominates
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Pathways of Photosynthesis• Light reaction: driven by light, produces ATP and reduced electron
carrier NADPH+H+
• Calvin-Bensen reaction: doesn’t use light. Use ATP, NADPH+H+ from light reaction and CO2 to produce sugars
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Absorbed wavelengths and biological activity
Blue and Red light cause highest rate of photosynthesis
Absorbtion spectrum
Action spectrum
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Chlorophyll molecule
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The light reaction
Energy absorbing antenna system
Converts absorbed light into chemical energy
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Excited chlorophyll in reaction acts as reducing agent in electron transport
Oxidizing agent
• Chl acts as reducing agent and participates in a redox reaction
• Reduce electron carrier NADP+, generates a proton motive form used in ATP synthesis
The light reaction
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The light reaction (Non cyclic photophosphorylation)
680nm 700nm
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Photosystem II
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Cyclic photophosphorylation (PSI)
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Summary
Lumen
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Light reaction summary
• http://bcs.whfreeman.com/thelifewire/content/chp08/0802002.html
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Tracing the pathway of CO2
• http://bcs.whfreeman.com/thelifewire/content/chp08/0802003.html
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Conclusion
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The light independent reaction
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