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Structure of Leaves WorksheetStructure of Leaves Worksheet

Section 29-4, p. 599Section 29-4, p. 599

Chapter 6: Chapter 6: PhotosynthesisPhotosynthesis

Section 1: Capturing the Energy in Section 1: Capturing the Energy in LightLight

Q.O.D:Q.O.D:

Briefly describe the two reactions of Briefly describe the two reactions of photosynthesisphotosynthesis

Energy and Life ProcessesEnergy and Life Processes

AutotrophsAutotrophs PhotosynthesisPhotosynthesis ChemosynthesisChemosynthesis

HeterotrophsHeterotrophs Biochemical pathwayBiochemical pathway

PhotosynthesisPhotosynthesis Cellular respirationCellular respiration

The ChloroplastThe Chloroplast

Structure:Structure: Double-membraneDouble-membrane Thylakoid discsThylakoid discs

Thylakoid spaceThylakoid space

GranaGrana StromaStroma Chlorophyll and other Chlorophyll and other

pigmentspigments

The ProcessThe Process

6CO6CO22 + 6H + 6H22O + energy O + energy C C66HH1212O6 + 6OO6 + 6O22

Overview: 2 reactionsOverview: 2 reactions Light ReactionsLight Reactions

Light energy Light energy Chemical energy Chemical energy Creates ATP and NADPH (an energy carrier)Creates ATP and NADPH (an energy carrier)

Calvin Cycle or Dark ReactionCalvin Cycle or Dark Reaction Takes in COTakes in CO22 and produces sugars and produces sugars Uses energy produced in light reactionUses energy produced in light reaction

Light and PigmentsLight and Pigments

LightLight Visible spectrum of colorsVisible spectrum of colors Travels as waves of energyTravels as waves of energy Wavelengths – shorter = more energyWavelengths – shorter = more energy Colors can be reflected, transmitted or absorbedColors can be reflected, transmitted or absorbed

PigmentsPigments Compound that absorbs lightCompound that absorbs light

LE 10-6

Visible light

Gammarays

X-rays UV InfraredMicro-waves

Radiowaves

10–5 nm 10–3 nm 1 nm 103 nm 106 nm1 m

(109 nm) 103 m

380 450 500 550 600 650 700 750 nm

Longer wavelength

Lower energy

Shorter wavelength

Higher energy

Chloroplast PigmentsChloroplast Pigments

Primary pigment:Primary pigment: Chlorophyll aChlorophyll a Accessory pigments:Accessory pigments:

Chlorophyll bChlorophyll b CarotenoidsCarotenoids

CarotenesCarotenes XanthophyllsXanthophylls

LE 10-9a

Chlorophyll a

Chlorophyll b

Carotenoids

Wavelength of light (nm)

Absorption spectra

Ab

sorp

tio

n o

f lig

ht

by

chlo

rop

last

pig

men

ts

400 500 600 700

The Light ReactionThe Light Reaction

Occurs in the thylakoid membranesOccurs in the thylakoid membranes In:In:

Light energyLight energy HH22OO

Out:Out: OO22

ATPATP NADPHNADPH

Stages: Electron transport and ChemiosmosisStages: Electron transport and Chemiosmosis

Electron Transport ChainElectron Transport Chain

PhotosystemsPhotosystems Cluster of pigments + proteins imbedded in Cluster of pigments + proteins imbedded in

membrane of thylakoidmembrane of thylakoid Contain light harvesting complex and reaction Contain light harvesting complex and reaction

centercenter Transfers energy from light to electronsTransfers energy from light to electrons Electrons move down electron transport chainElectrons move down electron transport chain Energy is used to produce ATP and NADPHEnergy is used to produce ATP and NADPH

LE 10-12

Thylakoid

Photon

Light-harvestingcomplexes

Photosystem

Reactioncenter

STROMA

Primary electronacceptor

e–

Transferof energy

Specialchlorophyll amolecules

Pigmentmolecules

THYLAKOID SPACE(INTERIOR OF THYLAKOID)

Th

ylak

oid

mem

bra

ne

Section 1 The Light ReactionsChapter 6Light Reactions in Light Reactions in

PhotosynthesisPhotosynthesis

Steps of Electron TransportSteps of Electron Transport

1: Light energy excites a pair of electrons in 2 1: Light energy excites a pair of electrons in 2 chlorophyll a molecules in photosystem IIchlorophyll a molecules in photosystem II

2: These electrons leave chlorophyll a 2: These electrons leave chlorophyll a (oxidation) and is picked up by the (oxidation) and is picked up by the primary primary electron acceptorelectron acceptor (reduction) (reduction)

3: Electron transport chain – energy from 3: Electron transport chain – energy from electrons used to move H+ from stroma into electrons used to move H+ from stroma into the thylakoidthe thylakoid

4: Light is absorbed by photosystem I, 4: Light is absorbed by photosystem I, exciting a pair of electrons in chlorophyll aexciting a pair of electrons in chlorophyll a Electrons are replaced by electrons from Electrons are replaced by electrons from

photosystem IIphotosystem II 5: These electrons move down another ETC 5: These electrons move down another ETC

and are picked up by NADP+ to form NADPHand are picked up by NADP+ to form NADPH Restoring Photosystem II – replacing lost Restoring Photosystem II – replacing lost

electronselectrons Photolysis: Light breaks up water into 4H+, OPhotolysis: Light breaks up water into 4H+, O22 and and

electronselectrons

Section 1 The Light ReactionsChapter 6Converting Light Energy To Converting Light Energy To

Chemical EnergyChemical Energy

Section 1 The Light ReactionsChapter 6Light Reactions in Light Reactions in

PhotosynthesisPhotosynthesis

Q.O.D:Q.O.D:

What is chemiosmosis? What drives What is chemiosmosis? What drives this process?this process?

Section 1 The Light ReactionsChapter 6Converting Light Energy To Converting Light Energy To Chemical EnergyChemical Energy

ChemiosmosisChemiosmosis

Concentration gradient of H+ ions created by Concentration gradient of H+ ions created by ETC and photolysisETC and photolysis More H+ in thylakoid than in stromaMore H+ in thylakoid than in stroma Creates a potential energyCreates a potential energy

ATP synthase embedded in thylakoid ATP synthase embedded in thylakoid membranemembrane As H+ diffuse back into stroma, they flow through As H+ diffuse back into stroma, they flow through

the ATP synthasethe ATP synthase Movement spins the enzyme, driving the Movement spins the enzyme, driving the

production of ATP from ADPproduction of ATP from ADP

Light Reaction ReviewedLight Reaction Reviewed

Reactants:Reactants: HH22OO LightLight

Products:Products: OO22

ATP and NADPHATP and NADPH Looking forward:Looking forward:

ATP and NADPH provide energy for Calvin cycleATP and NADPH provide energy for Calvin cycle

Section 1 The Light ReactionsChapter 6Summary of Processes in Summary of Processes in Light ReactionsLight Reactions

Chapter 6: Chapter 6: PhotosynthesisPhotosynthesis

Section 2: The Calvin CycleSection 2: The Calvin Cycle

Calvin Cycle: An OverviewCalvin Cycle: An Overview

Light-independentLight-independent Location: The stromaLocation: The stroma In:In:

COCO22

ATPATP NADPHNADPH

Out:Out: CC66HH1212OO66

ADP + PADP + P NADP+NADP+

Steps of the Calvin CycleSteps of the Calvin Cycle

1: Carbon fixation: CO1: Carbon fixation: CO22 is added to RuBP, a 5- is added to RuBP, a 5-

Carbon compoundCarbon compound Enzyme: RubiscoEnzyme: Rubisco Intermediate 6-C compound immediately breaks Intermediate 6-C compound immediately breaks

down into 2 3-C compounds (PGA)down into 2 3-C compounds (PGA) 2: PGA is converted to PGAL2: PGA is converted to PGAL

a: ATP gives a P to each PGAa: ATP gives a P to each PGA b: NADPH gives a proton and energy b: NADPH gives a proton and energy PGAL PGAL

3: RuBP is replenished3: RuBP is replenished Most of the PGAL is converted back to RuBPMost of the PGAL is converted back to RuBP

Allows cycle to continueAllows cycle to continue One PGAL for every 3 COOne PGAL for every 3 CO22 exits cycle to be exits cycle to be

incorporated into sugarincorporated into sugar Results:Results:

For every 3COFor every 3CO22 entering cycle, we get 6 PGAL. entering cycle, we get 6 PGAL. 1 PGAL exits1 PGAL exits 5 PGAL converted back to RuBP5 PGAL converted back to RuBP

Need 6CONeed 6CO22 for 2 PGAL for 2 PGAL sugar sugar

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Calvin Cycle

Chapter 6 Section 2 The Calvin Cycle

The Calvin Cycle

Chapter 6 Section 2 The Calvin Cycle

Ongoing Cycle of Photosynthesis

Alternative PathwaysAlternative Pathways

CC33 plants plants TypicalTypical

Alternative pathwaysAlternative pathways Role of climateRole of climate StomataStomata Gas exchangeGas exchange Gas levelsGas levels

CC44 Plants Plants

CC44 Pathway Pathway Carbon fixation Carbon fixation 4-Carbon compound 4-Carbon compound Source COSource CO22 for Calvin cycle for Calvin cycle Sugar cane, corn, crab grassSugar cane, corn, crab grass

LE 10-19

Photosyntheticcells of C4 plantleaf

Mesophyll cell

Bundle-sheathcell

Vein(vascular tissue)

C4 leaf anatomy

StomaBundle-sheathcell

Pyruvate (3 C)

CO2

Sugar

Vasculartissue

CALVINCYCLE

PEP (3 C)

ATP

ADP

Malate (4 C)

Oxaloacetate (4 C)

The C4 pathway

CO2PEP carboxylase

Mesophyllcell

CAM PlantsCAM Plants

CAM PathwayCAM Pathway Stomata open at nightStomata open at night Fix carbon at night Fix carbon at night organic compounds organic compounds Day, organic compounds release CODay, organic compounds release CO22 to Calvin to Calvin

cyclecycle Cacti, Pineapple – slower growthCacti, Pineapple – slower growth

LE 10-20

Bundle-sheathcell

Mesophyllcell Organic acid

C4

CO2

CO2

CALVINCYCLE

Sugarcane Pineapple

Organic acidsrelease CO2 toCalvin cycle

CO2 incorporatedinto four-carbonorganic acids(carbon fixation)

Organic acid

CAM

CO2

CO2

CALVINCYCLE

Sugar

Spatial separation of steps Temporal separation of steps

Sugar

Day

Night

Rate of PhotosynthesisRate of Photosynthesis

How it’s measuredHow it’s measured OO22

MassMass COCO22

Influenced by:Influenced by: Light intensityLight intensity CO2CO2 TemperatureTemperature

Section 1 The Light ReactionsChapter 6

Overview of PhotosynthesisOverview of Photosynthesis