PHOTOSYNTHESIPHOTOSYNTHESISS
2
PhotosynthesisPhotosynthesisAnAn anabolic, endergonic, carbon anabolic, endergonic, carbon
dioxide (COdioxide (CO22)) requiring requiring process that uses process that uses light energy light energy (photons)(photons) and and water (Hwater (H22O)O) to to produce produce organic organic macromolecules (glucose).macromolecules (glucose).
6CO2 + 6H2O C6H12O6 + 6O2
glucoseglucose
SUN
photonsphotons
3
Question:Question:
Where does Where does photosynthesiphotosynthesis take place?s take place?
4
PlantsPlants• Autotrophs Autotrophs – produce their own – produce their own
food food (glucose)(glucose)• Process called Process called photosynthesisphotosynthesis• Mainly occurs in the Mainly occurs in the leaves:leaves:
a.a.stoma - poresstoma - pores
b.b.mesophyll cellsmesophyll cells
StomaMesophyllCell
Chloroplast
5
Stomata (stoma)Stomata (stoma)PoresPores in a plant’s cuticle in a plant’s cuticle
through which through which waterwater and and gasesgases are exchanged are exchanged between the plant and the between the plant and the atmosphere.atmosphere.
Guard Cell
Guard CellCarbon Dioxide
(CO2)
Oxygen (O2)
Found on the underside of Found on the underside of leavesleaves
6
Mesophyll Cell of LeafMesophyll Cell of Leaf
Cell WallNucleusNucleus
Chloroplast
Central Vacuole
Photosynthesis occurs in these Photosynthesis occurs in these cells!cells!
7
ChloroplastChloroplast
OrganelleOrganelle where photosynthesisphotosynthesis takes place.
GranumThylakoid
Stroma
Outer Membrane
Inner Membrane
Thylakoid stacks are connected Thylakoid stacks are connected togethertogether
8
ThylakoidThylakoid
Thylakoid Membrane
Thylakoid SpaceGranum
Grana make up the inner Grana make up the inner membranemembrane
9
Question:Question:
Why are Why are plants plants green?green?
10
Chlorophyll MoleculesChlorophyll Molecules
• Located in the Located in the thylakoid membranesthylakoid membranes• Chlorophyll have Chlorophyll have MgMg++ in the center in the center• Chlorophyll pigments Chlorophyll pigments harvest energy harvest energy
(photons)(photons) by absorbing certain by absorbing certain wavelengths wavelengths (blue-420 nm and red-(blue-420 nm and red-660 nm660 nm are most important) are most important)
• Plants are Plants are greengreen because the because the green green wavelength is reflectedwavelength is reflected, not absorbed, not absorbed.
11
Wavelength of Light (nm)Wavelength of Light (nm)
400 500 600 700
Short wave Long wave(more energy) (less energy)
12
Absorption of Light by Absorption of Light by ChlorophyllChlorophyll
wavelengthwavelength
Absorption
violet blue green yellow orange red
13
Question:Question:
During the fall, During the fall, what causes what causes the leaves to the leaves to
change colors?change colors?
14
Fall ColorsFall Colors• In addition to the chlorophyll In addition to the chlorophyll
pigments, there are pigments, there are other other pigmentspigments present present
• During the fall, the During the fall, the green green chlorophyll pigments are chlorophyll pigments are greatly reducedgreatly reduced revealing the revealing the other pigmentsother pigments
• CarotenoidsCarotenoids are pigments that are pigments that are either are either redred, , orangeorange, or , or yellowyellow
15
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--
16
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
17
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
18
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
19
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). ATAT
PP
20
Light Reaction (Electron Light Reaction (Electron Flow)Flow)
• Occurs in the Occurs in the Thylakoid Thylakoid membranesmembranes (inner (inner membrane)membrane)
• During the light reaction, During the light reaction, there are there are two possible two possible routes for electron flowroutes for electron flow
A.A. CyclicCyclic Electron Flow Electron Flow
B.B. NoncyclicNoncyclic Electron Flow Electron Flow
21
Cyclic Electron FlowCyclic Electron Flow• Occurs in the Occurs in the thylakoid membranethylakoid membrane• Uses Uses Photosystem IPhotosystem I only only• P700 reactionP700 reaction center- center- chlorophyll chlorophyll
aa • Uses Electron Transport Chain Uses Electron Transport Chain
(ETC)(ETC)• Generates Generates ATPATP only only
ADP + ADP + ATP ATPP
22
Cyclic Electron FlowCyclic Electron Flow
P700
PrimaryElectronAcceptor
e-
e-
e-
e-
ATPATPproducedby ETC
Photosystem I
AccessoryPigments
SUN
Photons
Pigments absorb photons, excite electrons, which Pigments absorb photons, excite electrons, which produce ATPproduce ATP
23
Noncyclic Electron FlowNoncyclic Electron Flow
• Occurs in the Occurs in the thylakoid membranethylakoid membrane• Uses Uses PS II and PS IPS II and PS I• P680P680 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
24
Noncyclic Electron FlowNoncyclic Electron Flow
P700
Photosystem IP680
Photosystem II
PrimaryElectronAcceptor
PrimaryElectronAcceptor
ETC
EnzymeReaction
H2O
1/2O1/2O22 + 2H+
ATPATP
NADPHNADPHPhoton
2e-
2e-
2e-
2e-
2e-
SUN
Photon
25
B. Noncyclic Electron FlowB. Noncyclic Electron Flow• ADP + ATPATP
• NADP+ + H NADPHNADPH
• Oxygen comes from the Oxygen comes from the splitting of splitting of HH22OO, not , not COCO22
HH22O O 1/2 O2 + 2H+
(Reduced)
P(Reduced)
(Oxidized)
26
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.
27
ChemiosmosisChemiosmosis
H+ 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)
28
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.
• Uses CO2.
• To produce glucose: it takes 6 turns and uses 18 ATP and 12 NADPH.
29
ChloroplastChloroplast
GranumThylakoid
Stroma
Outer Membrane
Inner Membrane
30
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
31
Calvin CycleCalvin Cycle• Remember:Remember: C3 = Calvin CycleC3 = Calvin Cycle
C3
Glucose
32
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 3-3-C sugar moleculesC sugar molecules.
• Produces no sugar molecules or no ATP.
33
PhotorespirationPhotorespiration• Because of photorespirationBecause of photorespiration:
PlantsPlants have special adaptationsspecial adaptations to limit the effect of photorespirationphotorespiration.
1.1. C4 plantsC4 plants
2.2. CAM plantsCAM plants
34
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.
35
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
36
CAM PlantsCAM Plants
• Hot, dry environmentsHot, dry environments.
• 5% of plants (cactus and ice 5% of plants (cactus and ice plants).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.
37
CAM PlantsCAM Plants
Night (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
38
Question:Question:
Why would CAM Why would CAM plants close plants close their stomates their stomates during the day?during the day?