3. Autotrophic organismsAutotrophic organisms use anuse an
inorganic form of carbon, e.g.inorganic form of carbon, e.g.
carbon dioxidecarbon dioxide, to make up, to make up
complex organic compounds, withcomplex organic compounds, with
energy from two sources:energy from two sources:
Rhizobium
in root nodules
1) light 2) chemicals
5. PhotosynthesisPhotosynthesis
Photosynthesis is more common andPhotosynthesis is more common and
important because:important because:
1. It provides a source of
complex organic molecules
for heterotrophic
organisms.
2. It releases oxygen for use
by aerobic organisms.
6. PhotosynthesisPhotosynthesis
PhotosynthesisPhotosynthesis
Photosynthesis takes place in the greenPhotosynthesis takes place in the green
portions of plantsportions of plants
Leaf of flowering plant contains mesophyllLeaf of flowering plant contains mesophyll
tissuetissue
Cells containing chloroplastsCells containing chloroplasts
Specialized to carry on photosynthesisSpecialized to carry on photosynthesis
COCO22 enters leaf through stomataenters leaf through stomata
Diffuses into chloroplasts in mesophyll cellsDiffuses into chloroplasts in mesophyll cells
In stroma, COIn stroma, CO22 combined with Hcombined with H22O to formO to form
CC66HH1212OO66 (sugar)(sugar)
Energy supplied by lightEnergy supplied by light
8. PhotosynthesisPhotosynthesisPhotosynthetic Reactions:Photosynthetic Reactions:
OverviewOverview
Light ReactionLight Reaction::
Chlorophyll absorbs solar energyChlorophyll absorbs solar energy
This energizes electronsThis energizes electrons
Electrons move downElectrons move down electron transport chainelectron transport chain
PumpsPumps HH++
intointo thylakoidsthylakoids
Used to makeUsed to make ATPATP out ofout of ADPADP andand NADPHNADPH outout
ofof NADPNADP
Calvin Cycle ReactionCalvin Cycle Reaction
COCO22 is reduced to a carbohydrateis reduced to a carbohydrate
Reduction requires the ATP and NADPHReduction requires the ATP and NADPH
produced aboveproduced above
9. PhotosynthesisPhotosynthesis
Light Dependent ReactionsLight Dependent Reactions
A.A. Light absorptionLight absorption
1.1. As chlorophyll absorbs light its electronsAs chlorophyll absorbs light its electrons
are raised to a higher energy level byare raised to a higher energy level by
photons at certain wavelengthsphotons at certain wavelengths
2.2. The electrons at higher energy levels areThe electrons at higher energy levels are
said to besaid to be excited electronsexcited electrons
3.3. The excited electrons cause theThe excited electrons cause the
chlorophyll to become photoactivatedchlorophyll to become photoactivated
4.4. Photoactivation is the activation of aPhotoactivation is the activation of a
particular pigment’s electrons (It isparticular pigment’s electrons (It is
caused by absorbing energy fromcaused by absorbing energy from
photons.)photons.)
11. PhotosynthesisPhotosynthesisLight Reactions:Light Reactions:
The Noncyclic Electron PathwayThe Noncyclic Electron Pathway
Takes place in thylakoid membraneTakes place in thylakoid membrane
Uses two photosystems,Uses two photosystems, PS-IPS-I andand PS-IIPS-II
PS II captures light energyPS II captures light energy
Causes an electron to be ejected from theCauses an electron to be ejected from the reactionreaction
centercenter ((chlorophyllchlorophyll aa))
Electron travels down electron transport chain to PS IElectron travels down electron transport chain to PS I
Replaced with an electron from waterReplaced with an electron from water
Which causes HWhich causes H++
to concentrate in thylakoidto concentrate in thylakoid
chamberschambers
Which causesWhich causes ATP productionATP production
PS I captures light energy and ejects an electronPS I captures light energy and ejects an electron
TransferredTransferred permanentlypermanently to a molecule of NADPto a molecule of NADP++
CausesCauses NADPH productionNADPH production
13. PhotosynthesisPhotosynthesisLight Reactions:Light Reactions:
The Cyclic Electron PathwayThe Cyclic Electron Pathway
Uses only photosystem I (PS-I)Uses only photosystem I (PS-I)
Begins when PS I complex absorbs solarBegins when PS I complex absorbs solar
energyenergy
Electron ejected from reaction centerElectron ejected from reaction center
Travels down electron transport chainTravels down electron transport chain
Causes HCauses H++
to concentrate in thylakoidto concentrate in thylakoid
chamberschambers
Which causesWhich causes ATP productionATP production
Electron returns to PS-I (cyclic)Electron returns to PS-I (cyclic)
Pathway only results in ATP productionPathway only results in ATP production
15. Chapte15Light-Independent Reactions
NADPH and ATP from light-NADPH and ATP from light-
dependent reactions used to powerdependent reactions used to power
glucose synthesisglucose synthesis
Light notLight not directlydirectly necessary for light-necessary for light-
independent reactions if ATP &independent reactions if ATP &
NADPH availableNADPH available
Light-independent reactions calledLight-independent reactions called
thethe Calvin-BensonCalvin-Benson CycleCycle oror CC33 CycleCycle
16. Chapte16The C3 Cycle
6 CO6 CO22 used to synthesize 1 glucoseused to synthesize 1 glucose
(C(C66HH1212OO66))
Carbon dioxide is captured andCarbon dioxide is captured and
linked to ribulose bisphosphatelinked to ribulose bisphosphate
(RuBP)(RuBP)
ATP and NADPH from lightATP and NADPH from light
dependent reactions used to powerdependent reactions used to power
CC33 reactionsreactions
17. PhotosynthesisPhotosynthesisOrganization of theOrganization of the
Thylakoid MembraneThylakoid Membrane
PS IIPS II::
Pigment complex and electron-acceptorsPigment complex and electron-acceptors
Adjacent to an enzyme that oxidizes waterAdjacent to an enzyme that oxidizes water
Oxygen is released as a gasOxygen is released as a gas
Electron transport chainElectron transport chain::
Consists of cytochrome complexesConsists of cytochrome complexes
Carries electrons between PS II and PS ICarries electrons between PS II and PS I
Also pump HAlso pump H++
from the stroma into thylakoid spacefrom the stroma into thylakoid space
PS IPS I::
Pigment complex and electron acceptorsPigment complex and electron acceptors
Adjacent to enzyme that reduces NADPAdjacent to enzyme that reduces NADP++
to NADPHto NADPH
ATP synthase complexATP synthase complex::
Has a channel for HHas a channel for H++
flowflow
Which drives ATP synthase to join ADP and PWhich drives ATP synthase to join ADP and Pii
18. PhotosynthesisPhotosynthesis
CC33 Cycle Has Three PartsCycle Has Three Parts
2.2. Synthesis of Glyceraldehyde 3-Synthesis of Glyceraldehyde 3-
Phosphate (G3P)Phosphate (G3P)
Energy is donated by ATP and NADPHEnergy is donated by ATP and NADPH
Phosphoglyceric acid (PGA)Phosphoglyceric acid (PGA)
molecules are converted intomolecules are converted into
glyceraldehyde 3-Phophate (G3P)glyceraldehyde 3-Phophate (G3P)
molecules …molecules …
18Ch
ap
ter
7
19. PhotosynthesisPhotosynthesis
CC33 Cycle Has Three PartsCycle Has Three Parts
3.3. Regeneration of Ribulose bis-Regeneration of Ribulose bis-
phosphate (RuBP)phosphate (RuBP)
10 of 12 G3P molecules converted into10 of 12 G3P molecules converted into
6 RuBP molecules6 RuBP molecules
2 of 12 G3P molecules used to2 of 12 G3P molecules used to
synthesize 1 glucosesynthesize 1 glucose
ATP energy used for these reactionsATP energy used for these reactions
19Ch
ap
ter
7
20. PhotosynthesisPhotosynthesis
A Summary of PhotosynthesisA Summary of Photosynthesis
20Ch
ap
ter
7
Light-Light-
dependentdependent
reactionsreactions
occur inoccur in
thylakoidsthylakoids
Light-Light-
independentindependent
reactions (creactions (c33
cycle) occurcycle) occur
in stromain stroma
22. PhotosynthesisPhotosynthesisCalvin Cycle Reactions:Calvin Cycle Reactions:
Overview of C3 PhotosynthesisOverview of C3 Photosynthesis
A cyclical series of reactionsA cyclical series of reactions
Utilizes atmospheric carbon dioxide toUtilizes atmospheric carbon dioxide to
produce carbohydratesproduce carbohydrates
Known as C3 photosynthesisKnown as C3 photosynthesis
Involves three stages:Involves three stages:
Carbon dioxide fixationCarbon dioxide fixation
Carbon dioxide reductionCarbon dioxide reduction
RuBP RegenerationRuBP Regeneration
23. PhotosynthesisPhotosynthesisCalvin Cycle Reactions:Calvin Cycle Reactions:
Carbon Dioxide FixationCarbon Dioxide Fixation
COCO22 is attached to 5-carbonis attached to 5-carbon RuBPRuBP moleculemolecule
Result in a 6-carbon moleculeResult in a 6-carbon molecule
This splits into two 3-carbon molecules (This splits into two 3-carbon molecules (3PG3PG))
Reaction accelerated byReaction accelerated by RuBPRuBP CarboxylaseCarboxylase
(Rubisco)(Rubisco)
COCO22 now “fixed” because it is part of anow “fixed” because it is part of a
carbohydratecarbohydrate
25. PhotosynthesisPhotosynthesisCalvin Cycle Reactions:Calvin Cycle Reactions:
Carbon Dioxide ReductionCarbon Dioxide Reduction
3PG reduced to3PG reduced to BPGBPG
BPG then reduced toBPG then reduced to G3PG3P
Utilizes NADPH and some ATP produced inUtilizes NADPH and some ATP produced in
light reactionslight reactions
27. PhotosynthesisPhotosynthesisCalvin Cycle Reactions:Calvin Cycle Reactions:
Regeneration of RuBPRegeneration of RuBP
RuBP used in CORuBP used in CO22 fixation must be replacedfixation must be replaced
Every three turns of Calvin Cycle,Every three turns of Calvin Cycle,
Five G3P (a 3-carbon molecule) usedFive G3P (a 3-carbon molecule) used
To remake three RuBP (a 5-carbon molecule)To remake three RuBP (a 5-carbon molecule)
5 X 3 = 3 X 55 X 3 = 3 X 5
29. PhotosynthesisPhotosynthesis
Importance of Calvin CycleImportance of Calvin Cycle
G3P (glyceraldehyde-3-phosphate) can beG3P (glyceraldehyde-3-phosphate) can be
converted to many other moleculesconverted to many other molecules
The hydrocarbon skeleton of G3P can formThe hydrocarbon skeleton of G3P can form
Fatty acids and glycerol to make plant oilsFatty acids and glycerol to make plant oils
Glucose phosphate (simple sugar)Glucose phosphate (simple sugar)
Fructose (which with glucose = sucrose)Fructose (which with glucose = sucrose)
Starch and celluloseStarch and cellulose
Amino acidsAmino acids
30. PhotosynthesisPhotosynthesis
CC44 PhotosynthesisPhotosynthesis
In hot, dry climatesIn hot, dry climates
Stomata must close to avoid wiltingStomata must close to avoid wilting
COCO22 decreases and Odecreases and O22 increasesincreases
OO22 starts combining with RuBP instead of COstarts combining with RuBP instead of CO22
PhotorespirationPhotorespiration, a problem solve in C, a problem solve in C44 plantsplants
In CIn C44 plantsplants
Fix COFix CO22 to PEP a Cto PEP a C33 moleculemolecule
The result is oxaloacetate, a CThe result is oxaloacetate, a C44 moleculemolecule
In hot & dry climatesIn hot & dry climates
Avoid photorespirationAvoid photorespiration
Net productivity about 2-3 times CNet productivity about 2-3 times C33 plantsplants
In cool, moist, can’t compete with CIn cool, moist, can’t compete with C
33. PhotosynthesisPhotosynthesis
CAM PhotosynthesisCAM Photosynthesis
Crassulacean-Acid MetabolismCrassulacean-Acid Metabolism
CAM plants partition carbon fixation by timeCAM plants partition carbon fixation by time
During the nightDuring the night
CAM plants fix COCAM plants fix CO22
Forms CForms C44 molecules,molecules,
Stored in large vacuolesStored in large vacuoles
During daylightDuring daylight
NADPH and ATP are availableNADPH and ATP are available
Stomata closed for water conservationStomata closed for water conservation
CC44 molecules release COmolecules release CO22 to Calvin cycleto Calvin cycle
