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
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