Chapter 5Chapter 5

Photosynthesis & Cellular Photosynthesis & Cellular RespirationRespiration

5.1 – Matter and Energy 5.1 – Matter and Energy Pathways in Living SystemsPathways in Living Systems

Both cellular respiration and photosynthesis Both cellular respiration and photosynthesis are examples of biological processes that are examples of biological processes that involve matter & energyinvolve matter & energy

During photosynthesis, energy from the sun is During photosynthesis, energy from the sun is stored in the chemical bonds of glucosestored in the chemical bonds of glucose

This energy is released during cellular This energy is released during cellular respirationrespiration

The ChloroplastThe Chloroplast

The chloroplast is The chloroplast is the site of the site of photosynthesisphotosynthesis

They consist of a They consist of a series of series of membranesmembranes

The inner and outer membranes The inner and outer membranes surround the stromasurround the stroma

The stroma is a fluid that contains The stroma is a fluid that contains proteins and chemicals required for proteins and chemicals required for photosynthesisphotosynthesis

A third type of membrane is the thylakoid, A third type of membrane is the thylakoid, which creates a series of flattened sacswhich creates a series of flattened sacs

These thylakoids are stacked in These thylakoids are stacked in structures known as granastructures known as grana

The MitochondriaThe Mitochondria

The The mitochondria is mitochondria is the site of the site of cellular cellular respirationrespiration

They are found They are found in all organismsin all organisms

The mitochondria has two membranesThe mitochondria has two membranes The fluid-filled space within the inner The fluid-filled space within the inner

membrane is known as the matrixmembrane is known as the matrix This matrix contains many of the This matrix contains many of the

chemicals and proteins required to break chemicals and proteins required to break down carbohydratesdown carbohydrates

Metabolic PathwaysMetabolic Pathways

The common chemical equations that The common chemical equations that represent both photosynthesis and represent both photosynthesis and cellular respiration are only cellular respiration are only netnet reactions reactions

Both of these processes use a series of Both of these processes use a series of pathways that are set up in step-by-step pathways that are set up in step-by-step sequencessequences

The Role of EnzymesThe Role of Enzymes

Metabolism (the sum of the processes Metabolism (the sum of the processes within a cell) can be broken into two within a cell) can be broken into two distinct types of reactionsdistinct types of reactions

Anabolic reactions & pathways create Anabolic reactions & pathways create larger molecules from small subunitslarger molecules from small subunits

Catabolic reactions & pathways break Catabolic reactions & pathways break down large molecules into smaller piecesdown large molecules into smaller pieces

Often these reactions will not naturally Often these reactions will not naturally occur because they require energy to occur because they require energy to startstart

This energy required to start a reaction is This energy required to start a reaction is known as activation energyknown as activation energy

Catalysts and enzymes reduce the Catalysts and enzymes reduce the activation energy, allowing the reactions activation energy, allowing the reactions to proceed more rapidlyto proceed more rapidly

Enzymes are protein catalysts within Enzymes are protein catalysts within cellscells

Activation Energy – Activation Energy – Catalyzed vs. Catalyzed vs. UncatalyzedUncatalyzed

Oxidation & ReductionOxidation & Reduction

Recall that oxidation is a reaction where an Recall that oxidation is a reaction where an atom or molecule loses electrons (LEO – Loses atom or molecule loses electrons (LEO – Loses Electrons = Oxidation)Electrons = Oxidation)

When a reaction occurs where an atom or When a reaction occurs where an atom or molecule gains electrons, it is known as molecule gains electrons, it is known as reduction (GER – Gains Electrons = reduction (GER – Gains Electrons = Reduction)Reduction)

However, free electrons from oxidation cannot However, free electrons from oxidation cannot exist on their ownexist on their own

As a result, the electrons that are lost As a result, the electrons that are lost through oxidation of one substance through oxidation of one substance cause the reduction of another cause the reduction of another compoundcompound

Therefore, oxidation and reduction must Therefore, oxidation and reduction must occur at the same timeoccur at the same time

5.2 - Photosynthesis5.2 - Photosynthesis

Photosynthesis actually involves over Photosynthesis actually involves over 100 individual chemical reactions that 100 individual chemical reactions that work togetherwork together

These reactions can be summarized in These reactions can be summarized in two groups:two groups:

1.1. Light-Dependent ReactionsLight-Dependent Reactions

2.2. Light-Independent ReactionsLight-Independent Reactions

Light-Dependent Light-Dependent ReactionsReactions

During these reactions, the pigments During these reactions, the pigments contained inside the thylakoid absorb contained inside the thylakoid absorb light energylight energy

Although plants have a number of Although plants have a number of pigments, the most important for pigments, the most important for photosynthesis is chlorophyllphotosynthesis is chlorophyll

Chlorophyll & LightChlorophyll & Light

Chlorophyll appears green, so it absorbs Chlorophyll appears green, so it absorbs all but yellow and green lightall but yellow and green light

However, other pigments also contribute However, other pigments also contribute to photosynthesisto photosynthesis

For instance, Beta-carotene appears to For instance, Beta-carotene appears to be orange, which means that blue and be orange, which means that blue and green light are absorbedgreen light are absorbed

Absorption Spectrum – Absorption Spectrum – Chlorophyll & Chlorophyll & CarotenoidsCarotenoids

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PhotosystemsPhotosystems

In the thylakoid membrane, chlorophyll is In the thylakoid membrane, chlorophyll is organized along with proteins and organized along with proteins and smaller organic molecules into smaller organic molecules into photosystemsphotosystems..

A photosystem acts like a light-gathering A photosystem acts like a light-gathering “antenna complex” consisting of a few “antenna complex” consisting of a few hundred chlorophyll hundred chlorophyll a,a, chlorophyll chlorophyll b,b,and carotenoidand carotenoidmolecules.molecules.

The various pigment molecules produce The various pigment molecules produce free electrons when light hits themfree electrons when light hits them

These free electrons are passed along to These free electrons are passed along to the the reaction centerreaction center, a specialized , a specialized chlorophyll a molecule chlorophyll a molecule

When the electron in the reaction center When the electron in the reaction center is “excited” by the addition of energy, it is “excited” by the addition of energy, it passes to the electron-acceptor moleculepasses to the electron-acceptor molecule

This reduces the electron acceptor and This reduces the electron acceptor and puts it at a high energy levelputs it at a high energy level

A series of steps then takes place:A series of steps then takes place:

Step 1Step 1 The electron leaves the reaction center of The electron leaves the reaction center of

photosystem II and joins with the electron photosystem II and joins with the electron acceptoracceptor

This leaves an “electron hole” in This leaves an “electron hole” in photosystem IIphotosystem II

Enzymes break down a water molecule, Enzymes break down a water molecule, which releases Hwhich releases H++ ions, electrons, and ions, electrons, and oxygen (this is the step in photosynthesis oxygen (this is the step in photosynthesis that produces oxygen gas)that produces oxygen gas)

Step 2Step 2 The electron acceptor transfers the The electron acceptor transfers the

energized electron to a series of electron-energized electron to a series of electron-carrying molecules (known as the carrying molecules (known as the electron transport system)electron transport system)

As the electron moves through this As the electron moves through this system, it loses energysystem, it loses energy

The “lost” energy from the electrons are The “lost” energy from the electrons are used to push Hused to push H++ ions across the stroma, ions across the stroma, across the thylakoid membrane and into across the thylakoid membrane and into the thylakoid spacethe thylakoid space

The movement of the HThe movement of the H++ ions into the ions into the thylakoid space produces a concentration thylakoid space produces a concentration gradient (the pH within the thylakoid gradient (the pH within the thylakoid space is about 5, while the pH in the space is about 5, while the pH in the stroma is about 8)stroma is about 8)

This concentration gradient serves as a This concentration gradient serves as a source of potential energysource of potential energy

Step 3Step 3 While steps 1 & 2 are taking place, While steps 1 & 2 are taking place,

photosystem I is absorbing lightphotosystem I is absorbing light Again, an electron is released from the Again, an electron is released from the

action center and is passed to a high-action center and is passed to a high-energy electron-acceptorenergy electron-acceptor

The electron lost from photosystem I is The electron lost from photosystem I is replaced by the electron arriving through replaced by the electron arriving through the electron transport system from the electron transport system from photosystem Iphotosystem I

Step 4Step 4

The electron from photosystem I is used The electron from photosystem I is used to reduce NADPto reduce NADP++ to form NADPH to form NADPH

NADPH’s reducing power is then used NADPH’s reducing power is then used later in the light-independent reactionslater in the light-independent reactions

A summary of the Steps:A summary of the Steps: The light reactions The light reactions

use the solar power use the solar power of photons of photons absorbed by both absorbed by both photosystem I and photosystem I and photosystem II to photosystem II to provide chemical provide chemical energy in the form energy in the form of ATP and of ATP and reducing reducing power in the form power in the form of the electrons of the electrons carried by NADPH.carried by NADPH.

Fig. 10.13

Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

ATP Production - ATP Production - ChemiosmosisChemiosmosis

The energy from the electrons in The energy from the electrons in photosystem II is used to produce ATP photosystem II is used to produce ATP indirectlyindirectly

As previously mentioned, the energy of As previously mentioned, the energy of the electrons is used to push Hthe electrons is used to push H++ ions ions against the concentration gradient into against the concentration gradient into the thylakoid spacethe thylakoid space

What Happens During What Happens During Chemiosmosis?Chemiosmosis?

1.1. HH++ ions move into the thylakoid space ions move into the thylakoid space through active transportthrough active transport

2.2. To return to the stroma, the HTo return to the stroma, the H++ ions ions must move through a structure known must move through a structure known as ATP synthaseas ATP synthase

3.3. ATP synthase uses the movement of ATP synthase uses the movement of the Hthe H++ ions to run a mechanism that ions to run a mechanism that bonds together ADP and free bonds together ADP and free phosphates to form ATPphosphates to form ATP

ChemiosmosisChemiosmosis

Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

A Model for Efficient A Model for Efficient Energy?Energy?

Current methods of energy generation Current methods of energy generation are relatively inefficientare relatively inefficient

Current solar power technology is not Current solar power technology is not efficient – it produces too little energy per efficient – it produces too little energy per unit of area to be practicalunit of area to be practical

Most of our energy right now comes from Most of our energy right now comes from fossil fuel sources, which contribute to fossil fuel sources, which contribute to global warmingglobal warming

Hydrogen can be used as a clean fuel, Hydrogen can be used as a clean fuel, but the production of hydrogen gas but the production of hydrogen gas requires large amounts of energyrequires large amounts of energy

Recall that photosystem II produces Recall that photosystem II produces hydrogen ions (but not gas) from water hydrogen ions (but not gas) from water using only light energy and enzymesusing only light energy and enzymes

Scientists hope that a similar artificial Scientists hope that a similar artificial system might be developed to obtain system might be developed to obtain hydrogen gas efficiently from water to hydrogen gas efficiently from water to use in energy generationuse in energy generation

The Light-Independent The Light-Independent ReactionsReactions

Once enough ATP and NADPH has been Once enough ATP and NADPH has been produced by the chloroplasts, glucose produced by the chloroplasts, glucose can be synthesizedcan be synthesized

This involves a series of reactions known This involves a series of reactions known as the Calvin-Benson cycleas the Calvin-Benson cycle

The Calvin-Benson CycleThe Calvin-Benson Cycle

The Calvin cycle regenerates its starting The Calvin cycle regenerates its starting material after molecules enter and leave the material after molecules enter and leave the cyclecycle

COCO22 enters the cycle and leaves as sugar enters the cycle and leaves as sugar The cycle spends the energy of ATP and the The cycle spends the energy of ATP and the

reducing power of electrons carried by NADPH reducing power of electrons carried by NADPH to make the sugarto make the sugar

The actual sugar product of the Calvin cycle is The actual sugar product of the Calvin cycle is not glucose, but a three-carbon sugar, not glucose, but a three-carbon sugar, glyceraldehyde-3-phosphateglyceraldehyde-3-phosphate ( (G3PG3P))

Each turn of the Calvin cycle fixes one Each turn of the Calvin cycle fixes one carbon.carbon.

For the net synthesis of one G3P For the net synthesis of one G3P molecule, the cycle must take place three molecule, the cycle must take place three times, fixing three molecules of COtimes, fixing three molecules of CO22..

To make one glucose molecules would To make one glucose molecules would require six cycles and the fixation of six require six cycles and the fixation of six COCO22 molecules. molecules.

The Calvin cycle has three phases.The Calvin cycle has three phases.

Phase 1 – Carbon FixationPhase 1 – Carbon Fixation

In the carbon fixation phase, each COIn the carbon fixation phase, each CO22

molecule is attached to a five-carbon molecule is attached to a five-carbon sugar, ribulose bisphosphate (RuBP).sugar, ribulose bisphosphate (RuBP). This is catalyzed by RuBP carboxylase or This is catalyzed by RuBP carboxylase or rubiscorubisco..

The six-carbon intermediate splits in half to The six-carbon intermediate splits in half to form two molecules of 3-phosphoglycerate form two molecules of 3-phosphoglycerate per COper CO22..

Phase 2 - ReductionPhase 2 - Reduction

During reduction, each 3-During reduction, each 3-phosphoglycerate receives another phosphoglycerate receives another phosphate group from ATP to form 1,3 phosphate group from ATP to form 1,3 bisphosphoglycerate.bisphosphoglycerate.

A pair of electrons from NADPH reduces A pair of electrons from NADPH reduces each 1,3 bisphosphoglycerate to G3P.each 1,3 bisphosphoglycerate to G3P. The electrons reduce a carboxyl group to a The electrons reduce a carboxyl group to a

carbonyl group.carbonyl group.

Phase 3 - RegenerationPhase 3 - Regeneration

In the last phase, regeneration of the COIn the last phase, regeneration of the CO22

acceptor (RuBP), these five G3P acceptor (RuBP), these five G3P molecules are rearranged to form 3 molecules are rearranged to form 3 RuBP molecules.RuBP molecules.

To do this, the cycle must spend three To do this, the cycle must spend three more molecules of ATP (one per RuBP) more molecules of ATP (one per RuBP) to complete the cycle and prepare for the to complete the cycle and prepare for the next.next.

Overall Costs:Overall Costs: For the net synthesis of one G3P For the net synthesis of one G3P

molecule, the Calvin recycle consumes molecule, the Calvin recycle consumes nine ATP and six NAPDH.nine ATP and six NAPDH. It “costs” three ATP and two NADPH per It “costs” three ATP and two NADPH per

COCO22.. The G3P from the Calvin cycle is the The G3P from the Calvin cycle is the

starting material for metabolic pathways starting material for metabolic pathways that synthesize other organic that synthesize other organic compounds, including glucose and other compounds, including glucose and other carbohydrates.carbohydrates.

5.3 – Cellular Respiration 5.3 – Cellular Respiration Releases Energy from Releases Energy from Organic CompoundsOrganic Compounds

During photosynthesis electrons and During photosynthesis electrons and hydrogen ions are chemically bonded to hydrogen ions are chemically bonded to carbon dioxide reducing it to produce carbon dioxide reducing it to produce glucose moleculesglucose molecules

Cellular respiration is the reverse of thisCellular respiration is the reverse of this Glucose is oxidized to carbon dioxide Glucose is oxidized to carbon dioxide

while releasing energy and water while releasing energy and water

Photosynthesis Photosynthesis & Cellular & Cellular Respiration are Respiration are complimentary complimentary processesprocesses

Releasing Stored EnergyReleasing Stored Energy

There are three ways of releasing the energy There are three ways of releasing the energy stored in food:stored in food:

1.1. Aerobic cellular respiration is carried out by Aerobic cellular respiration is carried out by organisms that live in oxic (oxygen organisms that live in oxic (oxygen containing) environments containing) environments

2.2. Anaerobic cellular respiration is carried out by Anaerobic cellular respiration is carried out by organisms that live in anoxic (no-oxygen organisms that live in anoxic (no-oxygen containing) environments containing) environments

3.3. A third pathway for energy release is A third pathway for energy release is fermentation. This process is a modified form fermentation. This process is a modified form of anaerobic cellular respiration of anaerobic cellular respiration

Aerobic vs. Anaerobic Aerobic vs. Anaerobic RespirationRespiration

Aerobic Cellular Aerobic Cellular RespirationRespiration

This is an oxidation reaction in which This is an oxidation reaction in which reactions transfer electrons from high-reactions transfer electrons from high-energy molecules to oxygenenergy molecules to oxygen

Most of the energy in plants, animals and Most of the energy in plants, animals and most eukaryotic (membrane bound most eukaryotic (membrane bound nucleus) cells is produced in this processnucleus) cells is produced in this process

The process starts with glycolysis, an The process starts with glycolysis, an anaerobic reaction in the cytoplasm anaerobic reaction in the cytoplasm

GlycolysisGlycolysis

In glycolysis, a In glycolysis, a glucose glucose molecule is molecule is converted into converted into two molecules two molecules of pyruvic acidof pyruvic acid

ATP and NADH ATP and NADH are also are also producedproduced

Steps in GlycolysisSteps in Glycolysis1.1. 2 ATP are used to change glucose to fructose 2 ATP are used to change glucose to fructose

diphosphatediphosphate

2.2. The fructose molecule is split into two molecules The fructose molecule is split into two molecules of PGAL (or G3P)of PGAL (or G3P)

3.3. The G3P molecules are oxidized and their The G3P molecules are oxidized and their electrons are donated to NADelectrons are donated to NAD++ to form 2 NADH to form 2 NADH

4.4. Finally, the molecules are converted to pyruvate Finally, the molecules are converted to pyruvate and 4 molecules of ATP are producedand 4 molecules of ATP are produced

General Notes Regarding General Notes Regarding GlycolysisGlycolysis Note that oxygen is NOT required for Note that oxygen is NOT required for

glycolysisglycolysis Glycolysis occurs in the cytoplasm of cells, Glycolysis occurs in the cytoplasm of cells,

not in the mitochondrianot in the mitochondria Glycolysis produces 4 ATP while Glycolysis produces 4 ATP while

consuming 2 ATP, providing a net outcome consuming 2 ATP, providing a net outcome of 2 ATPof 2 ATP

2 reduced NADH molecules are also 2 reduced NADH molecules are also producedproduced

Glycolysis Animation

The Fate of PyruvateThe Fate of Pyruvate

Pyruvate contains large amounts of Pyruvate contains large amounts of chemical energy chemical energy

If there is no oxygen present the pyruvate If there is no oxygen present the pyruvate proceeds to fermentation proceeds to fermentation

When there is sufficient oxygen, the When there is sufficient oxygen, the pyruvate is transferred to the pyruvate is transferred to the mitochondria mitochondria

Pyruvate & Coenzyme APyruvate & Coenzyme A Pyruvate loses a carbon in the form of Pyruvate loses a carbon in the form of

carbon dioxidecarbon dioxide When this occurs, another molecule of When this occurs, another molecule of

NADNAD++ is reduced to form NADH is reduced to form NADH The remaining 2 carbon atoms from The remaining 2 carbon atoms from

pyruvate attach to a molecule called pyruvate attach to a molecule called Coenzyme ACoenzyme A

Coenzyme A “tows” the acetyl group into Coenzyme A “tows” the acetyl group into the Krebs cycle (in the form of acetyl-CoA)the Krebs cycle (in the form of acetyl-CoA)

The Krebs CycleThe Krebs Cycle

During this During this cycle ATP cycle ATP and reduced and reduced compounds compounds are formed are formed (NADH & (NADH & FADHFADH22))

Steps in the Krebs CycleSteps in the Krebs Cycle1.1. Acetyl CoA binds with a 4-carbon Acetyl CoA binds with a 4-carbon

molecule to form a 6-carbon molecule.molecule to form a 6-carbon molecule.2.2. The 6-carbon molecule loses a carbon in The 6-carbon molecule loses a carbon in

the form of COthe form of CO22. This releases an . This releases an electron and a hydrogen atom to form electron and a hydrogen atom to form NADH from NADNADH from NAD++. .

3.3. The new 5-carbon molecule loses a The new 5-carbon molecule loses a carbon in the form of COcarbon in the form of CO22. This releases . This releases an electron and a hydrogen atom to form an electron and a hydrogen atom to form NADH from NADNADH from NAD++. As well, ATP is . As well, ATP is formed.formed.

4.4. The four-carbon molecule undergoes a The four-carbon molecule undergoes a series of structural changes that release series of structural changes that release more electrons, allowing the production more electrons, allowing the production of 1 FADHof 1 FADH22 molecule from FAD, and the molecule from FAD, and the

production of another NADH molecule production of another NADH molecule from NADfrom NAD++

5.5. The four-carbon molecule is now the The four-carbon molecule is now the same as the original molecule that same as the original molecule that started the cycle binding to acetyl-coAstarted the cycle binding to acetyl-coA

Krebs Cycle Animation

The Electron Transport The Electron Transport ChainChain Electron transport produces large amounts Electron transport produces large amounts

of ATP during cellular respiration of ATP during cellular respiration Similar to photosynthesis the high energy Similar to photosynthesis the high energy

electrons are passed down a chain within electrons are passed down a chain within the mitochondrion membrane the mitochondrion membrane

The energy is used to drive hydrogen The energy is used to drive hydrogen pumps to get hydrogen across the pumps to get hydrogen across the membrane membrane

This pumping of hydrogen creates a This pumping of hydrogen creates a concentration gradient concentration gradient

This can be used to power the formation of This can be used to power the formation of ATP from ADP in chemiosmosisATP from ADP in chemiosmosis

Chemiosmosis Animation

Components of the Components of the Electron Transport ChainElectron Transport Chain

Oxygen & Electron Oxygen & Electron TransportTransport The electron transport chain requires The electron transport chain requires

oxygen in aerobic respirationoxygen in aerobic respiration As electrons move down the electron As electrons move down the electron

transport chain they eventually reach the transport chain they eventually reach the final electron acceptor, which is oxygenfinal electron acceptor, which is oxygen

The oxygen is reduced, picking up The oxygen is reduced, picking up hydrogen & its electrons and forming hydrogen & its electrons and forming water water

If oxygen were not present at this final If oxygen were not present at this final point, it would prevent electrons from point, it would prevent electrons from passing from the previous electron passing from the previous electron receptorreceptor

Without it the reaction would cease, much Without it the reaction would cease, much like a traffic jam backing up the freeway like a traffic jam backing up the freeway

Each preceding reaction would not be Each preceding reaction would not be able to take place all the way back to able to take place all the way back to glycolysis glycolysis

Glycolysis only produces 4 ATP Glycolysis only produces 4 ATP molecules while the electron transport molecules while the electron transport system produces 24 ATP molecules system produces 24 ATP molecules

As well, NADH and FADHAs well, NADH and FADH22 molecules molecules

would remain in their reduced forms, would remain in their reduced forms, unable to receive new electrons, further unable to receive new electrons, further reducing the amount of energy producedreducing the amount of energy produced

Cellular Respiration Review Animation

Anaerobic RespirationAnaerobic Respiration

When oxygen is not available the final electron When oxygen is not available the final electron acceptor in an anoxic environment other acceptor in an anoxic environment other molecules are used molecules are used

Anaerobic respiration is not as efficient at Anaerobic respiration is not as efficient at aerobic aerobic

The organisms that live in these types of The organisms that live in these types of environments use inorganic chemicals such as environments use inorganic chemicals such as sulfate, nitrate and carbon dioxide as acceptors sulfate, nitrate and carbon dioxide as acceptors

The Products of The Products of Anaerobic RespirationAnaerobic Respiration

The final byproducts are sulfur, nitrite, The final byproducts are sulfur, nitrite, nitrogen and methane (bacteria living in nitrogen and methane (bacteria living in large intestines live in an anaerobic large intestines live in an anaerobic environment) environment)

FermentationFermentation

Fermentation is the metabolic Fermentation is the metabolic pathway to produce ATP pathway to produce ATP when organisms lack oxygen when organisms lack oxygen

This pathway produces only This pathway produces only the ATP that is generated the ATP that is generated during glycolysis, therefore, it during glycolysis, therefore, it is less efficient than aerobic is less efficient than aerobic respiration respiration

What Carries out What Carries out Fermentation?Fermentation?

Many single-celled organisms carry out Many single-celled organisms carry out fermentation fermentation

Fermentation can also occur deep within Fermentation can also occur deep within tissues that are not near an oxygen tissues that are not near an oxygen source such as submerged plant tissue source such as submerged plant tissue

There are two types of fermentation:There are two types of fermentation:

Lactate FermentationLactate Fermentation

Cells that are temporarily without oxygen carry Cells that are temporarily without oxygen carry out lactate fermentation out lactate fermentation

The cells convert pyruvate to a molecule called The cells convert pyruvate to a molecule called lactate or lactic acid lactate or lactic acid

This lactate is then storedThis lactate is then stored When the oxygen content increases the lactate When the oxygen content increases the lactate

is converted to pyruvate which continues in the is converted to pyruvate which continues in the Krebs cycle in the aerobic pathway Krebs cycle in the aerobic pathway

Ethanol FermentationEthanol Fermentation

Some organism can function both Some organism can function both aerobically and anaerobically aerobically and anaerobically

When they function anaerobically they When they function anaerobically they carry out ethanol fermentation carry out ethanol fermentation

This process involves two steps:This process involves two steps:

Ethanol FermentationEthanol Fermentation

1.1. After glycolysis produces pyruvate the After glycolysis produces pyruvate the pyruvate is converted into a two carbon pyruvate is converted into a two carbon compound by the release of COcompound by the release of CO22

2.2. This two carbon compound is then This two carbon compound is then reduced by NADH to form ethanol reduced by NADH to form ethanol

Fermentation PathwaysFermentation Pathways

Uses of Fermentation Uses of Fermentation ProductsProducts

During WWI large amounts of butanol and During WWI large amounts of butanol and acetone were needed acetone were needed

Previously this attained by burning wood Previously this attained by burning wood without oxygen without oxygen

The yield was low – about 100:1 The yield was low – about 100:1 A scientist discovered the fermentation A scientist discovered the fermentation

pathway and could convert molasses or grain pathway and could convert molasses or grain to butanol and acetone with yields of 100:24 to butanol and acetone with yields of 100:24 and 100:12 respectively and 100:12 respectively

The process of fermentation produces The process of fermentation produces large amounts of ethanol which humans large amounts of ethanol which humans learned long ago could be burned learned long ago could be burned

Ethanol is being produced on a large scale Ethanol is being produced on a large scale to add to or in some cases replace hydro-to add to or in some cases replace hydro-carbons as a fuel source carbons as a fuel source

Most commonly it is produced from the Most commonly it is produced from the fermentation of corn or wheat fermentation of corn or wheat

The starch is converted to glucose by The starch is converted to glucose by enzymes which the yeast then enzymes which the yeast then anaerobically produce ethanol anaerobically produce ethanol

This can be distilled producing almost This can be distilled producing almost pure ethanol pure ethanol

Burning of ethanol results in carbon Burning of ethanol results in carbon dioxide, however, this produces less dioxide, however, this produces less carbon monoxide and other volatile carbon monoxide and other volatile organic compounds that contribute to organic compounds that contribute to smog smog

In 2007, the IndyCar series switched the type of fuel used by their cars to 100% ethanol

Manure as Fuel? Manure as Fuel?

Manure from pigs and cattle can be captured, Manure from pigs and cattle can be captured, stored in an oxygen free container, allowed to stored in an oxygen free container, allowed to decompose in the presence of anaerobic decompose in the presence of anaerobic bacteria to produce methane and carbon-bacteria to produce methane and carbon-dioxide dioxide

The methane can be burned to produce heat, The methane can be burned to produce heat, light or electricity light or electricity

One family of 4-6 could use the manure from 5 One family of 4-6 could use the manure from 5 pigs for their daily needs of heating rather than pigs for their daily needs of heating rather than 11 kg of propane 11 kg of propane

But Wait – What About that But Wait – What About that Pesky Carbon Dioxide I keep Pesky Carbon Dioxide I keep Hearing About?Hearing About?

The advantage of this is that the carbon that is The advantage of this is that the carbon that is created from the fermentation is recycled from created from the fermentation is recycled from the glucose created from the plants, therefore it the glucose created from the plants, therefore it is carbon neutral is carbon neutral

When we burn fossil fuels we are releasing When we burn fossil fuels we are releasing carbon that has been stored for millions of carbon that has been stored for millions of years after being taken out of circulation years after being taken out of circulation

The large amounts that are being released The large amounts that are being released over a short time now are concentrating it in over a short time now are concentrating it in the environment more than any other time in the environment more than any other time in history with devastating effects history with devastating effects