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PhotosynthesisPhotosynthesis
How Plants Make Food from How Plants Make Food from Sunlight and Low Energy Sunlight and Low Energy
MoleculesMolecules
PhotoautotrophsPhotoautotrophs
PhotoautotrophsPhotoautotrophs
Carbon source is carbon dioxideCarbon source is carbon dioxide
Energy source is sunlightEnergy source is sunlight
HeterotrophsHeterotrophs
Get carbon and energy by eating Get carbon and energy by eating
autotrophs or one anotherautotrophs or one another
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
T.E. Englemann’s T.E. Englemann’s Experiment Experiment
Background Background Certain bacterial cells will move Certain bacterial cells will move
toward places where oxygen toward places where oxygen concentration is highconcentration is high
Photosynthesis produces oxygenPhotosynthesis produces oxygen
T.E. Englemann’s T.E. Englemann’s ExperimentExperiment
HypothesisHypothesis Movement of bacteria can be used to Movement of bacteria can be used to
determine optimal light wavelengths determine optimal light wavelengths for photosynthesis for photosynthesis
T.E. Englemann’s T.E. Englemann’s ExperimentExperiment
MethodMethod Algal strand placed on microscope Algal strand placed on microscope
slide and illuminated by light of slide and illuminated by light of varying wavelengthsvarying wavelengths
Oxygen-requiring bacteria placed on Oxygen-requiring bacteria placed on same slidesame slide
T.E. Englemann’s T.E. Englemann’s ExperimentExperiment
T.E. Englemann’s T.E. Englemann’s ExperimentExperiment
Results Results Bacteria congregated where red and Bacteria congregated where red and violet wavelengths illuminated algaviolet wavelengths illuminated alga
ConclusionConclusionBacteria moved to where algal cells Bacteria moved to where algal cells released more oxygen--areas released more oxygen--areas illuminated by the most effective illuminated by the most effective light for photosynthesislight for photosynthesis
Linked ProcessesLinked Processes
PhotosynthesisPhotosynthesis
Energy-storing Energy-storing pathway pathway
Releases oxygenReleases oxygen
Requires carbon Requires carbon dioxidedioxide
Aerobic Aerobic RespirationRespiration
Energy-releasing Energy-releasing pathwaypathway
Requires oxygenRequires oxygen
Releases carbon Releases carbon dioxidedioxide
Focusing in on the location of photosynthesis in a plantFocusing in on the location of photosynthesis in a plant
Location and structure of chlorophyll molecules in plantsLocation and structure of chlorophyll molecules in plants
Photosynthesis EquationPhotosynthesis Equation
12H2O + 6CO2 6O2 + C6H12O6 + 6H2Owater carbon
dioxideoxygen glucose water
LIGHT ENERGY
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
Continual input of solar energy into Continual input of solar energy into
Earth’s atmosphere Earth’s atmosphere
Almost 1/3 is reflected back into Almost 1/3 is reflected back into
spacespace
Of the energy that reaches Earth’s Of the energy that reaches Earth’s
surface, about 1% is intercepted by surface, about 1% is intercepted by
photoautotrophsphotoautotrophs
Sunlight EnergySunlight Energy
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
PhotonsPhotons
Packets of light energyPackets of light energy
Each type of photon has fixed Each type of photon has fixed amount of energyamount of energy
Photons having most energy travel Photons having most energy travel as shortest wavelength (blue-green as shortest wavelength (blue-green light)light)
PigmentsPigments
Light-absorbing Light-absorbing moleculesmolecules
Absorb some Absorb some wavelengths and wavelengths and transmit otherstransmit others
Color you see are Color you see are the wavelengths the wavelengths NOT absorbed NOT absorbed
Wavelength (nanometers)
chlorophyll b
chlorophyll a
Pigments in Pigments in PhotosynthesisPhotosynthesis
BacteriaBacteria Pigments in plasma membranesPigments in plasma membranes
PlantsPlants Pigments embedded in thylakoid Pigments embedded in thylakoid
membrane systemmembrane system Pigments and proteins organized into Pigments and proteins organized into
photosystemsphotosystems Photosystems located next to electron Photosystems located next to electron
transport systemstransport systems
Pigments in a Pigments in a PhotosystemPhotosystem
reaction center (a specialized chlorophyll a molecule)
Pigments absorb light energy, give Pigments absorb light energy, give up eup e-- which enter electron transport which enter electron transport systemssystems
Water molecules are split, ATP and Water molecules are split, ATP and NADH are formed, and oxygen is NADH are formed, and oxygen is releasedreleased
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
Energy is reduced to level that can be Energy is reduced to level that can be captured by molecule of chlorophyll captured by molecule of chlorophyll aa
This molecule (P700 or P680) is the This molecule (P700 or P680) is the reaction center of a photosystemreaction center of a photosystem
Reaction center accepts energy and Reaction center accepts energy and donates electron to acceptor molecule donates electron to acceptor molecule
Cyclic Electron FlowCyclic Electron Flow
electron acceptor electron transport system
e–
e–
e–
e–
ATP
Electron Transport Electron Transport SystemSystem
Adjacent to photosystem Adjacent to photosystem Acceptor molecule donates electrons Acceptor molecule donates electrons
from reaction centerfrom reaction center
As electrons flow through system, As electrons flow through system, energy they release is used to energy they release is used to produce ATP and, in some cases, produce ATP and, in some cases, NADPHNADPH
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 transport system flow through electron transport system
and back to P700and back to P700
Electron flow drives ATP formationElectron flow drives ATP formation No NADPH is formedNo NADPH is formed
Energy ChangesEnergy ChangesP
ote
nti
al
to t
ran
sfer
en
erg
y (v
oid
s)
H2O 1/2 O2 + 2H+
(PHOTOSYSTEM II)
(PHOTOSYSTEM I)
e–
e–
e–e–
secondtransport
system
NADPHfirst
transport
system
Noncyclic Electron FlowNoncyclic Electron Flow
Two-step pathway for light Two-step pathway for light
absorption and electron excitationabsorption and electron excitation
Uses two photosystems: type I and Uses two photosystems: type I and
type II type II
Produces ATP and NADPHProduces ATP and NADPH
Involves photolysis - splitting of Involves photolysis - splitting of
waterwater
Figure 10.4 An overview of photosynthesis: cooperation of the light reactions Figure 10.4 An overview of photosynthesis: cooperation of the light reactions and the Calvin cycle (Layer 1)and the Calvin cycle (Layer 1)
Figure 10.4 An overview of photosynthesis: cooperation of the light reactions Figure 10.4 An overview of photosynthesis: cooperation of the light reactions and the Calvin cycle (Layer 2)and the Calvin cycle (Layer 2)
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
Melvin CalvinMelvin Calvin
The Calvin cycle (Layer 1)The Calvin cycle (Layer 1)
The Calvin cycle (Layer 2)The Calvin cycle (Layer 2)
The Calvin cycle (Layer 3)The Calvin cycle (Layer 3)
Using the Products of Using the Products of PhotosynthesisPhotosynthesis
Phosphorylated glucose is the Phosphorylated glucose is the building block for:building block for:
sucrosesucrose The most easily transported plant The most easily transported plant
carbohydratecarbohydrate starchstarch
The most common storage formThe most common storage form
In Calvin-Benson cycle, the first In Calvin-Benson cycle, the first stable intermediate is a three-carbon stable intermediate is a three-carbon PGAPGA
Because the first intermediate has Because the first intermediate has three carbons, the pathway is called three carbons, the pathway is called the C3 pathwaythe C3 pathway
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
Rubisco attaches RuBP to oxygen Rubisco attaches RuBP to oxygen instead of carbon dioxideinstead of carbon dioxide
Only one PGAL forms instead of twoOnly one PGAL forms instead of two
C4 Plants C4 Plants
Carbon dioxide is fixed twiceCarbon dioxide is fixed twice In mesophyll cells, carbon dioxide is In mesophyll cells, carbon dioxide is
fixed to form four-carbon oxaloacetate fixed to form four-carbon oxaloacetate
Oxaloacetate is transferred to bundle-Oxaloacetate is transferred to bundle-
sheath cellssheath cells
Carbon dioxide is released and fixed Carbon dioxide is released and fixed
again in Calvin-Benson cycleagain in Calvin-Benson cycle
Figure 10.18 CFigure 10.18 C4 4 leaf anatomy and the C leaf anatomy and the C4 4 pathway pathway
CAM PlantsCAM Plants
Carbon is fixed twice (in same cells)Carbon is fixed twice (in same cells) Night Night
Carbon dioxide is fixed to form organic Carbon dioxide is fixed to form organic acidsacids
DayDay Carbon dioxide is released and fixed in Carbon dioxide is released and fixed in
Calvin-Benson cycleCalvin-Benson cycle
Figure 10.19 CFigure 10.19 C4 4 and CAM photosynthesis comparedand CAM photosynthesis compared
Figure 10.20 A review of photosynthesisFigure 10.20 A review of photosynthesis