photosynthesis
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PhotosynthesisPhotosynthesis
PhotosynthesisPhotosynthesisPresentation by:Presentation by:
Mr M DlaminiMr M Dlamini201221083201221083
1
PhotosynthesisPhotosynthesisPhotosynthesis, the biochemical process by which plants capture energy from sunlight and
store it in carbohydrates.
Autotrophic organismsAutotrophic organisms use an inorganic use an inorganic form of carbon, e.g. form of carbon, e.g. carbon dioxidecarbon dioxide, to , to make up complex organic compounds, make up complex organic compounds, with energy from two sources: with energy from two sources:
Rhizobium in root nodules
1) light 2) chemicals
4Photosynthetic Organisms
PhotosynthesisPhotosynthesis
Photosynthesis is more common and Photosynthesis 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.
PhotosynthesisPhotosynthesis
PhotosynthesisPhotosynthesis
Photosynthesis takes place in the green Photosynthesis takes place in the green portions of plantsportions of plantsLeaf of flowering plant contains mesophyll Leaf of flowering plant contains mesophyll tissuetissue
Cells containing chloroplastsCells containing chloroplastsSpecialized to carry on photosynthesisSpecialized to carry on photosynthesis
COCO22 enters leaf through stomata enters leaf through stomataDiffuses into chloroplasts in mesophyll cellsDiffuses into chloroplasts in mesophyll cells In stroma, COIn stroma, CO22 combined with H combined with H22O to form O to form CC66HH1212OO66 (sugar) (sugar)
Energy supplied by lightEnergy supplied by light
6
7Leaves and Photosynthesis
PhotosynthesisPhotosynthesisPhotosynthetic Reactions:Photosynthetic Reactions:OverviewOverview
Light ReactionLight Reaction::Chlorophyll absorbs solar energyChlorophyll absorbs solar energyThis energizes electronsThis energizes electronsElectrons move down Electrons move down electron transport chainelectron transport chain Pumps Pumps HH++ into into thylakoidsthylakoids
Used to make Used to make ATPATP out of out of ADPADP and and NADPHNADPH out out of of NADPNADP
Calvin Cycle ReactionCalvin Cycle ReactionCOCO22 is reduced to a carbohydrate is reduced to a carbohydrate Reduction requires the ATP and NADPH Reduction requires the ATP and NADPH produced aboveproduced above
8
PhotosynthesisPhotosynthesis
Light Dependent ReactionsLight Dependent Reactions
A.A. Light absorptionLight absorption1.1. As chlorophyll absorbs light its electrons As chlorophyll absorbs light its electrons
are raised to a higher energy level by are raised to a higher energy level by photons at certain wavelengthsphotons at certain wavelengths
2.2. The electrons at higher energy levels are The electrons at higher energy levels are said to be said to be excited electronsexcited electrons
3.3. The excited electrons cause the The excited electrons cause the chlorophyll to become photoactivatedchlorophyll to become photoactivated
4.4. Photoactivation is the activation of a Photoactivation is the activation of a particular pigment’s electrons (It is particular pigment’s electrons (It is caused by absorbing energy from caused by absorbing energy from photons.)photons.)
10Photosynthesis Overview
PhotosynthesisPhotosynthesisLight Reactions:Light Reactions:The Noncyclic Electron PathwayThe Noncyclic Electron Pathway
Takes place in thylakoid membraneTakes place in thylakoid membraneUses two photosystems, Uses two photosystems, PS-IPS-I andand PS-IIPS-IIPS II captures light energyPS II captures light energyCauses an electron to be ejected from the Causes an electron to be ejected from the reaction reaction
centercenter ( (chlorophyll chlorophyll 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 thylakoid to concentrate in thylakoid
chamberschambers Which causes Which causes ATP productionATP production
PS I captures light energy and ejects an electronPS I captures light energy and ejects an electron Transferred Transferred permanentlypermanently to a molecule of NADP to a molecule of NADP++
Causes Causes NADPH productionNADPH production
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12Light Reactions:Noncyclic Electron
Pathway
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 solar Begins when PS I complex absorbs solar energyenergy
Electron ejected from reaction centerElectron ejected from reaction centerTravels down electron transport chainTravels down electron transport chainCauses HCauses H++ to concentrate in thylakoid to concentrate in thylakoid chamberschambers
Which causes Which causes ATP productionATP productionElectron returns to PS-I (cyclic)Electron returns to PS-I (cyclic)
Pathway only results in ATP productionPathway only results in ATP production
13
14Light Reactions:Cyclic Electron
Pathway
Chapter715Light-Independent Reactions
NADPH and ATP from light-NADPH and ATP from light-dependent reactions used to power dependent reactions used to power glucose synthesisglucose synthesis
Light not Light not directlydirectly necessary for light- necessary for light-independent reactions if ATP & independent reactions if ATP & NADPH availableNADPH available
Light-independent reactions called Light-independent reactions called the the Calvin-BensonCalvin-Benson CycleCycle or or CC33CycleCycle
Chapter716The C3 Cycle
6 CO6 CO22 used to synthesize 1 glucose used to synthesize 1 glucose (C(C66HH1212OO66))
Carbon dioxide is captured and Carbon dioxide is captured and linked to ribulose bisphosphate linked to ribulose bisphosphate (RuBP)(RuBP)
ATP and NADPH from light ATP and NADPH from light dependent reactions used to power dependent reactions used to power CC33 reactions reactions
PhotosynthesisPhotosynthesisOrganization of theOrganization of theThylakoid 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 space from 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 NADPH to NADPH
ATP synthase complexATP synthase complex:: Has a channel for HHas a channel for H++ flow flow Which drives ATP synthase to join ADP and PWhich drives ATP synthase to join ADP and P ii
17
PhotosynthesisPhotosynthesis
CC33 Cycle Has Three Parts Cycle 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 into molecules are converted into glyceraldehyde 3-Phophate (G3P) glyceraldehyde 3-Phophate (G3P) molecules …molecules …
18Chapter 7
PhotosynthesisPhotosynthesis
CC33 Cycle Has Three Parts Cycle Has Three Parts
3. 3. Regeneration of Ribulose bis-Regeneration of Ribulose bis-phosphate (RuBP)phosphate (RuBP)
10 of 12 G3P molecules converted into 10 of 12 G3P molecules converted into 6 RuBP molecules6 RuBP molecules
2 of 12 G3P molecules used to 2 of 12 G3P molecules used to synthesize 1 glucosesynthesize 1 glucose
ATP energy used for these reactionsATP energy used for these reactions
19Chapter 7
PhotosynthesisPhotosynthesis
A Summary of PhotosynthesisA Summary of Photosynthesis
20Chapter 7
Light-Light-dependent dependent reactions reactions occur in occur in
thylakoidsthylakoids
Light-Light-independent independent reactions (creactions (c33 cycle) occur cycle) occur
in stromain stroma
21Organization of a Thylakoid
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 to Utilizes atmospheric carbon dioxide to produce carbohydrates produce 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
22
PhotosynthesisPhotosynthesisCalvin Cycle Reactions:Calvin Cycle Reactions:Carbon Dioxide FixationCarbon Dioxide Fixation
COCO22 is attached to 5-carbon is attached to 5-carbon RuBP RuBP 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 by Reaction accelerated by RuBPRuBP Carboxylase Carboxylase (Rubisco)(Rubisco)
COCO22 now “fixed” because it is part of a now “fixed” because it is part of a carbohydratecarbohydrate
23
24The Calvin Cycle:
Fixation of CO2
PhotosynthesisPhotosynthesisCalvin Cycle Reactions:Calvin Cycle Reactions:Carbon Dioxide ReductionCarbon Dioxide Reduction
3PG reduced to 3PG reduced to BPGBPG
BPG then reduced to BPG then reduced to G3PG3P
Utilizes NADPH and some ATP produced in Utilizes NADPH and some ATP produced in light reactionslight reactions
25
26The Calvin CycleReduction of CO2
InLineFigurep125
PhotosynthesisPhotosynthesisCalvin Cycle Reactions:Calvin Cycle Reactions:Regeneration of RuBPRegeneration of RuBP
RuBP used in CORuBP used in CO22 fixation must be replaced fixation 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
27
28The Calvin CycleRegeneration of
RuBP
PhotosynthesisPhotosynthesis
Importance of Calvin CycleImportance of Calvin Cycle
G3P (glyceraldehyde-3-phosphate) can be G3P (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
29
PhotosynthesisPhotosynthesis
CC44 Photosynthesis Photosynthesis
In hot, dry climatesIn hot, dry climatesStomata must close to avoid wiltingStomata must close to avoid wiltingCOCO22 decreases and O decreases and O22 increases increasesOO22 starts combining with RuBP instead of CO starts combining with RuBP instead of CO22
PhotorespirationPhotorespiration, a problem solve in C, a problem solve in C44 plants plants
In CIn C44 plants plantsFix COFix CO22 to PEP a C to PEP a C33 molecule moleculeThe result is oxaloacetate, a CThe result is oxaloacetate, a C44 molecule molecule In hot & dry climatesIn hot & dry climates Avoid photorespirationAvoid photorespiration Net productivity about 2-3 times CNet productivity about 2-3 times C33 plants plants
In cool, moist, can’t compete with CIn cool, moist, can’t compete with C33
30
31Chloroplast distribution in
C4 vs. C3 Plants
32CO2 Fixation inC4 vs. C3 Plants
PhotosynthesisPhotosynthesis
CAM PhotosynthesisCAM Photosynthesis
Crassulacean-Acid MetabolismCrassulacean-Acid MetabolismCAM 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 CO molecules release CO22 to Calvin cycle to Calvin cycle
33
34CO2 Fixation in aCAM Plant
Reference list 35
http://www.slideshare.net/201221083/savedfiles?s_title=photosynthesis-29183537&user_login=mazz4
http://www.slideshare.net/201221083/savedfiles?s_title=chapter-7-powerpoint-le&user_login=guest121530
http://www.slideshare.net/201221083/savedfiles?s_title=ap-bio-ch7-power-point&user_login=MrDPMWest
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