PHOTOSYNTHESIS PHOTOSYNTHESIS
Jan 05, 2016
PHOTOSYNTHESISPHOTOSYNTHESIS
PhotosynthesisPhotosynthesis• An anabolicanabolic, , endergonicendergonic, carbon, carbon
dioxide (COdioxide (CO22)) requiring process that uses light energy (photons)light energy (photons) and water (Hwater (H22O)O) to produce organic organic macromolecules (glucose).macromolecules (glucose).
6CO2 + 6H2O C6H12O6 + 6O2
glucoseglucose
SUN
photonsphotons
Question:Question:
• In what types of organisms In what types of organisms does photosynthesis take does photosynthesis take place?place?
•In plants, bacteria, and protists
PlantsPlants
• AutotrophsAutotrophs:: self-producers.
• Location:
1. Leaves
a. stoma
b. mesophyll cells
StomaMesophyllCell
Chloroplast
StomataStomata • PoresPores in a plant’s cuticle through
which waterwater and gasesgases are exchanged between the plant and the atmosphere.
Guard Cell
Guard Cell
Carbon Dioxide (CO2)
Oxygen (O2)
Stomata Regulate Gas Exchange
Leaf Anatomy
ChloroplastChloroplast
• OrganelleOrganelle where photosynthesisphotosynthesis takes place.
GranumThylakoid
Stroma
Outer Membrane
Inner Membrane
• Chloroplasts
–Contain thylakoids and grana
Chloroplast
Mesophyll
5 µm
Outermembrane
Intermembranespace
Innermembrane
Thylakoidspace
Thylakoid
GranumStroma
1 µm
ThylakoidsThylakoids
Thylakoid Membrane
Thylakoid SpaceGranum
Mesophyll CellMesophyll Cell
Cell Wall
Nucleus
Chloroplast
Central Vacuole
QuestionQuestion::
• Why are plants green?Why are plants green?
Chlorophyll MoleculesChlorophyll Molecules• Located in the thylakoid membranesthylakoid membranes.• Chlorophyll have MgMg++ in the center.
• Chlorophyll pigmentsChlorophyll pigments harvest energy (photons) by absorbingabsorbing certain wavelengthswavelengths (blue-420 nmblue-420 nm and red-660 nm are most important).
• PlantsPlants are greengreen because the green wavelengthwavelength is reflectedreflected, not absorbednot absorbed.
Why leaves are green: interaction of light with chloroplasts
Location and Structure of Chlorophyll Molecules in Plants
Wavelength of LightWavelength of Light (nm)(nm)
400 500 600 700
Short wave Long wave(more energy) (less energy)
The Electromagnetic Spectrum
Absorption of ChlorophyllAbsorption of Chlorophyll
wavelengthwavelength
Absorption
violet blue green yellow orange red
Evidence that chloroplast pigments participate in photosynthesis: absorption and action spectra for
photosynthesis in an alga
Question:Question:
• During the fall, what causes the During the fall, what causes the leaves to change colors?leaves to change colors?
Fall ColorsFall Colors• In addition to the chlorophyll
pigments, there are other pigmentspigments present.
• During the fall, the green chlorophyllgreen chlorophyll pigments are greatly reducedgreatly reduced revealing the other pigmentspigments.
• CarotenoidsCarotenoids are pigments that are either redred or yellowyellow.
Redox ReactionRedox Reaction• The transfertransfer of oneone or more more
electronselectrons from one reactantone reactant to anotheranother.
• Two typesTwo types::
1.1. OxidationOxidation
2.2. ReductionReduction
Oxidation ReactionOxidation Reaction
• The lossloss of electronselectrons from a substance.
• Or the gaingain of oxygenoxygen.
glucoseglucose
6CO2 + 6H2O C6H12O6 + 6O2
OxidationOxidation
Reduction ReactionReduction Reaction
• The gaingain of electrons to a substance.
• Or the lossloss of oxygenoxygen.
glucoseglucose
6CO2 + 6H2O C6H12O6 + 6O2
ReductionReduction
Oxidation Oxidation (releases energy) (releases energy)• Combining with OxygenCombining with Oxygen•Loss of ElectronsLoss of Electrons•Loss of HydrogenLoss of Hydrogen
Reduction Reduction (absorbs energy)(absorbs energy)•Separation from OxygenSeparation from Oxygen•Gain of ElectronsGain of Electrons•Gain of HydrogenGain of Hydrogen
RememberRemember::““Leo says Ger”Leo says Ger”
Loss of electrons is oxidation;Loss of electrons is oxidation;Gain of electrons is reduction.Gain of electrons is reduction.
or or ““Oil Rig” Oil Rig”
Oxidation is loss; Reduction is Oxidation is loss; Reduction is gain.gain.
Breakdown of PhotosynthesisBreakdown of Photosynthesis
• Two main parts (reactions).Two main parts (reactions).
1. Light Reaction or1. Light Reaction or
Light Dependent ReactionLight Dependent Reaction
Produces energyenergy from solarsolar powerpower (photons)(photons) in the form of ATPATP and NADPHNADPH.
Breakdown of PhotosynthesisBreakdown of Photosynthesis
2.2. Calvin Cycle orCalvin Cycle or
Light Independent Reaction Light Independent Reaction oror
Carbon Fixation orCarbon Fixation or
CC33 Fixation Fixation
Uses energyenergy (ATP and NADPH)(ATP and NADPH) from light rxnlight rxn to make sugar sugar (glucose).(glucose).
An Overview of Photosynthesis: Cooperation of the Light Reactions and the Calvin Cycle
1. 1. Light ReactionLight Reaction (Electron Flow) (Electron Flow)• Occurs in the thylakoid thylakoid
membranesmembranes• During the light reactionlight reaction, there
are two possibletwo possible routes for electron flowelectron flow.
A.A. Cyclic Electron FlowCyclic Electron Flow
B.B. Noncyclic Electron FlowNoncyclic Electron Flow
A. A. Cyclic Electron FlowCyclic Electron Flow• Occurs in the thylakoid membranethylakoid membrane.
• Uses Photosystem I onlyPhotosystem I only
• P700 reaction center- chlorophyll a
• Uses Electron Transport Chain Electron Transport Chain (ETC)(ETC)
• Generates ATP only
ADP + ATPATPP
How a Photosystem Harvests Light
A. A. Cyclic Electron FlowCyclic Electron Flow
P700
PrimaryElectronAcceptor
e-
e-
e-
e-
ATPATPproducedby ETC
Photosystem I
AccessoryPigments
SUN
Photons
Cyclic Electron Flow
B. B. Noncyclic Electron FlowNoncyclic Electron Flow• Occurs in the thylakoid membranethylakoid membrane
• Uses PS IIPS II and PS IPS I
• P680 rxn center (PSII) - chlorophyll a
• P700 rxn center (PS I) - chlorophyll a
• Uses Electron Transport Chain (ETC)Electron Transport Chain (ETC)
• Generates OGenerates O22, ATP and NADPH, ATP and NADPH
• Produces NADPH, ATP, and oxygen
Figure 10.13Photosystem II
(PS II)
Photosystem-I(PS I)
ATP
NADPH
NADP+
ADP
CALVINCYCLE
CO2H2O
O2 [CH2O] (sugar)
LIGHTREACTIONS
Light
Primaryacceptor
Pq
Cytochromecomplex
PC
e
P680
e–
e–
O2
+
H2O
2 H+
Light
ATP
Primaryacceptor
Fd
ee–
NADP+
reductase
ElectronTransportchain
Electron transport chain
P700
Light
NADPH
NADP+
+ 2 H+
+ H+
1
5
7
2
3
4
6
8
B. B. Noncyclic Electron FlowNoncyclic Electron Flow
P700
Photosystem IP680
Photosystem II
PrimaryElectronAcceptor
PrimaryElectronAcceptor
ETC
EnzymeReaction
H2O
1/2O1/2O22 + 2H+
ATPATP
NADPHNADPH
Photon
2e-
2e-
2e-
2e-
2e-
SUN
Photon
B. B. Noncyclic Electron FlowNoncyclic Electron Flow• ADP + ATPATP
• NADP+ + H NADPHNADPH
• Oxygen comes from the splitting Oxygen comes from the splitting of of HH22OO, not , not COCO22
HH22O O 1/2 O2 + 2H+
(Reduced)
P(Reduced)
(Oxidized)
How Noncyclic Electron Flow During the Light Reactions Generates ATP and NADPH
ChemiosmosisChemiosmosis• Powers ATP synthesisATP synthesis.
• Located in the thylakoid thylakoid membranesmembranes.
• Uses ETC and ATP synthase (enzyme)(enzyme) to make ATP.
• Photophosphorylation:Photophosphorylation: addition of phosphatephosphate to ADPADP to make ATPATP.
ChloroplastChloroplast
GranumThylakoid
Stroma
Outer Membrane
Inner Membrane
ChemiosmosisChemiosmosisH+ H+
ATP Synthase
H+ H+ H+ H+
H+ H+ high Hhigh H++
concentrationconcentration
H+ADP + P ATP
PS II PS IE
TC
low Hlow H++
concentrationconcentration
H+ThylakoidThylakoidSpaceSpace
ThylakoidThylakoid
SUN (Proton Pumping)
The light reactions and chemiosmosis: the organization of the thylakoid membrane
Comparison of chemiosmosis in mitochondria and chloroplasts
Calvin Cycle• Carbon Fixation (light independent Carbon Fixation (light independent
rxn).rxn).
• C3 plants (80% of plants on earth).
• Occurs in the stroma.• Uses ATP and NADPH from light rxn
and also uses CO2 from air.
• To produce glucose: it takes 6 turns and uses 18 ATP and 12 NADPH.
The Calvin Cycle
Calvin CycleCalvin Cycle (C (C33 fixation) fixation)
6CO2
6C-C-C-C-C-C
6C-C-C 6C-C-C
6C-C-C-C-C
12PGA
RuBP
12G3P
(unstable)
6NADPH 6NADPH
6ATP 6ATP
6ATP
C-C-C-C-C-CGlucose
(6C)(36C)
(36C)
(36C)
(30C)
(30C)
(6C)
6C-C-C 6C-C-C
C3
glucose
Calvin CycleCalvin Cycle
• Remember:Remember: C3 = Calvin CycleC3 = Calvin Cycle
C3
Glucose
A Review of Photosynthesis
PhotorespirationPhotorespiration• Occurs on hot, dry, bright dayshot, dry, bright days.
• Stomates close.
• Fixation of O2 instead of CO2.
• Produces 2-C molecules2-C molecules instead of 3-C sugar molecules3-C sugar molecules.
• Produces no sugar molecules or no ATP.
PhotorespirationPhotorespiration• Because of photorespirationBecause of photorespiration:
PlantsPlants have special special adaptationsadaptations to limit the effect of photorespirationphotorespiration.
1.1. C4 plantsC4 plants
2.2. CAM plantsCAM plants
C4 PlantsC4 Plants• Hot, moist environmentsHot, moist environments.
• 15% of plants (grasses, corn, 15% of plants (grasses, corn, sugarcane).sugarcane).
• Divides photosynthesis spatially.Divides photosynthesis spatially.
• Light rxn - mesophyll cells.
• Calvin cycle - bundle sheath cells.
C4 PlantsC4 Plants
Mesophyll CellMesophyll Cell
CO2
C-C-C
PEP
C-C-C-CMalate
ATP
Bundle Sheath CellBundle Sheath Cell
C-C-C
Pyruvic Acid
C-C-C-C
CO2
C3
Malate
Transported
glucoseVascular Tissue
C4 leaf anatomy and the C4 pathway
CAM PlantsCAM Plants
• Hot, dry environmentsHot, dry environments.• 5% of plants (cactus and ice plants).5% of plants (cactus and ice plants).• Stomates Stomates closed during dayclosed during day..• Stomates Stomates open during the nightopen during the night.• Light rxn - occurs during the day.
• Calvin Cycle - occurs when CO2 is present.
CAM PlantsCAM Plants
Night (Stomata Open) Day (Stomata Closed)
Vacuole
C-C-C-CMalate
C-C-C-CMalate Malate
C-C-C-CCO2
CO2
C3
C-C-CPyruvic acid
ATPC-C-CPEP glucose
C4 and CAM Photosynthesis Compared
QuestionQuestion::
• Why would CAM plants Why would CAM plants close their stomata during close their stomata during the day?the day?