Biology 20 Unit CBiology 20 Unit CChapter 6 Photosynthesis Chapter 6 Photosynthesis

Nelson Pages 178 - 201Nelson Pages 178 - 201

6.1 CHLOROPLASTS AND 6.1 CHLOROPLASTS AND PHOTOSYNTHETIC PIGMENTSPHOTOSYNTHETIC PIGMENTS

Biology 20 Chapter 6 - PhotosynthesisBiology 20 Chapter 6 - Photosynthesis

Photosynthesis Photosynthesis A process that converts solar energy into A process that converts solar energy into

chemical energychemical energy Mean ‘Light” and “to make or build”.Mean ‘Light” and “to make or build”. Occurs in all plants, some algae, some Occurs in all plants, some algae, some

bacteria, some protistsbacteria, some protists

6H2O + 6CO2 ----------> C6H12O6+ 6O2

LightLight

Part of electromagnetic radiation (EMR)Part of electromagnetic radiation (EMR)

Can be described by its wave characteristic or as Can be described by its wave characteristic or as

particles of energy called particles of energy called photons.photons.

6.1 Chloroplasts and Photosynthetic Pigments 6.1 Chloroplasts and Photosynthetic Pigments

A spectroscope separates individual wavelengths of the Sun

Visible light is only 3 % of the total energy

A spectroscope separates individual wavelengths of the Sun

Visible light is only 3 % of the total energy

I) ChlorophyllI) Chlorophyll Light – absorbing, green colored Light – absorbing, green colored

pigment pigment Absorbs photons and begins Absorbs photons and begins

process of photosynthesisprocess of photosynthesis Color of pigment comes from Color of pigment comes from

wavelengths of light reflected (in wavelengths of light reflected (in other words, those not absorbed).other words, those not absorbed).

What color is absorbed if you see a What color is absorbed if you see a red shirt? What colors are reflected?red shirt? What colors are reflected?

•Types of ChlorophyllTypes of Chlorophyll

All photosynthetic organisms have chlorophyll "a" All photosynthetic organisms have chlorophyll "a" 

Accessory pigments Accessory pigments absorb energy that chlorophyll absorb energy that chlorophyll "a" does not absorb"a" does not absorb

Pigments include:Pigments include: Chlorophyll "b" (also c, d, and e in algae and protistans)Chlorophyll "b" (also c, d, and e in algae and protistans)

XanthophyllsXanthophylls

CarotenoidsCarotenoids

Spectrophotometer Spectrophotometer Instrument that determines wavelengths of Instrument that determines wavelengths of

light absorbed or reflected by a pigmentlight absorbed or reflected by a pigment Chlorophyll "a" reflects green light waves and Chlorophyll "a" reflects green light waves and

absorbs red and blueabsorbs red and blue

•Leaves during fall seasonLeaves during fall season

Onset of cooler autumn temperatures and less Onset of cooler autumn temperatures and less sunlightsunlight Plants stop producing chlorophyll moleculesPlants stop producing chlorophyll molecules Reveals yellow, red, brown colors of leaves.Reveals yellow, red, brown colors of leaves.

Pumpkin Eyes Games

leaves

II.) Chloroplasts II.) Chloroplasts Found in leavesFound in leaves

Primary photosynthetic organs of most Primary photosynthetic organs of most plantsplants

Structure of the leafStructure of the leaf ChloroplastsChloroplasts have chlorophyll have chlorophyll

Captures light for food productionCaptures light for food production XylemXylem and and phloemphloem transport water and food transport water and food

Gases enter and exit from Gases enter and exit from stomatastomata

Waxy Waxy cuticlecuticle and and epidermisepidermis protect plant protect plant from water lossfrom water loss

Leaf AnatomyLeaf Anatomy

Chloroplast anatomyChloroplast anatomy1. 2 membranes: 1. 2 membranes: outer and innerouter and inner

2. 2. StromaStroma Protein – rich semi liquid material in interior of chloroplastProtein – rich semi liquid material in interior of chloroplast Between two membranesBetween two membranes

3. Thylakoid3. Thylakoid System of interconnected System of interconnected

flattened membrane sacsflattened membrane sacs Form a separate Form a separate

compartment within stroma compartment within stroma of chloroplastof chloroplast

Stack on top of one Stack on top of one

another, forming another, forming granagrana 1 chloroplast has 60 grana1 chloroplast has 60 grana

Each has 30 – 50 Each has 30 – 50 thylakoidsthylakoids

4. Lamellae 4. Lamellae Groups of unstacked thylakoidsGroups of unstacked thylakoids Between granaBetween grana

5. Thylakoid membrane and lumen5. Thylakoid membrane and lumen Photosynthetic membrane Photosynthetic membrane

within chloroplastwithin chloroplast Contains:Contains:

Light – gathering pigment Light – gathering pigment moleculesmolecules

Electron transport chains Electron transport chains

Lumen: Lumen: Fluid – filled Fluid – filled space inside a thylakoidspace inside a thylakoid

Chloroplast structureChloroplast structure

Structure of thylakoid system greatly Structure of thylakoid system greatly surface area of thylakoid membranesurface area of thylakoid membrane Thus, Thus, efficiency of photosynthesis efficiency of photosynthesis

Chloroplasts are able to replicate, through Chloroplasts are able to replicate, through division, independently of celldivision, independently of cell

Lipid droplets and starch grains are also Lipid droplets and starch grains are also present in chloroplast present in chloroplast

Plant growth

Separating Pigments Using Chromatography

Paper chromatography is a method used to separate different compounds in a solution

As solvent moves up paper, it will carry dissolved compounds of solution

Compounds move up paper at different rates due to their solubility in the solvent and their size

tip of the filter paper is placed in solvent

as solvent moves up the paper it will carry pigments

size: smaller pigments travel further up paper

solubility: more soluble pigments travel further up paper

Check Your Understanding:Check Your Understanding:

1.1. What is chlorophyll?What is chlorophyll?

2.2. Identify the regions of the chloroplast indicated on Identify the regions of the chloroplast indicated on this diagram. Describe what happens in B and C.this diagram. Describe what happens in B and C.

3.3. Describe the major function of photosynthetic Describe the major function of photosynthetic pigments.pigments.

Assignments:Assignments: Supplementary diagramsSupplementary diagrams Practice Problems #1-4Practice Problems #1-4 Section 6.1 Questions – page 185 # 1-4Section 6.1 Questions – page 185 # 1-4 Using Satellite and Airborne Technology Using Satellite and Airborne Technology

Case Study Page 184Case Study Page 184

6.2 The Reactions of Photosynthesis 6.2 The Reactions of Photosynthesis A process made up of a series of complex A process made up of a series of complex

chemical reactions.chemical reactions. A variety of intermediate and final energy rich A variety of intermediate and final energy rich

molecules are formed.molecules are formed. Occurs in the thylakoid membrane and stroma Occurs in the thylakoid membrane and stroma

of the chloroplast.of the chloroplast.

6H2O + 6CO2 ----------> C6H12O6+ 6O2

light

Photosynthesis

PhotosynthesisPhotosynthesis

*Reworked equation: *Reworked equation:

12 H12 H22O + 6 COO + 6 CO22 + solar E → C + solar E → C66HH1212OO66 + 6 O + 6 O22 + 6 H + 6 H22OO

6H6H22O + 6COO + 6CO

22 ----------> C ----------> C66HH1212OO66+ 6O+ 6O

22

light

Melvin Calvin studied photosynthesis by working with organic compounds labeled with carbon-14. Using carbon-14 and the new techniques of ion exchange, paper chromatography, and radioautography, Calvin and his many associates mapped the complete path of carbon in photosynthesis. The accomplishment brought him the Nobel prize in chemistry in 1961.

Melvin Calvin shown with some of the apparatus he used to study the role of carbon in photosynthesis.

Energy Containing Molecules Energy Containing Molecules Formed During PhotosynthesisFormed During Photosynthesis

MoleculeMolecule FunctionFunction

ATPATP (adenosine (adenosine triphosphate)triphosphate)

PrincipalPrincipal energy – supply molecule energy – supply molecule for cellular functions of all cellsfor cellular functions of all cellsProvides an immediate source of Provides an immediate source of energy for cellular processesenergy for cellular processesFormed by addition of ADP and Pi Formed by addition of ADP and Pi (phosphate)(phosphate)

ATP (adenosine triphosphate)ATP (adenosine triphosphate)

ATP

ADP + Pi

•Energy is stored when ATP is formed

•Energy is released, when needed, by reversal of reaction

Energy input

Energy output

Energy Containing Molecules Formed Energy Containing Molecules Formed During PhotosynthesisDuring Photosynthesis

MoleculeMolecule FunctionFunction

NADPH NADPH (nicotinamide (nicotinamide dinucleotide dinucleotide phosphate)phosphate)

At several places during At several places during photosynthesis, NADPphotosynthesis, NADP++ accepts 1 H accepts 1 H atom and 2 e- to form NADPHatom and 2 e- to form NADPHNADPH is an electron donor, thus NADPH is an electron donor, thus becomes NADPbecomes NADP++ again againInvolved in energy transfersInvolved in energy transfers

Energy Containing Molecules Formed During Energy Containing Molecules Formed During PhotosynthesisPhotosynthesis

MoleculeMolecule FunctionFunction

glucoseglucose Transport molecule (“blood sugar”)Transport molecule (“blood sugar”)Medium – term energy storage in Medium – term energy storage in most cellsmost cells

Oxidation – Reduction ReactionsOxidation – Reduction Reactions OxidationOxidation

A reaction in which an atom or molecule loses electronsA reaction in which an atom or molecule loses electrons

ReductionReduction A reaction in which an atom or molecule gains electronsA reaction in which an atom or molecule gains electrons

Electron transfers between 2 substances always Electron transfers between 2 substances always involve both oxidation / reduction reactionsinvolve both oxidation / reduction reactions

““LEO” the lion says “GER” LEO” the lion says “GER”

Oxidation / reduction examplesOxidation / reduction examples

i.)i.) ATP ATP Reduction of ADP Reduction of ADP

ADP (accepts electrons) + PADP (accepts electrons) + Pii ATP ATP Storage of energyStorage of energy

Oxidation of ATP (energy) Oxidation of ATP (energy) ATP (releases elections) ATP (releases elections) ADP + P ADP + Pii

Release of energyRelease of energy ADP and PADP and Pi i can be reused in future reduction can be reused in future reduction

reactions reactions

ii.) NADPHii.) NADPH Reduction of NADPReduction of NADP++

NADPNADP++ + H + H NADPH NADPH NADPH is now stable and can release NADPH is now stable and can release

energy to the next electron acceptorenergy to the next electron acceptor Oxidation of NADPHOxidation of NADPH

NADPH NADPH NADP NADP++ + H + H NADPNADP+ + can be reused in future reduction can be reused in future reduction

reactionsreactions

Oxidation / reduction examplesOxidation / reduction examples

* Reactants of photosynthesis are the products of cellular respiration.

Photosynthesis

Photosynthesis is a two step process:Photosynthesis is a two step process:1.1. Light Dependent Reactions Light Dependent Reactions - energy - energy

from the sun is captured in energy carrying from the sun is captured in energy carrying molecules. Since it must take place in sunlight it is molecules. Since it must take place in sunlight it is often called the “often called the “light” reaction (s). Aka: light” reaction (s). Aka: noncyclic photophosphorylation or noncyclic electron flow

2.2. Light Independent Reactions Light Independent Reactions - - The energy from the “light” reactions is used to fix The energy from the “light” reactions is used to fix the carbon from atmospheric carbon dioxide into the carbon from atmospheric carbon dioxide into organic compounds. It does not have to take place organic compounds. It does not have to take place in the light so it is often called thein the light so it is often called the “dark” “dark” reactions(s), aka: creactions(s), aka: carbon-fixation reactions, arbon-fixation reactions, Calvin Calvin CycleCycle

An Overview of An Overview of PhotoPhotosynthesissynthesis Photo Photo - light required- light required

Light reactions - in thylakoid membraneLight reactions - in thylakoid membrane Energy from sun converted to chemical energyEnergy from sun converted to chemical energy

ATPATP NADPHNADPH

SynthesisSynthesis - aka Calvin Cycle- aka Calvin Cycle Makes sugar in stromaMakes sugar in stroma No light requiredNo light required COCO22 to C to C66HH1212OO66

Uses ATP and NADPHUses ATP and NADPH

. W. W

A summary of the Light Dependent A summary of the Light Dependent Reactions:Reactions:

Light Dependent Reactions Light Dependent Reactions Step 1a: Capturing Solar EnergyStep 1a: Capturing Solar Energy

Photosystems- Photosystems- in thylakoid membranes

Cluster of chlorophyll and other pigments packed into Cluster of chlorophyll and other pigments packed into thylakoid membranes.thylakoid membranes.

Photosystem I uses chlorophyll "a", in the form referred Photosystem I uses chlorophyll "a", in the form referred to as P700to as P700

Photosystem II uses a form of chlorophyll "a" known as Photosystem II uses a form of chlorophyll "a" known as P680P680

Operate so that a wide range of wavelengths can be Operate so that a wide range of wavelengths can be used for photosynthesis. Why?used for photosynthesis. Why?

All pigments within a All pigments within a photosystem capture and photosystem capture and absorb photons.absorb photons.

Only 1 pair of chlorophyll Only 1 pair of chlorophyll molecules/photosystem molecules/photosystem actually use solar Energyactually use solar Energy

Found at core of reaction Found at core of reaction center of photosystemcenter of photosystem

Antenna pigmentsAntenna pigments Other pigment moleculesOther pigment molecules

Gather light and transfer it Gather light and transfer it to chlorophyll moleculesto chlorophyll molecules

Capturing Solar Energy continued…Capturing Solar Energy continued…

Solar E is captured when a low energy Solar E is captured when a low energy e- in a chlorophyll molecule, from e- in a chlorophyll molecule, from photosystem II, absorbs a photon. photosystem II, absorbs a photon. Energy is channeled to chlorophyll a.Energy is channeled to chlorophyll a.

After a photon of light strikes, After a photon of light strikes, chlorophyll a molecules absorb solar E. chlorophyll a molecules absorb solar E. Donates the electron to the primary Donates the electron to the primary electron acceptor in the thylakoid electron acceptor in the thylakoid membrane.membrane.

Because chlorophyll a donates an Because chlorophyll a donates an electron, it must get another one from electron, it must get another one from somewhere… the splitting of water!somewhere… the splitting of water!

Capturing Solar Energy continued…Capturing Solar Energy continued…

TwoTwo energized e-, from chlorophyll, are removed energized e-, from chlorophyll, are removed from photosystem IIfrom photosystem II

e- enters an e- enters an electron transport chainelectron transport chain e- is passed from one molecular complex to e- is passed from one molecular complex to

another (like a hot potato)another (like a hot potato)

ATP is made because of the energy release ATP is made because of the energy release through the chain.through the chain.

Series of oxidation / reduction reactionsSeries of oxidation / reduction reactions

Capturing Solar Energy continued…Capturing Solar Energy continued…

PhotolysisPhotolysis

Occurs in thylakoid lumenOccurs in thylakoid lumen Solar E absorbed by chlorophyll Solar E absorbed by chlorophyll

is used to split water into His used to split water into H++, e, e--, , OO22 (g)(g)

e- replaces 2e- lost by chlorophyll e- replaces 2e- lost by chlorophyll molecules in photosystem IImolecules in photosystem II

OO22 (g)(g) exists plant through stomata in exists plant through stomata in leaves or is used to make Hleaves or is used to make H22OO

HH++ will be used later, to help reduce will be used later, to help reduce ADPADP

Light Dependent Reactions- PhotolysisLight Dependent Reactions- Photolysis

2 H2 H22O O (l)(l) + energy + energy 4 H 4 H++ + 4 e- + O + 4 e- + O22 (g)(g)

Light Dependent ReactionsLight Dependent ReactionsStage 2: Electron Transfer and ATP Synthesis Stage 2: Electron Transfer and ATP Synthesis Purpose:Purpose:

Form energy – rich moleculesForm energy – rich molecules Make ATP from ADP and PMake ATP from ADP and Pii

2 processes:2 processes: Build up of HBuild up of H++ ions (concentration gradient) ions (concentration gradient) Transfer of electronsTransfer of electrons

Stage 2a) Electron Transport ChainStage 2a) Electron Transport Chain Analogy: set of stairsAnalogy: set of stairs Solar E excites 2 e- that have Solar E excites 2 e- that have

been removed from Hbeen removed from H22OO This “boost” gives e- high This “boost” gives e- high

potential energypotential energy Potential E is gradually Potential E is gradually

released as e- travel down the released as e- travel down the stairsstairs

Some of this released E is Some of this released E is used to make ATPused to make ATP

e- eventually join He- eventually join H++ ions ions in the formation of new in the formation of new compounds compounds

ETC analogy:

http://www.nelson.com/ABbio20-30/teacher/protect/media/energy_staircase.html

H2O

2e-

2 H+ + 2e- + ½ O2 (g) H2O

2e-

*Series of oxidation – reduction reactions by electron acceptors and donors at each step

ATP

(Steps 1-2)(Steps 1-2) •e-, excited by light at photosystem II, are e-, excited by light at photosystem II, are

passed along an ETC. passed along an ETC. • e- release energy at each step.e- release energy at each step.

ETC how it works: ETC how it works:

(2)(2) Energy from e- is used to pump H Energy from e- is used to pump H++ ions across membrane into ions across membrane into lumen via active transport (from low to high Hlumen via active transport (from low to high H++ concentration) concentration) e- have lost most of their energye- have lost most of their energy

H+ ion concentration increases inside lumen and a positive H+ ion concentration increases inside lumen and a positive charge builds upcharge builds up

(3) (3) e- are transferred from ETC e- are transferred from ETC to photosystem Ito photosystem I e- are energized by lighte- are energized by light

(4)(4) e- are transferred to NADP e- are transferred to NADP++

Each NADPEach NADP++ accepts 2 e- accepts 2 e- and 1 Hand 1 H++

Thus, NADPThus, NADP++ is reduced to is reduced to NADPHNADPH

Light Dependent Reactions – summary diagramLight Dependent Reactions – summary diagram

b.) Chemiosmosisb.) Chemiosmosis Due to the build up of HDue to the build up of H++

in the lumen, in the lumen, concentration of positive concentration of positive ions increasesions increases

Electrical gradient resultsElectrical gradient results HH++ ions rush through ions rush through

ATP synthase complexATP synthase complex In doing so, HIn doing so, H++ ions ions

release energyrelease energy

Help combine ADP + PHelp combine ADP + Pii ATP ATPNote: energy stored in HNote: energy stored in H++ ion gradient is derived from ion gradient is derived from energy of e- by photosystem IIenergy of e- by photosystem IIThus, energy used by plant to make ATP comes from the Thus, energy used by plant to make ATP comes from the sun!sun!

Light Dependent Reactions SummaryLight Dependent Reactions Summary

1.1. Purpose = convert light energy to ATP and Purpose = convert light energy to ATP and NADPH.NADPH.

2.2. ATP and NADPH run the synthesis reactions.ATP and NADPH run the synthesis reactions.

3.3. ATP synthase channel is used to generate ATP ATP synthase channel is used to generate ATP via flow of H+ through ATP synthase channel.via flow of H+ through ATP synthase channel.

4.4. No sugar is produced.No sugar is produced.

5.5. Oxygen is produced as a waste product and Oxygen is produced as a waste product and released to the atmosphere (from splitting of released to the atmosphere (from splitting of water to produce electrons). water to produce electrons).

LinksLinksPhotophosphorylationPhotophosphorylation

http://bcs.whfreeman.com/thelifewire/content/http://bcs.whfreeman.com/thelifewire/content/chp08/0802002.htmlchp08/0802002.html

http://highered.mcgraw-hill.com/olc/dl/120072/http://highered.mcgraw-hill.com/olc/dl/120072/bio13.swfbio13.swf

Review of light dependent: Review of light dependent: http://highered.mcgraw-hill.com/sites/0072437316/http://highered.mcgraw-hill.com/sites/0072437316/

student_view0/chapter10/animations.html#student_view0/chapter10/animations.html#

Check Your Understanding:Check Your Understanding:

1.1. What are the two sets of reactions that are involved in What are the two sets of reactions that are involved in photosynthesis?photosynthesis?

2.2. Predict why most green plants contain more than one Predict why most green plants contain more than one photosynthetic pigment.photosynthetic pigment.

3.3. What is a photosystem? Where do you find photosystems?What is a photosystem? Where do you find photosystems?

4.4. Describe or sketch what happens to electrons in the ETC.Describe or sketch what happens to electrons in the ETC.

5.5. How are electrons replaced in photosystem I, and what is the How are electrons replaced in photosystem I, and what is the source of the replacement electrons?source of the replacement electrons?

6.6. Identify the source of oxygen released from the chloroplast Identify the source of oxygen released from the chloroplast during photosynthesis. Explain the main function of the during photosynthesis. Explain the main function of the reaction in which oxygen is released.reaction in which oxygen is released.

7.7. How does NADP+ become converted to NADPH?How does NADP+ become converted to NADPH?

8.8. Is NADPH and oxidized or reduced molecule? Explain.Is NADPH and oxidized or reduced molecule? Explain.

9.9. How are electrons replaced in photosystem I, and what is the source of the How are electrons replaced in photosystem I, and what is the source of the replacement electrons?replacement electrons?

10.10. What is the effect of having a greater concentration of hydrogen ions in the What is the effect of having a greater concentration of hydrogen ions in the thylakoid space (lumen), than in the stroma?thylakoid space (lumen), than in the stroma?

11.11. What is ATP synthase, and what is its significance?What is ATP synthase, and what is its significance?

12.12. The membranes of the thylakoids is impermeable to hydrogen ions (H+), The membranes of the thylakoids is impermeable to hydrogen ions (H+), meaning that these ions cannot diffuse across the membranes from the inner meaning that these ions cannot diffuse across the membranes from the inner space of the thylakoid to the stroma.space of the thylakoid to the stroma.

a.a. Identify the only path by which H+ ions can move down their concentration Identify the only path by which H+ ions can move down their concentration gradients across the membrane to the stroma.gradients across the membrane to the stroma.

b.b. Identify the process that is associated with the movment of H+ through the Identify the process that is associated with the movment of H+ through the pathway and identify the end product of this process.pathway and identify the end product of this process.

Assignments:Assignments:

1.1. Read Pages 186 – 190 in Your TextbookRead Pages 186 – 190 in Your Textbook

2.2. Complete practice problems 1-10 from your text – Complete practice problems 1-10 from your text – Page 187, 188, 190Page 187, 188, 190

3.3. Section 6.2 Questions – Page 194 #1-6Section 6.2 Questions – Page 194 #1-6

4.4. Label Supplementary Diagrams (Overview of P.S, Label Supplementary Diagrams (Overview of P.S, Photosystems, cyclic/noncyclic Photosystems, cyclic/noncyclic photophosporylation)photophosporylation)

5.5. Create a master study sheet for photosynthesis Create a master study sheet for photosynthesis including all of the key ideas for light dependent and including all of the key ideas for light dependent and light independent reactions.light independent reactions.

Cyclic Electron Flow or Cyclic Cyclic Electron Flow or Cyclic PhotophosphorylationPhotophosphorylation

If a chloroplast runs low on ATP but accumulates If a chloroplast runs low on ATP but accumulates NADPH, e- may take an alternative pathNADPH, e- may take an alternative path

Uses photosystem I but not photosystem IIUses photosystem I but not photosystem II e- cycle back to P700 chlorophyll molecule via the e- cycle back to P700 chlorophyll molecule via the

same ETC that functions in noncyclic e- flowsame ETC that functions in noncyclic e- flow ATP is producedATP is produced NADPH nor ONADPH nor O22 (g)(g) is produced is produced

The Light Independent Reactions: The Light Independent Reactions: Aka - The Calvin Cycle and Carbon FixationAka - The Calvin Cycle and Carbon Fixation

Occurs in Occurs in stromastroma of chloroplast of chloroplast Includes a large number of light – Includes a large number of light –

independent reactionsindependent reactions COCO22 enters plants through stomata of enters plants through stomata of

leavesleaves Upon entering Calvin cycle, COUpon entering Calvin cycle, CO22 is is

reducedreduced Utilizes both ATP and NADPH, which Utilizes both ATP and NADPH, which

were produced from stage 1 & 2were produced from stage 1 & 2 DirectDirect product of Calvin cycle is a 3 product of Calvin cycle is a 3

carbon sugar, PGAL (G3P).carbon sugar, PGAL (G3P). Used to create glucose, CUsed to create glucose, C66HH1212OO66

Light Independent Reactions (Calvin Cycle) continued…Light Independent Reactions (Calvin Cycle) continued…

C and O atoms are supplied by C and O atoms are supplied by COCO22

H atoms are supplied by H atoms are supplied by photolysis of Hphotolysis of H22O, from light O, from light

dependent reactionsdependent reactions 3 ATPs and 2 NADPHs are 3 ATPs and 2 NADPHs are

consumed per COconsumed per CO22 that enters that enters

the calvin cyclethe calvin cycle Thus, the building of one Thus, the building of one

glucose molecule requires glucose molecule requires 18 ATPs and 12 NADPHs18 ATPs and 12 NADPHs

Light Independent Reactions (Calvin Cycle) Light Independent Reactions (Calvin Cycle) The EventsThe Events 3 steps:3 steps:

1.1. COCO22 fixation fixation and reduction.and reduction.

2.2. PGAL PGAL molecules molecules produced.produced.

3.3. Regeneration of Regeneration of RUBPRUBP

Each stage requires Each stage requires enzymesenzymes for cycle to for cycle to occuroccur

Step 1: COStep 1: CO22 fixation and reduction fixation and reduction RUBP (ribulose biphosphate), a 5 – C RUBP (ribulose biphosphate), a 5 – C

molecule, attaches to COmolecule, attaches to CO22

Enzyme for this reaction is RUBP carboxylaseEnzyme for this reaction is RUBP carboxylase

RUBP + CORUBP + CO22 unstable 6 – C molecule unstable 6 – C molecule 6 – C molecule breaks down into 6 – C molecule breaks down into twotwo 3 – C 3 – C

molecules (PGA). molecules (PGA). Each 3 PGA molecule becomes reducedEach 3 PGA molecule becomes reduced

ATP and NADPH supply the energy for this stageATP and NADPH supply the energy for this stage

Step 2: PGAL productionStep 2: PGAL production Each PGA molecule accepts energy from ATP and Each PGA molecule accepts energy from ATP and

NADPH.NADPH. The 3-C PGA is reduced to form PGAL and water.The 3-C PGA is reduced to form PGAL and water. PGAL is stable, combines with another PGAL to PGAL is stable, combines with another PGAL to

form glucose.form glucose. PGAL has 3 purposes:PGAL has 3 purposes:

Provides chemical energy for the cell.Provides chemical energy for the cell. Combine to form glucose= stored energy for cell.Combine to form glucose= stored energy for cell. Recycle to form RuBP.Recycle to form RuBP.

Step 3: Regeneration of RUBPStep 3: Regeneration of RUBP

Needed so that cycle can continue.Needed so that cycle can continue. Uses ATP from the light dependant reaction.Uses ATP from the light dependant reaction. 5 molecules of PGAL are used to form RuBP; 5 molecules of PGAL are used to form RuBP;

only 1 carbon is available to form glucose.\only 1 carbon is available to form glucose.\ How many turns of the cycle must occur to get How many turns of the cycle must occur to get

1 glucose? Why?1 glucose? Why? Glucose is smaller, less reactive and has more Glucose is smaller, less reactive and has more

energy than ATP and NADPH.energy than ATP and NADPH.

The Calvin Cycle and Carbon Fixation The Calvin Cycle and Carbon Fixation ProductsProducts

Direct product – PGALDirect product – PGAL Glucose, CGlucose, C66HH1212OO66

NOTE: NOTE: sixsix revolutions of Calvin cycle are revolutions of Calvin cycle are required to make required to make oneone glucose molecule glucose molecule

6 H6 H22OO

ADP, PADP, Pii, NADP, NADP++, H, H++

SummarySummary

P/S is the process that uses sunlight to convert P/S is the process that uses sunlight to convert inorganic compounds into organic compounds.inorganic compounds into organic compounds.

Photons split water, create ATP and NAPDH. Photons split water, create ATP and NAPDH. These are used to combine CO2 from air with These are used to combine CO2 from air with a 5 Carbon sugar (RuBP).a 5 Carbon sugar (RuBP).

PGA is produced, is unstable, converts to PGA is produced, is unstable, converts to PGAL. PGAL combines to form RuBP and 1 PGAL. PGAL combines to form RuBP and 1 glucose for every 6 turns.glucose for every 6 turns.

Check Your UnderstandingCheck Your Understanding1.1. What does the term carbon dioxide fixation What does the term carbon dioxide fixation

mean?mean?

2.2. Identify the source of ATP and NADPH Identify the source of ATP and NADPH required to synthesize glucose.required to synthesize glucose.

3.3. Where in the chloroplast does the Light Where in the chloroplast does the Light Independent reactions take place?Independent reactions take place?

4.4. Outline the Calvin Cycle in terms of carbon Outline the Calvin Cycle in terms of carbon dioxide fixation, reduction, and regenerationdioxide fixation, reduction, and regeneration

Assignments to be completed: Read 191-194 of text Complete supplementary diagrams (label and color) Section 6.2 Questions – page 194 Textbook, #1-6 Photosynthesis (chapter 6) Review – Page 200

Complete #1-12, 19-24 Continue to construct a master study sheet using full

sheet of paper. Next up: Photosynthesis Quiz Next up: cellular respiration.