photosynthesis: capturing energy photosynthesis: capturing energy chapter 9

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Photosynthesis: Photosynthesis: Capturing Energy Capturing Energy Chapter 9

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Page 1: Photosynthesis: Capturing Energy Photosynthesis: Capturing Energy Chapter 9

Photosynthesis:Photosynthesis:Capturing EnergyCapturing Energy

Chapter 9

Page 2: Photosynthesis: Capturing Energy Photosynthesis: Capturing Energy Chapter 9

Learning Objective 1Learning Objective 1

• What are the physical properties of light?

• What is the relationship between a wavelength of light and its energy?

Page 3: Photosynthesis: Capturing Energy Photosynthesis: Capturing Energy Chapter 9

Electromagnetic SpectrumElectromagnetic Spectrum

Page 4: Photosynthesis: Capturing Energy Photosynthesis: Capturing Energy Chapter 9

Fig. 9-1, p. 192

One wavelength

Longer wavelength

TV and radio waves Red 700 nmMicro- waves

OrangeInfrared Color

spectrum of visible light

600 nm

YellowVisible

X-rays500 nm

Green

BlueGamma

raysViolet 400 nm

Electromagnetic spectrum Shorter wavelength

760 nm

380 nm

UV

Page 5: Photosynthesis: Capturing Energy Photosynthesis: Capturing Energy Chapter 9

LightLight

• Consists of particles (photons) that move as waves

• Photons with shorter wavelengths have more energy than those with longer wavelengths

Page 6: Photosynthesis: Capturing Energy Photosynthesis: Capturing Energy Chapter 9

SunlightSunlight

Page 7: Photosynthesis: Capturing Energy Photosynthesis: Capturing Energy Chapter 9

Fig. 9-2, p. 192

Sun

Sunlight is a mixture of many wavelengths

Page 8: Photosynthesis: Capturing Energy Photosynthesis: Capturing Energy Chapter 9

Light and EnergyLight and Energy

Page 9: Photosynthesis: Capturing Energy Photosynthesis: Capturing Energy Chapter 9

Fig. 9-3, p. 193

Photon Photon is absorbed by an excitable electron that moves into a higher energy level.

Low energy level

ElectronHigh energy level

Either

Electron acceptor molecule

The electron may return to ground level by emitting a less energetic photon.

The electron may be accepted by an electron acceptor molecule.

Or

Page 10: Photosynthesis: Capturing Energy Photosynthesis: Capturing Energy Chapter 9

KEY CONCEPTSKEY CONCEPTS

• Light energy powers photosynthesis, which is essential to plants and most life on Earth

Page 11: Photosynthesis: Capturing Energy Photosynthesis: Capturing Energy Chapter 9

Learning Objective 2Learning Objective 2

• What is the internal structure of a chloroplast?

• How do its components interact and facilitate the process of photosynthesis?

Page 12: Photosynthesis: Capturing Energy Photosynthesis: Capturing Energy Chapter 9

StructuresStructures

• Photosynthesis in plants• occurs in chloroplasts• located in mesophyll cells• inside the leaf

Page 13: Photosynthesis: Capturing Energy Photosynthesis: Capturing Energy Chapter 9

Leaf StructureLeaf Structure

Page 14: Photosynthesis: Capturing Energy Photosynthesis: Capturing Energy Chapter 9

Fig. 9-4a, p. 194

(a) This leaf cross section reveals that the mesophyll is the photosynthetic tissue. CO2 enters the leaf through tiny pores or stomata, and H2O is carried to the mesophyll in veins.

Palisade mesophyll

Vein

Air space

Stoma

Spongy mesophyll

Page 15: Photosynthesis: Capturing Energy Photosynthesis: Capturing Energy Chapter 9

Fig. 9-4b, p. 194

(b) Notice the numerous chloroplasts in this LM of plant cells.

Mesophyll cell

10 μm

Page 16: Photosynthesis: Capturing Energy Photosynthesis: Capturing Energy Chapter 9

Fig. 9-4c, p. 194

Outer membrane

Inner membrane

Stroma

1 μm

Intermembrane space

Thylakoid membrane

(c) In the chloroplast, pigments necessary for the light-capturing reactions of photosynthesis are part of thylakoid membranes, whereas the enzymes for the synthesis of carbohydrate molecules are in the stroma.

Granum (stack of thylakoids)

Thylakoid lumen

Page 17: Photosynthesis: Capturing Energy Photosynthesis: Capturing Energy Chapter 9

ChloroplastsChloroplasts

• Enclosed by a double membrane • inner membrane encloses stroma and

thylakoids

• Thylakoids • enclose thylakoid lumen• arranged in stacks (grana)

Page 18: Photosynthesis: Capturing Energy Photosynthesis: Capturing Energy Chapter 9

Photosynthetic PigmentsPhotosynthetic Pigments

• In thylakoid membranes• chlorophyll a• chlorophyll b • Carotenoids

Page 19: Photosynthesis: Capturing Energy Photosynthesis: Capturing Energy Chapter 9

Fig. 9-5, p. 195

Hydrocarbonside chain

Porphyrin ring(absorbs light)

in chlorophyll bin chlorophyll a

Page 20: Photosynthesis: Capturing Energy Photosynthesis: Capturing Energy Chapter 9

Learning Objective 3Learning Objective 3

• What happens to an electron in a biological molecule such as chlorophyll when a photon of light energy is absorbed?

Page 21: Photosynthesis: Capturing Energy Photosynthesis: Capturing Energy Chapter 9

Energizing ElectronsEnergizing Electrons

• Photons excite photosynthetic pigments• chlorophyll

• Energized electrons• move to electron acceptor compounds

Page 22: Photosynthesis: Capturing Energy Photosynthesis: Capturing Energy Chapter 9

Active WavelengthsActive Wavelengths

• Combined absorption spectra of chlorophylls a and b • action spectrum for photosynthesis

Page 23: Photosynthesis: Capturing Energy Photosynthesis: Capturing Energy Chapter 9

Absorption SpectraAbsorption Spectra

Page 24: Photosynthesis: Capturing Energy Photosynthesis: Capturing Energy Chapter 9

Fig. 9-6a, p. 195

Chlorophyll b

Chlorophyll a

Est

imat

ed a

bso

rpti

on

(%

)

Wavelength (nm)

(a) Chlorophylls a and b absorb light mainly in the blue (422 to 492 nm) and red (647 to 760 nm) regions.

Page 25: Photosynthesis: Capturing Energy Photosynthesis: Capturing Energy Chapter 9

Fig. 9-6b, p. 195

Rel

ativ

e ra

te o

f p

ho

tosy

nth

esis

Wavelength (nm)

(b) The action spectrum of photosynthesis indicates the effectiveness of various wavelengths of light in powering photosynthesis. Many plant species have action spectra for photosynthesis that resemble the generalized action spectrum shown here.

Page 26: Photosynthesis: Capturing Energy Photosynthesis: Capturing Energy Chapter 9

Action SpectrumAction Spectrum

Page 27: Photosynthesis: Capturing Energy Photosynthesis: Capturing Energy Chapter 9

Fig. 9-7a, p. 196

100 μm(a)

Page 28: Photosynthesis: Capturing Energy Photosynthesis: Capturing Energy Chapter 9

Fig. 9-7b, p. 196

Wavelength of light (nm)

Page 29: Photosynthesis: Capturing Energy Photosynthesis: Capturing Energy Chapter 9

Learning Objective 4Learning Objective 4

• Describe photosynthesis as a redox process

Page 30: Photosynthesis: Capturing Energy Photosynthesis: Capturing Energy Chapter 9

PhotosynthesisPhotosynthesis

• Light energy• is converted to chemical energy

(carbohydrates)

• Hydrogens from water• reduce carbon

• Oxygen from water• is oxidized, forming molecular oxygen

Page 31: Photosynthesis: Capturing Energy Photosynthesis: Capturing Energy Chapter 9

Learning Objective 5Learning Objective 5

• What is the difference between light-dependent reactions and carbon fixation reactions of photosynthesis?

Page 32: Photosynthesis: Capturing Energy Photosynthesis: Capturing Energy Chapter 9

Energy for ReactionsEnergy for Reactions

• Light-dependent reactions• light energizes electrons that generate ATP

and NADPH

• Carbon fixation reactions• use energy of ATP and NADPH to form

carbohydrate

Page 33: Photosynthesis: Capturing Energy Photosynthesis: Capturing Energy Chapter 9

PhotosynthesisPhotosynthesis

Page 34: Photosynthesis: Capturing Energy Photosynthesis: Capturing Energy Chapter 9

Fig. 9-8, p. 197

Light-dependent reactions (in thylakoids)

Carbon fixation reactions (in stroma)

Chloroplast

ATP

Light reactions

ADPCalvin cycle

NADPH

NADP+

H2O O2 CO2Carbohydrates

Page 35: Photosynthesis: Capturing Energy Photosynthesis: Capturing Energy Chapter 9

Stepped Art

Fig. 9-8, p. 197

Light-dependent reactions (in thylakoids)

Chloroplast

Carbon fixation reactions (in stroma)

Light reactions

ATP

ADP Calvin cycleNADPH

NADP+

H2O O2CO2 Carbohydrates

Page 36: Photosynthesis: Capturing Energy Photosynthesis: Capturing Energy Chapter 9

Learning Objective 6Learning Objective 6

• How do electrons flow through photosystems I and II in the noncyclic electron transport pathway?

• What products are produced?

• Contrast this with cyclic electron transport

Page 37: Photosynthesis: Capturing Energy Photosynthesis: Capturing Energy Chapter 9

The PhotosystemsThe Photosystems

• Photosystems I and II • photosynthetic units• include chlorophyll, accessory pigments• organized with pigment-binding proteins

into antenna complexes

Page 38: Photosynthesis: Capturing Energy Photosynthesis: Capturing Energy Chapter 9

A PhotosystemA Photosystem

Page 39: Photosynthesis: Capturing Energy Photosynthesis: Capturing Energy Chapter 9

Fig. 9-10, p. 198

Primary electron acceptor

e-

Chloroplast

Photon

Thylakoid membrane

Photosystem

Page 40: Photosynthesis: Capturing Energy Photosynthesis: Capturing Energy Chapter 9

Reaction CentersReaction Centers

• Reaction center of antenna complex• special pair of chlorophyll a molecules • release energized electrons to acceptor

• P700• reaction center for photosystem I

• P680• reaction center for photosystem II

Page 41: Photosynthesis: Capturing Energy Photosynthesis: Capturing Energy Chapter 9

Noncyclic Electron TransportNoncyclic Electron Transport

• Light-dependent reactions• form ATP and NADPH

Page 42: Photosynthesis: Capturing Energy Photosynthesis: Capturing Energy Chapter 9

Noncyclic SystemsNoncyclic Systems

• Electrons in photosystem I• energized by light• pass through electron transport chain • convert NADP+ to NADPH

• Redox reactions • pass energized electrons along ETC• from photosystem II to photosystem I

Page 43: Photosynthesis: Capturing Energy Photosynthesis: Capturing Energy Chapter 9

Noncyclic SystemsNoncyclic Systems

• Electrons given up by P700 (photosystem I) • replaced by electrons from P680

(photosystem II)

• Electrons given up by P680 (photosystem II)• replaced by electrons from photolysis of

H2O (releasing oxygen)

Page 44: Photosynthesis: Capturing Energy Photosynthesis: Capturing Energy Chapter 9

Cyclic Electron TransportCyclic Electron Transport

• Electrons from photosystem I• return to photosystem I

• ATP produced by chemiosmosis

• No NADPH or oxygen generated

Page 45: Photosynthesis: Capturing Energy Photosynthesis: Capturing Energy Chapter 9
Page 46: Photosynthesis: Capturing Energy Photosynthesis: Capturing Energy Chapter 9

Table 9-1, p. 200

Page 47: Photosynthesis: Capturing Energy Photosynthesis: Capturing Energy Chapter 9

KEY CONCEPTSKEY CONCEPTS

• Photosynthesis, which occurs in chloroplasts, is a redox process

Page 48: Photosynthesis: Capturing Energy Photosynthesis: Capturing Energy Chapter 9

Learning Objective 7Learning Objective 7

• Explain how a proton (H+) gradient is established across the thylakoid membrane and how this gradient functions in ATP synthesis

Page 49: Photosynthesis: Capturing Energy Photosynthesis: Capturing Energy Chapter 9

Proton GradientProton Gradient

Page 50: Photosynthesis: Capturing Energy Photosynthesis: Capturing Energy Chapter 9

Fig. 9-12, p. 200

Stroma

Thylakoid lumen

Thylakoid membrane Protons (H+)

Page 51: Photosynthesis: Capturing Energy Photosynthesis: Capturing Energy Chapter 9

PhotophosphorylationPhotophosphorylation

• Photophosphorylation • synthesis of ATP coupled to transport of

electrons energized by photons

• Electron energy pumps protons across thylakoid membrane • energy gradient generates ATP by

chemiosmosis

Page 52: Photosynthesis: Capturing Energy Photosynthesis: Capturing Energy Chapter 9

ATP SynthesisATP Synthesis

• ATP synthase• enzyme complex in thylakoid membrane• protons diffuse through enzyme• phosphorylate ADP to ATP

Page 53: Photosynthesis: Capturing Energy Photosynthesis: Capturing Energy Chapter 9

Electron Transport and Electron Transport and ChemiosmosisChemiosmosis

Page 54: Photosynthesis: Capturing Energy Photosynthesis: Capturing Energy Chapter 9

Fig. 9-13, p. 201

Thylakoid lumen

Thylakoid membrane

PhotosystemII

Photon

Thylakoidmembrane

Plastocyanin

Plastoquinone

Ferredoxin

Cytochromecomplex

Photosystem I

Photon

Ferredoxin-NADP+

reductase

NADPHNADP+

ADP Pi

ATP

ATPsynthase

Page 55: Photosynthesis: Capturing Energy Photosynthesis: Capturing Energy Chapter 9

KEY CONCEPTSKEY CONCEPTS

• Light-dependent reactions convert light energy to the chemical energy of NADPH and ATP

Page 56: Photosynthesis: Capturing Energy Photosynthesis: Capturing Energy Chapter 9

Learning Objective 8Learning Objective 8

• Summarize the three phases of the Calvin cycle, and the roles of ATP and NADPH

Page 57: Photosynthesis: Capturing Energy Photosynthesis: Capturing Energy Chapter 9

Calvin Cycle (CCalvin Cycle (C33 pathway) pathway)

• Carbon fixation reactions

• 3 phases• CO2 uptake phase• Carbon reduction phase• RuBP regeneration phase

Page 58: Photosynthesis: Capturing Energy Photosynthesis: Capturing Energy Chapter 9

COCO22 Uptake Phase Uptake Phase

• Enzyme rubisco • (ribulose bisphosphate carboxylase/

oxygenase)• combines CO2 with ribulose bisphosphate

(RuBP), a five-carbon sugar• forms 3-carbon phosphoglycerate (PGA)

Page 59: Photosynthesis: Capturing Energy Photosynthesis: Capturing Energy Chapter 9

Carbon Reduction PhaseCarbon Reduction Phase

• Energy of ATP and NADPH • convert PGA molecules to glyceraldehyde-

3-phosphate (G3P)

• For each 6 CO2 fixed• 12 G3P are produced• 2 G3P leave cycle to produce 1 glucose

Page 60: Photosynthesis: Capturing Energy Photosynthesis: Capturing Energy Chapter 9

RuBP Regeneration PhaseRuBP Regeneration Phase

• Remaining G3P molecules are modified to regenerate RuBP

Page 61: Photosynthesis: Capturing Energy Photosynthesis: Capturing Energy Chapter 9

The Calvin CycleThe Calvin Cycle

Page 62: Photosynthesis: Capturing Energy Photosynthesis: Capturing Energy Chapter 9

KEY CONCEPTSKEY CONCEPTS

• Carbon fixation reactions incorporate CO2 into organic molecules

Page 63: Photosynthesis: Capturing Energy Photosynthesis: Capturing Energy Chapter 9

Learning Objective 9Learning Objective 9

• How does photorespiration reduce photosynthetic efficiency?

Page 64: Photosynthesis: Capturing Energy Photosynthesis: Capturing Energy Chapter 9

PhotorespirationPhotorespiration

• C3 plants use O2 and generate CO2 • by degrading Calvin cycle intermediates• but do not produce ATP

• On bright, hot, dry days• plants close stomata, conserving water• prevents passage of CO2 into leaf

Page 65: Photosynthesis: Capturing Energy Photosynthesis: Capturing Energy Chapter 9

Learning Objective 10Learning Objective 10

• Compare the C4 and CAM pathways

Page 66: Photosynthesis: Capturing Energy Photosynthesis: Capturing Energy Chapter 9

CC44 Pathway Pathway

• Takes place in mesophyll cells

• Enzyme PEP carboxylase binds CO2

• CO2 fixed in oxaloacetate• converted to malate

• Malate moves into bundle sheath cell• CO2 is removed

• Released CO2 enters Calvin cycle

Page 67: Photosynthesis: Capturing Energy Photosynthesis: Capturing Energy Chapter 9

CC44 and C and C33 Plants Plants

Page 68: Photosynthesis: Capturing Energy Photosynthesis: Capturing Energy Chapter 9

Fig. 9-15a, p. 205

Upper epidermis

Palisade mesophyll

Bundle sheath cells of veins

Spongy mesophyll

Chloroplasts

(a) In C3 plants, the Calvin cycle takes place in the mesophyll cells and the bundle sheath cells are nonphotosynthetic.

Page 69: Photosynthesis: Capturing Energy Photosynthesis: Capturing Energy Chapter 9

Fig. 9-15b, p. 205

Upper epidermis

Bundle sheath cells of veins

Mesophyll

Chloroplasts

(b) In C4 plants, reactions that fix CO2 into four-carbon compounds take place in the mesophyll cells. The four-carbon compounds are transferred from the mesophyll cells to the photosynthetic bundle sheath cells, where the Calvin cycle takes place.

Page 70: Photosynthesis: Capturing Energy Photosynthesis: Capturing Energy Chapter 9

CC4 4 PathwayPathway

Page 71: Photosynthesis: Capturing Energy Photosynthesis: Capturing Energy Chapter 9

Fig. 9-16, p. 206

CO2

Mesophyll cell

Phosphoenol- pyruvate

Oxaloacetate

ADP NADPH

ATP NADP+

Pyruvate

Pyruvate Bundle sheath cellNADP+

CO2

Glucose NADPH

Vein

(4C)(3C)

(3C)Malate (4C)

Malate(3C) (4C)

Page 72: Photosynthesis: Capturing Energy Photosynthesis: Capturing Energy Chapter 9

(CAM) Pathway(CAM) Pathway

• Crassulacean acid metabolism (CAM)• similar to C4 pathway

• PEP carboxylase fixes carbon at night• in mesophyll cells

• Calvin cycle occurs during the day

Page 73: Photosynthesis: Capturing Energy Photosynthesis: Capturing Energy Chapter 9

A CAM PlantA CAM Plant

Page 74: Photosynthesis: Capturing Energy Photosynthesis: Capturing Energy Chapter 9

Learning Objective 11Learning Objective 11

• How do photoautotrophs and chemoheterotrophs differ with respect to their energy and carbon sources?

Page 75: Photosynthesis: Capturing Energy Photosynthesis: Capturing Energy Chapter 9

Energy SourcesEnergy Sources

• Photoautotrophs • use light as energy source• incorporate atmospheric CO2 into pre-

existing carbon skeletons

• Chemoheterotrophs • obtain energy by oxidizing chemicals• obtain carbon from other organisms

Page 76: Photosynthesis: Capturing Energy Photosynthesis: Capturing Energy Chapter 9

KEY CONCEPTSKEY CONCEPTS

• Most photosynthetic organisms are photoautotrophs

Page 77: Photosynthesis: Capturing Energy Photosynthesis: Capturing Energy Chapter 9

Learning Objective 12Learning Objective 12

• What is the importance of photosynthesis to plants and other organisms?

Page 78: Photosynthesis: Capturing Energy Photosynthesis: Capturing Energy Chapter 9

PhotosynthesisPhotosynthesis

• Ultimate source of all chemical energy and organic molecules• available to plants and other organisms

• Replenishes oxygen in the atmosphere• vital to all aerobic organisms

Page 79: Photosynthesis: Capturing Energy Photosynthesis: Capturing Energy Chapter 9

Summary ReactionsSummary Reactions

• Light-dependent reactions (noncyclic electron transport)

12 H2O + 12 NADP+ + 18 ADP + 18 Pi

→ (light energy, chlorophyll) →

6 O2 + 12 NADPH + 18 ATP

Page 80: Photosynthesis: Capturing Energy Photosynthesis: Capturing Energy Chapter 9

Summary ReactionsSummary Reactions

• Carbon fixation reactions (Calvin cycle)

12 NADPH + 18 ATP + 6 CO2 →

C6H12O6 + 12 NADP+ + 18 ADP

+ 18 Pi + 6 H2O

Page 81: Photosynthesis: Capturing Energy Photosynthesis: Capturing Energy Chapter 9

Summary ReactionsSummary Reactions

• Overall equation for photosynthesis

6 CO2 +12 H2O

→ (light energy, chlorophyll) →

C6H12O6 + 6 O2 + 6 H2O

Page 82: Photosynthesis: Capturing Energy Photosynthesis: Capturing Energy Chapter 9

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Calvin-Benson CycleCalvin-Benson Cycle

Page 83: Photosynthesis: Capturing Energy Photosynthesis: Capturing Energy Chapter 9

Sites of PhotosynthesisSites of Photosynthesis

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Page 84: Photosynthesis: Capturing Energy Photosynthesis: Capturing Energy Chapter 9

Wavelengths of LightWavelengths of Light

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Page 85: Photosynthesis: Capturing Energy Photosynthesis: Capturing Energy Chapter 9

Photosynthesis OverviewPhotosynthesis Overview

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