Biology 20 Unit 3Biology 20 Unit 3Chapter 5 Chapter 5 Photosynthesis Photosynthesis McGraw - Hill Ryerson pages 169 McGraw - Hill Ryerson pages 169

to 181to 181

Photosynthesis Photosynthesis

A process that converts solar energy into chemical energyA process that converts solar energy into chemical energy

Mean ‘Light” and “to make or build”.Mean ‘Light” and “to make or build”.

Occurs in all plants, some algae, some bacteria, some Occurs in all plants, some algae, some bacteria, some protistsprotists

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

light

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.

Chloroplasts and Photosynthetic Chloroplasts and Photosynthetic Pigments Pigments

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 process of Absorbs photons and begins process of photosynthesisphotosynthesis

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

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

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

XanthophyllsXanthophylls

CarotenoidsCarotenoids

Absorption spectrum Absorption spectrum of chlorophylls “a” of chlorophylls “a” and “b”and “b”

Spectrophotometer Spectrophotometer

Instrument that determines wavelengths of light absorbed Instrument that determines wavelengths of light absorbed or reflected by a pigmentor reflected by a pigment

Chlorophyll "a" reflects green light waves and absorbs Chlorophyll "a" reflects green light waves and absorbs red and bluered and blue

•Leaves during fall seasonLeaves during fall season

Onset of cooler autumn temperatures and less sunlightOnset of cooler autumn temperatures and less sunlight 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.II.) Chloroplasts) Chloroplasts

Found in leavesFound in leaves Primary photosynthetic organs of Primary photosynthetic organs of most plantsmost plants

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 transport water and foodand food

Gases enter and exit from Gases enter and exit from stomatastomata

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

Xylem Structure Phloem Structure

Leaf Anatomy

Chloroplast anatomyChloroplast anatomy

1. 2 membranes1. 2 membranes Outer and innerOuter and inner

2. Stroma2. Stroma Protein – rich semi liquid material in interior Protein – rich semi liquid material in interior

of chloroplastof chloroplast Between two membranesBetween two membranes

3. Thylakoid3. Thylakoid

System of interconnected flattened membrane sacsSystem of interconnected flattened membrane sacs Form a separate compartment within stroma of Form a separate compartment within stroma of chloroplastchloroplast

Stack on top of one another, forming Stack on top of one another, forming granagrana

1 chloroplast has 60 grana1 chloroplast has 60 grana Each has 30 – 50 thylakoidsEach has 30 – 50 thylakoids

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 within chloroplastPhotosynthetic membrane within chloroplast Contains:Contains:

Light – gathering pigment moleculesLight – gathering pigment molecules Electron transport chains Electron transport chains

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

Chloroplast

Chloroplast structureChloroplast structure Structure of thylakoid system greatly Structure of thylakoid system greatly surface area surface area of thylakoid membraneof thylakoid membrane Thus, Thus, efficiency of photosynthesis efficiency of photosynthesis

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

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

The Reactions of Photosynthesis The Reactions of Photosynthesis

A process made up of a series of complex chemical A process made up of a series of complex chemical reactions.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 of the Occurs in the thylakoid membrane and stroma of the chloroplast.chloroplast.

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

light

Photosynthesis

Energy Containing Molecules Formed During Energy Containing Molecules Formed During PhotosynthesisPhotosynthesis

MoleculeMolecule FunctionFunction

•ATPATP (adenosine (adenosine triphosphattriphosphate)e)

•PrincipalPrincipal energy – supply energy – supply molecule for cellular molecule for cellular functions of all cellsfunctions of all cells•Provides an immediate source Provides an immediate source of energy for cellular of energy for cellular processesprocesses•Formed by addition of ADP Formed by addition of ADP and Pi (phosphate)and Pi (phosphate)

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 During Energy Containing Molecules Formed During PhotosynthesisPhotosynthesis

MoleculeMolecule FunctionFunction

•NADPH NADPH (nicotinami(nicotinamide de dinucleotiddinucleotide e phosphate)phosphate)

•At several places during At several places during photosynthesis, NADPphotosynthesis, NADP++ accepts 1 H atom and 2 e- to accepts 1 H atom and 2 e- to form NADPHform NADPH•NADPH is an electron donor, NADPH is an electron donor, thus becomes NADPthus becomes NADP++ again again•Involved in energy transfersInvolved in energy transfers

Energy Containing Molecules Formed During Energy Containing Molecules Formed During PhotosynthesisPhotosynthesis

MoleculeMolecule FunctionFunction

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

Oxidation – Reduction Oxidation – Reduction ReactionsReactions

OxidationOxidation A reaction in which A reaction in which an atom or molecule an atom or molecule loses electronsloses electrons

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

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

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

Oxidation / reduction examplesOxidation / reduction examplesi.) ATPi.) 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 can be reused in future reduction reactions reduction 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 NADPHNADPH NADPH NADP NADP++ + H + H NADPNADP+ + can be reused in future reduction can be reused in future reduction reactionsreactions

Oxidation / reduction examplesOxidation / reduction examples

I.) An Overview of PhotosynthesisI.) An Overview of Photosynthesis

3 stages3 stages

1. Capture solar E and transfer it to e-1. Capture solar E and transfer it to e-

2. Use captured solar energy to make ATP; transfer 2. Use captured solar energy to make ATP; transfer high energy e- to NADPhigh energy e- to NADP++; NADPH is then used as a high ; NADPH is then used as a high energy e- carrierenergy e- carrier

3. Use energy stored in ATP and NADPH to form energy 3. Use energy stored in ATP and NADPH to form energy – rich molecules such as glucose, from CO– rich molecules such as glucose, from CO22

PhotosynthesisPhotosynthesis

*Reworked equation: *Reworked equation:

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

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

* Reactants of photosynthesis are the products of cellular respiration.

Photosynthesis

Light Dependant (Stages 1 and 2)Light Dependant (Stages 1 and 2)

A.k.a.A.k.a. noncyclic photophosphorylation or noncyclic noncyclic photophosphorylation or noncyclic electron flowelectron flow

I.e., linear and ADP + PI.e., linear and ADP + Pii

Require chlorophyllRequire chlorophyll

Occur in thylakoid membranes of chloroplastOccur in thylakoid membranes of chloroplast

Light Independent (Stage 3) Light Independent (Stage 3)

occur during day or nightoccur during day or night

AKA: Calvin cycleAKA: Calvin cycle

Carbon fixation occursCarbon fixation occurs Incorporation of COIncorporation of CO22 (g)(g) into organic into organic compounds such as glucosecompounds such as glucose

Occur in stroma of chloroplastOccur in stroma of chloroplast

Use ATP and NADPH from light Use ATP and NADPH from light dependent reactionsdependent reactions

Enzymes are requiredEnzymes are required

. W. W

Stage 1: Capturing Solar EnergyStage 1: Capturing Solar Energy

Photosystems- in thylakoid membranesPhotosystems- in thylakoid membranes

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

Photosystem I uses chlorophyll "a", in Photosystem I uses chlorophyll "a", in the form referred to as P700the form referred to as P700

Photosystem II uses a form of chlorophyll Photosystem II uses a form of chlorophyll "a" known as P680"a" known as P680

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

•Action of a photosystem

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

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

Found at core of reaction center of Found at core of reaction center of photosystemphotosystem

Antenna pigmentsAntenna pigments

Other pigment moleculesOther pigment molecules

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

Stage 1: Capturing Solar Stage 1: Capturing Solar EnergyEnergy

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 chlorophyll a molecules absorb solar E. Donates the electron to the primary E. 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!

Stage 1: Capturing Solar Stage 1: Capturing Solar EnergyEnergy

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

e- enters an e- enters an electron transport chainelectron transport chain

e- is passed from one molecular complex to another e- is passed from one molecular complex to another (like a hot potato)(like a hot potato)

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

Series of oxidation / reduction reactionsSeries of oxidation / reduction reactions

Stage 1: Capturing Solar EnergyStage 1: Capturing Solar Energy

PhotolysisPhotolysis Occurs in thylakoid lumenOccurs in thylakoid lumen Solar E absorbed by chlorophyll is used Solar E absorbed by chlorophyll is used to split water into Hto split water into H++, e, e--, O, O22 (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 leaves exists plant through stomata in leaves or is used to make Hor is used to make H22OO

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

Stage 1b- PhotolysisStage 1b- Photolysis

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

Stage 1: Capturing Solar EnergyStage 1: Capturing Solar Energy

Stage 2: Electron Transfer and ATP Stage 2: Electron Transfer and ATP Synthesis 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 ions Transfer of electronsTransfer of electrons

a) Electron Transport Chaina) Electron Transport Chain

Analogy: set of stairsAnalogy: set of stairs Solar E excites 2 e- that have been removed from HSolar E excites 2 e- that have been removed from H22OO

This “boost” gives e- high potential energyThis “boost” gives e- high potential energy Potential E is gradually released as e- travel Potential E is gradually released as e- travel down the stairsdown the stairs Some of this released E is used to make ATPSome of this released E is used to make ATP e- eventually join He- eventually join H++ ions in the formation of ions in the formation of new compounds new compounds

H2O

2e-

2 H+ + 2e- + ½ O2 (g) H2O

2e-

ETC analogy:

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

ATP

Electron transport chain

Photolysis

lumen

AB

C

D

E

(A)(A) e-, excited by light at e-, excited by light at photosystem II, are passed photosystem II, are passed along an ETC. along an ETC. e- release energy at each step.e- release energy at each step.

(B)(B) Energy from e- is used to Energy from e- is used to pull Hpull H++ ions across membrane ions across membrane into lumeninto lumen e- have lost most of their energye- have lost most of their energyH+ ion concentration increases H+ ion concentration increases inside lumen and a positive inside lumen and a positive charge builds upcharge builds up

Stage 2: Electron Transfer and ATP Stage 2: Electron Transfer and ATP Synthesis EventsSynthesis Events

(C) (C) e- are transferred from ETC to e- are transferred from ETC to photosystem Iphotosystem I e- are energized by lighte- are energized by light

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

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

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

b.) Chemiosmosisb.) Chemiosmosis

Due to the build up of HDue to the build up of H++ in the in the lumen, concentration of positive lumen, concentration of positive ions increasesions increases

Electrical gradient resultsElectrical gradient results(E)(E) H H++ ions rush through ions rush through ATP synthase ATP synthase complexcomplex In doing so, HIn doing so, H++ ions release energy ions release energy Help combine ADP + PHelp combine ADP + Pii ATP ATP Note: energy stored in HNote: energy stored in H++ ion gradient is ion gradient is derived from energy of e- by photosystem IIderived from energy of e- by photosystem II Thus, energy used by plant to make ATP comes Thus, energy used by plant to make ATP comes from the sun!from the sun!

Electron transport chain

Photolysis

lumen

AB

C

D

E

Stage 1 and 2 SummaryStage 1 and 2 Summary1. Purpose = convert light energy to ATP and 1. Purpose = convert light energy to ATP and

NADPH.NADPH.

2. ATP and NADPH run the synthesis 2. ATP and NADPH run the synthesis reactions.reactions.

3. ATP synthase channel is used to generate 3. ATP synthase channel is used to generate ATP flow of H+ through synthase.ATP flow of H+ through synthase.

4. No sugar is produced.4. No sugar is produced.

5. Oxygen is produced as a waste product and 5. Oxygen is produced as a waste product and released to the atmosphere (from released to the atmosphere (from splitting of water to produce electrons).splitting of water to produce electrons).

LinksLinks

PhotophosphorylationPhotophosphorylation

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

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

Cyclic Electron Flow or Cyclic Electron Flow or Cyclic PhotophosphorylationCyclic Photophosphorylation

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

Uses photosystem I but not Uses photosystem I but not photosystem IIphotosystem II

e- cycle back to P700 chlorophyll e- cycle back to P700 chlorophyll molecule via the same ETC that molecule via the same ETC that functions in noncyclic e- flowfunctions in noncyclic e- flow

ATP is producedATP is produced

NADPH nor ONADPH nor O22 (g)(g) is produced is produced

Cyclic Electron Flow (photophosphorylation) and Photosystem I

LinksLinks

Cyclic and Noncyclic Cyclic and Noncyclic PhotophosphorylationPhotophosphorylation

http://highered.mcgraw-hill.com/olc/http://highered.mcgraw-hill.com/olc/dl/120072/bio12.swfdl/120072/bio12.swf

Stage 3: The Calvin Cycle and Carbon Stage 3: The Calvin Cycle and Carbon FixationFixation

Occurs in Occurs in stromastroma of chloroplast of chloroplastIncludes 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 reduced is reduced

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 carbon sugar, G3P. product of Calvin cycle is a 3 carbon sugar, G3P. Used to create glucose, CUsed to create glucose, C66HH1212OO66

Stage 3: The Calvin Cycle and Carbon Stage 3: The Calvin Cycle and Carbon FixationFixation

C and O atoms are supplied by COC and O atoms are supplied by CO22

H atoms are supplied by photolysis of HH atoms are supplied by photolysis of H22O, from stage O, from stage 11

3 ATPs and 2 NADPHs are consumed per CO3 ATPs and 2 NADPHs are consumed per CO22 that enters that enters the calvin cyclethe calvin cycle Thus, the building of one glucose molecule requires Thus, the building of one glucose molecule requires 18 ATPs and 12 NADPHs18 ATPs and 12 NADPHs

Stage 3: The Calvin Cycle and Carbon Stage 3: The Calvin Cycle and Carbon Fixation Fixation EventsEvents

3 steps:3 steps:

1.1. COCO22 fixation and reduction. fixation and reduction.

2.2. PGAL molecules produced.PGAL molecules produced.

3.3. Regeneration of RUBPRegeneration of RUBP

Each stage requires Each stage requires enzymesenzymes for cycle to occur for cycle to occur

Step 1: COStep 1: CO22 fixation and reduction fixation and reduction RUBP (ribulose biphosphate), a 5 – C molecule, attaches RUBP (ribulose biphosphate), a 5 – C molecule, attaches to COto 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 molecules 3 – C molecules (PGA). (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 Each PGA molecule accepts energy from ATP and NADPH.and NADPH.

The 3-C PGA is reduced to form PGAL and The 3-C PGA is reduced to form PGAL and water.water.

PGAL is stable, combines with another PGAL PGAL is stable, combines with another PGAL to form glucose.to 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.

H2O

From light reactions

From light reactions

Back to thylakoid

Step 3: Regeneration of RUBPStep 3: Regeneration of RUBPNeeded so that cycle can continue.Needed so that cycle can continue.

Uses ATP from the light dependant Uses ATP from the light dependant reaction.reaction.

5 molecules of PGAL are used to form 5 molecules of PGAL are used to form RuBP; only 1 carbon is available to form RuBP; only 1 carbon is available to form glucose.glucose.

How many turns of the cycle must occur to How many turns of the cycle must occur to get 1 glucose? Why?get 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.

Stage 3: The Calvin Cycle and Carbon Stage 3: The Calvin Cycle and Carbon Fixation Fixation ProductsProducts

Direct product – PGA Direct product – PGA

Glucose, CGlucose, C66HH1212OO66

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

6 H6 H22OO

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

Calvin-Benson Cycle

SummarySummary

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

Photons split water, create ATP and Photons split water, create ATP and NAPDH. These are used to combine CONAPDH. These are used to combine CO22 from air with a 5 Carbon sugar (RuBP).from air with a 5 Carbon sugar (RuBP).

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