Post on 14-Jan-2016
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Chapter 6 - Chapter 6 - PhotosynthesisPhotosynthesis
6-1: The Light Reactions6-1: The Light Reactions 6-2: The Calvin Cycle6-2: The Calvin Cycle
6-1: The Light Reactions6-1: The Light Reactions
All organisms use All organisms use ENERGYENERGY to carry out to carry out life processeslife processes
The energy comes directly or indirectly The energy comes directly or indirectly from the from the SUNSUN
Obtaining EnergyObtaining Energy Organisms are classified by how they get Organisms are classified by how they get
energyenergy AutotrophsAutotrophs
Organisms that use energy from sunlight or Organisms that use energy from sunlight or from chemical bonds in inorganic from chemical bonds in inorganic substances to make organic substancessubstances to make organic substances
Use the process of Use the process of photosynthesisphotosynthesis Convert light energy (sun) to chemical energy Convert light energy (sun) to chemical energy
(carbohydrates)(carbohydrates) Examples: Trees, algaeExamples: Trees, algae
Obtaining EnergyObtaining Energy HeterotrophsHeterotrophs
Animals or other organisms that must get Animals or other organisms that must get energy from energy from foodfood, not the sun or inorganic , not the sun or inorganic substancessubstances
Examples:Examples: CaterpillarsCaterpillars BirdsBirds HumansHumans
Biochemical PathwayBiochemical Pathway A series of linked A series of linked
reactions where the reactions where the productsproducts of the 1 of the 1stst reaction are the reaction are the reactantsreactants for the next for the next reactionreaction
PhotosynthesisPhotosynthesis is a is a biochemical pathway biochemical pathway with with Cellular Cellular RespirationRespiration
Overview of Overview of PhotosynthesisPhotosynthesis
PhotosynthesisPhotosynthesis produces organic produces organic compounds from compounds from COCO22 + + HH22OO
Oxygen and some organic compounds Oxygen and some organic compounds are used in a process known as are used in a process known as Cellular Cellular RespirationRespiration, which produces , which produces COCO22 + + HH22OO
Products of Products of PhotosynthesisPhotosynthesis are reactants are reactants in in Cellular RespirationCellular Respiration
Products of Products of Cellular Respiration Cellular Respiration are are reactants in reactants in PhotosynthesisPhotosynthesis
Photo./C.R. CyclePhoto./C.R. Cycle
Two Stages of PhotosynthesisTwo Stages of Photosynthesis
LightLight ReactionsReactions Light energy is absorbed and converted + Light energy is absorbed and converted +
stored to chemical energy (stored to chemical energy (ATPATP + + NADPHNADPH))
CalvinCalvin CycleCycle Organic compounds are made using Organic compounds are made using COCO22, ,
ATPATP, + , + NADPHNADPH
Biochemical EquationsBiochemical Equations
Photosynthetic EquationPhotosynthetic Equation 66 COCO22 + + 66 HH22OO + + nrgnrg 11 C C66HH1212OO66 + + 66 O O22
Cellular Respiration EquationCellular Respiration Equation 11 C C66HH1212OO6 6 + + 66 O O22 66 COCO22 + + 66 HH22OO + + nrgnrg
Capturing Light EnergyCapturing Light Energy LightLight ReactionsReactions – 1– 1stst rxns in rxns in
PhotosynthesisPhotosynthesis Begins with the absorption of Begins with the absorption of
lightlight Occurs in the Occurs in the chloroplastschloroplasts
Structure:Structure: Surrounded by double membraneSurrounded by double membrane Thylakoids – flattened sacs (inner Thylakoids – flattened sacs (inner
membrane)membrane) Grana – stacks of thylakoidsGrana – stacks of thylakoids Stroma – fluid surrounding granaStroma – fluid surrounding grana
Light travels from the Sun to Light travels from the Sun to Earth in waves of energyEarth in waves of energy ROYGBIVROYGBIV
When white light hits an When white light hits an object, its component colors object, its component colors can be:can be: ReflectedReflected TransmittedTransmitted AbsorbedAbsorbed
LIGHT & PIGMENTSLIGHT & PIGMENTS
LIGHT & PIGMENTSLIGHT & PIGMENTS If an object contains a If an object contains a pigmentpigment
((compound that absorbs lightcompound that absorbs light), the ), the colors will react differentlycolors will react differently
The pigments will absorb certain colors, The pigments will absorb certain colors, removing it from the visible spectrumremoving it from the visible spectrum
Chloroplast PigmentsChloroplast Pigments CHLOROPHYLLSCHLOROPHYLLS
Most important pigments in PhotosynthesisMost important pigments in Photosynthesis
Chlorophyll aChlorophyll a Absorbs more Absorbs more redred light; less light; less blueblue light light Involved directly in the Involved directly in the Light RxnsLight Rxns
Chlorophyll bChlorophyll b Absorbs more Absorbs more blueblue light; less light; less redred light light An An accessory pigment accessory pigment – helps capture light for – helps capture light for
chlorophyll a chlorophyll a moleculesmolecules
**ChlorophyllChlorophyll does not absorb any does not absorb any greengreen light therefore most plants appear light therefore most plants appear greengreen in in color*color*
ChlorophyllsChlorophylls CarotenoidsCarotenoids
Other pigments found in thylakoid Other pigments found in thylakoid membrane such as yellow, brown, membrane such as yellow, brown, + orange+ orange
Acts as anActs as an accessory pigment accessory pigment to help to help capture light for capture light for chlorophyll achlorophyll a Most abundant in Most abundant in
nonphotosynthetic plant parts:nonphotosynthetic plant parts:
FruitsFruits FlowersFlowers
Most of these colors can be seen in Most of these colors can be seen in leaves when leaves when chlorophyllschlorophylls break break down in the falldown in the fall
Absorption SpectraAbsorption Spectra
Converting Light Energy to Converting Light Energy to ChemicalChemical EnergyEnergy
Once the pigments capture the light energy, it must get Once the pigments capture the light energy, it must get convertedconverted into chemical energy into chemical energy
The energy is temporarily stored in The energy is temporarily stored in ATPATP + + NADPHNADPH; ; OO22 is is
given off given off
(it’s importance will be discussed in Ch. 7)(it’s importance will be discussed in Ch. 7)
Converting Light Energy to Converting Light Energy to ChemicalChemical EnergyEnergy
Photosystems (I+II)Photosystems (I+II) Groups of chlorophyll + carotenoid pigments Groups of chlorophyll + carotenoid pigments
embedded in the thylakoid membraneembedded in the thylakoid membrane Trying to capture as much light as possibleTrying to capture as much light as possible
Light reactions begin when Light reactions begin when accessory accessory pigments pigments absorb light energy from the sunabsorb light energy from the sun
The captured energy must find its way to a The captured energy must find its way to a specificspecific pairpair of of chlorophyll a chlorophyll a molecules for molecules for photosynthesis to beginphotosynthesis to begin
Two Stages of the Light Two Stages of the Light ReactionsReactions
Electron Transport ChainElectron Transport Chain ChemiosmosisChemiosmosis
Electron Transport Chain Electron Transport Chain (5 Steps)(5 Steps)1.1. Light energy forces Light energy forces electronselectrons to enter a higher to enter a higher
energy level in two energy level in two chlorophyll achlorophyll a molecules of molecules of PSIIPSII (“ (“excited electronsexcited electrons”)”)
Energy allows Energy allows electronselectrons to leave to leave chlorophyll achlorophyll a moleculesmolecules
Chlorophyll a Chlorophyll a molecules have been oxidizedmolecules have been oxidized REDOX must occur!REDOX must occur!
2.2. The acceptor of the The acceptor of the electronselectrons from from chlorophyll chlorophyll aa is a molecule in the thylakoid membrane is a molecule in the thylakoid membrane called the called the primary electron acceptorprimary electron acceptor
Electron Transport Chain Electron Transport Chain (5 Steps)(5 Steps)
3.3. The The primary electron acceptor primary electron acceptor then donates then donates the electrons to the first the electrons to the first ETCETC
A series of molecules that as they pass the A series of molecules that as they pass the electronselectrons from one to another, cause the movement of from one to another, cause the movement of protonsprotons ((HH++) into the thylakoid) into the thylakoid
4.4. Light is absorbed by Light is absorbed by PSIPSI causing causing electronselectrons to to become excited. become excited. Chlorophyll a Chlorophyll a loses those loses those electronselectrons to another to another primary electron primary electron acceptoracceptor, which then donates them to a , which then donates them to a second second ETCETC
Electron Transport Chain Electron Transport Chain (5 Steps)(5 Steps)
5.5. As the electrons make it to the end of the As the electrons make it to the end of the second second ETCETC, they are combined with a proton , they are combined with a proton and NADPand NADP++
ee-- + + HH++ + NADP+ NADP++ = = NADPHNADPH
Replacing Electrons in Light Replacing Electrons in Light ReactionsReactions
In order to keep the In order to keep the ETCETC going, going, waterwater is split is split to provide to provide PSII PSII with with electronselectrons
As As waterwater splits, it releases splits, it releases OO22 molecules to the molecules to the
environment environment It also helps to build up a concentration It also helps to build up a concentration
gradient of gradient of protonsprotons ((HH++) inside the thylakoid) inside the thylakoid The The purposepurpose of the of the ETCETC is to make: is to make:
NADPHNADPH
Restoring PSII (cont.)Restoring PSII (cont.)
For every 2 For every 2 waterwater molecules that are molecules that are split, 4 split, 4 ee-- are available for are available for PSIIPSII
ETC REVIEWETC REVIEW
After the ETCs, Chemiosmosis After the ETCs, Chemiosmosis takes placetakes place
ATP is main energy currency of cellsATP is main energy currency of cells
ChemiosmosisChemiosmosis – synthesis of – synthesis of ATPATP Relies on concentration gradient of Relies on concentration gradient of protonsprotons
((HH++) across thylakoid membrane ) across thylakoid membrane Where does Where does HH++ come from?come from?
Splitting of Splitting of waterwater PumpedPumped in from stroma to interior of in from stroma to interior of
thylakoidthylakoid Known as Known as Proton Pump Proton Pump (needs (needs nrgnrg to work) to work)
Proton pumpProton pump
Chemiosmosis cont.Chemiosmosis cont. ATP synthase ATP synthase – –
an enzyme that catalyzes the synthesis of an enzyme that catalyzes the synthesis of ATP from ADP + PATP from ADP + Pii
Converts potential energy (Converts potential energy (protonsprotons) into ) into chemical energy (chemical energy (ATPATP))
The The purposepurpose of Chemiosmosis is to of Chemiosmosis is to make:make:
ATPATP
Let’s look at Let’s look at Chemiosmosis…Chemiosmosis…
So what have we So what have we accomplish thus far?accomplish thus far?
Together, Together, ATPATP + + NADPHNADPH will provide will provide the energy needed for the 2the energy needed for the 2ndnd set of set of reactions for Photosynthesis to reactions for Photosynthesis to occur…..the occur…..the Calvin CycleCalvin Cycle
ATP
NADPH
Photosynthesis VideoPhotosynthesis Video
Video Recap