BIOL 223 Ch 10 Photosynthesis part 1 - …€¦ · Chapter 10 Photosynthesis BIOL 223...
Transcript of BIOL 223 Ch 10 Photosynthesis part 1 - …€¦ · Chapter 10 Photosynthesis BIOL 223...
Chapter10Chapter10
PhotosynthesisPhotosynthesis
BIOL223
PhotosynthesisandEnergy
• Photosynthesis
• Makingfoodfromlightenergy
• Photoautotrophs
• UseCO2andwatertomakesugars
• Madelifepossibleasweknowit
• Providescarbohydratesforall
higherlevelsoffoodchain
• PrimaryproducEon
• Liberatesatmosphericoxygen
• O2wasteproduct
PhotosynthesisandEnergy
• Carbondioxideconvertedtosugar
• ProcesscalledcarbonfixaEon
• SeriesofredoxreacEons
• Water(hydrogenatoms)loseselectrons
• Oxidized(OIL)
• Carbondioxidegainselectrons
• Reduced(RIG)
PhotosynthesisandEnergy
• SummaryequaEonforphotosynthesis
CO2+2H2O+photons→(CH2O)n+H2O+O2
carbondioxide+water+lightenergy→carbohydrate+oxygen+water
PhotosynthesisandEnergy
• SomewhatoppositeofcellularrespiraEon
Photosynthesis
CO2+2H2O+photons→(CH2O)n+H2O+O2
carbondioxide+water+lightenergy→carbohydrate+oxygen+water
CellularRespiraEon
(CH2O)6
C6H12O6+O2→CO2+H2O+energy
PhotosynthesisandEnergy• Energytrappedbyphotosynthesis
• approx100terawaSs
• 6xyearlyglobalpowerconsumpEonofhumancivilizaEon
• convertaround100,000,000,000(billion)tonsofcarbonintobiomassper
year
ThreeTypesofPhotosynthesizers
Domain: EukaryotaKingdom: Plantae
Domain: EukaryotaKingdom: Protista
Domain: ProkaryotaKingdom: Eubacteria
TheComponentsofPhotosynthesis• Chloroplasts
• Organellesinplantsandalgae,wherephotosynthesistakesplace
• Lightcapturedhere
• Existingreatabundanceinthemesophyllcellsofplantleaves
• Doublemembranebound
• likemitochondria
• Containthylakoids
• Stackedasgrana
• Intheliquidfilledstroma
Photosynthesis• Capturedenergycomesmostlyfromblueandredwavelengthsofvisiblesunlight
• Absorbedbypigmentsinthethylakoids
• Chlorophylla
• Accessorypigments
• Whyplantslookgreen
low energyhigh energylong wavelengthshort wavelength
gammarays
visiblelight
x-rays ultra-violet infrared microwaves radiowaves
SiteofPhotosynthesis
petiole
blade
epidermis
epidermis
stomata
cell wall
nucleus
vacuole
chloroplast
thylakoids
outer membrane
stroma
inner membranegranum
thylakoid
thylakoid compartment
mesophyllcells
Energy from sunlight is
absorbed by pigments in the
thylakoid membrane.
LeafThe primary site of photosynthesis in plants, leaves have a two-part structure: a petiole (or stalk) and a blade (normally thought of as the leaf).
Leaf cross sectionIn cross section, leaves have a sandwich-like structure, with epidermal layers at top and bottom and mesophyll cells in between. Most photosynthesis is performed within mesophyll cells. Leaf epidermis is pocked with a large number of microscopic openings, called stomata,that allow carbon dioxide to pass in and water vapor to pass out.
Mesophyll cellA single mesophyll cell within a leaf contains all the component parts of plant cells in general, including the organelles—called chloroplasts—that are the actual sites of photosynthesis.
ChloroplastEach chloroplast has an outermembrane at its periphery; then an inner membrane; then a liquid material, called the stroma, that has immersed within it a network of membranes, the thylakoids. These thylakoids sometimesstack on one another to create. . .
A GranumElectrons used in photosynthesis will come from water contained in the thylakoid compartment, and all the steps of photosynthesis will take place either within the thylakoid membrane, or in the stroma that surrounds the thylakoids.
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thylakoid membrane
StagesofPhotosynthesis
• Twoprimarystages
• LightreacEons
• Stripselectronsfromwater
• oxidaEon
• Booststheseelectronstohigherenergylevels
• MakesATPandNADPH
• Calvincycle
• Makescarbohydratesfromhighenergyelectronsand
atmosphericCO2
TheLightReacEons
• Electronsderivedfromwater
• energeEcallyboostedby
photons
• Electronsphysicallytransferred
• passedalongthroughaseriesof
electroncarriers
• NADP+⇒NADPH
• carriesthemtosecondstage
StagesofPhotosynthesis
• Twoprimarystages(conEnued)
• LightreacEons
• Stripselectronsfromwater
• Booststheseelectronstohigherenergylevels
• Calvincycle
• LightindependentreacEons
• Makescarbohydratesfromhighenergyelectronsand
atmosphericCO2
• reducEon
TheCalvinCycle
• ElectronscarriedbyNADPH
• combinedwithcarbondioxide
• formshigh‐energysugar
• Glyceraldehyde3‐Phosphate(G3P)
• combinedintocomplexcarbohydrates
• poweredbyATPfromlightreacEons
• Occursinthestromaofthechloroplast
• FirstdescribedbyMelvinCalvin
LightReacEons• Photosynthesisworksthroughtwo
molecularcomplexes
• PhotosystemsIIandI
• Onthylakoidmembranes
• composedpartlyof
antennaemolecules
• chlorophyllandsome
accessorymolecules
• absorband
transmitsolar
energy
LightExcitaEon• pigmentabsorbslight
• goesfromagroundstatetoexcitedstate
• whichisunstable
• excitedelectronsfallbacktothegroundstate
• photonsaregivenoff
• fluorescence
(a) Excitation of isolated chlorophyll molecule
Heat
Excitedstate
(b) Fluorescence
Photon Groundstate
Photon(fluorescence)
Ener
gy o
f ele
ctro
n
e–
Chlorophyllmolecule
PhotosystemStructure• Photosystemantennaemolecules
• Afewhundredchlorophyllaandsomeaccessorymolecules(pigments)
• Pigments
• Carotene‐anorangepigment
• Xanthophyll‐ayellowpigment
• PhaeophyEna[1]‐agray‐brownpigment
• PhaeophyEnb[1]‐ayellow‐brownpigment
• Chlorophylla‐ablue‐greenpigment
• Chlorophyllb‐ayellow‐greenpigment
• transmitsolarenergytoreacEoncenters
PhotosystemStructure• ReacEoncentermolecules
• Pairofmodifiedchlorophyllamolecules
• pheophyEn
• Receivelightenergy
• transformittochemicalenergy
• splitswaterandstripselectronsoffliberatedhydrogenatoms
• alsoenergizesstrippedelectrons
• Includesprimaryelectronacceptors
• Receivethesehighenergyelectrons
THYLAKOID SPACE(INTERIOR OF THYLAKOID)
STROMA
e–
Pigmentmolecules
Photon
Transferof energy
Special pair ofchlorophyll amolecules
Thyl
akoi
d m
embr
ane
Photosystem
Primaryelectronacceptor
Reaction-centercomplex
Light-harvestingcomplexes
ElectronFlow
Pigmentmolecules
Light
P680
e–2
1
Photosystem II(PS II)
Primaryacceptor
• twopossibleroutesforelectronflow
• cyclicandlinear
• Linearelectronflow
• primarypathway
• involvesbothphotosystems
• producesATPandNADPHusinglightenergy
• photonhitspigmentmolecule
• energypassedamongpigmentmolecules
• unElitexcitesP680
• excitedelectronfromP680
• transferredtotheprimaryelectronacceptor
LinearElectronFlow(PSI)
Pigmentmolecules
Light
P680
e–
Primaryacceptor
2
1
e–
e–
2 H+
O2
+3
H2O
1/2
Photosystem II(PS II)
• P680+(missinganelectron)
• verystrongoxidizingagent
• H2Oissplitbyenzymes
• electronstransferredfrom
hydrogenatomstoP680+
• reducingittoP680
• O2isreleased
LinearElectronFlow(PSII)
Pigmentmolecules
Light
P680
e–
Primaryacceptor
2
1
e–
e–
2 H+
O2
+3
H2O
1/2
4
Pq
Pc
Cytochromecomplex
Electron transport chain
5
ATP
Photosystem II(PS II)
• Electronspasseddownelectrontransportchain
• fromprimaryelectron
acceptorofPSIItoPSI
• Energyreleasedbyfall
• drivesthecreaEonofaprotongradient
• intothylakoidspace
• DiffusionofH+
• acrossmembranedrives
ATPsynthase