How Cells Acquire How Cells Acquire EnergyEnergyChapter 7Chapter 7

PhotoautotrophsPhotoautotrophs

Carbon source is carbon dioxideCarbon source is carbon dioxide

Energy source is sunlightEnergy source is sunlight

HeterotrophsHeterotrophs

Get carbon and energy by eating autotrophs or one Get carbon and energy by eating autotrophs or one

anotheranother

Carbon and Energy Carbon and Energy SourcesSources

Photoautotrophs Photoautotrophs

Capture sunlight energy and use it to Capture sunlight energy and use it to carry out photosynthesiscarry out photosynthesis

PlantsPlants

Some bacteriaSome bacteria

Many protistansMany protistans

Linked ProcessesLinked Processes

PhotosynthesisPhotosynthesis

Energy-storing Energy-storing pathway pathway

Releases oxygenReleases oxygen

Requires carbon Requires carbon dioxidedioxide

Aerobic RespirationAerobic Respiration

Energy-releasing Energy-releasing pathwaypathway

Requires oxygenRequires oxygen

Releases carbon Releases carbon dioxidedioxide

Chloroplast StructureChloroplast Structure

two outer membranes

inner membrane system(thylakoids connected by channels)

stroma

Figure 7.3d, Page 116

Photosynthesis EquationPhotosynthesis Equation

12H2O + 6CO2 6O2 + C2H12O6 + 6H2O

Water Carbon Dioxide

Oxygen Glucose Water

LIGHT ENERGY

In-text figurePage 115

Where Atoms End UpWhere Atoms End Up

Products 6O2 C6H12O6 6H2O

Reactants 12H2O 6CO2

In-text figurePage 116

Two Stages of Two Stages of PhotosynthesisPhotosynthesis

sunlight water uptake carbon dioxide uptake

ATP

ADP + Pi

NADPH

NADP+

glucoseP

oxygen release

LIGHT-INDEPENDENT

REACTIONS

LIGHT-DEPENDENT REACTIONS

new water

In-text figurePage 117

Electromagnetic Electromagnetic Spectrum Spectrum

Shortest Shortest Gamma raysGamma rays

wavelength wavelength X-raysX-rays

UV radiationUV radiation

Visible lightVisible light

Infrared radiationInfrared radiation

MicrowavesMicrowaves

LongestLongest Radio wavesRadio waves

wavelengthwavelength

Visible Light Visible Light

Wavelengths humans perceive as Wavelengths humans perceive as different colorsdifferent colors

Violet (380 nm) to red (750 nm) Violet (380 nm) to red (750 nm) Longer wavelengths, lower energyLonger wavelengths, lower energy

Figure 7.5aPage 118

PhotonsPhotons

Packets of light energyPackets of light energy

Each type of photon has fixed amount of Each type of photon has fixed amount of energyenergy

Photons having most energy travel as Photons having most energy travel as shortest wavelength (blue-violet light)shortest wavelength (blue-violet light)

PigmentsPigments

Color you see is the wavelengths not Color you see is the wavelengths not absorbed absorbed

Variety of Pigments Variety of Pigments

Chlorophylls Chlorophylls aa and and bb

CarotenoidsCarotenoids

AnthocyaninsAnthocyanins

ChlorophyllsChlorophyllsW

avel

eng

th a

bso

rpti

on

(%

)

Wavelength (nanometers)

chlorophyll b

chlorophyll a

Main pigments in most photoautotrophsMain pigments in most photoautotrophs

Figure 7.6a Page 119 Figure 7.7Page 120

Accessory PigmentsAccessory Pigmentsp

erce

nt

of

wav

elen

gth

s ab

sorb

ed

wavelengths (nanometers)

beta-carotenephycoerythrin (a phycobilin)

Carotenoids, Phycobilins, Anthocyanins

Pigments in Pigments in PhotosynthesisPhotosynthesis

BacteriaBacteria Pigments in plasma membranesPigments in plasma membranes

PlantsPlants Pigments and proteins organized into Pigments and proteins organized into

photosystems that are embedded in photosystems that are embedded in thylakoid membrane systemthylakoid membrane system

Arrangement of Arrangement of PhotosystemsPhotosystems

water-splitting complex thylakoidcompartment

H2O 2H + 1/2O2

P680

acceptor

P700

acceptor

pool of electron carriers stromaPHOTOSYSTEM II

PHOTOSYSTEM I

Figure 7.10Page 121

Pigments absorb light energy, give up ePigments absorb light energy, give up e--, , which enter electron transfer chainswhich enter electron transfer chains

Water molecules split, ATP and NADH Water molecules split, ATP and NADH form, and oxygen is releasedform, and oxygen is released

Pigments that gave up electrons get Pigments that gave up electrons get replacementsreplacements

Light-Dependent Light-Dependent ReactionsReactions

Photosystem Function: Photosystem Function: Harvester Pigments Harvester Pigments

Most pigments in photosystem are Most pigments in photosystem are harvester pigmentsharvester pigments

When excited by light energy, these When excited by light energy, these pigments transfer energy to adjacent pigments transfer energy to adjacent pigment moleculespigment molecules

Each transfer involves energy loss Each transfer involves energy loss

Photosystem Function: Photosystem Function: Reaction Center Reaction Center

This molecule (P700 or P680) is the This molecule (P700 or P680) is the reaction center of a photosystemreaction center of a photosystem

Pigments in a Pigments in a PhotosystemPhotosystem

reaction center

Figure 7.11Page 122

Electron Transfer ChainElectron Transfer Chain

Adjacent to photosystem Adjacent to photosystem

As electrons pass along chain, energy As electrons pass along chain, energy they release is used to produce ATP they release is used to produce ATP

Cyclic Electron FlowCyclic Electron Flow

Electrons Electrons are donated by P700 in photosystem I to are donated by P700 in photosystem I to

acceptor moleculeacceptor molecule

flow through electron transfer chain and flow through electron transfer chain and back to P700back to P700

Electron flow drives ATP formationElectron flow drives ATP formation

No NADPH is formedNo NADPH is formed

Synthesis of ATPSynthesis of ATP(chemiosmotic (chemiosmotic phosphorylation)phosphorylation)

photolysis

H2O

NADP+ NADPH

e–

ATP

ATP SYNTHASE

PHOTOSYSTEM IPHOTOSYSTEM II ADP + Pi

e–

first electron transfer chain

second electron transfer chain

Figure 7.13aPage 123

Chemiosmotic Model Chemiosmotic Model of ATP Formationof ATP Formation

Electrons within the membrane of the Electrons within the membrane of the chloroplast attract H+ protonschloroplast attract H+ protons

The H+ protons are pumped inside the The H+ protons are pumped inside the chloroplast membraneschloroplast membranes

The Protons are allowed to pass out of the The Protons are allowed to pass out of the membrane through the CF1 particle that is rich membrane through the CF1 particle that is rich in ADP + P plus phosphorylating enzymes.in ADP + P plus phosphorylating enzymes.

Chemiosmotic Model for Chemiosmotic Model for ATP FormationATP Formation

ADP + Pi

ATP SYNTHASE

Gradients propel H+ through ATP synthases;ATP forms by phosphate-group transfer

ATP

H+ is shunted across membrane by some components of the first electron transfer chain

PHOTOSYSTEM II

H2Oe–

acceptor

Photolysis in the thylakoid compartment splits water

Figure 7.15Page 124

Synthesis part of Synthesis part of

photosynthesisphotosynthesis

Can proceed in the darkCan proceed in the dark

Take place in the stromaTake place in the stroma

Calvin-Benson cycleCalvin-Benson cycle

Light-Independent Light-Independent ReactionsReactions

Calvin-Benson Cycle Calvin-Benson Cycle

Overall reactantsOverall reactants

Carbon dioxideCarbon dioxide

ATPATP

NADPHNADPH

Overall productsOverall products

GlucoseGlucose

ADPADP

NADPNADP++

Reaction pathway is cyclic and RuBP (ribulose bisphosphate) is regenerated

Calvin- Calvin- Benson Benson Cycle Cycle

CARBON FIXATION

6 CO2 (from the air)

6 6RuBP

PGA

unstable intermediate

6 ADP

6

12

12ATP

ATP

NADPH

10

12PGAL

glucoseP

PGAL2

Pi

12 ADP12 Pi

12 NADP+

12

4 Pi

PGAL

Figure 7.16Page 125

In Calvin-Benson cycle, the first stable In Calvin-Benson cycle, the first stable intermediate is a three-carbon PGAintermediate is a three-carbon PGA

Because the first intermediate has three Because the first intermediate has three carbons, the pathway is called the C3 carbons, the pathway is called the C3 pathwaypathway

The C3 PathwayThe C3 Pathway

Photorespiration in C3 Photorespiration in C3 PlantsPlants

On hot, dry days stomata closeOn hot, dry days stomata close Inside leaf Inside leaf

Oxygen levels riseOxygen levels rise Carbon dioxide levels dropCarbon dioxide levels drop

The plant is in trouble because it does not The plant is in trouble because it does not enough Carbon dioxide to undergo enough Carbon dioxide to undergo photosynthesisphotosynthesis

The plant still needs energy so it taps its own The plant still needs energy so it taps its own store of glucosestore of glucose

C4 Plants C4 Plants

Carbon dioxide is fixed twiceCarbon dioxide is fixed twice

In mesophyll cells, carbon dioxide is fixed to form In mesophyll cells, carbon dioxide is fixed to form

four-carbon oxaloacetate four-carbon oxaloacetate

Oxaloacetate is stored as a crystalOxaloacetate is stored as a crystal

When times get bad (drought conditions), the plant When times get bad (drought conditions), the plant

can now convert the crystalline form of can now convert the crystalline form of

oxaloacetate back to Carbon dioxide and undergo oxaloacetate back to Carbon dioxide and undergo

photosynthesis.photosynthesis.

Summary of Summary of PhotosynthesisPhotosynthesis

Figure 7.21Page 129

light6O2

12H2O

CALVIN-BENSON CYCLE

C6H12O6

(phosphorylated glucose)

NADPHNADP+ATPADP + Pi

PGA PGAL

RuBP

P

6CO2

end product (e.g., sucrose, starch, cellulose)

LIGHT-DEPENDENT REACTIONS

6H2O

LIGHT-INDEPENDENT REACTIONS

Satellite Images Show Satellite Images Show PhotosynthesisPhotosynthesis

 Photosynthetic activity in spring

Atlantic Ocean

Figure 7.20Page 128