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PHOTOSYNTHESISPHOTOSYNTHESIS
PhotosynthesisPhotosynthesis
• An anabolic, endergonic, carbon dioxide anabolic, endergonic, carbon dioxide (CO(CO22)) requiring process that uses light energy light energy
(photons)(photons) and water (Hwater (H22O)O) to produce organic organic
macromolecules (glucose).macromolecules (glucose).
6CO2 + 6H2O C6H12O6 + 6O2glucoseglucose
SUN
photonsphotons
Question:Question:
• Where does photosynthesis take place?Where does photosynthesis take place?
PlantsPlants
• Autotrophs:Autotrophs: self-producers.• Location:
1. Leaves
a. stoma
b. mesophyll cells
StomaMesophyllCell
Chloroplast
Stomata (stoma)Stomata (stoma)
• PoresPores in a plant’s cuticle through which waterwater and gasesgases are exchanged between the plant and the atmosphere.
Guard Cell
Guard Cell
Carbon Dioxide (CO2)
Oxygen (O2)
Mesophyll CellMesophyll Cell
Cell Wall
Nucleus
Chloroplast
Central Vacuole
ChloroplastChloroplast• OrganelleOrganelle where photosynthesisphotosynthesis takes place.
GranumThylakoid
Stroma
Outer Membrane
Inner Membrane
ThylakoidThylakoid
Thylakoid Membrane
Thylakoid SpaceGranum
Question:Question:
• Why are plants green?Why are plants green?
Chlorophyll MoleculesChlorophyll Molecules
• Located in the thylakoid membranesthylakoid membranes.
• Chlorophyll have MgMg++ in the center.
• Chlorophyll pigmentsChlorophyll pigments harvest energy (photons) by absorbingabsorbing certain wavelengthswavelengths (blue-420 blue-420 nmnm and red-660 nm are most important).
• PlantsPlants are greengreen because the green wavelengthwavelength is reflectedreflected, not absorbednot absorbed.
Wavelength of Light (nm)Wavelength of Light (nm)
400 500 600 700
Short wave Long wave(more energy) (less energy)
Absorption of ChlorophyllAbsorption of Chlorophyll
wavelengthwavelength
Absorption
violet blue green yellow orange red
Question:Question:
• During the fall, what causes the leaves to During the fall, what causes the leaves to change colors?change colors?
Fall ColorsFall Colors
• In addition to the chlorophyll pigments, there are other pigmentspigments present.
• During the fall, the green chlorophyllgreen chlorophyll pigments are greatly reducedgreatly reduced revealing the other pigmentspigments.
• CarotenoidsCarotenoids are pigments that are either redred or yellowyellow.
Redox ReactionRedox Reaction
• The transfertransfer of oneone or more electronsmore electrons from one reactantone reactant to anotheranother.
• Two types:Two types:
1.1. OxidationOxidation
2.2. ReductionReduction
Oxidation ReactionOxidation Reaction
• The lossloss of electronselectrons from a substance.• Or the gaingain of oxygenoxygen.
glucoseglucose
6CO2 + 6H2O C6H12O6 + 6O2
OxidationOxidation
Reduction ReactionReduction Reaction
• The gaingain of electrons to a substance.• Or the lossloss of oxygenoxygen.
glucoseglucose
6CO2 + 6H2O C6H12O6 + 6O2
ReductionReduction
Breakdown of PhotosynthesisBreakdown of Photosynthesis
• Two main parts (reactions).Two main parts (reactions).
1. Light Reaction or1. Light Reaction or
Light Dependent ReactionLight Dependent Reaction
Produces energyenergy from solar powersolar power (photons)(photons) in the form of ATPATP and NADPHNADPH.
Breakdown of PhotosynthesisBreakdown of Photosynthesis
2.2. Calvin Cycle orCalvin Cycle or
Light Independent Reaction orLight Independent Reaction or
Carbon Fixation orCarbon Fixation or
CC33 Fixation Fixation
Uses energyenergy (ATP and NADPH)(ATP and NADPH) from light light rxnrxn to make sugar (glucose).sugar (glucose).
1. Light Reaction (Electron Flow)1. Light Reaction (Electron Flow)
• Occurs in the Thylakoid membranesThylakoid membranes
• During the light reactionlight reaction, there are two two possiblepossible routes for electron flowelectron flow.
A.A. Cyclic Electron FlowCyclic Electron Flow
B.B. Noncyclic Electron FlowNoncyclic Electron Flow
A. Cyclic Electron FlowA. Cyclic Electron Flow
• Occurs in the thylakoid membranethylakoid membrane.• Uses Photosystem I onlyPhotosystem I only• P700 reaction center- chlorophyll a • Uses Electron Transport Chain (ETC)Electron Transport Chain (ETC)• Generates ATP only
ADP + ATPATPP
A. Cyclic Electron FlowA. Cyclic Electron Flow
P700
PrimaryElectronAcceptor
e-
e-
e-
e-
ATPATPproducedby ETC
Photosystem I
AccessoryPigments
SUN
Photons
B. Noncyclic Electron FlowB. Noncyclic Electron Flow
• Occurs in the thylakoid membranethylakoid membrane
• Uses PS IIPS II and PS IPS I
• P680 rxn center (PSII) - chlorophyll a
• P700 rxn center (PS I) - chlorophyll a
• Uses Electron Transport Chain (ETC)Electron Transport Chain (ETC)
• Generates OGenerates O22, ATP and NADPH, ATP and NADPH
B. Noncyclic Electron FlowB. Noncyclic Electron Flow
P700
Photosystem IP680
Photosystem II
PrimaryElectronAcceptor
PrimaryElectronAcceptor
ETC
EnzymeReaction
H2O
1/2O1/2O22 + 2H+
ATPATP
NADPHNADPHPhoton
2e-
2e-
2e-
2e-
2e-
SUN
Photon
B. Noncyclic Electron FlowB. Noncyclic Electron Flow
• ADP + ATPATP
• NADP+ + H NADPHNADPH
• Oxygen comes from the splitting of Oxygen comes from the splitting of HH22OO, not , not COCO22
HH22O O 1/2 O2 + 2H+
(Reduced)
P(Reduced)
(Oxidized)
ChemiosmosisChemiosmosis
• Powers ATP synthesisATP synthesis.
• Located in the thylakoid membranesthylakoid membranes.
• Uses ETC and ATP synthase (enzyme)(enzyme) to make ATP.
• Photophosphorylation:Photophosphorylation: addition of phosphatephosphate to ADPADP to make ATPATP.
ChemiosmosisChemiosmosis
H+ H+
ATP Synthase
H+ H+ H+ H+
H+ H+ high Hhigh H++
concentrationconcentration
H+ADP + P ATP
PS II PS IE
TC
low Hlow H++
concentrationconcentration
H+ThylakoidThylakoidSpaceSpace
ThylakoidThylakoid
SUN (Proton Pumping)
Calvin Cycle• Carbon Fixation (light independent rxn).Carbon Fixation (light independent rxn).
• C3 plants (80% of plants on earth).
• Occurs in the stroma.
• Uses ATP and NADPH from light rxn.
• Uses CO2.
• To produce glucose: it takes 6 turns and uses 18 ATP and 12 NADPH.
ChloroplastChloroplast
GranumThylakoid
Stroma
Outer Membrane
Inner Membrane
Calvin Cycle (CCalvin Cycle (C33 fixation) fixation)
6CO2
6C-C-C-C-C-C
6C-C-C 6C-C-C
6C-C-C-C-C
12PGA
RuBP
12G3P
(unstable)
6NADPH 6NADPH
6ATP 6ATP
6ATP
C-C-C-C-C-CGlucose
(6C)(36C)
(36C)
(36C)
(30C)
(30C)
(6C)
6C-C-C 6C-C-C
C3
glucose
Calvin CycleCalvin Cycle
• Remember:Remember: C3 = Calvin CycleC3 = Calvin Cycle
C3
Glucose
PhotorespirationPhotorespiration
• Occurs on hot, dry, bright dayshot, dry, bright days.
• Stomates close.
• Fixation of O2 instead of CO2.
• Produces 2-C molecules2-C molecules instead of 3-C sugar 3-C sugar moleculesmolecules.
• Produces no sugar molecules or no ATP.
PhotorespirationPhotorespiration
• Because of photorespirationBecause of photorespiration: PlantsPlants have special adaptationsspecial adaptations to limit the effect of photorespirationphotorespiration.
1.1. C4 plantsC4 plants
2.2. CAM plantsCAM plants
C4 PlantsC4 Plants
• Hot, moist environmentsHot, moist environments.
• 15% of plants (grasses, corn, sugarcane).15% of plants (grasses, corn, sugarcane).
• Divides photosynthesis spatially.Divides photosynthesis spatially.
• Light rxn - mesophyll cells.
• Calvin cycle - bundle sheath cells.
C4 PlantsC4 Plants
Mesophyll CellMesophyll Cell
CO2
C-C-C
PEP
C-C-C-CMalate
ATP
Bundle Sheath CellBundle Sheath Cell
C-C-C
Pyruvic Acid
C-C-C-C
CO2
C3
Malate
Transported
glucoseVascular Tissue
CAM PlantsCAM Plants• Hot, dry environmentsHot, dry environments.
• 5% of plants (cactus and ice plants).5% of plants (cactus and ice plants).
• Stomates Stomates closed during dayclosed during day..
• Stomates Stomates open during the nightopen during the night.
• Light rxn - occurs during the day.
• Calvin Cycle - occurs when CO2 is present.
CAM PlantsCAM PlantsNight (Stomates Open) Day (Stomates Closed)
Vacuole
C-C-C-CMalate
C-C-C-CMalate Malate
C-C-C-CCO2
CO2
C3
C-C-CPyruvic acid
ATPC-C-CPEP glucose
Question:Question:
• Why would CAM plants close their Why would CAM plants close their stomates during the day?stomates during the day?