PHOTOSYNTHESIPHOTOSYNTHESISS

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PhotosynthesisPhotosynthesis• Anabolic (small molecules combined)Anabolic (small molecules combined)• Endergonic (stores energy)Endergonic (stores energy)• Carbon dioxide (COCarbon dioxide (CO22)) requiring requiring

process that uses process that uses light energy light energy (photons)(photons) and and water (Hwater (H22O)O) to produce to produce organic macromolecules (glucose).organic macromolecules (glucose).

6CO2 + 6H2O C6H12O6 + 6O2

glucoseglucose

SUNphotonsphotons

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Question:Question:

Where does Where does photosynthesiphotosynthesis take place?s take place?

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PlantsPlants• Autotrophs Autotrophs – produce their own – produce their own

food food (glucose)(glucose)• Process called Process called photosynthesisphotosynthesis• Mainly occurs in the Mainly occurs in the leaves:leaves:

a.a.stoma - poresstoma - pores

b.b.mesophyll cellsmesophyll cells

StomaMesophyllCell

Chloroplast

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Stomata (stoma)Stomata (stoma)PoresPores in a plant’s cuticle in a plant’s cuticle

through which through which waterwater and and gasesgases are exchanged are exchanged between the plant and the between the plant and the atmosphere.atmosphere.

Guard CellGuard CellCarbon Dioxide (CO2)

Oxygen (O2)

Found on the underside of Found on the underside of leavesleaves

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Mesophyll Cell of LeafMesophyll Cell of Leaf

Cell WallNucleusNucleus

Chloroplast

Central Vacuole

Photosynthesis occurs in these Photosynthesis occurs in these cells!cells!

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ChloroplastChloroplast

OrganelleOrganelle where photosynthesisphotosynthesis takes place.

GranumThylakoid

Stroma

Outer Membrane

Inner Membrane

Thylakoid stacks are connected Thylakoid stacks are connected togethertogether

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ThylakoidThylakoid

Thylakoid Membrane

Thylakoid SpaceGranum

Grana make up the inner Grana make up the inner membranemembrane

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Question:Question:

Why are Why are plants plants green?green?

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Chlorophyll MoleculesChlorophyll Molecules

• Located in the Located in the thylakoid membranesthylakoid membranes• Chlorophyll have Chlorophyll have MgMg++ in the center in the center• Chlorophyll pigments Chlorophyll pigments harvest energy harvest energy

(photons)(photons) by absorbing certain by absorbing certain wavelengths wavelengths (blue-420 nm and red-(blue-420 nm and red-660 nm660 nm are most important) are most important)

• Plants are Plants are greengreen because the because the green green wavelength is reflectedwavelength is reflected, not absorbed, not absorbed.

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Wavelength of Light (nm)Wavelength of Light (nm)

400 500 600 700

Short wave Long wave(more energy) (less energy)

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Absorption of Light by Absorption of Light by ChlorophyllChlorophyll

wavelengthwavelength

Absorption

violet blue green yellow orange red

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Question:Question:

During the fall, During the fall, what causes what causes the leaves to the leaves to

change colors?change colors?

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Fall ColorsFall Colors• In addition to the chlorophyll In addition to the chlorophyll

pigments, there are pigments, there are other other pigmentspigments present present

• During the fall, the During the fall, the green green chlorophyll pigments are chlorophyll pigments are greatly reducedgreatly reduced revealing the revealing the other pigmentsother pigments

• CarotenoidsCarotenoids are pigments that are pigments that are either are either redred, , orangeorange, or , or yellowyellow

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Redox ReactionRedox Reaction

The The transfertransfer of one or more of one or more electronselectrons from one reactant from one reactant to anotherto another

Two types:Two types:

1.1. Oxidation is the Oxidation is the lossloss of e of e--

2.2. Reduction is the Reduction is the gaingain of of ee--

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Oxidation ReactionOxidation Reaction

The The loss of electronsloss of electrons from a from a substance or the substance or the gain of gain of oxygen.oxygen.

glucoseglucose

6CO2 + 6H2O C6H12O6 + 6O2

OxidationOxidation

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Reduction ReactionReduction Reaction

The The gain of electronsgain of electrons to a to a substance or the substance or the loss of loss of oxygen.oxygen.

glucoseglucose

6CO2 + 6H2O C6H12O6 + 6O2

ReductionReduction

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Two Parts of Two Parts of PhotosynthesisPhotosynthesis

Two reactions make up Two reactions make up photosynthesis:photosynthesis:

1.1.Light Reaction or Light Light Reaction or Light Dependent ReactionDependent Reaction - -

Produces energy from solar Produces energy from solar power (photons) in the form power (photons) in the form of ATP and NADPH.of ATP and NADPH.

SUNSUN

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Two Parts of Two Parts of PhotosynthesisPhotosynthesis

2. 2. Calvin Cycle or Light Calvin Cycle or Light Independent Independent ReactionReaction

• Also called Also called Carbon Carbon FixationFixation or or CC33 Fixation Fixation

• Uses energy (Uses energy (ATP and ATP and NADPHNADPH) from light ) from light reaction to make sugar reaction to make sugar (glucose).(glucose).

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Light Reaction (Electron Light Reaction (Electron Flow)Flow)

• Occurs in the Occurs in the Thylakoid Thylakoid membranesmembranes

• During the During the light reactionlight reaction, , there are there are twotwo possible routes possible routes for electron flow:for electron flow:

A.A. Cyclic Electron FlowCyclic Electron Flow

B.B. Noncyclic Electron FlowNoncyclic Electron Flow

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Cyclic Electron FlowCyclic Electron Flow• Occurs in the Occurs in the thylakoidthylakoid

membrane.membrane.• Uses Uses Photosystem I onlyPhotosystem I only• P700P700 reaction center- chlorophyll reaction center- chlorophyll

a a • Uses Electron Transport Chain Uses Electron Transport Chain

(ETC)(ETC)• Generates Generates ATP onlyATP only

ADP + ADP + ATP ATP

P

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Cyclic Electron FlowCyclic Electron Flow

P700

PrimaryElectronAcceptor

e-

e-

e-

e-

ATPATPproducedby ETC

Photosystem I

AccessoryPigments

SUN

Photons

Pigments absorb light energy & excite Pigments absorb light energy & excite e- of Chlorophyll a to produce ATP e- of Chlorophyll a to produce ATP

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Noncyclic Electron FlowNoncyclic Electron Flow• Occurs in the Occurs in the thylakoidthylakoid membrane membrane• Uses Uses Photosystem II Photosystem II and and

Photosystem IPhotosystem I• P680 P680 reaction center reaction center (PSII)(PSII) - -

chlorophyll achlorophyll a• P700P700 reaction center reaction center (PS I)(PS I) - -

chlorophyll achlorophyll a• Uses Electron Transport Chain Uses Electron Transport Chain

(ETC)(ETC)• Generates Generates OO22, ATP and NADPH, ATP and NADPH

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Noncyclic Electron FlowNoncyclic Electron Flow

P700

Photosystem IP680

Photosystem II

PrimaryElectronAcceptor

PrimaryElectronAcceptor

ETC

EnzymeReaction

H2O

1/2O1/2O22 + 2H+

ATPATP

NADPHNADPH

Photon

2e-

2e-

2e-

2e-

2e-

SUN

Photon

HH22O is split in PSII & ATP is made, while the energy carrier O is split in PSII & ATP is made, while the energy carrier NADPH is made in PSINADPH is made in PSI

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Noncyclic Electron FlowNoncyclic Electron Flow

• ADP +ADP + ATPATP• NADPNADP++ + H + H NADPHNADPH• OxygenOxygen comes from the comes from the

splitting of Hsplitting of H22O, not COO, not CO22

HH22O O 1/2 O 1/2 O22 + 2H + 2H++

PP

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ChemiosmosisChemiosmosis

•Powers Powers ATP synthesisATP synthesis•Located in the Located in the thylakoid thylakoid

membranesmembranes•Uses Uses ETETC and C and ATP ATP

synthase (enzyme)synthase (enzyme) to to make ATPmake ATP

•Photophosphorylation:Photophosphorylation: addition of phosphate to addition of phosphate to ADP to make ATPADP to make ATP

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ChemiosmosisChemiosmosisH+ 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)

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Calvin CycleCalvin Cycle• Carbon Fixation Carbon Fixation (light independent (light independent

reaction)reaction)• CC33 plants (80% of plants on earth) plants (80% of plants on earth)• Occurs in the Occurs in the stromastroma• Uses Uses ATP and NADPHATP and NADPH from light from light

reaction as energyreaction as energy• Uses Uses COCO22

• To produce To produce glucoseglucose: it takes : it takes 6 6 turns and uses 18 ATP and 12 turns and uses 18 ATP and 12 NADPH. NADPH.

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ChloroplastChloroplast

GranumThylakoid

STROMA– where Calvin Cycle occursOuter Membrane

Inner Membrane

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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

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Calvin CycleCalvin Cycle

Remember: CRemember: C33 = Calvin Cycle = Calvin Cycle

C3

Glucose

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PhotorespirationPhotorespiration

• Occurs on hot, dry, bright daysOccurs on hot, dry, bright days• Stomates closeStomates close

• Fixation of OFixation of O22 instead of CO instead of CO22

• Produces Produces 2-C molecules 2-C molecules instead of 3-C sugar moleculesinstead of 3-C sugar molecules

• Produces Produces no sugarno sugar molecules molecules or or no ATPno ATP

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PhotorespirationPhotorespiration

Because of photorespiration, Because of photorespiration, plants have special plants have special adaptations to limit the effect adaptations to limit the effect of photorespiration:of photorespiration:

1.1. CC44 plants plants

2.2. CAM plantsCAM plants

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CC44 Plants Plants• Hot, moist Hot, moist

environmentsenvironments• 15% of plants 15% of plants

((grasses, corn, grasses, corn, sugarcane)sugarcane)

• Photosynthesis Photosynthesis occurs in 2 placesoccurs in 2 places

• Light reactionLight reaction - - mesophyll cellsmesophyll cells

• Calvin cycleCalvin cycle - - bundle sheath bundle sheath cellscells

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CC44 Plants Plants

Mesophyll CellMesophyll Cell

CO2

C-C-C

PEP

C-C-C-CMalate-4C sugar

ATP

Bundle Sheath CellBundle Sheath Cell

C-C-C

Pyruvic Acid

C-C-C-C

CO2

C3

Malate

Transported

glucoseVascular Tissue

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CAM PlantsCAM Plants• Hot, dry environmentsHot, dry environments• 5%5% of plants (cactus and ice of plants (cactus and ice

plants)plants)• Stomates closed during dayStomates closed during day• Stomates open during the nightStomates open during the night• Light reaction - occurs during Light reaction - occurs during

the daythe day• Calvin Cycle - occurs when COCalvin Cycle - occurs when CO22

is presentis present

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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

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Question:Question:

Why do CAM Why do CAM plants close plants close

their stomata their stomata during the day?during the day?

Cam plants Cam plants close their close their

stomata in the stomata in the hottest part hottest part of the day to of the day to

conserve conserve waterwater