PHOTOSYNTHESIPHOTOSYNTHESISS

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PhotosynthesisPhotosynthesisAnAn anabolic, endergonic, carbon anabolic, endergonic, carbon

dioxide (COdioxide (CO22)) requiring requiring process that uses process that uses light energy light energy (photons)(photons) and and water (Hwater (H22O)O) to to produce produce organic organic macromolecules (glucose).macromolecules (glucose).

6CO2 + 6H2O C6H12O6 + 6O2

glucoseglucose

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photonsphotons

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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 Cell

Guard 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.

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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). ATAT

PP

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

• Occurs in the Occurs in the Thylakoid Thylakoid membranesmembranes (inner (inner membrane)membrane)

• During the light reaction, During the light reaction, there are there are two possible two possible routes for electron flowroutes for electron flow

A.A. CyclicCyclic Electron Flow Electron Flow

B.B. NoncyclicNoncyclic Electron Flow Electron Flow

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Cyclic Electron FlowCyclic Electron Flow• Occurs in the Occurs in the thylakoid membranethylakoid membrane• Uses Uses Photosystem IPhotosystem I only only• P700 reactionP700 reaction center- center- chlorophyll chlorophyll

aa • Uses Electron Transport Chain Uses Electron Transport Chain

(ETC)(ETC)• Generates Generates ATPATP only only

ADP + ADP + ATP ATPP

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Cyclic Electron FlowCyclic Electron Flow

P700

PrimaryElectronAcceptor

e-

e-

e-

e-

ATPATPproducedby ETC

Photosystem I

AccessoryPigments

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Photons

Pigments absorb photons, excite electrons, which Pigments absorb photons, excite electrons, which produce ATPproduce ATP

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Noncyclic Electron FlowNoncyclic Electron Flow

• Occurs in the Occurs in the thylakoid membranethylakoid membrane• Uses Uses PS II and PS IPS II and PS I• P680P680 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

NADPHNADPHPhoton

2e-

2e-

2e-

2e-

2e-

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Photon

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B. Noncyclic Electron FlowB. Noncyclic Electron Flow• ADP + ATPATP

• NADP+ + H NADPHNADPH

• Oxygen comes from the Oxygen comes from the splitting of splitting of HH22OO, not , not COCO22

HH22O O 1/2 O2 + 2H+

(Reduced)

P(Reduced)

(Oxidized)

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ChemiosmosisChemiosmosis• Powers ATP synthesisATP synthesis.

• Located in the thylakoid thylakoid membranesmembranes.

• Uses ETC and ATP synthase (enzyme)(enzyme) to make ATP.

• Photophosphorylation:Photophosphorylation: addition of phosphatephosphate to ADPADP to make ATPATP.

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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

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

rxn).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.

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ChloroplastChloroplast

GranumThylakoid

Stroma

Outer 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:Remember: C3 = Calvin CycleC3 = Calvin Cycle

C3

Glucose

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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 3-3-C sugar moleculesC sugar molecules.

• Produces no sugar molecules or no ATP.

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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

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C4 PlantsC4 Plants• Hot, moist environmentsHot, moist environments.

• 15% of plants (grasses, corn, 15% of plants (grasses, corn, sugarcane).sugarcane).

• Divides photosynthesis spatially.Divides photosynthesis spatially.

• Light rxn - mesophyll cells.

• Calvin cycle - bundle sheath cells.

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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

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CAM PlantsCAM Plants

• Hot, dry environmentsHot, dry environments.

• 5% of plants (cactus and ice 5% of plants (cactus and ice plants).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.

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CAM PlantsCAM Plants

Night (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 would CAM Why would CAM plants close plants close their stomates their stomates during the day?during the day?