Photosynthesis Chapter 07. Photosynthesis 2Outline Flowering Plants Photosynthetic Pigments...

PhotosynthesisChapter 07

2PhotosynthesisPhotosynthesis

OutlineOutline

Flowering PlantsFlowering Plants

Photosynthetic PigmentsPhotosynthetic Pigments

Photosynthesis Photosynthesis Light ReactionsLight Reactions NoncyclicNoncyclic

CyclicCyclicCarbon FixationCarbon Fixation Calvin Cycle ReactionsCalvin Cycle Reactions

C4 C4

CAMCAM


Photosynthetic OrganismsPhotosynthetic Organisms

All life on Earth depends on a star 93 million All life on Earth depends on a star 93 million miles awaymiles away

Provides photosynthesizers with solar energyProvides photosynthesizers with solar energyPhotosynthesis:Photosynthesis:

A process that captures solar energyA process that captures solar energyTransforms solar energy into chemical energyTransforms solar energy into chemical energy Energy ends up stored in a carbohydrateEnergy ends up stored in a carbohydrate

Photosynthesizers produce all food energyPhotosynthesizers produce all food energyOnly 42% of sun’s energy directed towards Only 42% of sun’s energy directed towards Earth reaches surfaceEarth reaches surface

Of this, only 2% is captured by Of this, only 2% is captured by photosynthesizersphotosynthesizers

Of this, only a tiny portion results in biomassOf this, only a tiny portion results in biomass

4Photosynthetic Organisms


PhotosynthesisPhotosynthesis

Photosynthesis takes place in the green Photosynthesis takes place in the green portions of plantsportions of plantsLeaf of flowering plant contains mesophyll Leaf of flowering plant contains mesophyll tissuetissue

Cells containing chloroplastsCells containing chloroplastsSpecialized to carry on photosynthesisSpecialized to carry on photosynthesis

COCO22 enters leaf through stomata enters leaf through stomataDiffuses into chloroplasts in mesophyll cellsDiffuses into chloroplasts in mesophyll cells In stroma, COIn stroma, CO22 combined with H combined with H22O to form O to form CC66HH1212OO66 (sugar) (sugar)

Energy supplied by lightEnergy supplied by light

6Leaves and Photosynthesis



Pigments:Pigments:

Chemicals that absorb some colors in rainbow Chemicals that absorb some colors in rainbow more than othersmore than others

Colors least absorbed reflected/transmitted Colors least absorbed reflected/transmitted mostmost

Absorption SpectraAbsorption Spectra

Graph showing relative absorption of the Graph showing relative absorption of the various colors of the rainbowvarious colors of the rainbow

Chlorophyll is green because it absorbs much Chlorophyll is green because it absorbs much of the reds and blues of white lightof the reds and blues of white light

8Photosynthetic Pigments

9PhotosynthesisPhotosynthesisPhotosynthetic Reactions:Photosynthetic Reactions:OverviewOverview

Light ReactionLight Reaction::Chlorophyll absorbs solar energyChlorophyll absorbs solar energyThis energizes electronsThis energizes electronsElectrons move down Electrons move down electron transport chainelectron transport chain Pumps Pumps HH++ into into thylakoidsthylakoids

Used to make Used to make ATPATP out of out of ADPADP and and NADPHNADPH out out of of NADPNADP

Calvin Cycle ReactionCalvin Cycle ReactionCOCO22 is reduced to a carbohydrate is reduced to a carbohydrate Reduction requires the ATP and NADPH Reduction requires the ATP and NADPH produced aboveproduced above

10Photosynthesis Overview

11PhotosynthesisPhotosynthesisPhotosynthetic Reactions:Photosynthetic Reactions:The Light ReactionsThe Light Reactions

Light reactionsLight reactions consist of two alternate consist of two alternate electron pathways:electron pathways:Noncyclic electron pathwayNoncyclic electron pathwayCyclic electron pathwayCyclic electron pathway

Capture light energy with Capture light energy with photosystemsphotosystemsPigment complex helps collect solar energy Pigment complex helps collect solar energy like an antennalike an antenna

Occur in the Occur in the thylakoid membranesthylakoid membranes

Both pathways produce ATPBoth pathways produce ATP

The noncyclic pathway also produces NADPHThe noncyclic pathway also produces NADPH

12PhotosynthesisPhotosynthesisLight Reactions:Light Reactions:The Noncyclic Electron PathwayThe Noncyclic Electron Pathway

Takes place in thylakoid membraneTakes place in thylakoid membraneUses two photosystems, Uses two photosystems, PS-I PS-I andand PS-II PS-IIPS II captures light energyPS II captures light energyCauses an electron to be ejected from the Causes an electron to be ejected from the reaction reaction

centercenter ( (chlorophyll chlorophyll aa)) Electron travels down electron transport chain to PS IElectron travels down electron transport chain to PS I Replaced with an electron from waterReplaced with an electron from water Which causes HWhich causes H++ to concentrate in thylakoid to concentrate in thylakoid

chamberschambers Which causes Which causes ATP productionATP production

PS I captures light energy and ejects an electronPS I captures light energy and ejects an electron Transferred Transferred permanentlypermanently to a molecule of NADP to a molecule of NADP++

Causes Causes NADPH productionNADPH production

13Light Reactions:Noncyclic Electron

Pathway

14PhotosynthesisPhotosynthesisLight Reactions:Light Reactions:The Cyclic Electron PathwayThe Cyclic Electron Pathway

Uses only photosystem I (PS-I)Uses only photosystem I (PS-I)

Begins when PS I complex absorbs solar Begins when PS I complex absorbs solar energyenergy

Electron ejected from reaction centerElectron ejected from reaction centerTravels down electron transport chainTravels down electron transport chainCauses HCauses H++ to concentrate in thylakoid to concentrate in thylakoid chamberschambers

Which causes Which causes ATP productionATP productionElectron returns to PS-I (cyclic)Electron returns to PS-I (cyclic)

Pathway only results in ATP productionPathway only results in ATP production

15Light Reactions:Cyclic Electron

Pathway

16PhotosynthesisPhotosynthesisOrganization of theOrganization of theThylakoid MembraneThylakoid Membrane

PS II:PS II: Pigment complex and electron-acceptorsPigment complex and electron-acceptors Adjacent to an enzyme that oxidizes waterAdjacent to an enzyme that oxidizes water Oxygen is released as a gasOxygen is released as a gas

Electron transport chain:Electron transport chain: Consists of cytochrome complexesConsists of cytochrome complexes Carries electrons between PS II and PS ICarries electrons between PS II and PS I Also pump HAlso pump H++ from the stroma into thylakoid space from the stroma into thylakoid space

PS I:PS I: Pigment complex and electron acceptorsPigment complex and electron acceptors Adjacent to enzyme that reduces NADPAdjacent to enzyme that reduces NADP++ to NADPH to NADPH

ATP synthase complex:ATP synthase complex: Has a channel for HHas a channel for H++ flow flow Which drives ATP synthase to join ADP and PWhich drives ATP synthase to join ADP and P ii

17Organization of a Thylakoid


ATP ProductionATP Production

Thylakoid space acts as a reservoir for hydrogen Thylakoid space acts as a reservoir for hydrogen ions (Hions (H++))

Each time water is oxidized, two HH++ remain in the thylakoid space

Electrons yield energyUsed to pump HH++ across thylakoid membraneMove from stroma into the thylakoid space

Flow of HH++ back across thylakoid membraneEnergizes ATP synthaseEnzymatically produces ATP from ADP + Pi

This method of producing ATP is called chemiosmosis


Tropical Rain ForestsTropical Rain Forests

Equatorial; Temp>26Equatorial; Temp>26ººC; Rainfall>200cm & C; Rainfall>200cm & uniformuniform

Most plants woody; many vines and Most plants woody; many vines and epiphytes; little or no undergrowthepiphytes; little or no undergrowth

Contribute greatly to COContribute greatly to CO22 uptake, slowing uptake, slowing global warmingglobal warmingDevelopment has reduced them from 14% to Development has reduced them from 14% to 6% of Earth’s surface6% of Earth’s surface

Deforestation adds 20-30% of atmospheric Deforestation adds 20-30% of atmospheric COCO22, but also removes CO, but also removes CO22 sink sink

Increasing temps also reduce productivityIncreasing temps also reduce productivity

ecologyecologyFocusFocus

2020Global Warming andGlobal Warming andTropical Rain ForestsTropical Rain Forestsecologyecology

FocusFocus

21PhotosynthesisPhotosynthesisCalvin Cycle Reactions:Calvin Cycle Reactions:Overview of C3 PhotosynthesisOverview of C3 Photosynthesis

A cyclical series of reactionsA cyclical series of reactions

Utilizes atmospheric carbon dioxide to Utilizes atmospheric carbon dioxide to produce carbohydrates produce carbohydrates

Known as C3 photosynthesisKnown as C3 photosynthesis

Involves three stages: Involves three stages:

Carbon dioxide fixationCarbon dioxide fixation

Carbon dioxide reductionCarbon dioxide reduction

RuBP RegenerationRuBP Regeneration

22PhotosynthesisPhotosynthesisCalvin Cycle Reactions:Calvin Cycle Reactions:Carbon Dioxide FixationCarbon Dioxide Fixation

COCO22 is attached to is attached to 5-carbon 5-carbon RuBPRuBP molecule molecule

Result in a 6-carbon moleculeResult in a 6-carbon molecule

This splits into two 3-carbon molecules (This splits into two 3-carbon molecules (3PG3PG))

Reaction accelerated by Reaction accelerated by RuBP CarboxylaseRuBP Carboxylase ((RubiscoRubisco))

COCO22 now “fixed” because it is part of a now “fixed” because it is part of a carbohydratecarbohydrate

23The Calvin Cycle:

Fixation of CO2

24PhotosynthesisPhotosynthesisCalvin Cycle Reactions:Calvin Cycle Reactions:Carbon Dioxide ReductionCarbon Dioxide Reduction

3PG reduced to 3PG reduced to BPGBPG

BPG then reduced to BPG then reduced to G3PG3P

Utilizes NADPH and some ATP produced in Utilizes NADPH and some ATP produced in light reactionslight reactions

25The Calvin CycleReduction of CO2

InLineFigurep125

26PhotosynthesisPhotosynthesisCalvin Cycle Reactions:Calvin Cycle Reactions:Regeneration of RuBPRegeneration of RuBP

RuBP used in CORuBP used in CO22 fixation must be replaced fixation must be replaced

Every three turns of Calvin Cycle,Every three turns of Calvin Cycle,

Five G3P (a 3-carbon molecule) usedFive G3P (a 3-carbon molecule) used

To remake three RuBP (a 5-carbon molecule)To remake three RuBP (a 5-carbon molecule)

5 X 3 = 3 X 55 X 3 = 3 X 5

27The Calvin CycleRegeneration of

RuBP


Importance of Calvin CycleImportance of Calvin Cycle

G3P (glyceraldehyde-3-phosphate) can be G3P (glyceraldehyde-3-phosphate) can be converted to many other moleculesconverted to many other molecules

The hydrocarbon skeleton of G3P can formThe hydrocarbon skeleton of G3P can form

Fatty acids and glycerol to make plant oilsFatty acids and glycerol to make plant oils

Glucose phosphate (simple sugar)Glucose phosphate (simple sugar)

Fructose (which with glucose = sucrose)Fructose (which with glucose = sucrose)

Starch and celluloseStarch and cellulose

Amino acidsAmino acids


CC44 Photosynthesis Photosynthesis

In hot, dry climatesIn hot, dry climatesStomata must close to avoid wiltingStomata must close to avoid wiltingCOCO22 decreases and O decreases and O22 increases increasesOO22 starts combining with RuBP instead of CO starts combining with RuBP instead of CO22

PhotorespirationPhotorespiration, a problem solve in C, a problem solve in C44 plants plants

In CIn C44 plants plantsFix COFix CO22 to PEP a C to PEP a C33 molecule moleculeThe result is oxaloacetate, a CThe result is oxaloacetate, a C44 molecule molecule In hot & dry climatesIn hot & dry climates Avoid photorespirationAvoid photorespiration Net productivity about 2-3 times CNet productivity about 2-3 times C33 plants plants

In cool, moist, can’t compete with CIn cool, moist, can’t compete with C33

30Chloroplast distribution in

C4 vs. C3 Plants

31CO2 Fixation inC4 vs. C3 Plants


CAM PhotosynthesisCAM Photosynthesis

Crassulacean-Acid MetabolismCrassulacean-Acid MetabolismCAM plants partition carbon fixation by timeCAM plants partition carbon fixation by time During the nightDuring the night

CAM plants fix COCAM plants fix CO22

Forms CForms C44 molecules, molecules, Stored in large vacuolesStored in large vacuoles

During daylightDuring daylight NADPH and ATP are availableNADPH and ATP are available Stomata closed for water conservationStomata closed for water conservation CC44 molecules release CO molecules release CO22 to Calvin cycle to Calvin cycle

33CO2 Fixation in aCAM Plant

34PhotosynthesisPhotosynthesisClimatic Adaptation:Climatic Adaptation:PhotosynthesisPhotosynthesis

Each method of photosynthesis hasEach method of photosynthesis hasadvantages and disadvantagesadvantages and disadvantagesDepends on the climateDepends on the climate

CC44 plants most adapted to: plants most adapted to: high light intensitieshigh light intensities high temperatureshigh temperatures Limited rainfallLimited rainfall

CC33 plants better adapted to plants better adapted to Cold (below 25C)Cold (below 25C) High moistureHigh moisture

CAM plants better adapted to extreme aridityCAM plants better adapted to extreme aridity CAM occurs in 23 families of flowering plantsCAM occurs in 23 families of flowering plants Also found among nonflowering plantsAlso found among nonflowering plants


ReviewReview

Flowering PlantsFlowering Plants


Photosynthesis Photosynthesis Light ReactionsLight Reactions NoncyclicNoncyclic

CyclicCyclicCarbon FixationCarbon Fixation Calvin Cycle ReactionsCalvin Cycle Reactions

C4 C4

CAMCAM

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