3
Redox ReactionRedox Reaction
The The transfertransfer of one or more of one or more electronselectrons from one reactant from one reactant to anotherto another
Two types:Two types:
1.1. Oxidation is the Oxidation is the lossloss of e of e--
2.2. Reduction is the Reduction is the gaingain of of ee--
4
Oxidation ReactionOxidation Reaction
The The loss of electronsloss of electrons from a from a substance or the substance or the gain of gain of oxygen.oxygen.
glucoseglucose
6CO2 + 6H2O C6H12O6 + 6O2
OxidationOxidation
Carbon Carbon dioxidedioxide WaterWater
OxygenOxygen
5
Reduction ReactionReduction Reaction
The The gain of electronsgain of electrons to a to a substance or the substance or the loss of loss of oxygen.oxygen.
glucoseglucose
6CO2 + 6H2O C6H12O6 + 6O2
ReductionReduction
7
Two Parts of Two Parts of PhotosynthesisPhotosynthesis
Two reactions make up Two reactions make up photosynthesis:photosynthesis:
1.1.Light Reaction or Light Light Reaction or Light Dependent ReactionDependent Reaction - -
Produces energy from solar Produces energy from solar power (photons) in the form power (photons) in the form of ATP and NADPH.of ATP and NADPH.
SUNSUN
8
Light Reaction (Electron Light Reaction (Electron Flow)Flow)
•Occurs in the Occurs in the Thylakoid Thylakoid membranesmembranes
•During the During the light reactionlight reaction, , there are there are twotwo possible routes possible routes for electron flow:for electron flow:
A.A. Cyclic Electron FlowCyclic Electron Flow
B.B. Noncyclic Electron FlowNoncyclic Electron Flow
9
Cyclic Electron FlowCyclic Electron Flow• Occurs in the Occurs in the thylakoidthylakoid
membrane.membrane.• Uses Uses Photosystem I onlyPhotosystem I only• P700P700 reaction center- chlorophyll reaction center- chlorophyll
a a • Uses Electron Transport Chain Uses Electron Transport Chain
(ETC)(ETC)• Generates Generates ATP onlyATP only
ADP + ADP + ATP ATP
P
10
Cyclic Electron FlowCyclic Electron Flow
P700
PrimaryElectronAcceptor
e-
e-
e-
e-
ATPATPproducedby ETC
Photosystem I
AccessoryPigments
SUN
Photons
Pigments absorb light energy & excite Pigments absorb light energy & excite e- of Chlorophyll a to produce ATP e- of Chlorophyll a to produce ATP
11
Noncyclic Electron FlowNoncyclic Electron Flow•Occurs in the Occurs in the thylakoidthylakoid membrane membrane•Uses Uses Photosystem II Photosystem II and and
Photosystem IPhotosystem I•P680 P680 reaction center reaction center (PSII)(PSII) - -
chlorophyll achlorophyll a•P700P700 reaction center reaction center (PS I)(PS I) - -
chlorophyll achlorophyll a•Uses Electron Transport Chain Uses Electron Transport Chain
(ETC)(ETC)•Generates Generates OO22, ATP and NADPH, ATP and NADPH
12
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
HH22O is split in PSII & ATP is made, while the energy carrier O is split in PSII & ATP is made, while the energy carrier NADPH is made in PSINADPH is made in PSI
13
Noncyclic Electron FlowNoncyclic Electron Flow
•ADP +ADP + ATPATP•NADPNADP++ + H + H NADPHNADPH•OxygenOxygen comes from the comes from the
splitting of Hsplitting of H22O, not COO, not CO22
HH22O O 1/2 O 1/2 O22 + 2H + 2H++
PP
14
ChemiosmosisChemiosmosis
•Powers Powers ATP synthesisATP synthesis• Takes place across the Takes place across the
thylakoid membranethylakoid membrane•Uses Uses ETCETC and and ATP synthase ATP synthase
(enzyme)(enzyme)•H+H+ move down their move down their
concentration gradient through concentration gradient through channels of ATP synthasechannels of ATP synthase forming forming ATP from ADPATP from ADP
15
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)
16
ChloroplastChloroplast
GranumThylakoid
STROMA– where Calvin Cycle occursOuter Membrane
Inner Membrane
Thylakoid Membrane– where light reactions occur
17
Two Parts of Two Parts of PhotosynthesisPhotosynthesis
2. 2. Calvin Cycle or Light Calvin Cycle or Light Independent Independent ReactionReaction
•Also called Also called Carbon Carbon FixationFixation or or CC33 Fixation Fixation
•Uses energy (Uses energy (ATP and ATP and NADPHNADPH) from light ) from light reaction to make sugar reaction to make sugar (glucose).(glucose).
18
Calvin CycleCalvin Cycle• Carbon Fixation Carbon Fixation (light independent (light independent
reaction)reaction)• CC33 plants (80% of plants on earth) plants (80% of plants on earth)• Occurs in the Occurs in the stromastroma• Uses Uses ATP and NADPHATP and NADPH from light from light
reaction as energyreaction as energy• Uses Uses COCO22
• To produce To produce glucoseglucose: it takes : it takes 6 6 turns and uses 18 ATP and 12 turns and uses 18 ATP and 12 NADPH. NADPH.
19
Calvin Cycle (CCalvin Cycle (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
21
Stomata (stoma)Stomata (stoma)PoresPores in a plant’s cuticle in a plant’s cuticle
through which through which water vaporwater vapor and and gasesgases (CO(CO22 & O & O22)) are are exchanged between the plant exchanged between the plant and the atmosphere.and the atmosphere.
Guard CellGuard CellCarbon Dioxide (CO2)
Oxygen (O2)
Found on the underside of Found on the underside of leavesleaves
StomStomaa
22
PhotorespirationPhotorespiration
•Occurs on hot, dry, bright daysOccurs on hot, dry, bright days•Stomates closeStomates close
• Fixation of OFixation of O22 instead of CO instead of CO22
•Produces Produces 2-C molecules 2-C molecules instead of 3-C sugar moleculesinstead of 3-C sugar molecules
•Produces Produces no sugarno sugar molecules molecules or or no ATPno ATP
23
PhotorespirationPhotorespiration
Because of photorespiration, Because of photorespiration, plants have special plants have special adaptations to limit the effect adaptations to limit the effect of photorespiration:of photorespiration:
1.1. CC44 plants plants
2.2. CAM plantsCAM plants
24
CC44 Plants Plants• Hot, moist Hot, moist
environmentsenvironments• 15% of plants 15% of plants
((grasses, corn, grasses, corn, sugarcane)sugarcane)
• Photosynthesis Photosynthesis occurs in 2 placesoccurs in 2 places
• Light reactionLight reaction - - mesophyll cellsmesophyll cells
• Calvin cycleCalvin cycle - - bundle sheath bundle sheath cellscells
25
CC44 Plants Plants
Mesophyll CellMesophyll Cell
CO2
C-C-C
PEP
C-C-C-CMalate-4C sugar
ATP
Bundle Sheath CellBundle Sheath Cell
C-C-C
Pyruvic Acid
C-C-C-C
CO2
C3
Malate
Transported
glucoseVascular Tissue
26
CAM PlantsCAM Plants•Hot, dry environmentsHot, dry environments• 5%5% of plants (cactus and ice of plants (cactus and ice
plants)plants)•Stomates closed during dayStomates closed during day•Stomates open during the nightStomates open during the night• Light reaction - occurs during Light reaction - occurs during
the daythe day•Calvin Cycle - occurs when COCalvin Cycle - occurs when CO22
is presentis present
27
CAM PlantsCAM PlantsNight (Stomates Open) Day (Stomates 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
28
Question:Question:
Why do CAM Why do CAM plants close plants close
their stomata their stomata during the day?during the day?