What Yoursquoll Learn You will recognize why organ-

isms need a constant supply ofenergy and where that energycomes from

You will identify how cells storeand release energy as ATP

You will describe the pathwaysby which cells obtain energy

You will compare ATP produc-tion in mitochondria and inchloroplasts

Why Itrsquos ImportantEvery cell in your body needsenergy in order to function The energy your cells store is the fuel for basic body functionssuch as walking and breathing

Energy in a CellEnergy in a Cell

Johann SchumacherPeter Arnold Inc

Visit tobull study the entire chapter

onlinebull access Web Links for more

information and activities oncell energy

bull review content with theInteractive Tutor and self-check quizzes

This squirrel is eating seeds produced by the conifer Theconifer traps light energy andstores it in the bonds of certainmolecules for later use How dothe squirrelrsquos cells which cannottrap light energy use the mole-cules in the seeds to supplyenergy for the squirrel

Understandingthe Photo

220

ncbdolglencoecom

0220 C9CO BDOL-829900 8404 423 AM Page 220

91SECTION PREVIEWObjectivesExplain why organismsneed a supply of energyDescribe how energy isstored and released by ATP

Review Vocabularyactive transport movement

of materials through amembrane against a concentration gradientrequires energy from the cell (p 199)

New VocabularyATP (adenosine triphosphate)

ADP (adenosine diphosphate)

91 THE NEED FOR ENERGY 221

Why ATPUsing an Analogy A spring stores energywhen it is compressed When the com-pressed spring is released energy also isreleased energy that sends this smiley-faced toy flying into the air Likethis coiled spring chemical bondsstore energy that can be releasedwhen the bond is broken Just assome springs are tighter than oth-ers some chemical bonds storemore energy than othersSummarize Scan this section and make a list of general ways in which cells use energy

The Need for Energy

Stored energy

Cell EnergyEnergy is essential to life All living

organisms must be able to obtain energyfrom the environment in which they livePlants and other green organisms are ableto trap the light energy in sunlight andstore it in the bonds of certain moleculesfor later use Other organisms such as thepanda shown in Figure 91 cannot usesunlight directly Instead they eat greenplants In that way they obtain the energystored in plants

Work and the need for energyYoursquove learned about several cell

processes that require energy Activetransport cell division movement of fla-gella or cilia and the production trans-port and storage of proteins are someexamples You can probably come up withother examples of biological work such asmuscles contracting during exercise your

Figure 91Because this pandacannot trap thesunrsquos energy foruse in its body iteats bambooMolecules in bam-boo leaves containenergy in theirchemical bondsSome of thosemolecules supplyenergy for thepanda

(tl tr)Aaron Haupt (bl)Tom McHughPhoto Researchers

Objective 203 Investigatethe cell as a living system including Energy use andrelease in biochemical reactions

North Carolina Objectives

0221-0224 C9S1 BDOL-829900 8404 429 AM Page 221

BDOL-91

null

29697336

heart pumping and your brain control-ling your entire body This work can-not be done without energy

When you finish strenuous physi-cal exercise such as running crosscountry your body needs a quicksource of energy so you may eat agranola bar On a cellular level thereis a molecule in your cells that is aquick source of energy for anyorganelle in the cell that needs it

This energy is stored in the chemicalbonds of the molecule and can beused quickly and easily by the cell

The name of this energy moleculeis adenosine triphosphate (uh DEH

nuh seen bull tri FAHS fayt) or ATP forshort ATP is composed of an adeno-sine molecule with three phosphategroups attached Recall that phos-phate groups are charged particlesand remember that particles with thesame charge do not like being tooclose to each other

Forming and Breaking Down ATP

The charged phosphate groups actlike the positive poles of two mag-nets If like poles of a magnet areplaced next to each other it is diffi-cult to force the magnets togetherLikewise bonding three phosphategroups to form adenosine triphos-phate requires considerable energyWhen only one phosphate groupbonds a small amount of energy isrequired and the chemical bond doesnot store much energy This mole-cule is called adenosine monophos-phate (AMP) When a secondphosphate group is added moreenergy is required to force the twogroups together This molecule iscalled adenosine diphosphate orADP An even greater amount ofenergy is required to force a thirdcharged phosphate group closeenough to the other two to form abond When this bond is brokenenergy is released

The energy of ATP becomes avail-able to a cell when the molecule is broken down In other words whenthe chemical bond between the sec-ond and third phosphate groups inATP is broken energy is released andthe resulting molecule is ADP At this

222 ENERGY IN A CELLMel VictorThe Stock Shop

mono- di- tri- fromthe Greek wordsmono and di andthe Latin word trimeaning ldquoonerdquoldquotwordquo and ldquothreerdquorespectivelyAdenosine triphos-phate contains threephosphate groups

Recognize Cause and EffectWhy is fat the choiceHumans store their excess energy as fat rather than as car-bohydrates Why is this From an evolutionary and efficiencypoint of view fats are better for storage than carbohydrates Find out why

Solve the ProblemThe following facts compare certain characteristics of fats andcarbohydratesA When broken down by the body each six-carbon molecule

of fat yields 51 ATP molecules Each six-carbon carbo-hydrate molecule yields 36 ATP molecules

B Carbohydrates bind and store water The metabolism ofwater yields no ATP Fat has no water bound to it

C An adult who weighs 70 kg can survive on the energyderived from stored fat for 30 days without eating Thesame person would have to weigh nearly 140 kg to survive30 days on stored carbohydrates

Thinking Critically1 Analyze From an ATP production viewpoint use fact B

to make a statement regarding the efficiency of fats vs carbohydrates

2 Define Operationally Explain why the average weightfor humans is close to 70 kg and not 140 kg

0221-0224 C9S1 BDOL-829900 8404 430 AM Page 222

point ADP can form ATP again bybonding with another phosphategroup This process creates a renew-able cycle of ATP formation andbreakdown Figure 92A illustratesthe chemical reactions that areinvolved in the cycle

The formationbreakdown recy-cling activity is important because itrelieves the cell of having to store allof the ATP it needs As long as phos-phate groups are available the cellcan make more ATP Another benefitof the formationbreakdown cycle isthat ADP also can be used as anenergy source Although most cellfunctions require the amount ofenergy in ATP some cell functions donot require as much energy and canuse the energy stored in ADP Readthe Problem-Solving Lab on the oppo-site page and think about how thehuman body stores energy

How cells tap into the energystored in ATP

When ATP is broken down and theenergy is released as shown in Figure 92B the energy must be cap-tured and used efficiently by cellsOtherwise it is wasted ATP is a smallmolecule Many proteins have a spe-cific site where ATP can bind Thenwhen the phosphate bond is brokenand the energy released the cell canuse the energy for activities such asmaking a protein or transporting mol-ecules through the plasma membraneThis cellular process is similar to theway energy in batteries is used by aradio Batteries sitting on a table are oflittle use if the energy stored withinthe batteries cannot be accessedWhen the batteries are snapped intothe holder in the radio the radio thenhas access to the stored energy andcan use it When the energy in the

91 THE NEED FOR ENERGY 223

ADP

ADP

ATP

Adenosine

Protein

P P P

P

P

P

Adenosine P P

Adenosine triphosphate (ATP)

Adenosine diphosphate (ADP)

+ Energy

The addition and release of a phosphate group onadenosine diphosphate creates a cycle of ATP forma-tion and breakdown

A To access the energy stored in ATP proteins bind ATPand uncouple the phosphate group The ADP that isformed is released and the protein binding site canonce again bind ATP

B

Figure 92The formation and breakdown of ATP is cyclic

0221-0224 C9S1 BDOL-829900 8404 431 AM Page 223

Understanding Main Ideas1 Identify cellular processes that need energy

from ATP

2 How does ATP store energy

3 How can ADP be ldquorecycledrdquo to form ATP again

4 How do proteins in your cells access the energystored in ATP

5 List three biological activities that require energy

Thinking Critically6 Phosphate groups in ATP repel each other because

they have negative charges What charge mightbe present in the ATP binding site of a protein toattract ATP

7 Get the Big Picture How does an animal accessthe energy in sunlight For more help refer toGet the Big Picture in the Skill Handbook

SKILL REVIEWSKILL REVIEW

224 ENERGY IN A CELL(t)Dr KS KimPeter Arnold Inc (b)National Geographic Society Image Collection

Figure 93ATP fuels the cellular activitythat drives the organism DefineOperationally What organelles do these cells or organismsuse for movement

Some organisms(left) use energyfrom ATP to move

C

batteries has been used the batteriescan be taken out recharged andreplaced in the holder In a similarfashion in a cell when ATP has beenbroken down to ADP the ADP isreleased from the binding site in theprotein and the binding site may thenbe filled by another ATP molecule

Uses of Cell EnergyYou can probably think of hun-

dreds of physical activities thatrequire energy but energy is equallyimportant at the cellular level

Making new molecules is one waythat cells use energy Some of thesemolecules are enzymes Other mole-cules build membranes and cellorganelles Cells use energy tomaintain homeostasis Kidneys useenergy to move molecules and ions in order to eliminate waste substances while keeping needed substances in the bloodstreamFigure 93 shows several ways thatcells use energy

List three cellularactivities that require energy

Stained TEM Magnification 18 000

Nerve cells transmitimpulses by usingATP to power theactive transport ofcertain ions

A

Fireflies and many marine organisms such asthe jellyfish shown here produce light by aprocess called bioluminescence The light resultsfrom a chemical reaction that is powered by thebreakdown of ATP

B

ncbdolglencoecomself_check_quiz

0221-0224 C9S1 BDOL-829900 8404 431 AM Page 224

heart pumping and your brain control-ling your entire body This work can-not be done without energy

When you finish strenuous physi-cal exercise such as running crosscountry your body needs a quicksource of energy so you may eat agranola bar On a cellular level thereis a molecule in your cells that is aquick source of energy for anyorganelle in the cell that needs it

This energy is stored in the chemicalbonds of the molecule and can beused quickly and easily by the cell

The name of this energy moleculeis adenosine triphosphate (uh DEH

nuh seen bull tri FAHS fayt) or ATP forshort ATP is composed of an adeno-sine molecule with three phosphategroups attached Recall that phos-phate groups are charged particlesand remember that particles with thesame charge do not like being tooclose to each other

Forming and Breaking Down ATP

The charged phosphate groups actlike the positive poles of two mag-nets If like poles of a magnet areplaced next to each other it is diffi-cult to force the magnets togetherLikewise bonding three phosphategroups to form adenosine triphos-phate requires considerable energyWhen only one phosphate groupbonds a small amount of energy isrequired and the chemical bond doesnot store much energy This mole-cule is called adenosine monophos-phate (AMP) When a secondphosphate group is added moreenergy is required to force the twogroups together This molecule iscalled adenosine diphosphate orADP An even greater amount ofenergy is required to force a thirdcharged phosphate group closeenough to the other two to form abond When this bond is brokenenergy is released

The energy of ATP becomes avail-able to a cell when the molecule is broken down In other words whenthe chemical bond between the sec-ond and third phosphate groups inATP is broken energy is released andthe resulting molecule is ADP At this

222 ENERGY IN A CELLMel VictorThe Stock Shop

mono- di- tri- fromthe Greek wordsmono and di andthe Latin word trimeaning ldquoonerdquoldquotwordquo and ldquothreerdquorespectivelyAdenosine triphos-phate contains threephosphate groups

Recognize Cause and EffectWhy is fat the choiceHumans store their excess energy as fat rather than as car-bohydrates Why is this From an evolutionary and efficiencypoint of view fats are better for storage than carbohydrates Find out why

Solve the ProblemThe following facts compare certain characteristics of fats andcarbohydratesA When broken down by the body each six-carbon molecule

of fat yields 51 ATP molecules Each six-carbon carbo-hydrate molecule yields 36 ATP molecules

B Carbohydrates bind and store water The metabolism ofwater yields no ATP Fat has no water bound to it

C An adult who weighs 70 kg can survive on the energyderived from stored fat for 30 days without eating Thesame person would have to weigh nearly 140 kg to survive30 days on stored carbohydrates

Thinking Critically1 Analyze From an ATP production viewpoint use fact B

to make a statement regarding the efficiency of fats vs carbohydrates

2 Define Operationally Explain why the average weightfor humans is close to 70 kg and not 140 kg

0221-0224 C9S1 BDOL-829900 8404 430 AM Page 222

point ADP can form ATP again bybonding with another phosphategroup This process creates a renew-able cycle of ATP formation andbreakdown Figure 92A illustratesthe chemical reactions that areinvolved in the cycle

The formationbreakdown recy-cling activity is important because itrelieves the cell of having to store allof the ATP it needs As long as phos-phate groups are available the cellcan make more ATP Another benefitof the formationbreakdown cycle isthat ADP also can be used as anenergy source Although most cellfunctions require the amount ofenergy in ATP some cell functions donot require as much energy and canuse the energy stored in ADP Readthe Problem-Solving Lab on the oppo-site page and think about how thehuman body stores energy

How cells tap into the energystored in ATP

When ATP is broken down and theenergy is released as shown in Figure 92B the energy must be cap-tured and used efficiently by cellsOtherwise it is wasted ATP is a smallmolecule Many proteins have a spe-cific site where ATP can bind Thenwhen the phosphate bond is brokenand the energy released the cell canuse the energy for activities such asmaking a protein or transporting mol-ecules through the plasma membraneThis cellular process is similar to theway energy in batteries is used by aradio Batteries sitting on a table are oflittle use if the energy stored withinthe batteries cannot be accessedWhen the batteries are snapped intothe holder in the radio the radio thenhas access to the stored energy andcan use it When the energy in the

91 THE NEED FOR ENERGY 223

ADP

ADP

ATP

Adenosine

Protein

P P P

P

P

P

Adenosine P P

Adenosine triphosphate (ATP)

Adenosine diphosphate (ADP)

+ Energy

The addition and release of a phosphate group onadenosine diphosphate creates a cycle of ATP forma-tion and breakdown

A To access the energy stored in ATP proteins bind ATPand uncouple the phosphate group The ADP that isformed is released and the protein binding site canonce again bind ATP

B

Figure 92The formation and breakdown of ATP is cyclic

0221-0224 C9S1 BDOL-829900 8404 431 AM Page 223

Understanding Main Ideas1 Identify cellular processes that need energy

from ATP

2 How does ATP store energy

3 How can ADP be ldquorecycledrdquo to form ATP again

4 How do proteins in your cells access the energystored in ATP

5 List three biological activities that require energy

Thinking Critically6 Phosphate groups in ATP repel each other because

they have negative charges What charge mightbe present in the ATP binding site of a protein toattract ATP

7 Get the Big Picture How does an animal accessthe energy in sunlight For more help refer toGet the Big Picture in the Skill Handbook

SKILL REVIEWSKILL REVIEW

224 ENERGY IN A CELL(t)Dr KS KimPeter Arnold Inc (b)National Geographic Society Image Collection

Figure 93ATP fuels the cellular activitythat drives the organism DefineOperationally What organelles do these cells or organismsuse for movement

Some organisms(left) use energyfrom ATP to move

C

batteries has been used the batteriescan be taken out recharged andreplaced in the holder In a similarfashion in a cell when ATP has beenbroken down to ADP the ADP isreleased from the binding site in theprotein and the binding site may thenbe filled by another ATP molecule

Uses of Cell EnergyYou can probably think of hun-

dreds of physical activities thatrequire energy but energy is equallyimportant at the cellular level

Making new molecules is one waythat cells use energy Some of thesemolecules are enzymes Other mole-cules build membranes and cellorganelles Cells use energy tomaintain homeostasis Kidneys useenergy to move molecules and ions in order to eliminate waste substances while keeping needed substances in the bloodstreamFigure 93 shows several ways thatcells use energy

List three cellularactivities that require energy

Stained TEM Magnification 18 000

Nerve cells transmitimpulses by usingATP to power theactive transport ofcertain ions

A

Fireflies and many marine organisms such asthe jellyfish shown here produce light by aprocess called bioluminescence The light resultsfrom a chemical reaction that is powered by thebreakdown of ATP

B

ncbdolglencoecomself_check_quiz

0221-0224 C9S1 BDOL-829900 8404 431 AM Page 224

point ADP can form ATP again bybonding with another phosphategroup This process creates a renew-able cycle of ATP formation andbreakdown Figure 92A illustratesthe chemical reactions that areinvolved in the cycle

The formationbreakdown recy-cling activity is important because itrelieves the cell of having to store allof the ATP it needs As long as phos-phate groups are available the cellcan make more ATP Another benefitof the formationbreakdown cycle isthat ADP also can be used as anenergy source Although most cellfunctions require the amount ofenergy in ATP some cell functions donot require as much energy and canuse the energy stored in ADP Readthe Problem-Solving Lab on the oppo-site page and think about how thehuman body stores energy

How cells tap into the energystored in ATP

When ATP is broken down and theenergy is released as shown in Figure 92B the energy must be cap-tured and used efficiently by cellsOtherwise it is wasted ATP is a smallmolecule Many proteins have a spe-cific site where ATP can bind Thenwhen the phosphate bond is brokenand the energy released the cell canuse the energy for activities such asmaking a protein or transporting mol-ecules through the plasma membraneThis cellular process is similar to theway energy in batteries is used by aradio Batteries sitting on a table are oflittle use if the energy stored withinthe batteries cannot be accessedWhen the batteries are snapped intothe holder in the radio the radio thenhas access to the stored energy andcan use it When the energy in the

91 THE NEED FOR ENERGY 223

ADP

ADP

ATP

Adenosine

Protein

P P P

P

P

P

Adenosine P P

Adenosine triphosphate (ATP)

Adenosine diphosphate (ADP)

+ Energy

The addition and release of a phosphate group onadenosine diphosphate creates a cycle of ATP forma-tion and breakdown

A To access the energy stored in ATP proteins bind ATPand uncouple the phosphate group The ADP that isformed is released and the protein binding site canonce again bind ATP

B

Figure 92The formation and breakdown of ATP is cyclic

0221-0224 C9S1 BDOL-829900 8404 431 AM Page 223

Understanding Main Ideas1 Identify cellular processes that need energy

from ATP

2 How does ATP store energy

3 How can ADP be ldquorecycledrdquo to form ATP again

4 How do proteins in your cells access the energystored in ATP

5 List three biological activities that require energy

Thinking Critically6 Phosphate groups in ATP repel each other because

they have negative charges What charge mightbe present in the ATP binding site of a protein toattract ATP

7 Get the Big Picture How does an animal accessthe energy in sunlight For more help refer toGet the Big Picture in the Skill Handbook

SKILL REVIEWSKILL REVIEW

224 ENERGY IN A CELL(t)Dr KS KimPeter Arnold Inc (b)National Geographic Society Image Collection

Figure 93ATP fuels the cellular activitythat drives the organism DefineOperationally What organelles do these cells or organismsuse for movement

Some organisms(left) use energyfrom ATP to move

C

batteries has been used the batteriescan be taken out recharged andreplaced in the holder In a similarfashion in a cell when ATP has beenbroken down to ADP the ADP isreleased from the binding site in theprotein and the binding site may thenbe filled by another ATP molecule

Uses of Cell EnergyYou can probably think of hun-

dreds of physical activities thatrequire energy but energy is equallyimportant at the cellular level

Making new molecules is one waythat cells use energy Some of thesemolecules are enzymes Other mole-cules build membranes and cellorganelles Cells use energy tomaintain homeostasis Kidneys useenergy to move molecules and ions in order to eliminate waste substances while keeping needed substances in the bloodstreamFigure 93 shows several ways thatcells use energy

List three cellularactivities that require energy

Stained TEM Magnification 18 000

Nerve cells transmitimpulses by usingATP to power theactive transport ofcertain ions

A

Fireflies and many marine organisms such asthe jellyfish shown here produce light by aprocess called bioluminescence The light resultsfrom a chemical reaction that is powered by thebreakdown of ATP

B

ncbdolglencoecomself_check_quiz

0221-0224 C9S1 BDOL-829900 8404 431 AM Page 224

Understanding Main Ideas1 Identify cellular processes that need energy

from ATP

2 How does ATP store energy

3 How can ADP be ldquorecycledrdquo to form ATP again

4 How do proteins in your cells access the energystored in ATP

5 List three biological activities that require energy

Thinking Critically6 Phosphate groups in ATP repel each other because

they have negative charges What charge mightbe present in the ATP binding site of a protein toattract ATP

7 Get the Big Picture How does an animal accessthe energy in sunlight For more help refer toGet the Big Picture in the Skill Handbook

SKILL REVIEWSKILL REVIEW

224 ENERGY IN A CELL(t)Dr KS KimPeter Arnold Inc (b)National Geographic Society Image Collection

Figure 93ATP fuels the cellular activitythat drives the organism DefineOperationally What organelles do these cells or organismsuse for movement

Some organisms(left) use energyfrom ATP to move

C

batteries has been used the batteriescan be taken out recharged andreplaced in the holder In a similarfashion in a cell when ATP has beenbroken down to ADP the ADP isreleased from the binding site in theprotein and the binding site may thenbe filled by another ATP molecule

Uses of Cell EnergyYou can probably think of hun-

dreds of physical activities thatrequire energy but energy is equallyimportant at the cellular level

Making new molecules is one waythat cells use energy Some of thesemolecules are enzymes Other mole-cules build membranes and cellorganelles Cells use energy tomaintain homeostasis Kidneys useenergy to move molecules and ions in order to eliminate waste substances while keeping needed substances in the bloodstreamFigure 93 shows several ways thatcells use energy

List three cellularactivities that require energy

Stained TEM Magnification 18 000

Nerve cells transmitimpulses by usingATP to power theactive transport ofcertain ions

A

Fireflies and many marine organisms such asthe jellyfish shown here produce light by aprocess called bioluminescence The light resultsfrom a chemical reaction that is powered by thebreakdown of ATP

B

ncbdolglencoecomself_check_quiz

0221-0224 C9S1 BDOL-829900 8404 431 AM Page 224

Photosynthesis Trapping the Sunrsquos Energy

92 PHOTOSYNTHESIS TRAPPING THE SUNrsquoS ENERGY 225

SECTION PREVIEWObjectivesRelate the structure ofchloroplasts to the events inphotosynthesisDescribe light-dependentreactionsExplain the reactions and products of the light-independent Calvin cycle

Review Vocabularychloroplast cell organelle

that captures lightenergy and producesfood to store for lateruse (p 184)

New Vocabularyphotosynthesislight-dependent reactionslight-independent reactionspigmentchlorophyllelectron transport chainNADP+photolysisCalvin cycle

92

Photosynthesis Make the following Foldable to help you illustrate what happens during each phase of photosynthesis

Fold a vertical sheet of paper in half from top to bottom

Fold in half from side to side with the fold at the top

STEP 1 STEP 2

1st PhaseLight-

Dependent

2nd PhaseLight-

Independent

Unfold the paper once Cut only the fold of the top flap to make two tabs

Turn the paper vertically and label on the front tabs as shown

STEP 3 STEP 4

Compare and Contrast As you read Section 92 compare and contrast the two phases of photosynthesis under the appropriate tab

Trapping Energy from SunlightTo use the energy in sunlight the cells of green organisms must trap light

energy and store it in a manner that is readily usable by cell organellesmdashinthe chemical bonds of ATP However light energy is not available 24 hoursa day so the cell must also store some of the energy for use during the darkhours The process that uses the sunrsquos energy to make simple sugars is calledphotosynthesis These simple sugars are then converted into complex car-bohydrates such as starches which store energy

Photosynthesis happens in two phases The light-dependent reactionsconvert light energy into chemical energy The molecules of ATP produced in the light-dependent reactions are then used to fuel the light-independent reactions that produce simple sugars The generalequation for photosynthesis is written as follows

6CO2 6H2O rarr C6H12O6 6O2

The BioLab at the end of this chapter can be performed to study whatfactors influence the rate of photosynthesis

photosynthesisfrom the Greekwords photomeaning ldquolightrdquoand syntithenaimeaning ldquoto puttogetherrdquoPhotosynthesisputs togethersugar moleculesusing water car-bon dioxide andenergy from light

Objective 205 Investigate and analyze the bioener-getic reactions Photosynthesis

North Carolina Objectives

0225-0230 C9S2 BDOL-829900 8404 441 AM Page 225

BDOL-92

null

36719736

ExperimentSeparating PigmentsChromatography is an impor-tant diagnostic tool In thisexperiment you will use paperchromatography to separatedifferent pigments from plantleaves

Procedure Obtain a pre-made plant solution from your teacher Place a few drops 2 cm high on a 5-cm 14-cm strip of

filter paper Let it dry Make sure a small colored spot isvisible

Pour rubbing alcohol in a 100-mL beaker to a depth of1 cm

$ Place the filter paper into the beaker The filter papershould touch the alcohol but the dot should not Hold it in place 15 minutes and observe what happens

Analysis 1 Explain What did you observe as the solvent moved

up the filter paper2 Infer Why did you see different colors at different

locations on the filter paper

(t)Matt Meadows (b)James Westwater

Figure 94The red yellow andpurple pigments arevisible in the autumnRecognize Cause andEffect Why canrsquot yousee these colors dur-ing the summer

226 ENERGY IN A CELL

The chloroplast and pigmentsRecall that the chloroplast is the

cell organelle where photosynthesisoccurs It is in the membranes of thethylakoid discs in chloroplasts that thelight-dependent reactions take place

To trap the energy in the sunrsquos light the thylakoid membranes con-tain pigments molecules that absorbspecific wavelengths of sunlight Pig-ments are arranged within the thy-lakoid membranes in clusters known asphotosystems Although a photosys-tem contains several kinds of pig-ments the most common ischlorophyll Chlorophyll absorbsmost wavelengths of light exceptgreen Because chlorophyll cannotabsorb this wavelength it is reflectedgiving leaves a green appearance Inthe fall trees stop producing chloro-phyll in their leaves Other pigmentsbecome visible giving leaves like thosein Figure 94 a wide variety of colorsThe MiniLab on this page will allowyou to separate the pigments in a leafRead the Connection to Chemistry at theend of this chapter to find out moreabout biological pigments

Light-DependentReactions

The first phase of photosynthesisrequires sunlight As sunlight strikesthe chlorophyll molecules in a photo-system of the thylakoid membrane theenergy in the light is transferred toelectrons These highly energized orexcited electrons are passed fromchlorophyll to an electron transportchain a series of proteins embedded inthe thylakoid membrane Figure 95summarizes this process

Each protein in the chain passesenergized electrons along to the nextprotein similar to a bucket brigade inwhich a line of people pass a bucket of

0225-0230 C9S2 BDOL-829900 8404 442 AM Page 226

92 PHOTOSYNTHESIS TRAPPING THE SUNrsquoS ENERGY 227

water from person to person to fight afire At each step along the transportchain the electrons lose energy just assome of the water might be spilledfrom buckets in the fire-fightingchain This ldquolostrdquo energy can be usedto form ATP from ADP or to pumphydrogen ions into the center of thethylakoid disc

After the electrons have traveleddown the electron transport chainthey are re-energized in a secondphotosystem and passed down a sec-ond electron transport chain At thebottom of this chain the electronsare still very energized So that thisenergy is not wasted the electronsare transferred to the stroma of thechloroplast To do this an electroncarrier molecule called NADP

(nicotinamide adenine dinucleotidephosphate) is used NADP cancombine with two excited electronsand a hydrogen ion (H) to becomeNADPH NADPH does not use theenergy present in the energized elec-trons it simply stores the energyuntil it can transfer it to the stromaThere NADPH will play an impor-tant role in the light-independentreactions

Explain how energyfrom electrons is released

Restoring electronsRecall that at the beginning of

photosynthesis electrons are lostfrom chlorophyll molecules whenlight is absorbed If these electronsare not replaced the chlorophyll willbe unable to absorb additional lightand the light-dependent reactionswill stop as will the production ofATP To replace the lost electronsmolecules of water are split in thefirst photosystem This reaction iscalled photolysis (fo TAH luh sis)For every water molecule that is

Light-Dependent Reactions

Light energy

Chlorophyllpasses energy

down through theelectron transport chain

Energized electrons provideenergy that

transfers to chlorophyll

Sun

splitsH2O

bonds to ADP

formingATPH+

oxygenreleased

for use in thelight-independent reactions

NADP+

NADPH

P

Figure 95Chlorophyll molecules absorb light energyand energize electrons for producing ATPand NADPH

0225-0230 C9S2 BDOL-829900 8404 443 AM Page 227

split one half molecule of oxygentwo electrons and two hydrogenions are formed as shown inFigure 96 The oxygen producedby photolysis is released into the airand supplies the oxygen we breatheThe electrons are returned tochlorophyll The hydrogen ions arepumped into the thylakoid wherethey accumulate in high concentra-tion Because this difference in con-centration forms a concentrationgradient across the membrane H

ions diffuse out of the thylakoid andprovide energy for the production ofATP This coupling of the move-ment of H ions to ATP productionis called chemiosmosis (keh mee ozMOH sis) The MiniLab on this pageshows how the steps of photosynthe-sis were traced

Light-IndependentReactions

The second phase of photosynthe-sis does not require light It is calledthe Calvin cycle which is a series ofreactions that use carbon dioxide toform sugars The Calvin cycle takesplace in the stroma of the chloroplastas shown in Figure 97

228 ENERGY IN A CELL

Sun

Chlorophyll O2 + 2H+

H2O

2endash

H2O 2H+ + O2 + 2endash 1

2

1

2

Figure 96In photolysis a molecule of water is split toreplace electrons lost from chlorophyll H+

for chemiosmosis and oxygen Infer Howmany molecules of water must be splitto make a molecule of oxygen gas

Formulate ModelsUse Isotopes to UnderstandPhotosynthesis C B van Nieldemonstrated that photosynthesis is a light-dependent reaction inwhich the O2 comes from waterOther scientists confirmed his find-ings by using radioactive isotopes ofoxygen as tracers Radioactive tracersare used to follow a particular moleculethrough a chemical reaction

Procedure Study the following general equation that resulted from

the van Niel experimentCO2 2H2O rarr CH2O H2O O2

Radioactive water water tagged with an isotope of oxygenas a tracer (shown by the ) was used Note where thetagged oxygen ends up on the right side of the equation

Assume that the experiment was repeated but this time aradioactive tag was put on the oxygen in CO2

$ Using materials provided by your teacher model what youpredict the appearance of the results would be Yourmodel must include a ldquotagrdquo to indicate the oxygen isotopeon the left side of the arrow as well as where it ends upon the right side of the arrow

You also must use labels or different colors in your modelto indicate what happens to the carbon and hydrogen

Analysis1 Explain How can an isotope be used as a tag2 Use Models Using your model predict what happens to

a all oxygen molecules that originated from carbon dioxideb all carbon molecules that originated from carbon dioxidec all hydrogen molecules that originated from water

van Niel

0225-0230 C9S2 BDOL-829900 8404 443 AM Page 228

92 PHOTOSYNTHESIS TRAPPING THE SUNrsquoS ENERGY 229

C C C C C

C

C C C C C C

C C C

C C C

C C CC C C

C C C

C C C C C C

C C C

(Sugars and other carbohydrates)

ADP +

ADP + ATP

ATP

NADP+

NADPH

(RuBP)

(CO2)

(Unstable intermediate)

(PGAL)(PGAL)

(PGAL)

CalvinCycle

P

P

Formation of 3-carbon moleculesThe six-carbon sugarformed in Step Aimmediately splits to form two three-carbonmolecules

BB

Use of ATP andNADPH A series of reactions involving ATP and NADPH from the light-dependent reactionsconverts the three-carbonmolecules into phospho-glyceraldehyde (PGAL)three-carbon sugars withhigher energy bonds

CC

Sugar production One outof every six molecules of PGALis transferred to the cytoplasmand used in the synthesis ofsugars and other carbohydratesAfter three rounds of the cyclesix molecules of PGAL areproduced

DD

RuBP is replenishedFive molecules of PGALeach with three carbonatoms produce threemolecules of the five-carbon RuBP Thisreplenishes the RuBP thatwas used up and the cyclecan continue

EE

Carbon fixationThe carbon atom from CO2bonds with a five-carbonsugar called ribulosebiphosphate (RuBP) toform an unstable six-carbon sugar

AA

The stroma in chloroplastshosts the Calvin cycle

Color-enhanced TEMMagnification 6300

The Calvin CycleFigure 97The Calvin cycle takes the carbon in CO2 adds it to one mole-cule of RuBP and forms sugars through a series of reactionsin the stroma of chloroplasts The NADPH and ATP producedduring the earlier light-dependent reactions are importantmolecules for this series of reactions Critical Thinking Whyis the Calvin cycle in plants directly and indirectlyimportant to animals

0225-0230 C9S2 BDOL-829900 8404 443 AM Page 229

Understanding Main Ideas1 Why do you see green when you look at a leaf on

a tree Why do you see other colors in the fall

2 How do the light-dependent reactions of photosynthesis relate to the Calvin cycle

3 What is the function of water in photosynthesisExplain the reaction that achieves this function

4 How does the electron transport chain transferlight energy in photosynthesis

Thinking Critically5 In photosynthesis is chlorophyll considered a reac-

tant a product or neither How does the role ofchlorophyll compare with the roles of CO2 and H2O

6 Get the Big Picture Identify the parts of thechloroplast in which the various steps of photo-synthesis take place For more help refer to Getthe Big Picture in the Skill Handbook

SKILL REVIEWSKILL REVIEW

230 ENERGY IN A CELLCORBISBettmann-UPI

The Calvin cycleThe Calvin cycle named after

Melvin Calvin who worked out thedetails of the reactions is called a cyclebecause one of the last moleculesformed in the series of chemical reac-tions is also one of the moleculesneeded for the first reaction of thecycle Therefore one of the productscan be used again to continue the cycle

You have learned that in the elec-tron transport chain an energizedelectron is passed from protein toprotein and the energy is releasedslowly You can imagine that making acomplex carbohydrate from a mole-cule of CO2 would be a large task fora cell so the light-independent reac-tions in the stroma of the chloroplastbreak down the complicated processinto small steps

At the beginning of the Calvincycle one molecule of carbon diox-ide is added to one molecule ofRuBP to form a six-carbon sugarThis step is called carbon fixationbecause carbon is ldquofixedrdquo into a six-carbon sugar In a series of reactionsthe sugar breaks down and is eventu-ally converted to two three-carbonsugars called phosphoglyceralde-hyde or PGAL After three roundsof the cycle with each round fixingone molecule of CO2 six moleculesof PGAL are produced Five of thesemolecules are rearranged to formthree molecules of RuBP the start-ing material The sixth molecule ofPGAL is available to the organismfor making sugars complex carbo-hydrates and other organic com-pounds As you will see in the nextsection PGAL is important to allorganisms because it plays a role incellular respiration

Biochemist

I f you are curious about whatmakes plants and animals grow

and develop consider a career as abiochemist The basic research ofbiochemists seeks to understandhow processes in an organism workto ensure the organismrsquos survival

Skills for the JobA bachelorrsquos degree in chemistry or

biochemistry will qualify you to be a lab assistant For a more involved position you will need a masterrsquos degree advanced research requires a PhD Somebiochemists work with genes to create new plants and newchemicals from plants Others research the causes and curesof diseases or the effects of poor nutrition Still othersinvestigate solutions for urgent problems such as findingbetter ways of growing storing and caring for crops

To find out more about careers in related fieldsvisit ncbdolglencoecomcareers

ncbdolglencoecomself_check_quiz

0225-0230 C9S2 BDOL-829900 8404 444 AM Page 230

ExperimentSeparating PigmentsChromatography is an impor-tant diagnostic tool In thisexperiment you will use paperchromatography to separatedifferent pigments from plantleaves

Procedure Obtain a pre-made plant solution from your teacher Place a few drops 2 cm high on a 5-cm 14-cm strip of

filter paper Let it dry Make sure a small colored spot isvisible

Pour rubbing alcohol in a 100-mL beaker to a depth of1 cm

$ Place the filter paper into the beaker The filter papershould touch the alcohol but the dot should not Hold it in place 15 minutes and observe what happens

Analysis 1 Explain What did you observe as the solvent moved

up the filter paper2 Infer Why did you see different colors at different

locations on the filter paper

(t)Matt Meadows (b)James Westwater

Figure 94The red yellow andpurple pigments arevisible in the autumnRecognize Cause andEffect Why canrsquot yousee these colors dur-ing the summer

226 ENERGY IN A CELL

The chloroplast and pigmentsRecall that the chloroplast is the

cell organelle where photosynthesisoccurs It is in the membranes of thethylakoid discs in chloroplasts that thelight-dependent reactions take place

To trap the energy in the sunrsquos light the thylakoid membranes con-tain pigments molecules that absorbspecific wavelengths of sunlight Pig-ments are arranged within the thy-lakoid membranes in clusters known asphotosystems Although a photosys-tem contains several kinds of pig-ments the most common ischlorophyll Chlorophyll absorbsmost wavelengths of light exceptgreen Because chlorophyll cannotabsorb this wavelength it is reflectedgiving leaves a green appearance Inthe fall trees stop producing chloro-phyll in their leaves Other pigmentsbecome visible giving leaves like thosein Figure 94 a wide variety of colorsThe MiniLab on this page will allowyou to separate the pigments in a leafRead the Connection to Chemistry at theend of this chapter to find out moreabout biological pigments

Light-DependentReactions

The first phase of photosynthesisrequires sunlight As sunlight strikesthe chlorophyll molecules in a photo-system of the thylakoid membrane theenergy in the light is transferred toelectrons These highly energized orexcited electrons are passed fromchlorophyll to an electron transportchain a series of proteins embedded inthe thylakoid membrane Figure 95summarizes this process

Each protein in the chain passesenergized electrons along to the nextprotein similar to a bucket brigade inwhich a line of people pass a bucket of

0225-0230 C9S2 BDOL-829900 8404 442 AM Page 226

92 PHOTOSYNTHESIS TRAPPING THE SUNrsquoS ENERGY 227

water from person to person to fight afire At each step along the transportchain the electrons lose energy just assome of the water might be spilledfrom buckets in the fire-fightingchain This ldquolostrdquo energy can be usedto form ATP from ADP or to pumphydrogen ions into the center of thethylakoid disc

After the electrons have traveleddown the electron transport chainthey are re-energized in a secondphotosystem and passed down a sec-ond electron transport chain At thebottom of this chain the electronsare still very energized So that thisenergy is not wasted the electronsare transferred to the stroma of thechloroplast To do this an electroncarrier molecule called NADP

(nicotinamide adenine dinucleotidephosphate) is used NADP cancombine with two excited electronsand a hydrogen ion (H) to becomeNADPH NADPH does not use theenergy present in the energized elec-trons it simply stores the energyuntil it can transfer it to the stromaThere NADPH will play an impor-tant role in the light-independentreactions

Explain how energyfrom electrons is released

Restoring electronsRecall that at the beginning of

photosynthesis electrons are lostfrom chlorophyll molecules whenlight is absorbed If these electronsare not replaced the chlorophyll willbe unable to absorb additional lightand the light-dependent reactionswill stop as will the production ofATP To replace the lost electronsmolecules of water are split in thefirst photosystem This reaction iscalled photolysis (fo TAH luh sis)For every water molecule that is

Light-Dependent Reactions

Light energy

Chlorophyllpasses energy

down through theelectron transport chain

Energized electrons provideenergy that

transfers to chlorophyll

Sun

splitsH2O

bonds to ADP

formingATPH+

oxygenreleased

for use in thelight-independent reactions

NADP+

NADPH

P

Figure 95Chlorophyll molecules absorb light energyand energize electrons for producing ATPand NADPH

0225-0230 C9S2 BDOL-829900 8404 443 AM Page 227

split one half molecule of oxygentwo electrons and two hydrogenions are formed as shown inFigure 96 The oxygen producedby photolysis is released into the airand supplies the oxygen we breatheThe electrons are returned tochlorophyll The hydrogen ions arepumped into the thylakoid wherethey accumulate in high concentra-tion Because this difference in con-centration forms a concentrationgradient across the membrane H

ions diffuse out of the thylakoid andprovide energy for the production ofATP This coupling of the move-ment of H ions to ATP productionis called chemiosmosis (keh mee ozMOH sis) The MiniLab on this pageshows how the steps of photosynthe-sis were traced

Light-IndependentReactions

The second phase of photosynthe-sis does not require light It is calledthe Calvin cycle which is a series ofreactions that use carbon dioxide toform sugars The Calvin cycle takesplace in the stroma of the chloroplastas shown in Figure 97

228 ENERGY IN A CELL

Sun

Chlorophyll O2 + 2H+

H2O

2endash

H2O 2H+ + O2 + 2endash 1

2

1

2

Figure 96In photolysis a molecule of water is split toreplace electrons lost from chlorophyll H+

for chemiosmosis and oxygen Infer Howmany molecules of water must be splitto make a molecule of oxygen gas

Formulate ModelsUse Isotopes to UnderstandPhotosynthesis C B van Nieldemonstrated that photosynthesis is a light-dependent reaction inwhich the O2 comes from waterOther scientists confirmed his find-ings by using radioactive isotopes ofoxygen as tracers Radioactive tracersare used to follow a particular moleculethrough a chemical reaction

Procedure Study the following general equation that resulted from

the van Niel experimentCO2 2H2O rarr CH2O H2O O2

Radioactive water water tagged with an isotope of oxygenas a tracer (shown by the ) was used Note where thetagged oxygen ends up on the right side of the equation

Assume that the experiment was repeated but this time aradioactive tag was put on the oxygen in CO2

$ Using materials provided by your teacher model what youpredict the appearance of the results would be Yourmodel must include a ldquotagrdquo to indicate the oxygen isotopeon the left side of the arrow as well as where it ends upon the right side of the arrow

You also must use labels or different colors in your modelto indicate what happens to the carbon and hydrogen

Analysis1 Explain How can an isotope be used as a tag2 Use Models Using your model predict what happens to

a all oxygen molecules that originated from carbon dioxideb all carbon molecules that originated from carbon dioxidec all hydrogen molecules that originated from water

van Niel

0225-0230 C9S2 BDOL-829900 8404 443 AM Page 228

92 PHOTOSYNTHESIS TRAPPING THE SUNrsquoS ENERGY 229

C C C C C

C

C C C C C C

C C C

C C C

C C CC C C

C C C

C C C C C C

C C C

(Sugars and other carbohydrates)

ADP +

ADP + ATP

ATP

NADP+

NADPH

(RuBP)

(CO2)

(Unstable intermediate)

(PGAL)(PGAL)

(PGAL)

CalvinCycle

P

P

Formation of 3-carbon moleculesThe six-carbon sugarformed in Step Aimmediately splits to form two three-carbonmolecules

BB

Use of ATP andNADPH A series of reactions involving ATP and NADPH from the light-dependent reactionsconverts the three-carbonmolecules into phospho-glyceraldehyde (PGAL)three-carbon sugars withhigher energy bonds

CC

Sugar production One outof every six molecules of PGALis transferred to the cytoplasmand used in the synthesis ofsugars and other carbohydratesAfter three rounds of the cyclesix molecules of PGAL areproduced

DD

RuBP is replenishedFive molecules of PGALeach with three carbonatoms produce threemolecules of the five-carbon RuBP Thisreplenishes the RuBP thatwas used up and the cyclecan continue

EE

Carbon fixationThe carbon atom from CO2bonds with a five-carbonsugar called ribulosebiphosphate (RuBP) toform an unstable six-carbon sugar

AA

The stroma in chloroplastshosts the Calvin cycle

Color-enhanced TEMMagnification 6300

The Calvin CycleFigure 97The Calvin cycle takes the carbon in CO2 adds it to one mole-cule of RuBP and forms sugars through a series of reactionsin the stroma of chloroplasts The NADPH and ATP producedduring the earlier light-dependent reactions are importantmolecules for this series of reactions Critical Thinking Whyis the Calvin cycle in plants directly and indirectlyimportant to animals

0225-0230 C9S2 BDOL-829900 8404 443 AM Page 229

Understanding Main Ideas1 Why do you see green when you look at a leaf on

a tree Why do you see other colors in the fall

2 How do the light-dependent reactions of photosynthesis relate to the Calvin cycle

3 What is the function of water in photosynthesisExplain the reaction that achieves this function

4 How does the electron transport chain transferlight energy in photosynthesis

Thinking Critically5 In photosynthesis is chlorophyll considered a reac-

tant a product or neither How does the role ofchlorophyll compare with the roles of CO2 and H2O

6 Get the Big Picture Identify the parts of thechloroplast in which the various steps of photo-synthesis take place For more help refer to Getthe Big Picture in the Skill Handbook

SKILL REVIEWSKILL REVIEW

230 ENERGY IN A CELLCORBISBettmann-UPI

The Calvin cycleThe Calvin cycle named after

Melvin Calvin who worked out thedetails of the reactions is called a cyclebecause one of the last moleculesformed in the series of chemical reac-tions is also one of the moleculesneeded for the first reaction of thecycle Therefore one of the productscan be used again to continue the cycle

You have learned that in the elec-tron transport chain an energizedelectron is passed from protein toprotein and the energy is releasedslowly You can imagine that making acomplex carbohydrate from a mole-cule of CO2 would be a large task fora cell so the light-independent reac-tions in the stroma of the chloroplastbreak down the complicated processinto small steps

At the beginning of the Calvincycle one molecule of carbon diox-ide is added to one molecule ofRuBP to form a six-carbon sugarThis step is called carbon fixationbecause carbon is ldquofixedrdquo into a six-carbon sugar In a series of reactionsthe sugar breaks down and is eventu-ally converted to two three-carbonsugars called phosphoglyceralde-hyde or PGAL After three roundsof the cycle with each round fixingone molecule of CO2 six moleculesof PGAL are produced Five of thesemolecules are rearranged to formthree molecules of RuBP the start-ing material The sixth molecule ofPGAL is available to the organismfor making sugars complex carbo-hydrates and other organic com-pounds As you will see in the nextsection PGAL is important to allorganisms because it plays a role incellular respiration

Biochemist

I f you are curious about whatmakes plants and animals grow

and develop consider a career as abiochemist The basic research ofbiochemists seeks to understandhow processes in an organism workto ensure the organismrsquos survival

Skills for the JobA bachelorrsquos degree in chemistry or

biochemistry will qualify you to be a lab assistant For a more involved position you will need a masterrsquos degree advanced research requires a PhD Somebiochemists work with genes to create new plants and newchemicals from plants Others research the causes and curesof diseases or the effects of poor nutrition Still othersinvestigate solutions for urgent problems such as findingbetter ways of growing storing and caring for crops

To find out more about careers in related fieldsvisit ncbdolglencoecomcareers

ncbdolglencoecomself_check_quiz

0225-0230 C9S2 BDOL-829900 8404 444 AM Page 230

92 PHOTOSYNTHESIS TRAPPING THE SUNrsquoS ENERGY 227

water from person to person to fight afire At each step along the transportchain the electrons lose energy just assome of the water might be spilledfrom buckets in the fire-fightingchain This ldquolostrdquo energy can be usedto form ATP from ADP or to pumphydrogen ions into the center of thethylakoid disc

After the electrons have traveleddown the electron transport chainthey are re-energized in a secondphotosystem and passed down a sec-ond electron transport chain At thebottom of this chain the electronsare still very energized So that thisenergy is not wasted the electronsare transferred to the stroma of thechloroplast To do this an electroncarrier molecule called NADP

(nicotinamide adenine dinucleotidephosphate) is used NADP cancombine with two excited electronsand a hydrogen ion (H) to becomeNADPH NADPH does not use theenergy present in the energized elec-trons it simply stores the energyuntil it can transfer it to the stromaThere NADPH will play an impor-tant role in the light-independentreactions

Explain how energyfrom electrons is released

Restoring electronsRecall that at the beginning of

photosynthesis electrons are lostfrom chlorophyll molecules whenlight is absorbed If these electronsare not replaced the chlorophyll willbe unable to absorb additional lightand the light-dependent reactionswill stop as will the production ofATP To replace the lost electronsmolecules of water are split in thefirst photosystem This reaction iscalled photolysis (fo TAH luh sis)For every water molecule that is

Light-Dependent Reactions

Light energy

Chlorophyllpasses energy

down through theelectron transport chain

Energized electrons provideenergy that

transfers to chlorophyll

Sun

splitsH2O

bonds to ADP

formingATPH+

oxygenreleased

for use in thelight-independent reactions

NADP+

NADPH

P

Figure 95Chlorophyll molecules absorb light energyand energize electrons for producing ATPand NADPH

0225-0230 C9S2 BDOL-829900 8404 443 AM Page 227

split one half molecule of oxygentwo electrons and two hydrogenions are formed as shown inFigure 96 The oxygen producedby photolysis is released into the airand supplies the oxygen we breatheThe electrons are returned tochlorophyll The hydrogen ions arepumped into the thylakoid wherethey accumulate in high concentra-tion Because this difference in con-centration forms a concentrationgradient across the membrane H

ions diffuse out of the thylakoid andprovide energy for the production ofATP This coupling of the move-ment of H ions to ATP productionis called chemiosmosis (keh mee ozMOH sis) The MiniLab on this pageshows how the steps of photosynthe-sis were traced

Light-IndependentReactions

The second phase of photosynthe-sis does not require light It is calledthe Calvin cycle which is a series ofreactions that use carbon dioxide toform sugars The Calvin cycle takesplace in the stroma of the chloroplastas shown in Figure 97

228 ENERGY IN A CELL

Sun

Chlorophyll O2 + 2H+

H2O

2endash

H2O 2H+ + O2 + 2endash 1

2

1

2

Figure 96In photolysis a molecule of water is split toreplace electrons lost from chlorophyll H+

for chemiosmosis and oxygen Infer Howmany molecules of water must be splitto make a molecule of oxygen gas

Formulate ModelsUse Isotopes to UnderstandPhotosynthesis C B van Nieldemonstrated that photosynthesis is a light-dependent reaction inwhich the O2 comes from waterOther scientists confirmed his find-ings by using radioactive isotopes ofoxygen as tracers Radioactive tracersare used to follow a particular moleculethrough a chemical reaction

Procedure Study the following general equation that resulted from

the van Niel experimentCO2 2H2O rarr CH2O H2O O2

Radioactive water water tagged with an isotope of oxygenas a tracer (shown by the ) was used Note where thetagged oxygen ends up on the right side of the equation

Assume that the experiment was repeated but this time aradioactive tag was put on the oxygen in CO2

$ Using materials provided by your teacher model what youpredict the appearance of the results would be Yourmodel must include a ldquotagrdquo to indicate the oxygen isotopeon the left side of the arrow as well as where it ends upon the right side of the arrow

You also must use labels or different colors in your modelto indicate what happens to the carbon and hydrogen

Analysis1 Explain How can an isotope be used as a tag2 Use Models Using your model predict what happens to

a all oxygen molecules that originated from carbon dioxideb all carbon molecules that originated from carbon dioxidec all hydrogen molecules that originated from water

van Niel

0225-0230 C9S2 BDOL-829900 8404 443 AM Page 228

92 PHOTOSYNTHESIS TRAPPING THE SUNrsquoS ENERGY 229

C C C C C

C

C C C C C C

C C C

C C C

C C CC C C

C C C

C C C C C C

C C C

(Sugars and other carbohydrates)

ADP +

ADP + ATP

ATP

NADP+

NADPH

(RuBP)

(CO2)

(Unstable intermediate)

(PGAL)(PGAL)

(PGAL)

CalvinCycle

P

P

Formation of 3-carbon moleculesThe six-carbon sugarformed in Step Aimmediately splits to form two three-carbonmolecules

BB

Use of ATP andNADPH A series of reactions involving ATP and NADPH from the light-dependent reactionsconverts the three-carbonmolecules into phospho-glyceraldehyde (PGAL)three-carbon sugars withhigher energy bonds

CC

Sugar production One outof every six molecules of PGALis transferred to the cytoplasmand used in the synthesis ofsugars and other carbohydratesAfter three rounds of the cyclesix molecules of PGAL areproduced

DD

RuBP is replenishedFive molecules of PGALeach with three carbonatoms produce threemolecules of the five-carbon RuBP Thisreplenishes the RuBP thatwas used up and the cyclecan continue

EE

Carbon fixationThe carbon atom from CO2bonds with a five-carbonsugar called ribulosebiphosphate (RuBP) toform an unstable six-carbon sugar

AA

The stroma in chloroplastshosts the Calvin cycle

Color-enhanced TEMMagnification 6300

The Calvin CycleFigure 97The Calvin cycle takes the carbon in CO2 adds it to one mole-cule of RuBP and forms sugars through a series of reactionsin the stroma of chloroplasts The NADPH and ATP producedduring the earlier light-dependent reactions are importantmolecules for this series of reactions Critical Thinking Whyis the Calvin cycle in plants directly and indirectlyimportant to animals

0225-0230 C9S2 BDOL-829900 8404 443 AM Page 229

Understanding Main Ideas1 Why do you see green when you look at a leaf on

a tree Why do you see other colors in the fall

2 How do the light-dependent reactions of photosynthesis relate to the Calvin cycle

3 What is the function of water in photosynthesisExplain the reaction that achieves this function

4 How does the electron transport chain transferlight energy in photosynthesis

Thinking Critically5 In photosynthesis is chlorophyll considered a reac-

tant a product or neither How does the role ofchlorophyll compare with the roles of CO2 and H2O

6 Get the Big Picture Identify the parts of thechloroplast in which the various steps of photo-synthesis take place For more help refer to Getthe Big Picture in the Skill Handbook

SKILL REVIEWSKILL REVIEW

230 ENERGY IN A CELLCORBISBettmann-UPI

The Calvin cycleThe Calvin cycle named after

Melvin Calvin who worked out thedetails of the reactions is called a cyclebecause one of the last moleculesformed in the series of chemical reac-tions is also one of the moleculesneeded for the first reaction of thecycle Therefore one of the productscan be used again to continue the cycle

You have learned that in the elec-tron transport chain an energizedelectron is passed from protein toprotein and the energy is releasedslowly You can imagine that making acomplex carbohydrate from a mole-cule of CO2 would be a large task fora cell so the light-independent reac-tions in the stroma of the chloroplastbreak down the complicated processinto small steps

At the beginning of the Calvincycle one molecule of carbon diox-ide is added to one molecule ofRuBP to form a six-carbon sugarThis step is called carbon fixationbecause carbon is ldquofixedrdquo into a six-carbon sugar In a series of reactionsthe sugar breaks down and is eventu-ally converted to two three-carbonsugars called phosphoglyceralde-hyde or PGAL After three roundsof the cycle with each round fixingone molecule of CO2 six moleculesof PGAL are produced Five of thesemolecules are rearranged to formthree molecules of RuBP the start-ing material The sixth molecule ofPGAL is available to the organismfor making sugars complex carbo-hydrates and other organic com-pounds As you will see in the nextsection PGAL is important to allorganisms because it plays a role incellular respiration

Biochemist

I f you are curious about whatmakes plants and animals grow

and develop consider a career as abiochemist The basic research ofbiochemists seeks to understandhow processes in an organism workto ensure the organismrsquos survival

Skills for the JobA bachelorrsquos degree in chemistry or

biochemistry will qualify you to be a lab assistant For a more involved position you will need a masterrsquos degree advanced research requires a PhD Somebiochemists work with genes to create new plants and newchemicals from plants Others research the causes and curesof diseases or the effects of poor nutrition Still othersinvestigate solutions for urgent problems such as findingbetter ways of growing storing and caring for crops

To find out more about careers in related fieldsvisit ncbdolglencoecomcareers

ncbdolglencoecomself_check_quiz

0225-0230 C9S2 BDOL-829900 8404 444 AM Page 230

split one half molecule of oxygentwo electrons and two hydrogenions are formed as shown inFigure 96 The oxygen producedby photolysis is released into the airand supplies the oxygen we breatheThe electrons are returned tochlorophyll The hydrogen ions arepumped into the thylakoid wherethey accumulate in high concentra-tion Because this difference in con-centration forms a concentrationgradient across the membrane H

ions diffuse out of the thylakoid andprovide energy for the production ofATP This coupling of the move-ment of H ions to ATP productionis called chemiosmosis (keh mee ozMOH sis) The MiniLab on this pageshows how the steps of photosynthe-sis were traced

Light-IndependentReactions

The second phase of photosynthe-sis does not require light It is calledthe Calvin cycle which is a series ofreactions that use carbon dioxide toform sugars The Calvin cycle takesplace in the stroma of the chloroplastas shown in Figure 97

228 ENERGY IN A CELL

Sun

Chlorophyll O2 + 2H+

H2O

2endash

H2O 2H+ + O2 + 2endash 1

2

1

2

Figure 96In photolysis a molecule of water is split toreplace electrons lost from chlorophyll H+

for chemiosmosis and oxygen Infer Howmany molecules of water must be splitto make a molecule of oxygen gas

Formulate ModelsUse Isotopes to UnderstandPhotosynthesis C B van Nieldemonstrated that photosynthesis is a light-dependent reaction inwhich the O2 comes from waterOther scientists confirmed his find-ings by using radioactive isotopes ofoxygen as tracers Radioactive tracersare used to follow a particular moleculethrough a chemical reaction

Procedure Study the following general equation that resulted from

the van Niel experimentCO2 2H2O rarr CH2O H2O O2

Radioactive water water tagged with an isotope of oxygenas a tracer (shown by the ) was used Note where thetagged oxygen ends up on the right side of the equation

Assume that the experiment was repeated but this time aradioactive tag was put on the oxygen in CO2

$ Using materials provided by your teacher model what youpredict the appearance of the results would be Yourmodel must include a ldquotagrdquo to indicate the oxygen isotopeon the left side of the arrow as well as where it ends upon the right side of the arrow

You also must use labels or different colors in your modelto indicate what happens to the carbon and hydrogen

Analysis1 Explain How can an isotope be used as a tag2 Use Models Using your model predict what happens to

a all oxygen molecules that originated from carbon dioxideb all carbon molecules that originated from carbon dioxidec all hydrogen molecules that originated from water

van Niel

0225-0230 C9S2 BDOL-829900 8404 443 AM Page 228

92 PHOTOSYNTHESIS TRAPPING THE SUNrsquoS ENERGY 229

C C C C C

C

C C C C C C

C C C

C C C

C C CC C C

C C C

C C C C C C

C C C

(Sugars and other carbohydrates)

ADP +

ADP + ATP

ATP

NADP+

NADPH

(RuBP)

(CO2)

(Unstable intermediate)

(PGAL)(PGAL)

(PGAL)

CalvinCycle

P

P

Formation of 3-carbon moleculesThe six-carbon sugarformed in Step Aimmediately splits to form two three-carbonmolecules

BB

Use of ATP andNADPH A series of reactions involving ATP and NADPH from the light-dependent reactionsconverts the three-carbonmolecules into phospho-glyceraldehyde (PGAL)three-carbon sugars withhigher energy bonds

CC

Sugar production One outof every six molecules of PGALis transferred to the cytoplasmand used in the synthesis ofsugars and other carbohydratesAfter three rounds of the cyclesix molecules of PGAL areproduced

DD

RuBP is replenishedFive molecules of PGALeach with three carbonatoms produce threemolecules of the five-carbon RuBP Thisreplenishes the RuBP thatwas used up and the cyclecan continue

EE

Carbon fixationThe carbon atom from CO2bonds with a five-carbonsugar called ribulosebiphosphate (RuBP) toform an unstable six-carbon sugar

AA

The stroma in chloroplastshosts the Calvin cycle

Color-enhanced TEMMagnification 6300

The Calvin CycleFigure 97The Calvin cycle takes the carbon in CO2 adds it to one mole-cule of RuBP and forms sugars through a series of reactionsin the stroma of chloroplasts The NADPH and ATP producedduring the earlier light-dependent reactions are importantmolecules for this series of reactions Critical Thinking Whyis the Calvin cycle in plants directly and indirectlyimportant to animals

0225-0230 C9S2 BDOL-829900 8404 443 AM Page 229

Understanding Main Ideas1 Why do you see green when you look at a leaf on

a tree Why do you see other colors in the fall

2 How do the light-dependent reactions of photosynthesis relate to the Calvin cycle

3 What is the function of water in photosynthesisExplain the reaction that achieves this function

4 How does the electron transport chain transferlight energy in photosynthesis

Thinking Critically5 In photosynthesis is chlorophyll considered a reac-

tant a product or neither How does the role ofchlorophyll compare with the roles of CO2 and H2O

6 Get the Big Picture Identify the parts of thechloroplast in which the various steps of photo-synthesis take place For more help refer to Getthe Big Picture in the Skill Handbook

SKILL REVIEWSKILL REVIEW

230 ENERGY IN A CELLCORBISBettmann-UPI

The Calvin cycleThe Calvin cycle named after

Melvin Calvin who worked out thedetails of the reactions is called a cyclebecause one of the last moleculesformed in the series of chemical reac-tions is also one of the moleculesneeded for the first reaction of thecycle Therefore one of the productscan be used again to continue the cycle

You have learned that in the elec-tron transport chain an energizedelectron is passed from protein toprotein and the energy is releasedslowly You can imagine that making acomplex carbohydrate from a mole-cule of CO2 would be a large task fora cell so the light-independent reac-tions in the stroma of the chloroplastbreak down the complicated processinto small steps

At the beginning of the Calvincycle one molecule of carbon diox-ide is added to one molecule ofRuBP to form a six-carbon sugarThis step is called carbon fixationbecause carbon is ldquofixedrdquo into a six-carbon sugar In a series of reactionsthe sugar breaks down and is eventu-ally converted to two three-carbonsugars called phosphoglyceralde-hyde or PGAL After three roundsof the cycle with each round fixingone molecule of CO2 six moleculesof PGAL are produced Five of thesemolecules are rearranged to formthree molecules of RuBP the start-ing material The sixth molecule ofPGAL is available to the organismfor making sugars complex carbo-hydrates and other organic com-pounds As you will see in the nextsection PGAL is important to allorganisms because it plays a role incellular respiration

Biochemist

I f you are curious about whatmakes plants and animals grow

and develop consider a career as abiochemist The basic research ofbiochemists seeks to understandhow processes in an organism workto ensure the organismrsquos survival

Skills for the JobA bachelorrsquos degree in chemistry or

biochemistry will qualify you to be a lab assistant For a more involved position you will need a masterrsquos degree advanced research requires a PhD Somebiochemists work with genes to create new plants and newchemicals from plants Others research the causes and curesof diseases or the effects of poor nutrition Still othersinvestigate solutions for urgent problems such as findingbetter ways of growing storing and caring for crops

To find out more about careers in related fieldsvisit ncbdolglencoecomcareers

ncbdolglencoecomself_check_quiz

0225-0230 C9S2 BDOL-829900 8404 444 AM Page 230

92 PHOTOSYNTHESIS TRAPPING THE SUNrsquoS ENERGY 229

C C C C C

C

C C C C C C

C C C

C C C

C C CC C C

C C C

C C C C C C

C C C

(Sugars and other carbohydrates)

ADP +

ADP + ATP

ATP

NADP+

NADPH

(RuBP)

(CO2)

(Unstable intermediate)

(PGAL)(PGAL)

(PGAL)

CalvinCycle

P

P

Formation of 3-carbon moleculesThe six-carbon sugarformed in Step Aimmediately splits to form two three-carbonmolecules

BB

Use of ATP andNADPH A series of reactions involving ATP and NADPH from the light-dependent reactionsconverts the three-carbonmolecules into phospho-glyceraldehyde (PGAL)three-carbon sugars withhigher energy bonds

CC

Sugar production One outof every six molecules of PGALis transferred to the cytoplasmand used in the synthesis ofsugars and other carbohydratesAfter three rounds of the cyclesix molecules of PGAL areproduced

DD

RuBP is replenishedFive molecules of PGALeach with three carbonatoms produce threemolecules of the five-carbon RuBP Thisreplenishes the RuBP thatwas used up and the cyclecan continue

EE

Carbon fixationThe carbon atom from CO2bonds with a five-carbonsugar called ribulosebiphosphate (RuBP) toform an unstable six-carbon sugar

AA

The stroma in chloroplastshosts the Calvin cycle

Color-enhanced TEMMagnification 6300

The Calvin CycleFigure 97The Calvin cycle takes the carbon in CO2 adds it to one mole-cule of RuBP and forms sugars through a series of reactionsin the stroma of chloroplasts The NADPH and ATP producedduring the earlier light-dependent reactions are importantmolecules for this series of reactions Critical Thinking Whyis the Calvin cycle in plants directly and indirectlyimportant to animals

0225-0230 C9S2 BDOL-829900 8404 443 AM Page 229

Understanding Main Ideas1 Why do you see green when you look at a leaf on

a tree Why do you see other colors in the fall

2 How do the light-dependent reactions of photosynthesis relate to the Calvin cycle

3 What is the function of water in photosynthesisExplain the reaction that achieves this function

4 How does the electron transport chain transferlight energy in photosynthesis

Thinking Critically5 In photosynthesis is chlorophyll considered a reac-

tant a product or neither How does the role ofchlorophyll compare with the roles of CO2 and H2O

6 Get the Big Picture Identify the parts of thechloroplast in which the various steps of photo-synthesis take place For more help refer to Getthe Big Picture in the Skill Handbook

SKILL REVIEWSKILL REVIEW

230 ENERGY IN A CELLCORBISBettmann-UPI

The Calvin cycleThe Calvin cycle named after

Melvin Calvin who worked out thedetails of the reactions is called a cyclebecause one of the last moleculesformed in the series of chemical reac-tions is also one of the moleculesneeded for the first reaction of thecycle Therefore one of the productscan be used again to continue the cycle

You have learned that in the elec-tron transport chain an energizedelectron is passed from protein toprotein and the energy is releasedslowly You can imagine that making acomplex carbohydrate from a mole-cule of CO2 would be a large task fora cell so the light-independent reac-tions in the stroma of the chloroplastbreak down the complicated processinto small steps

At the beginning of the Calvincycle one molecule of carbon diox-ide is added to one molecule ofRuBP to form a six-carbon sugarThis step is called carbon fixationbecause carbon is ldquofixedrdquo into a six-carbon sugar In a series of reactionsthe sugar breaks down and is eventu-ally converted to two three-carbonsugars called phosphoglyceralde-hyde or PGAL After three roundsof the cycle with each round fixingone molecule of CO2 six moleculesof PGAL are produced Five of thesemolecules are rearranged to formthree molecules of RuBP the start-ing material The sixth molecule ofPGAL is available to the organismfor making sugars complex carbo-hydrates and other organic com-pounds As you will see in the nextsection PGAL is important to allorganisms because it plays a role incellular respiration

Biochemist

I f you are curious about whatmakes plants and animals grow

and develop consider a career as abiochemist The basic research ofbiochemists seeks to understandhow processes in an organism workto ensure the organismrsquos survival

Skills for the JobA bachelorrsquos degree in chemistry or

biochemistry will qualify you to be a lab assistant For a more involved position you will need a masterrsquos degree advanced research requires a PhD Somebiochemists work with genes to create new plants and newchemicals from plants Others research the causes and curesof diseases or the effects of poor nutrition Still othersinvestigate solutions for urgent problems such as findingbetter ways of growing storing and caring for crops

To find out more about careers in related fieldsvisit ncbdolglencoecomcareers

ncbdolglencoecomself_check_quiz

0225-0230 C9S2 BDOL-829900 8404 444 AM Page 230

Understanding Main Ideas1 Why do you see green when you look at a leaf on

a tree Why do you see other colors in the fall

2 How do the light-dependent reactions of photosynthesis relate to the Calvin cycle

3 What is the function of water in photosynthesisExplain the reaction that achieves this function

4 How does the electron transport chain transferlight energy in photosynthesis

Thinking Critically5 In photosynthesis is chlorophyll considered a reac-

tant a product or neither How does the role ofchlorophyll compare with the roles of CO2 and H2O

6 Get the Big Picture Identify the parts of thechloroplast in which the various steps of photo-synthesis take place For more help refer to Getthe Big Picture in the Skill Handbook

SKILL REVIEWSKILL REVIEW

230 ENERGY IN A CELLCORBISBettmann-UPI

The Calvin cycleThe Calvin cycle named after

Melvin Calvin who worked out thedetails of the reactions is called a cyclebecause one of the last moleculesformed in the series of chemical reac-tions is also one of the moleculesneeded for the first reaction of thecycle Therefore one of the productscan be used again to continue the cycle

You have learned that in the elec-tron transport chain an energizedelectron is passed from protein toprotein and the energy is releasedslowly You can imagine that making acomplex carbohydrate from a mole-cule of CO2 would be a large task fora cell so the light-independent reac-tions in the stroma of the chloroplastbreak down the complicated processinto small steps

At the beginning of the Calvincycle one molecule of carbon diox-ide is added to one molecule ofRuBP to form a six-carbon sugarThis step is called carbon fixationbecause carbon is ldquofixedrdquo into a six-carbon sugar In a series of reactionsthe sugar breaks down and is eventu-ally converted to two three-carbonsugars called phosphoglyceralde-hyde or PGAL After three roundsof the cycle with each round fixingone molecule of CO2 six moleculesof PGAL are produced Five of thesemolecules are rearranged to formthree molecules of RuBP the start-ing material The sixth molecule ofPGAL is available to the organismfor making sugars complex carbo-hydrates and other organic com-pounds As you will see in the nextsection PGAL is important to allorganisms because it plays a role incellular respiration

Biochemist

I f you are curious about whatmakes plants and animals grow

and develop consider a career as abiochemist The basic research ofbiochemists seeks to understandhow processes in an organism workto ensure the organismrsquos survival

Skills for the JobA bachelorrsquos degree in chemistry or

biochemistry will qualify you to be a lab assistant For a more involved position you will need a masterrsquos degree advanced research requires a PhD Somebiochemists work with genes to create new plants and newchemicals from plants Others research the causes and curesof diseases or the effects of poor nutrition Still othersinvestigate solutions for urgent problems such as findingbetter ways of growing storing and caring for crops

To find out more about careers in related fieldsvisit ncbdolglencoecomcareers

ncbdolglencoecomself_check_quiz

0225-0230 C9S2 BDOL-829900 8404 444 AM Page 230

93SECTION PREVIEWObjectivesCompare and contrastcellular respiration andfermentationExplain how cells obtainenergy from cellular respiration

Review Vocabularymitochondria cell organ-

elles that transformenergy for the cell (p 185)

New Vocabularycellular respirationanaerobicaerobicglycolysiscitric acid cyclelactic acid fermentationalcoholic fermentation

anaerobic fromthe Greek wordsan meaningldquowithoutrdquo andaeros meaningldquoairrdquo Anaerobicorganisms can livewithout oxygen

93 GETTING ENERGY TO MAKE ATP 231

What happens to sugarsUsing Prior Knowledge Youknow that the chlorophyll ingreen plants is the key to photo-synthesis and that sugars are pro-duced You also know that yourbody needs energy to surviveSugars can be broken down incells to yield large amounts ofenergy But your cells canrsquot con-vert light energy to sugars Whatwill you do Fortunately the cellsof all organisms can use the sug-ars made by plants during theCalvin cycle By eating plantmaterial animals too can accessthe sunrsquos energyIdentify In which organelle are sugars converted to ATP

Getting Energy to Make ATP

Michael KellerCORBIS

Cellular RespirationThe process by which mitochondria break down food molecules to pro-

duce ATP is called cellular respiration There are three stages of cellularrespiration glycolysis the citric acid cycle and the electron transport chainThe first stage glycolysis is anaerobicmdashno oxygen is required The lasttwo stages are aerobic and require oxygen to be completed

GlycolysisGlycolysis (gli KAH lih sis) is a series of chemical reactions in the cyto-

plasm of a cell that break down glucose a six-carbon compound into twomolecules of pyruvic (pie RUE vik) acid a three-carbon compoundBecause two molecules of ATP are used to start glycolysis and only fourATP molecules are produced glycolysis is not very effective producingonly two ATP molecules for each glucose molecule broken down

In the electron transport chain of photosynthesis an electron carriercalled NADP was described as carrying energized electrons toanother location in the cell for further chemical reactions Glycolysisalso uses an electron carrier called NAD (nicotinamide adenine di-nucleotide) NAD forms NADH when it accepts two electrons

Objective 205 Investigate and analyze the bioener-getic reactions Aerobic Respiration Anaerobic Respiration

North Carolina Objectives

0231-0243 C9S3 BDOL-829900 8404 459 AM Page 231

BDOL-93

null

48737234

Notice in Figure 98 that twomolecules of PGAL are formed dur-ing glycolysis Recall that PGALalso forms in the Calvin cycle ThePGAL made during photosynthesiscan enter the glycolysis pathway andlead to the formation of ATP andorganic molecules

Following glycolysis the pyruvicacid molecules move into the mito-chondria the organelles that transformenergy for the cell In the presence ofoxygen two more stages complete cel-lular respiration the citric acid cycleand the electron transport chain of themitochondrion Before these twostages can begin however pyruvic acidundergoes a series of reactions in whichit gives off a molecule of CO2 and com-bines with a molecule called coenzymeA to form acetyl-CoA The reactionwith coenzyme A produces a molecule

of NADH and H These reactionsare shown in Figure 99

The citric acid cycleThe citric acid cycle also called

the Krebs cycle is a series of chemicalreactions similar to the Calvin cyclein that the molecule used in the firstreaction is also one of the end prod-ucts Read Figure 910 to study thecitric acid cycle

For every turn of the cycle one mol-ecule of ATP and two molecules of car-bon dioxide are produced Twoelectron carriers are used NAD andFAD (flavin adenine dinucleotide) Atotal of three NADH three H ionsand one FADH2 are formed The elec-tron carriers each pass two energizedelectrons along to the electron trans-port chain in the inner membrane ofthe mitochondrion

232 ENERGY IN A CELL

C C C CC C C P

C C C

C C C

C C CPC C

ENERGY ENERGY

2ATP2ADP

4ADP + 4 P

2NAD+2PGAL

Glucose

4ATP

2NADH + 2H+

2 Pyruvicacid

C C C C C C C C C CC

NAD+

CO2

NADH + H+

Pyruvicacid

Outside themitochondrion

Mitochondrialmembrane

Coenzyme A

Pyruvicacid

Inside themitochondrion

Intermediateby-product

- CoAAcetyl-CoA

+

Figure 98Glycolysis breaks downa molecule of glucoseinto two molecules ofpyruvic acid In theprocess it forms a netof two molecules ofATP two molecules ofNADH and two hydro-gen ions

Figure 99Before the citric acidcycle and electron trans-port chain begin pyruvicacid undergoes a seriesof reactions InferWhat products areformed as a result ofthe reactions withinthe mitochondrion

0231-0243 C9S3 BDOL-829900 8404 500 AM Page 232

The Citric Acid CycleFigure 910The citric acid cycle breaks down a molecule ofacetyl-CoA and forms ATP and CO2 The electroncarriers NAD and FAD pick up energized electronsand pass them to the electron transport chain inthe inner mitochondrial membrane Critical ThinkingHow many CO2 molecules are produced for everyglucose molecule that entered the cellular respira-tion pathways

93 GETTING ENERGY TO MAKE ATP 233

P

NAD+

NAD+

NAD+

FADH2FAD

C C

NADH + H+

NADH + H+

ATP

ADP +

(Acetyl-CoA)

(Oxaloacetic acid)(Citric acid)

CitricAcidCycle

O O(CO2)

O O(CO2)

NADH + H+

C C C C

C C C C

C C C C

C C C C

C C C C C

C

C C C C C

C

C

Formation of the second CO2 Anothermolecule of CO2 is released forming a four-carboncompound One molecule of ATP and a moleculeof NADH are also produced

CC

Citric acid The two-carboncompound acetyl-CoA reactswith a four-carbon compoundcalled oxaloacetic acid to formcitric acid a six-carbonmolecule

AA Formation of CO2 A moleculeof CO2 is formed reducing theeventual product to a five-carboncompound In the process amolecule of NADH and H+ isproduced

BB

Profs P Motta amp T NaguroScience Photo LibraryCustom Medical Stock Photo

Recycling of oxaloacetic acid The four-carbon molecule goesthrough a series of reactions in which FADH2 NADH and H+

are formed The carbon chainis rearranged and oxaloaceticacid is again made availablefor the cycle

DD

The mitochondria hostthe citric acid cycle

Magnification unavailable

0231-0243 C9S3 BDOL-829900 8404 500 AM Page 233

The electron transport chainThe electron transport chain in

the inner membrane of the mito-chondrion is very similar to the elec-tron transport chains of thethylakoid membrane in the chloro-plasts of plant cells during photo-synthesis NADH and FADH2deliver energized electrons at thetop of the chain The electrons arepassed from protein to proteinwithin the membrane slowly releas-ing their energy in steps Some ofthat energy is used directly to formATP some is used by an enzyme topump H ions into the center of themitochondrion Consequently themitochondrion inner membranebecomes positively charged becauseof the high concentration of posi-tively charged hydrogen ions At thesame time the exterior of the mem-brane is negatively charged whichfurther attracts hydrogen ions Thegradient of H ions that resultsacross the inner membrane of themitochondrion provides the energy

for ATP production just as it does in the chemiosmotic process that takes place at the thylakoid mem-branes in the chloroplasts Figure 911summarizes the electron transportchain and the formation of ATP

The final electron acceptor at thebottom of the chain is oxygen whichreacts with four hydrogen ions (4H)and four electrons to form two mole-cules of water (H2O) This is why oxy-gen is so important to our bodiesWithout oxygen the proteins in theelectron transport chain cannot passalong the electrons If a protein cannotpass along an electron to oxygen itcannot accept another electron Veryquickly the entire chain becomesblocked and ATP production stops

Overall the electron transportchain adds 32 ATP molecules to thefour already produced Obviouslythe aerobic process of ATP produc-tion is very effective In the absenceof oxygen however an anaerobicprocess can produce small amountsof ATP to keep the cell from dying

234 ENERGY IN A CELL

H H

H

H

H

H

P

Electroncarrier proteins

Electronpathway

Space betweeninner and outer

membranes

Enzyme

ADP ATP

Innermembrane

Center ofmitochondrion

NAD

FAD

NADH

FADH2

4 H O2 4 electrons

H2O

H2O

e

Figure 911In the electron transportchain the carrier mole-cules NADH and FADH2give up electrons thatpass through a series ofreactions Oxygen is thefinal electron acceptor

0231-0243 C9S3 BDOL-829900 8404 501 AM Page 234

93 GETTING ENERGY TO MAKE ATP 235

FermentationThere are times such as during

heavy exercise when your cells arewithout oxygen for a short period oftime When this happens an anaero-bic process called fermentation fol-lows glycolysis and provides a meansto continue producing ATP until oxy-gen is available again There are twomajor types of fermentation lacticacid fermentation and alcoholic fer-mentation The table in Figure 912compares the two processes with res-piration Perform the Problem-SolvingLab shown here to further compareand contrast cellular respiration andfermentation

Infer when yourbody might perform fermentationreactions

Lactic acid fermentationYou know that under anaerobic con-

ditions the electron transport chainbacks up because oxygen is not present

Gerard VandystadtVandystadt AgencyPhoto Researchers

Figure 912Lactic acid and alcoholic fermentations are comparablein the production of ATP but compared to cellular respi-ration it is obvious that fermentation is far less efficientin ATP production This runnerrsquos muscles have beendepleted of oxygen and fermentation is taking place

Comparison of Fermentation to Cellular Respiration

Lactic Acid Alcoholic Cellular respiration

glucose glucose glucose

glycolysis (pyruvic acid) glycolysis (pyruvic acid) glycolysis (pyruvic acid)

carbon dioxide carbon dioxide

lactic acid alcohol water

2 ATP 2 ATP 36 ATP

Acquire InformationCellular respiration or fermentation The methods bywhich organisms derive ATP may differ however the resultthe production of ATP molecules is similar

Solve the ProblemStudy the table in Figure 912 and evaluate cellular respirationlactic acid fermentation and alcoholic fermentation

Thinking Critically1 Describe Why does cellular respiration produce so much

more ATP than does fermentation2 Use Scientific Explanations Describe a situation when a

human would need to use more than one of the processeslisted above

3 Analyze Think of an organism that might generate ATPonly by fermentation and consider why fermentation is thebest process for the organism

0231-0243 C9S3 BDOL-829900 8404 501 AM Page 235

as the final electron acceptor AsNADH and FADH2 arrive at the chainfrom the citric acid cycle and glycolysisthey cannot release their energizedelectrons The citric acid cycle and gly-colysis cannot continue without asteady supply of NAD and FAD

The cell does not have a method toreplace FAD during anaerobic condi-tions however NAD can bereplaced through lactic acid fermenta-tion Lactic acid fermentation is oneof the processes that supplies energywhen oxygen is scarce Two moleculesof pyruvic acid produced in glycolysisuse NADH to form two molecules oflactic acid This releases NAD to beused in glycolysis allowing two ATPmolecules to be formed for each glu-cose molecule The lactic acid is trans-ferred from muscle cells where it isproduced during strenuous exerciseto the liver that converts it back topyruvic acid The lactic acid thatbuilds up in muscle cells results inmuscle fatigue

Alcoholic fermentationAnother type of fermentation

alcoholic fermentation is used by yeast cells and some bacteria toproduce CO2 and ethyl alcoholWhen making bread like that shownin Figure 913 yeast cells produceCO2 that forms bubbles in the doughEventually the heat of the oven killsthe yeast and the bubble pockets areleft to lighten the bread You can dothe MiniLab on this page to studyalcoholic fermentation in apple juice

236 ENERGY IN A CELL

Figure 913Alcoholic fermentation by the yeast in breaddough produces CO2 bubbles that raise thedough Think Critically What happens tothe CO2

PredictDetermine if Apple Juice Ferments Some organ-isms such as yeast can breakdown food molecules and syn-thesize ATP when no oxygen isavailable When food is avail-able yeast carry out alcoholicfermentation producing CO2Thus the production of CO2 inthe absence of oxygen can beused to judge whether alcoholicfermentation is taking place

Procedure Carefully study the diagram

and set up the experimentas shown

Hold the test tube in abeaker of warm (not hot)water and observe

Analysis1 Interpret Data What were the gas bubbles that came

from the plastic pipette2 Hypothesize What would happen to the rate of bubbles

given off if more yeast were present in the mixture3 Analyze Why was the test tube placed in warm water4 Draw Conclusions Was the process you demonstrated

aerobic or anaerobic Explain

Yeast andapple juice

Plastic pipette

Water

Test tube

Metalwashers

Matt Meadows

0231-0243 C9S3 BDOL-829900 8404 502 AM Page 236

ComparingPhotosynthesis andCellular Respiration

The production and breakdownof food molecules are accomplishedby distinct processes that bear cer-tain similarities Both photosynthe-sis and cellular respiration useelectron carriers and a cycle ofchemical reactions to form ATPBoth use electron transport chainsto form ATP and to create a chemi-cal and a concentration gradient ofH within a cell This hydrogen iongradient can be used to form ATP bychemiosmosis

However despite using such simi-lar tools the two cellular processesaccomplish quite different tasksPhotosynthesis produces high-energycarbohydrates and oxygen from thesunrsquos energy whereas cellular respira-tion uses oxygen to break down car-bohydrates to form ATP andcompounds that provide less energyAlso one of the end products of cel-lular respiration is CO2 which is oneof the beginning products for photo-synthesis The oxygen produced dur-ing photosynthesis is a criticalmolecule necessary for cellular respi-ration Table 91 compares thesecomplementary processes

Understanding Main Ideas1 Compare the ATP yields of glycolysis the citric

acid cycle and the electron transport chain2 How do alcoholic fermentation and lactic acid fer-

mentation differ3 How is most of the ATP from aerobic respiration

produced4 Why is lactic acid fermentation important to the

cell when oxygen is scarce5 How many ATP molecules are produced after the

electrons go down the electron transport chain

Thinking Critically6 Compare the energy-producing processes in a

joggerrsquos leg muscles with those of a sprinterrsquosleg muscles Which is likely to build up more lactic acid Explain

7 Get the Big Picture How are the chemical reac-tions of photosynthesis and cellular respirationconnected What is the significance of this con-nection For more help refer to Get the BigPicture in the Skill Handbook

SKILL REVIEWSKILL REVIEW

93 GETTING ENERGY TO MAKE ATP 237(l)file photo (r)George Robbins

Table 91 Comparison of Photosynthesis and Cellular Respiration

Photosynthesis Cellular Respiration

Food synthesized Food broken down

Energy from sun stored in glucose Energy of glucose released

Carbon dioxide taken in Carbon dioxide given off

Oxygen given off Oxygen taken inProduces sugars Produces CO2from PGAL and H2ORequires Does notlight require lightOccurs only in Occurs in allpresence of living cellschlorophyll

ncbdolglencoecomself_check_quiz

0231-0243 C9S3 BDOL-829900 8404 502 AM Page 237

Notice in Figure 98 that twomolecules of PGAL are formed dur-ing glycolysis Recall that PGALalso forms in the Calvin cycle ThePGAL made during photosynthesiscan enter the glycolysis pathway andlead to the formation of ATP andorganic molecules

Following glycolysis the pyruvicacid molecules move into the mito-chondria the organelles that transformenergy for the cell In the presence ofoxygen two more stages complete cel-lular respiration the citric acid cycleand the electron transport chain of themitochondrion Before these twostages can begin however pyruvic acidundergoes a series of reactions in whichit gives off a molecule of CO2 and com-bines with a molecule called coenzymeA to form acetyl-CoA The reactionwith coenzyme A produces a molecule

of NADH and H These reactionsare shown in Figure 99

The citric acid cycleThe citric acid cycle also called

the Krebs cycle is a series of chemicalreactions similar to the Calvin cyclein that the molecule used in the firstreaction is also one of the end prod-ucts Read Figure 910 to study thecitric acid cycle

For every turn of the cycle one mol-ecule of ATP and two molecules of car-bon dioxide are produced Twoelectron carriers are used NAD andFAD (flavin adenine dinucleotide) Atotal of three NADH three H ionsand one FADH2 are formed The elec-tron carriers each pass two energizedelectrons along to the electron trans-port chain in the inner membrane ofthe mitochondrion

232 ENERGY IN A CELL

C C C CC C C P

C C C

C C C

C C CPC C

ENERGY ENERGY

2ATP2ADP

4ADP + 4 P

2NAD+2PGAL

Glucose

4ATP

2NADH + 2H+

2 Pyruvicacid

C C C C C C C C C CC

NAD+

CO2

NADH + H+

Pyruvicacid

Outside themitochondrion

Mitochondrialmembrane

Coenzyme A

Pyruvicacid

Inside themitochondrion

Intermediateby-product

- CoAAcetyl-CoA

+

Figure 98Glycolysis breaks downa molecule of glucoseinto two molecules ofpyruvic acid In theprocess it forms a netof two molecules ofATP two molecules ofNADH and two hydro-gen ions

Figure 99Before the citric acidcycle and electron trans-port chain begin pyruvicacid undergoes a seriesof reactions InferWhat products areformed as a result ofthe reactions withinthe mitochondrion

0231-0243 C9S3 BDOL-829900 8404 500 AM Page 232

The Citric Acid CycleFigure 910The citric acid cycle breaks down a molecule ofacetyl-CoA and forms ATP and CO2 The electroncarriers NAD and FAD pick up energized electronsand pass them to the electron transport chain inthe inner mitochondrial membrane Critical ThinkingHow many CO2 molecules are produced for everyglucose molecule that entered the cellular respira-tion pathways

93 GETTING ENERGY TO MAKE ATP 233

P

NAD+

NAD+

NAD+

FADH2FAD

C C

NADH + H+

NADH + H+

ATP

ADP +

(Acetyl-CoA)

(Oxaloacetic acid)(Citric acid)

CitricAcidCycle

O O(CO2)

O O(CO2)

NADH + H+

C C C C

C C C C

C C C C

C C C C

C C C C C

C

C C C C C

C

C

Formation of the second CO2 Anothermolecule of CO2 is released forming a four-carboncompound One molecule of ATP and a moleculeof NADH are also produced

CC

Citric acid The two-carboncompound acetyl-CoA reactswith a four-carbon compoundcalled oxaloacetic acid to formcitric acid a six-carbonmolecule

AA Formation of CO2 A moleculeof CO2 is formed reducing theeventual product to a five-carboncompound In the process amolecule of NADH and H+ isproduced

BB

Profs P Motta amp T NaguroScience Photo LibraryCustom Medical Stock Photo

Recycling of oxaloacetic acid The four-carbon molecule goesthrough a series of reactions in which FADH2 NADH and H+

are formed The carbon chainis rearranged and oxaloaceticacid is again made availablefor the cycle

DD

The mitochondria hostthe citric acid cycle

Magnification unavailable

0231-0243 C9S3 BDOL-829900 8404 500 AM Page 233

The electron transport chainThe electron transport chain in

the inner membrane of the mito-chondrion is very similar to the elec-tron transport chains of thethylakoid membrane in the chloro-plasts of plant cells during photo-synthesis NADH and FADH2deliver energized electrons at thetop of the chain The electrons arepassed from protein to proteinwithin the membrane slowly releas-ing their energy in steps Some ofthat energy is used directly to formATP some is used by an enzyme topump H ions into the center of themitochondrion Consequently themitochondrion inner membranebecomes positively charged becauseof the high concentration of posi-tively charged hydrogen ions At thesame time the exterior of the mem-brane is negatively charged whichfurther attracts hydrogen ions Thegradient of H ions that resultsacross the inner membrane of themitochondrion provides the energy

for ATP production just as it does in the chemiosmotic process that takes place at the thylakoid mem-branes in the chloroplasts Figure 911summarizes the electron transportchain and the formation of ATP

The final electron acceptor at thebottom of the chain is oxygen whichreacts with four hydrogen ions (4H)and four electrons to form two mole-cules of water (H2O) This is why oxy-gen is so important to our bodiesWithout oxygen the proteins in theelectron transport chain cannot passalong the electrons If a protein cannotpass along an electron to oxygen itcannot accept another electron Veryquickly the entire chain becomesblocked and ATP production stops

Overall the electron transportchain adds 32 ATP molecules to thefour already produced Obviouslythe aerobic process of ATP produc-tion is very effective In the absenceof oxygen however an anaerobicprocess can produce small amountsof ATP to keep the cell from dying

234 ENERGY IN A CELL

H H

H

H

H

H

P

Electroncarrier proteins

Electronpathway

Space betweeninner and outer

membranes

Enzyme

ADP ATP

Innermembrane

Center ofmitochondrion

NAD

FAD

NADH

FADH2

4 H O2 4 electrons

H2O

H2O

e

Figure 911In the electron transportchain the carrier mole-cules NADH and FADH2give up electrons thatpass through a series ofreactions Oxygen is thefinal electron acceptor

0231-0243 C9S3 BDOL-829900 8404 501 AM Page 234

93 GETTING ENERGY TO MAKE ATP 235

FermentationThere are times such as during

heavy exercise when your cells arewithout oxygen for a short period oftime When this happens an anaero-bic process called fermentation fol-lows glycolysis and provides a meansto continue producing ATP until oxy-gen is available again There are twomajor types of fermentation lacticacid fermentation and alcoholic fer-mentation The table in Figure 912compares the two processes with res-piration Perform the Problem-SolvingLab shown here to further compareand contrast cellular respiration andfermentation

Infer when yourbody might perform fermentationreactions

Lactic acid fermentationYou know that under anaerobic con-

ditions the electron transport chainbacks up because oxygen is not present

Gerard VandystadtVandystadt AgencyPhoto Researchers

Figure 912Lactic acid and alcoholic fermentations are comparablein the production of ATP but compared to cellular respi-ration it is obvious that fermentation is far less efficientin ATP production This runnerrsquos muscles have beendepleted of oxygen and fermentation is taking place

Comparison of Fermentation to Cellular Respiration

Lactic Acid Alcoholic Cellular respiration

glucose glucose glucose

glycolysis (pyruvic acid) glycolysis (pyruvic acid) glycolysis (pyruvic acid)

carbon dioxide carbon dioxide

lactic acid alcohol water

2 ATP 2 ATP 36 ATP

Acquire InformationCellular respiration or fermentation The methods bywhich organisms derive ATP may differ however the resultthe production of ATP molecules is similar

Solve the ProblemStudy the table in Figure 912 and evaluate cellular respirationlactic acid fermentation and alcoholic fermentation

Thinking Critically1 Describe Why does cellular respiration produce so much

more ATP than does fermentation2 Use Scientific Explanations Describe a situation when a

human would need to use more than one of the processeslisted above

3 Analyze Think of an organism that might generate ATPonly by fermentation and consider why fermentation is thebest process for the organism

0231-0243 C9S3 BDOL-829900 8404 501 AM Page 235

as the final electron acceptor AsNADH and FADH2 arrive at the chainfrom the citric acid cycle and glycolysisthey cannot release their energizedelectrons The citric acid cycle and gly-colysis cannot continue without asteady supply of NAD and FAD

The cell does not have a method toreplace FAD during anaerobic condi-tions however NAD can bereplaced through lactic acid fermenta-tion Lactic acid fermentation is oneof the processes that supplies energywhen oxygen is scarce Two moleculesof pyruvic acid produced in glycolysisuse NADH to form two molecules oflactic acid This releases NAD to beused in glycolysis allowing two ATPmolecules to be formed for each glu-cose molecule The lactic acid is trans-ferred from muscle cells where it isproduced during strenuous exerciseto the liver that converts it back topyruvic acid The lactic acid thatbuilds up in muscle cells results inmuscle fatigue

Alcoholic fermentationAnother type of fermentation

alcoholic fermentation is used by yeast cells and some bacteria toproduce CO2 and ethyl alcoholWhen making bread like that shownin Figure 913 yeast cells produceCO2 that forms bubbles in the doughEventually the heat of the oven killsthe yeast and the bubble pockets areleft to lighten the bread You can dothe MiniLab on this page to studyalcoholic fermentation in apple juice

236 ENERGY IN A CELL

Figure 913Alcoholic fermentation by the yeast in breaddough produces CO2 bubbles that raise thedough Think Critically What happens tothe CO2

PredictDetermine if Apple Juice Ferments Some organ-isms such as yeast can breakdown food molecules and syn-thesize ATP when no oxygen isavailable When food is avail-able yeast carry out alcoholicfermentation producing CO2Thus the production of CO2 inthe absence of oxygen can beused to judge whether alcoholicfermentation is taking place

Procedure Carefully study the diagram

and set up the experimentas shown

Hold the test tube in abeaker of warm (not hot)water and observe

Analysis1 Interpret Data What were the gas bubbles that came

from the plastic pipette2 Hypothesize What would happen to the rate of bubbles

given off if more yeast were present in the mixture3 Analyze Why was the test tube placed in warm water4 Draw Conclusions Was the process you demonstrated

aerobic or anaerobic Explain

Yeast andapple juice

Plastic pipette

Water

Test tube

Metalwashers

Matt Meadows

0231-0243 C9S3 BDOL-829900 8404 502 AM Page 236

ComparingPhotosynthesis andCellular Respiration

The production and breakdownof food molecules are accomplishedby distinct processes that bear cer-tain similarities Both photosynthe-sis and cellular respiration useelectron carriers and a cycle ofchemical reactions to form ATPBoth use electron transport chainsto form ATP and to create a chemi-cal and a concentration gradient ofH within a cell This hydrogen iongradient can be used to form ATP bychemiosmosis

However despite using such simi-lar tools the two cellular processesaccomplish quite different tasksPhotosynthesis produces high-energycarbohydrates and oxygen from thesunrsquos energy whereas cellular respira-tion uses oxygen to break down car-bohydrates to form ATP andcompounds that provide less energyAlso one of the end products of cel-lular respiration is CO2 which is oneof the beginning products for photo-synthesis The oxygen produced dur-ing photosynthesis is a criticalmolecule necessary for cellular respi-ration Table 91 compares thesecomplementary processes

Understanding Main Ideas1 Compare the ATP yields of glycolysis the citric

acid cycle and the electron transport chain2 How do alcoholic fermentation and lactic acid fer-

mentation differ3 How is most of the ATP from aerobic respiration

produced4 Why is lactic acid fermentation important to the

cell when oxygen is scarce5 How many ATP molecules are produced after the

electrons go down the electron transport chain

Thinking Critically6 Compare the energy-producing processes in a

joggerrsquos leg muscles with those of a sprinterrsquosleg muscles Which is likely to build up more lactic acid Explain

7 Get the Big Picture How are the chemical reac-tions of photosynthesis and cellular respirationconnected What is the significance of this con-nection For more help refer to Get the BigPicture in the Skill Handbook

SKILL REVIEWSKILL REVIEW

93 GETTING ENERGY TO MAKE ATP 237(l)file photo (r)George Robbins

Table 91 Comparison of Photosynthesis and Cellular Respiration

Photosynthesis Cellular Respiration

Food synthesized Food broken down

Energy from sun stored in glucose Energy of glucose released

Carbon dioxide taken in Carbon dioxide given off

Oxygen given off Oxygen taken inProduces sugars Produces CO2from PGAL and H2ORequires Does notlight require lightOccurs only in Occurs in allpresence of living cellschlorophyll

ncbdolglencoecomself_check_quiz

0231-0243 C9S3 BDOL-829900 8404 502 AM Page 237

The Citric Acid CycleFigure 910The citric acid cycle breaks down a molecule ofacetyl-CoA and forms ATP and CO2 The electroncarriers NAD and FAD pick up energized electronsand pass them to the electron transport chain inthe inner mitochondrial membrane Critical ThinkingHow many CO2 molecules are produced for everyglucose molecule that entered the cellular respira-tion pathways

93 GETTING ENERGY TO MAKE ATP 233

P

NAD+

NAD+

NAD+

FADH2FAD

C C

NADH + H+

NADH + H+

ATP

ADP +

(Acetyl-CoA)

(Oxaloacetic acid)(Citric acid)

CitricAcidCycle

O O(CO2)

O O(CO2)

NADH + H+

C C C C

C C C C

C C C C

C C C C

C C C C C

C

C C C C C

C

C

Formation of the second CO2 Anothermolecule of CO2 is released forming a four-carboncompound One molecule of ATP and a moleculeof NADH are also produced

CC

Citric acid The two-carboncompound acetyl-CoA reactswith a four-carbon compoundcalled oxaloacetic acid to formcitric acid a six-carbonmolecule

AA Formation of CO2 A moleculeof CO2 is formed reducing theeventual product to a five-carboncompound In the process amolecule of NADH and H+ isproduced

BB

Profs P Motta amp T NaguroScience Photo LibraryCustom Medical Stock Photo

Recycling of oxaloacetic acid The four-carbon molecule goesthrough a series of reactions in which FADH2 NADH and H+

are formed The carbon chainis rearranged and oxaloaceticacid is again made availablefor the cycle

DD

The mitochondria hostthe citric acid cycle

Magnification unavailable

0231-0243 C9S3 BDOL-829900 8404 500 AM Page 233

The electron transport chainThe electron transport chain in

the inner membrane of the mito-chondrion is very similar to the elec-tron transport chains of thethylakoid membrane in the chloro-plasts of plant cells during photo-synthesis NADH and FADH2deliver energized electrons at thetop of the chain The electrons arepassed from protein to proteinwithin the membrane slowly releas-ing their energy in steps Some ofthat energy is used directly to formATP some is used by an enzyme topump H ions into the center of themitochondrion Consequently themitochondrion inner membranebecomes positively charged becauseof the high concentration of posi-tively charged hydrogen ions At thesame time the exterior of the mem-brane is negatively charged whichfurther attracts hydrogen ions Thegradient of H ions that resultsacross the inner membrane of themitochondrion provides the energy

for ATP production just as it does in the chemiosmotic process that takes place at the thylakoid mem-branes in the chloroplasts Figure 911summarizes the electron transportchain and the formation of ATP

The final electron acceptor at thebottom of the chain is oxygen whichreacts with four hydrogen ions (4H)and four electrons to form two mole-cules of water (H2O) This is why oxy-gen is so important to our bodiesWithout oxygen the proteins in theelectron transport chain cannot passalong the electrons If a protein cannotpass along an electron to oxygen itcannot accept another electron Veryquickly the entire chain becomesblocked and ATP production stops

Overall the electron transportchain adds 32 ATP molecules to thefour already produced Obviouslythe aerobic process of ATP produc-tion is very effective In the absenceof oxygen however an anaerobicprocess can produce small amountsof ATP to keep the cell from dying

234 ENERGY IN A CELL

H H

H

H

H

H

P

Electroncarrier proteins

Electronpathway

Space betweeninner and outer

membranes

Enzyme

ADP ATP

Innermembrane

Center ofmitochondrion

NAD

FAD

NADH

FADH2

4 H O2 4 electrons

H2O

H2O

e

Figure 911In the electron transportchain the carrier mole-cules NADH and FADH2give up electrons thatpass through a series ofreactions Oxygen is thefinal electron acceptor

0231-0243 C9S3 BDOL-829900 8404 501 AM Page 234

93 GETTING ENERGY TO MAKE ATP 235

FermentationThere are times such as during

heavy exercise when your cells arewithout oxygen for a short period oftime When this happens an anaero-bic process called fermentation fol-lows glycolysis and provides a meansto continue producing ATP until oxy-gen is available again There are twomajor types of fermentation lacticacid fermentation and alcoholic fer-mentation The table in Figure 912compares the two processes with res-piration Perform the Problem-SolvingLab shown here to further compareand contrast cellular respiration andfermentation

Infer when yourbody might perform fermentationreactions

Lactic acid fermentationYou know that under anaerobic con-

ditions the electron transport chainbacks up because oxygen is not present

Gerard VandystadtVandystadt AgencyPhoto Researchers

Figure 912Lactic acid and alcoholic fermentations are comparablein the production of ATP but compared to cellular respi-ration it is obvious that fermentation is far less efficientin ATP production This runnerrsquos muscles have beendepleted of oxygen and fermentation is taking place

Comparison of Fermentation to Cellular Respiration

Lactic Acid Alcoholic Cellular respiration

glucose glucose glucose

glycolysis (pyruvic acid) glycolysis (pyruvic acid) glycolysis (pyruvic acid)

carbon dioxide carbon dioxide

lactic acid alcohol water

2 ATP 2 ATP 36 ATP

Acquire InformationCellular respiration or fermentation The methods bywhich organisms derive ATP may differ however the resultthe production of ATP molecules is similar

Solve the ProblemStudy the table in Figure 912 and evaluate cellular respirationlactic acid fermentation and alcoholic fermentation

Thinking Critically1 Describe Why does cellular respiration produce so much

more ATP than does fermentation2 Use Scientific Explanations Describe a situation when a

human would need to use more than one of the processeslisted above

3 Analyze Think of an organism that might generate ATPonly by fermentation and consider why fermentation is thebest process for the organism

0231-0243 C9S3 BDOL-829900 8404 501 AM Page 235

as the final electron acceptor AsNADH and FADH2 arrive at the chainfrom the citric acid cycle and glycolysisthey cannot release their energizedelectrons The citric acid cycle and gly-colysis cannot continue without asteady supply of NAD and FAD

The cell does not have a method toreplace FAD during anaerobic condi-tions however NAD can bereplaced through lactic acid fermenta-tion Lactic acid fermentation is oneof the processes that supplies energywhen oxygen is scarce Two moleculesof pyruvic acid produced in glycolysisuse NADH to form two molecules oflactic acid This releases NAD to beused in glycolysis allowing two ATPmolecules to be formed for each glu-cose molecule The lactic acid is trans-ferred from muscle cells where it isproduced during strenuous exerciseto the liver that converts it back topyruvic acid The lactic acid thatbuilds up in muscle cells results inmuscle fatigue

Alcoholic fermentationAnother type of fermentation

alcoholic fermentation is used by yeast cells and some bacteria toproduce CO2 and ethyl alcoholWhen making bread like that shownin Figure 913 yeast cells produceCO2 that forms bubbles in the doughEventually the heat of the oven killsthe yeast and the bubble pockets areleft to lighten the bread You can dothe MiniLab on this page to studyalcoholic fermentation in apple juice

236 ENERGY IN A CELL

Figure 913Alcoholic fermentation by the yeast in breaddough produces CO2 bubbles that raise thedough Think Critically What happens tothe CO2

PredictDetermine if Apple Juice Ferments Some organ-isms such as yeast can breakdown food molecules and syn-thesize ATP when no oxygen isavailable When food is avail-able yeast carry out alcoholicfermentation producing CO2Thus the production of CO2 inthe absence of oxygen can beused to judge whether alcoholicfermentation is taking place

Procedure Carefully study the diagram

and set up the experimentas shown

Hold the test tube in abeaker of warm (not hot)water and observe

Analysis1 Interpret Data What were the gas bubbles that came

from the plastic pipette2 Hypothesize What would happen to the rate of bubbles

given off if more yeast were present in the mixture3 Analyze Why was the test tube placed in warm water4 Draw Conclusions Was the process you demonstrated

aerobic or anaerobic Explain

Yeast andapple juice

Plastic pipette

Water

Test tube

Metalwashers

Matt Meadows

0231-0243 C9S3 BDOL-829900 8404 502 AM Page 236

ComparingPhotosynthesis andCellular Respiration

The production and breakdownof food molecules are accomplishedby distinct processes that bear cer-tain similarities Both photosynthe-sis and cellular respiration useelectron carriers and a cycle ofchemical reactions to form ATPBoth use electron transport chainsto form ATP and to create a chemi-cal and a concentration gradient ofH within a cell This hydrogen iongradient can be used to form ATP bychemiosmosis

However despite using such simi-lar tools the two cellular processesaccomplish quite different tasksPhotosynthesis produces high-energycarbohydrates and oxygen from thesunrsquos energy whereas cellular respira-tion uses oxygen to break down car-bohydrates to form ATP andcompounds that provide less energyAlso one of the end products of cel-lular respiration is CO2 which is oneof the beginning products for photo-synthesis The oxygen produced dur-ing photosynthesis is a criticalmolecule necessary for cellular respi-ration Table 91 compares thesecomplementary processes

Understanding Main Ideas1 Compare the ATP yields of glycolysis the citric

acid cycle and the electron transport chain2 How do alcoholic fermentation and lactic acid fer-

mentation differ3 How is most of the ATP from aerobic respiration

produced4 Why is lactic acid fermentation important to the

cell when oxygen is scarce5 How many ATP molecules are produced after the

electrons go down the electron transport chain

Thinking Critically6 Compare the energy-producing processes in a

joggerrsquos leg muscles with those of a sprinterrsquosleg muscles Which is likely to build up more lactic acid Explain

7 Get the Big Picture How are the chemical reac-tions of photosynthesis and cellular respirationconnected What is the significance of this con-nection For more help refer to Get the BigPicture in the Skill Handbook

SKILL REVIEWSKILL REVIEW

93 GETTING ENERGY TO MAKE ATP 237(l)file photo (r)George Robbins

Table 91 Comparison of Photosynthesis and Cellular Respiration

Photosynthesis Cellular Respiration

Food synthesized Food broken down

Energy from sun stored in glucose Energy of glucose released

Carbon dioxide taken in Carbon dioxide given off

Oxygen given off Oxygen taken inProduces sugars Produces CO2from PGAL and H2ORequires Does notlight require lightOccurs only in Occurs in allpresence of living cellschlorophyll

ncbdolglencoecomself_check_quiz

0231-0243 C9S3 BDOL-829900 8404 502 AM Page 237

The electron transport chainThe electron transport chain in

the inner membrane of the mito-chondrion is very similar to the elec-tron transport chains of thethylakoid membrane in the chloro-plasts of plant cells during photo-synthesis NADH and FADH2deliver energized electrons at thetop of the chain The electrons arepassed from protein to proteinwithin the membrane slowly releas-ing their energy in steps Some ofthat energy is used directly to formATP some is used by an enzyme topump H ions into the center of themitochondrion Consequently themitochondrion inner membranebecomes positively charged becauseof the high concentration of posi-tively charged hydrogen ions At thesame time the exterior of the mem-brane is negatively charged whichfurther attracts hydrogen ions Thegradient of H ions that resultsacross the inner membrane of themitochondrion provides the energy

for ATP production just as it does in the chemiosmotic process that takes place at the thylakoid mem-branes in the chloroplasts Figure 911summarizes the electron transportchain and the formation of ATP

The final electron acceptor at thebottom of the chain is oxygen whichreacts with four hydrogen ions (4H)and four electrons to form two mole-cules of water (H2O) This is why oxy-gen is so important to our bodiesWithout oxygen the proteins in theelectron transport chain cannot passalong the electrons If a protein cannotpass along an electron to oxygen itcannot accept another electron Veryquickly the entire chain becomesblocked and ATP production stops

Overall the electron transportchain adds 32 ATP molecules to thefour already produced Obviouslythe aerobic process of ATP produc-tion is very effective In the absenceof oxygen however an anaerobicprocess can produce small amountsof ATP to keep the cell from dying

234 ENERGY IN A CELL

H H

H

H

H

H

P

Electroncarrier proteins

Electronpathway

Space betweeninner and outer

membranes

Enzyme

ADP ATP

Innermembrane

Center ofmitochondrion

NAD

FAD

NADH

FADH2

4 H O2 4 electrons

H2O

H2O

e

Figure 911In the electron transportchain the carrier mole-cules NADH and FADH2give up electrons thatpass through a series ofreactions Oxygen is thefinal electron acceptor

0231-0243 C9S3 BDOL-829900 8404 501 AM Page 234

93 GETTING ENERGY TO MAKE ATP 235

FermentationThere are times such as during

heavy exercise when your cells arewithout oxygen for a short period oftime When this happens an anaero-bic process called fermentation fol-lows glycolysis and provides a meansto continue producing ATP until oxy-gen is available again There are twomajor types of fermentation lacticacid fermentation and alcoholic fer-mentation The table in Figure 912compares the two processes with res-piration Perform the Problem-SolvingLab shown here to further compareand contrast cellular respiration andfermentation

Infer when yourbody might perform fermentationreactions

Lactic acid fermentationYou know that under anaerobic con-

ditions the electron transport chainbacks up because oxygen is not present

Gerard VandystadtVandystadt AgencyPhoto Researchers

Figure 912Lactic acid and alcoholic fermentations are comparablein the production of ATP but compared to cellular respi-ration it is obvious that fermentation is far less efficientin ATP production This runnerrsquos muscles have beendepleted of oxygen and fermentation is taking place

Comparison of Fermentation to Cellular Respiration

Lactic Acid Alcoholic Cellular respiration

glucose glucose glucose

glycolysis (pyruvic acid) glycolysis (pyruvic acid) glycolysis (pyruvic acid)

carbon dioxide carbon dioxide

lactic acid alcohol water

2 ATP 2 ATP 36 ATP

Acquire InformationCellular respiration or fermentation The methods bywhich organisms derive ATP may differ however the resultthe production of ATP molecules is similar

Solve the ProblemStudy the table in Figure 912 and evaluate cellular respirationlactic acid fermentation and alcoholic fermentation

Thinking Critically1 Describe Why does cellular respiration produce so much

more ATP than does fermentation2 Use Scientific Explanations Describe a situation when a

human would need to use more than one of the processeslisted above

3 Analyze Think of an organism that might generate ATPonly by fermentation and consider why fermentation is thebest process for the organism

0231-0243 C9S3 BDOL-829900 8404 501 AM Page 235

as the final electron acceptor AsNADH and FADH2 arrive at the chainfrom the citric acid cycle and glycolysisthey cannot release their energizedelectrons The citric acid cycle and gly-colysis cannot continue without asteady supply of NAD and FAD

The cell does not have a method toreplace FAD during anaerobic condi-tions however NAD can bereplaced through lactic acid fermenta-tion Lactic acid fermentation is oneof the processes that supplies energywhen oxygen is scarce Two moleculesof pyruvic acid produced in glycolysisuse NADH to form two molecules oflactic acid This releases NAD to beused in glycolysis allowing two ATPmolecules to be formed for each glu-cose molecule The lactic acid is trans-ferred from muscle cells where it isproduced during strenuous exerciseto the liver that converts it back topyruvic acid The lactic acid thatbuilds up in muscle cells results inmuscle fatigue

Alcoholic fermentationAnother type of fermentation

alcoholic fermentation is used by yeast cells and some bacteria toproduce CO2 and ethyl alcoholWhen making bread like that shownin Figure 913 yeast cells produceCO2 that forms bubbles in the doughEventually the heat of the oven killsthe yeast and the bubble pockets areleft to lighten the bread You can dothe MiniLab on this page to studyalcoholic fermentation in apple juice

236 ENERGY IN A CELL

Figure 913Alcoholic fermentation by the yeast in breaddough produces CO2 bubbles that raise thedough Think Critically What happens tothe CO2

PredictDetermine if Apple Juice Ferments Some organ-isms such as yeast can breakdown food molecules and syn-thesize ATP when no oxygen isavailable When food is avail-able yeast carry out alcoholicfermentation producing CO2Thus the production of CO2 inthe absence of oxygen can beused to judge whether alcoholicfermentation is taking place

Procedure Carefully study the diagram

and set up the experimentas shown

Hold the test tube in abeaker of warm (not hot)water and observe

Analysis1 Interpret Data What were the gas bubbles that came

from the plastic pipette2 Hypothesize What would happen to the rate of bubbles

given off if more yeast were present in the mixture3 Analyze Why was the test tube placed in warm water4 Draw Conclusions Was the process you demonstrated

aerobic or anaerobic Explain

Yeast andapple juice

Plastic pipette

Water

Test tube

Metalwashers

Matt Meadows

0231-0243 C9S3 BDOL-829900 8404 502 AM Page 236

ComparingPhotosynthesis andCellular Respiration

The production and breakdownof food molecules are accomplishedby distinct processes that bear cer-tain similarities Both photosynthe-sis and cellular respiration useelectron carriers and a cycle ofchemical reactions to form ATPBoth use electron transport chainsto form ATP and to create a chemi-cal and a concentration gradient ofH within a cell This hydrogen iongradient can be used to form ATP bychemiosmosis

However despite using such simi-lar tools the two cellular processesaccomplish quite different tasksPhotosynthesis produces high-energycarbohydrates and oxygen from thesunrsquos energy whereas cellular respira-tion uses oxygen to break down car-bohydrates to form ATP andcompounds that provide less energyAlso one of the end products of cel-lular respiration is CO2 which is oneof the beginning products for photo-synthesis The oxygen produced dur-ing photosynthesis is a criticalmolecule necessary for cellular respi-ration Table 91 compares thesecomplementary processes

Understanding Main Ideas1 Compare the ATP yields of glycolysis the citric

acid cycle and the electron transport chain2 How do alcoholic fermentation and lactic acid fer-

mentation differ3 How is most of the ATP from aerobic respiration

produced4 Why is lactic acid fermentation important to the

cell when oxygen is scarce5 How many ATP molecules are produced after the

electrons go down the electron transport chain

Thinking Critically6 Compare the energy-producing processes in a

joggerrsquos leg muscles with those of a sprinterrsquosleg muscles Which is likely to build up more lactic acid Explain

7 Get the Big Picture How are the chemical reac-tions of photosynthesis and cellular respirationconnected What is the significance of this con-nection For more help refer to Get the BigPicture in the Skill Handbook

SKILL REVIEWSKILL REVIEW

93 GETTING ENERGY TO MAKE ATP 237(l)file photo (r)George Robbins

Table 91 Comparison of Photosynthesis and Cellular Respiration

Photosynthesis Cellular Respiration

Food synthesized Food broken down

Energy from sun stored in glucose Energy of glucose released

Carbon dioxide taken in Carbon dioxide given off

Oxygen given off Oxygen taken inProduces sugars Produces CO2from PGAL and H2ORequires Does notlight require lightOccurs only in Occurs in allpresence of living cellschlorophyll

ncbdolglencoecomself_check_quiz

0231-0243 C9S3 BDOL-829900 8404 502 AM Page 237

93 GETTING ENERGY TO MAKE ATP 235

FermentationThere are times such as during

heavy exercise when your cells arewithout oxygen for a short period oftime When this happens an anaero-bic process called fermentation fol-lows glycolysis and provides a meansto continue producing ATP until oxy-gen is available again There are twomajor types of fermentation lacticacid fermentation and alcoholic fer-mentation The table in Figure 912compares the two processes with res-piration Perform the Problem-SolvingLab shown here to further compareand contrast cellular respiration andfermentation

Infer when yourbody might perform fermentationreactions

Lactic acid fermentationYou know that under anaerobic con-

ditions the electron transport chainbacks up because oxygen is not present

Gerard VandystadtVandystadt AgencyPhoto Researchers

Figure 912Lactic acid and alcoholic fermentations are comparablein the production of ATP but compared to cellular respi-ration it is obvious that fermentation is far less efficientin ATP production This runnerrsquos muscles have beendepleted of oxygen and fermentation is taking place

Comparison of Fermentation to Cellular Respiration

Lactic Acid Alcoholic Cellular respiration

glucose glucose glucose

glycolysis (pyruvic acid) glycolysis (pyruvic acid) glycolysis (pyruvic acid)

carbon dioxide carbon dioxide

lactic acid alcohol water

2 ATP 2 ATP 36 ATP

Acquire InformationCellular respiration or fermentation The methods bywhich organisms derive ATP may differ however the resultthe production of ATP molecules is similar

Solve the ProblemStudy the table in Figure 912 and evaluate cellular respirationlactic acid fermentation and alcoholic fermentation

Thinking Critically1 Describe Why does cellular respiration produce so much

more ATP than does fermentation2 Use Scientific Explanations Describe a situation when a

human would need to use more than one of the processeslisted above

3 Analyze Think of an organism that might generate ATPonly by fermentation and consider why fermentation is thebest process for the organism

0231-0243 C9S3 BDOL-829900 8404 501 AM Page 235

as the final electron acceptor AsNADH and FADH2 arrive at the chainfrom the citric acid cycle and glycolysisthey cannot release their energizedelectrons The citric acid cycle and gly-colysis cannot continue without asteady supply of NAD and FAD

The cell does not have a method toreplace FAD during anaerobic condi-tions however NAD can bereplaced through lactic acid fermenta-tion Lactic acid fermentation is oneof the processes that supplies energywhen oxygen is scarce Two moleculesof pyruvic acid produced in glycolysisuse NADH to form two molecules oflactic acid This releases NAD to beused in glycolysis allowing two ATPmolecules to be formed for each glu-cose molecule The lactic acid is trans-ferred from muscle cells where it isproduced during strenuous exerciseto the liver that converts it back topyruvic acid The lactic acid thatbuilds up in muscle cells results inmuscle fatigue

Alcoholic fermentationAnother type of fermentation

alcoholic fermentation is used by yeast cells and some bacteria toproduce CO2 and ethyl alcoholWhen making bread like that shownin Figure 913 yeast cells produceCO2 that forms bubbles in the doughEventually the heat of the oven killsthe yeast and the bubble pockets areleft to lighten the bread You can dothe MiniLab on this page to studyalcoholic fermentation in apple juice

236 ENERGY IN A CELL

Figure 913Alcoholic fermentation by the yeast in breaddough produces CO2 bubbles that raise thedough Think Critically What happens tothe CO2

PredictDetermine if Apple Juice Ferments Some organ-isms such as yeast can breakdown food molecules and syn-thesize ATP when no oxygen isavailable When food is avail-able yeast carry out alcoholicfermentation producing CO2Thus the production of CO2 inthe absence of oxygen can beused to judge whether alcoholicfermentation is taking place

Procedure Carefully study the diagram

and set up the experimentas shown

Hold the test tube in abeaker of warm (not hot)water and observe

Analysis1 Interpret Data What were the gas bubbles that came

from the plastic pipette2 Hypothesize What would happen to the rate of bubbles

given off if more yeast were present in the mixture3 Analyze Why was the test tube placed in warm water4 Draw Conclusions Was the process you demonstrated

aerobic or anaerobic Explain

Yeast andapple juice

Plastic pipette

Water

Test tube

Metalwashers

Matt Meadows

0231-0243 C9S3 BDOL-829900 8404 502 AM Page 236

ComparingPhotosynthesis andCellular Respiration

The production and breakdownof food molecules are accomplishedby distinct processes that bear cer-tain similarities Both photosynthe-sis and cellular respiration useelectron carriers and a cycle ofchemical reactions to form ATPBoth use electron transport chainsto form ATP and to create a chemi-cal and a concentration gradient ofH within a cell This hydrogen iongradient can be used to form ATP bychemiosmosis

However despite using such simi-lar tools the two cellular processesaccomplish quite different tasksPhotosynthesis produces high-energycarbohydrates and oxygen from thesunrsquos energy whereas cellular respira-tion uses oxygen to break down car-bohydrates to form ATP andcompounds that provide less energyAlso one of the end products of cel-lular respiration is CO2 which is oneof the beginning products for photo-synthesis The oxygen produced dur-ing photosynthesis is a criticalmolecule necessary for cellular respi-ration Table 91 compares thesecomplementary processes

Understanding Main Ideas1 Compare the ATP yields of glycolysis the citric

acid cycle and the electron transport chain2 How do alcoholic fermentation and lactic acid fer-

mentation differ3 How is most of the ATP from aerobic respiration

produced4 Why is lactic acid fermentation important to the

cell when oxygen is scarce5 How many ATP molecules are produced after the

electrons go down the electron transport chain

Thinking Critically6 Compare the energy-producing processes in a

joggerrsquos leg muscles with those of a sprinterrsquosleg muscles Which is likely to build up more lactic acid Explain

7 Get the Big Picture How are the chemical reac-tions of photosynthesis and cellular respirationconnected What is the significance of this con-nection For more help refer to Get the BigPicture in the Skill Handbook

SKILL REVIEWSKILL REVIEW

93 GETTING ENERGY TO MAKE ATP 237(l)file photo (r)George Robbins

Table 91 Comparison of Photosynthesis and Cellular Respiration

Photosynthesis Cellular Respiration

Food synthesized Food broken down

Energy from sun stored in glucose Energy of glucose released

Carbon dioxide taken in Carbon dioxide given off

Oxygen given off Oxygen taken inProduces sugars Produces CO2from PGAL and H2ORequires Does notlight require lightOccurs only in Occurs in allpresence of living cellschlorophyll

ncbdolglencoecomself_check_quiz

0231-0243 C9S3 BDOL-829900 8404 502 AM Page 237

as the final electron acceptor AsNADH and FADH2 arrive at the chainfrom the citric acid cycle and glycolysisthey cannot release their energizedelectrons The citric acid cycle and gly-colysis cannot continue without asteady supply of NAD and FAD

The cell does not have a method toreplace FAD during anaerobic condi-tions however NAD can bereplaced through lactic acid fermenta-tion Lactic acid fermentation is oneof the processes that supplies energywhen oxygen is scarce Two moleculesof pyruvic acid produced in glycolysisuse NADH to form two molecules oflactic acid This releases NAD to beused in glycolysis allowing two ATPmolecules to be formed for each glu-cose molecule The lactic acid is trans-ferred from muscle cells where it isproduced during strenuous exerciseto the liver that converts it back topyruvic acid The lactic acid thatbuilds up in muscle cells results inmuscle fatigue

Alcoholic fermentationAnother type of fermentation

alcoholic fermentation is used by yeast cells and some bacteria toproduce CO2 and ethyl alcoholWhen making bread like that shownin Figure 913 yeast cells produceCO2 that forms bubbles in the doughEventually the heat of the oven killsthe yeast and the bubble pockets areleft to lighten the bread You can dothe MiniLab on this page to studyalcoholic fermentation in apple juice

236 ENERGY IN A CELL

Figure 913Alcoholic fermentation by the yeast in breaddough produces CO2 bubbles that raise thedough Think Critically What happens tothe CO2

PredictDetermine if Apple Juice Ferments Some organ-isms such as yeast can breakdown food molecules and syn-thesize ATP when no oxygen isavailable When food is avail-able yeast carry out alcoholicfermentation producing CO2Thus the production of CO2 inthe absence of oxygen can beused to judge whether alcoholicfermentation is taking place

Procedure Carefully study the diagram

and set up the experimentas shown

Hold the test tube in abeaker of warm (not hot)water and observe

Analysis1 Interpret Data What were the gas bubbles that came

from the plastic pipette2 Hypothesize What would happen to the rate of bubbles

given off if more yeast were present in the mixture3 Analyze Why was the test tube placed in warm water4 Draw Conclusions Was the process you demonstrated

aerobic or anaerobic Explain

Yeast andapple juice

Plastic pipette

Water

Test tube

Metalwashers

Matt Meadows

0231-0243 C9S3 BDOL-829900 8404 502 AM Page 236

ComparingPhotosynthesis andCellular Respiration

The production and breakdownof food molecules are accomplishedby distinct processes that bear cer-tain similarities Both photosynthe-sis and cellular respiration useelectron carriers and a cycle ofchemical reactions to form ATPBoth use electron transport chainsto form ATP and to create a chemi-cal and a concentration gradient ofH within a cell This hydrogen iongradient can be used to form ATP bychemiosmosis

However despite using such simi-lar tools the two cellular processesaccomplish quite different tasksPhotosynthesis produces high-energycarbohydrates and oxygen from thesunrsquos energy whereas cellular respira-tion uses oxygen to break down car-bohydrates to form ATP andcompounds that provide less energyAlso one of the end products of cel-lular respiration is CO2 which is oneof the beginning products for photo-synthesis The oxygen produced dur-ing photosynthesis is a criticalmolecule necessary for cellular respi-ration Table 91 compares thesecomplementary processes

Understanding Main Ideas1 Compare the ATP yields of glycolysis the citric

acid cycle and the electron transport chain2 How do alcoholic fermentation and lactic acid fer-

mentation differ3 How is most of the ATP from aerobic respiration

produced4 Why is lactic acid fermentation important to the

cell when oxygen is scarce5 How many ATP molecules are produced after the

electrons go down the electron transport chain

Thinking Critically6 Compare the energy-producing processes in a

joggerrsquos leg muscles with those of a sprinterrsquosleg muscles Which is likely to build up more lactic acid Explain

7 Get the Big Picture How are the chemical reac-tions of photosynthesis and cellular respirationconnected What is the significance of this con-nection For more help refer to Get the BigPicture in the Skill Handbook

SKILL REVIEWSKILL REVIEW

93 GETTING ENERGY TO MAKE ATP 237(l)file photo (r)George Robbins

Table 91 Comparison of Photosynthesis and Cellular Respiration

Photosynthesis Cellular Respiration

Food synthesized Food broken down

Energy from sun stored in glucose Energy of glucose released

Carbon dioxide taken in Carbon dioxide given off

Oxygen given off Oxygen taken inProduces sugars Produces CO2from PGAL and H2ORequires Does notlight require lightOccurs only in Occurs in allpresence of living cellschlorophyll

ncbdolglencoecomself_check_quiz

0231-0243 C9S3 BDOL-829900 8404 502 AM Page 237

ComparingPhotosynthesis andCellular Respiration

The production and breakdownof food molecules are accomplishedby distinct processes that bear cer-tain similarities Both photosynthe-sis and cellular respiration useelectron carriers and a cycle ofchemical reactions to form ATPBoth use electron transport chainsto form ATP and to create a chemi-cal and a concentration gradient ofH within a cell This hydrogen iongradient can be used to form ATP bychemiosmosis

However despite using such simi-lar tools the two cellular processesaccomplish quite different tasksPhotosynthesis produces high-energycarbohydrates and oxygen from thesunrsquos energy whereas cellular respira-tion uses oxygen to break down car-bohydrates to form ATP andcompounds that provide less energyAlso one of the end products of cel-lular respiration is CO2 which is oneof the beginning products for photo-synthesis The oxygen produced dur-ing photosynthesis is a criticalmolecule necessary for cellular respi-ration Table 91 compares thesecomplementary processes

Understanding Main Ideas1 Compare the ATP yields of glycolysis the citric

acid cycle and the electron transport chain2 How do alcoholic fermentation and lactic acid fer-

mentation differ3 How is most of the ATP from aerobic respiration

produced4 Why is lactic acid fermentation important to the

cell when oxygen is scarce5 How many ATP molecules are produced after the

electrons go down the electron transport chain

Thinking Critically6 Compare the energy-producing processes in a

joggerrsquos leg muscles with those of a sprinterrsquosleg muscles Which is likely to build up more lactic acid Explain

7 Get the Big Picture How are the chemical reac-tions of photosynthesis and cellular respirationconnected What is the significance of this con-nection For more help refer to Get the BigPicture in the Skill Handbook

SKILL REVIEWSKILL REVIEW

93 GETTING ENERGY TO MAKE ATP 237(l)file photo (r)George Robbins

Table 91 Comparison of Photosynthesis and Cellular Respiration

Photosynthesis Cellular Respiration

Food synthesized Food broken down

Energy from sun stored in glucose Energy of glucose released

Carbon dioxide taken in Carbon dioxide given off

Oxygen given off Oxygen taken inProduces sugars Produces CO2from PGAL and H2ORequires Does notlight require lightOccurs only in Occurs in allpresence of living cellschlorophyll

ncbdolglencoecomself_check_quiz

0231-0243 C9S3 BDOL-829900 8404 502 AM Page 237

What factors influence photosynthesis

ProblemHow do different wavelengths of light that a plant receivesaffect its rate of photosynthesis

ObjectivesIn this BioLab you will Observe photosynthesis in an aquatic organism Measure the rate of photosynthesis Research the wavelengths of various colors of light Observe how various wavelengths of light influence the

rate of photosynthesis Use the Internet to collect and compare data from other

students

Materials1000-mL beaker lamp with reflector andthree Elodea plants 150-watt bulbstring 025 sodium hydrogenwashers carbonate (baking soda) colored cellophane solution

assorted colors watch with second hand

Safety PrecautionsCAUTION Always wear goggles in the lab

Skill HandbookIf you need help with this lab refer to the Skill Handbook

1 Construct a basic setup like the one shown here2 Create a data table to record your measurements Be sure

to include a column for each color of light you will inves-tigate and a column for the control

3 Place the Elodea plants in the beaker thencompletely cover them with water Addsome of the baking soda solution The solu-tion provides CO2 for the aquarium plantsBe sure to use the same amount of waterand solution for each trial

PROCEDUREPROCEDURE

PREPARATIONPREPARATIONBefore YouBegin

Oxygen is one of the prod-ucts of photosynthesisBecause oxygen is onlyslightly soluble in wateraquatic plants such asElodea give off visiblebubbles of oxygen as theycarry out photosynthesis By measuring the rate atwhich bubbles form youcan measure the rate ofphotosynthesis

Matt Meadows

0231-0243 C9S3 BDOL-829900 8404 504 AM Page 238

ANALYZE AND CONCLUDEANALYZE AND CONCLUDE

93 GETTING ENERGY TO MAKE ATP 239

1 Interpret Observations From wheredid the bubbles of oxygen emerge

2 Make Inferences Explain how counting bubbles measures the rate of photosynthesis

3 Use the Internet Look up the wave-lengths of the colors of light you usedMake a graph of your data and dataposted by other students with the rateof photosynthesis per minute plottedagainst the wavelengths of light youtested for both the control and experi-mental setups Write a sentence or twoexplaining the graph

4 Why was it important to use the same amount of sodiumhydrogen carbonate in each trialERROR ANALYSIS

4 Conduct a control by directing the lamp (without col-ored cellophane) on the plant and noticing when you seethe bubbles

5 Observe and record the number of oxygen bubbles thatElodea generates in five minutes

6 Cover the lamp with a piece of colored cellophane andrepeat steps 4 and 5

7 Repeat steps 4 and 5 with a different color of cellophane8 Go to to post

your data9 Return plant material to an

aquarium to prevent it from drying outCLEANUP AND DISPOSAL

Bubbles observed in five minutes

Color 1 Color 2Control

Data Table

Find this BioLab using the link below and postyour data in the data table provided for thisactivity Using the additional data from otherstudents on the Internet analyze the com-bined data and expand your graph

ncbdolglencoecominternet_lab

ncbdolglencoecominternet_lab

Runk-SchoenbergerGrant Heilman Photography

0231-0243 C9S3 BDOL-829900 8404 508 AM Page 239

ANALYZE AND CONCLUDEANALYZE AND CONCLUDE

93 GETTING ENERGY TO MAKE ATP 239

1 Interpret Observations From wheredid the bubbles of oxygen emerge

2 Make Inferences Explain how counting bubbles measures the rate of photosynthesis

3 Use the Internet Look up the wave-lengths of the colors of light you usedMake a graph of your data and dataposted by other students with the rateof photosynthesis per minute plottedagainst the wavelengths of light youtested for both the control and experi-mental setups Write a sentence or twoexplaining the graph

4 Why was it important to use the same amount of sodiumhydrogen carbonate in each trialERROR ANALYSIS

4 Conduct a control by directing the lamp (without col-ored cellophane) on the plant and noticing when you seethe bubbles

5 Observe and record the number of oxygen bubbles thatElodea generates in five minutes

6 Cover the lamp with a piece of colored cellophane andrepeat steps 4 and 5

7 Repeat steps 4 and 5 with a different color of cellophane8 Go to to post

your data9 Return plant material to an

aquarium to prevent it from drying outCLEANUP AND DISPOSAL

Bubbles observed in five minutes

Color 1 Color 2Control

Data Table

Find this BioLab using the link below and postyour data in the data table provided for thisactivity Using the additional data from otherstudents on the Internet analyze the com-bined data and expand your graph

ncbdolglencoecominternet_lab

ncbdolglencoecominternet_lab

Runk-SchoenbergerGrant Heilman Photography

0231-0243 C9S3 BDOL-829900 8404 508 AM Page 239

240 ENERGY IN A CELL

Plant Pigments

In photosynthesis light energy is converted intochemical energy To begin the process light is

absorbed by colorful pigment molecules containedin chloroplasts

A pigment is a substance that can absorb spe-cific wavelengths of visible light You can observethe colors of the various wavelengths of light byletting sunlight pass through a prism to create aldquorainbowrdquo or spectrum that has red light on oneend violet on the other and orange yellowgreen blue and indigo light in between

Every photosynthetic pigment is distinctive inthat it absorbs specific wavelengths in the visiblelight spectrum

Chlorophylls a and b The principal pig-ment of photosynthesis is chlorophyllChlorophyll exists in two forms designated as aand b Chlorophyll a and b both absorb light inthe violet to blue and the red to red-orange partsof the spectrum although at somewhat differentwavelengths These pigments also reflect greenlight which is why plant leaves appear green

When chlorophyll b absorbs light it transfersthe energy it acquires to chlorophyll a which thenfeeds that energy into the chemical reactions thatlead to the production of ATP and NADPH Inthis way chlorophyll b acts as an ldquoaccessoryrdquo pig-ment by making it possible for photosynthesis tooccur over a broader spectrum of light than wouldbe possible with chlorophyll a alone

Carotenoids and phycobilins Carotenoidsand phycobilins are other kinds of accessory pig-ments that absorb wavelengths of light differentfrom those absorbed by chlorophyll a and b andso extend the range of light that can be used forphotosynthesis

Carotenoids are yellow-orange pigmentsThey are found in all green plants but theircolor is usually masked by chlorophyll

Carotenoids are also found in cyanobacteria andin brown algae A particular carotenoid calledfucoxanthin gives brown algae their characteris-tic dark brown or olive green color

Phycobilins are blue and red Red algae gettheir distinctive blood-red coloration from phy-cobilins Some phycobilins can absorb wave-lengths of green violet and blue light whichpenetrate deep water One species of red algaethat contains these pigments is able to live atocean depths of 269 meters (8825 feet) Thealgaersquos pigments absorb enough of the incrediblyfaint light that penetrates to this depthmdashonly atiny percent of what is available at the waterrsquossurfacemdashto power photosynthesis

Think Critically How do you think accessorypigments may have influenced the spread of pho-tosynthetic organisms into diverse habitats such asthe deep sea

To find out more about pigments visit ncbdolglencoecomchemistry

(t)Robert CalentineVisuals Unlimited (inset)Dan GotshallVisuals Unlimited

Pigments color cyanobacteria(above) and red algae (inset)

LM Magnification 450

0231-0243 C9S3 BDOL-829900 8404 511 AM Page 240

Section 91Vocabulary(ADP) adenosine

diphosphate (p 222)(ATP) adenosine

triphosphate (p 222)

VocabularyCalvin cycle (p 228)chlorophyll (p 226)electron transport chain

(p 226)light-dependent

reactions (p 225)light-independent

reactions (p 225)NADP (p 227)photolysis (p 227)photosynthesis (p 225)pigment (p 226)

PhotosynthesisTrapping theSunrsquos Energy

Getting Energyto Make ATP

STUDY GUIDESTUDY GUIDE

CHAPTER 9 ASSESSMENT 241

To help you review photo-synthesis and cellular respiration use theOrganizational Study Fold on page 225

(t)Tom McHughPhoto Researchers (b)Matt Meadows

The Need forEnergy

Section 92

Section 93 Vocabularyaerobic (p 231)alcoholic fermentation

(p 236)anaerobic (p 231)cellular respiration

(p 231)citric acid cycle (p 232)glycolysis (p 231)lactic acid fermentation

(p 236)

Key Concepts ATP is the molecule that stores energy for

easy use within the cell ATP is formed when a phosphate group is

added to ADP When ATP is brokendown ADP and phosphate are formed andenergy is released

Green organisms trap the energy in sun-light and store it in the bonds of certainmolecules for later use

Organisms that cannot use sunlight directlyobtain energy by consuming plants or otherorganisms that have consumed plants

Key Concepts Photosynthesis is the process by which cells

use light energy to make simple sugars Chlorophyll in the chloroplasts of plant

cells traps light energy needed for photosynthesis

The light reactions of photosynthesis pro-duce ATP and result in the splitting ofwater molecules

The reactions of the Calvin cycle makecarbohydrates using CO2 along with ATPand NADPH from the light reactions

Key Concepts In cellular respiration cells break down

carbohydrates to release energy The first stage of cellular respiration gly-

colysis takes place in the cytoplasm anddoes not require oxygen

The citric acid cycle takes place in mito-chondria and requires oxygen

ncbdolglencoecomvocabulary_puzzlemaker

0231-0243 C9S3 BDOL-829900 8404 511 AM Page 241

242 CHAPTER 9 ASSESSMENT

Review the Chapter 9 vocabulary words listed inthe Study Guide on page 241 For each set ofvocabulary words choose the one that does notbelong Explain why it does not belong

1 light-dependent reactionsmdashCalvin cyclemdashchlorophyll

2 glycolysismdashalcoholic fermentationmdashaerobic3 NADPmdashchlorophyllmdashpigment4 photolysismdashCalvin cyclemdashlight-dependent

reactions5 cellular respirationmdashcitric acid cyclemdash

photosynthesis

6 Which of the following is a product of theCalvin cycleA carbon dioxideB NADP

C oxygenD FADH2

7 ________ processes require oxygen whereas________ processes do notA AnaerobicmdashaerobicB AerobicmdashanaerobicC PhotolysismdashaerobicD Aerobicmdashrespiration

8 Four molecules of glucose would give a netyield of ________ ATP following glycolysisA 8 C 4B 16 D 12

9 In which of the following structures do thelight-independent reactions of photosynthesistake placeA C

B D

10 What is the first process in an animal cell tobe affected by anaerobic conditionsA citric acid cycleB fermentationC glycolysisD electron transport chain

11 In which stage of cellular respiration is glucose broken down into two molecules of pyruvic acidA Calvin cycleB glycolysisC citric acid cycle D electron transport chain

12 Which of the following is a similarity betweenthe citric acid cycle and the Calvin cycleA Both cycles utilize oxygenB Both cycles produce carbon dioxideC Both cycles utilize ATP to break down

carbon bondsD Both cycles recycle the molecule needed

for the first reaction13 When yeast ferments the sugar in a bread

mixture what is produced that causes thebread dough to riseA carbon dioxide C ethyl alcoholB water D oxygen

14 Open Ended Why would human musclecells contain many more mitochondria thanskin cells

15 Open Ended How are cellular respirationand photosynthesis complementaryprocesses

16 Open Ended What happens to sunlight that strikes a leaf but is not trapped bychlorophyll

17 Sequence Describe the pathway of elec-trons from the time they enter the inter-membrane space of the mitochondrion tothe time they are returned to the inside ofthe mitochondrion

ncbdolglencoecomchapter_test

0231-0243 C9S3 BDOL-829900 8404 512 AM Page 242

CHAPTER 9 ASSESSMENT 243

18 Concept Map Make a concept map usingthe following vocabulary terms cellular res-piration glycolysis citric acid cycle electrontransport chain

19 Muscle tissueis made of different types of fibersmdashfast-twitchand slow-twitch These fibers vary in meta-bolic activities Visit to find out about the various types of musclefibers How do the metabolic activities ofthese fibers vary What types of fibers areused for different movements and why

REAL WORLD BIOCHALLENGE

are the steps of

2

4

1 3

which takes place in mitochondria

Multiple ChoiceStudy the table and answer questions20ndash23

The following experimental data wascollected by placing equal amounts ofvarious plant parts in sealed containersand exposing them to various light col-ors After eight hours in the containerthe increase in oxygen was measured in the container

Rate of PhotosynthesisContainer Plant Plant Part Light Color Temperature Increase

(degC) in O2 (mL)

1 Geranium Leaf Red 22 120

2 Geranium Leaf Green 22 15

3 Geranium Root Red 22 0

4 Violet Leaf Red 22 80

5 Violet Leaf Green 22 10

ncbdolglencoecom

20 One could compare the amount of oxygenproduced in eight hours at two differentlight colors by comparing _________A 1 and 3 C 1 and 5B 2 and 4 D 1 and 2

21 In which container was photosynthesis tak-ing place at the fastest rateA 1 C 3B 2 D 4

22 In which container was photosynthesis notoccurringA 1 C 3B 2 D 4

23 According to the data which variable determined whether or not photosynthesisoccurredA plant C temperatureB light color D plant part

Constructed ResponseGrid InRecord your answers on your answer document

24 Open Ended Compare the energy storage in photosynthesis to the energy storage in cellular respiration

25 Open Ended Compare alcoholic fermentation and lactic acid fermentation in terms of startingand ending material and ATP production

The assessed North Carolina objective appears next to the question

205

205

205

102

205

205

ncbdolglencoecomstandardized_test

0231-0243 C9S3 BDOL-829900 8404 513 AM Page 243

The Chemistry of LifeAlthough you are studying biology chemistry is

fundamental to all biological functions Under-standing some of the basic concepts of chemistrywill enhance your understanding of the biologicalworld

Elements and AtomsEvery substance in and on Earth is composed

of one or more kinds of elements An atom thesmallest component of an element is made ofeven smaller particles called electrons protonsand neutrons Atoms react to form compounds

The Life of a CellAll organisms are made of cells and each cell

is like a complex self-contained machine thatcan perform life functions Yet as small as they areall of the mechanisms and processes of these littlemachines are not fully known and scientistscontinue to unravel the marvelous mysteries of the living cell

The Cell Theory

Van Leeuwenhoek might haveviewed microorganisms likethese found in a droplet ofpond water

LM Magnification 100

Carbon IsotopesIsotopes of carbon contain different numbersof neutronsCarbon-12 six protons and six neutronsCarbon-13 six protons and seven neutronsCarbon-14 six protons and eight neutrons

Cells are microscopic machines

244

In the 1600s Anton van Leeuwenhoek was the first personto view living organisms through a microscope Another sci-

entist Robert Hooke named the structures cells Two hundredyears later several scientists including Matthias SchleidenTheodor Schwann and Rudolf Virchow continued to studyanimal and plant tissues under the microscope Conclusionsfrom many scientists were combined to form the cell theory

1 All organisms are composed of one or more cells2 The cell is the basic unit of organization of organisms3 All cells come from preexisting cells

(t)Michael RosenfelfTony Stone Images (b)Science VUVisuals Unlimited

0244-0249 U3 BDRev BDOL-829900 8404 144 PM Page 244

r-phosphate bone

rogen bonds betweengenous bases

A

A

A

P

P

P

P

D

D

D

D

D

D

D

DT

T

T

G

G

C

C

Substrate

Activesite

The Life of a Cell

Color-enhanced TEM Magnification 41 150

An enzyme has an area called anactive site in which a specific sub-strate undergoes a chemical reaction

Color-enhanced TEMMagnification 4800

Nucleic acids are made of subunits called nucleo-tides Each one consists of a sugar a phosphate groupand a nitrogenous base

Organelles

THE LIFE OF A CELL 245

A prokaryotic cell does notcontain membrane-boundorganelles

Organic CompoundsCarbohydrates are chemical compounds made

of carbon hydrogen and oxygen Common carbo-hydrates include sugars starches and celluloseLipids known as fats and oils contain a glycerolbackbone and three fatty acid chains Proteins arelarge molecules made of amino acids connected bypeptide bonds Enzymes are proteins that changethe rates of chemical reactions Nucleic acids suchas DNA and RNA are complex biomolecules thatstore cellular information in the form of a code

Eukaryotes and Prokaryotes All cells are surrounded by a plasma membrane

Eukaryotic cells contain membrane-bound organelleswithin the cell Cells without internal membrane-bound organelles are called prokaryotic cells

A eukaryotic cell con-tains membrane-bound organelles

(t)Dr Kari LounatmaaScience Photo LibraryPhoto Researchers (b)Moredun Animal Health LtdScience Photo LibraryPhoto Researchers

0244-0249 U3 BDRev BDOL-829900 8404 145 PM Page 245

246 BIODIGEST UNIT 3 REVIEW

Carbohydrate

Phospholipidbilayer

ProteinFatty acid tail

Phosphate head

The plasma membrane is composed ofa lipid bilayer with embedded proteins

Plasma membrane

Mitochondrion

Nucleus

Chloroplast

Cell wall

Vacuole

Golgi apparatus

Ribosomes

Roughendoplasmic

reticulum

Plant cell Animal cell

The Life of a Cell

Color-enhanced TEM Magnification unavailable Color-enhanced TEM Magnification 1250

Cell Organelles The organelles of a cell work together to carry

out the functions necessary for cell survival

Gateway to the CellAccording to the fluid mosaic model the

plasma membrane is formed by two layers ofphospholipids with the fatty acid chains facingeach other the phosphate groups face the cellrsquosinternal and external environments and proteinsare embedded in the membrane

Control of Cell FunctionsThe nucleus contains the master plans for pro-

teins which are then produced by organellescalled ribosomes The nucleus also controls cellularfunctions

Assembly Transport and Storage The cytoplasm suspends the cellrsquos organelles

including endoplasmic reticulum Golgi apparatusvacuoles and lysosomes The endoplasmic reticulumand Golgi apparatus transport and modify proteins

Energy Transformers Chloroplasts are found in plant cells They

capture the sunrsquos light energy so it can be trans-formed into useable chemical energy Mitochon-dria are found in both animal and plant cells They transform the food you eat into a useableenergy form

Support and LocomotionA network of microfilaments and microtubules

attach to the plasma membrane to give the cellstructure Cilia are short numerous projections thatmove like the oars of a boat Flagella are longerprojections that move in a whiplike fashion to propel a cell

(l)Biophoto AssociatesPhoto Researchers (r) Dr Gopel MurtiPhototake NYC

0244-0249 U3 BDRev BDOL-829900 8404 146 PM Page 246

The Life of a Cell

Cellular EnvironmentsIsotonic solution same number of dissolvedsubstances inside and outside the cellHypotonic solution more dissolved sub-stances inside the cell water enters the cellHypertonic solution fewer dissolved sub-stances inside the cell water leaves the cell

ATP production for eachmolecule of glucoseGlycolysis produces a net gain of two ATPtwo NADH and two H+

Citric acid cycle (Krebs cycle) producestwo ATP six NADH and two FADH2Electron transport chain produces 32 ATPfrom NADH and FADH2Lactic acid fermentation produces two ATPand lactic acid

THE LIFE OF A CELL 247

Interphase

Prophase

Metaphase

Anaphase

Telophase

During the stages of mitosis chromosomes are sepa-rated into two daughter cells

Carrier protein

Higher concentrationof ions

Ions Lower concentrationof ions Energy

Active transport

Diffusion and OsmosisThe selectively permeable plasma membrane

allows only certain substances to cross Diffusion is the movement of a substance from an area ofhigher concentration to an area of lower concen-tration Diffusion of water across a selectively per-meable membrane is called osmosis

Simple diffusion occurs by random movementof molecules or ions In facilitated diffusion pro-teins bind to and move molecules across a mem-brane Active transport uses energy to movemolecules against a concentration gradient

Energy in a Cell Adenosine triphosphate (ATP) is the most com-

mon energy source in a cell Two organelles helpform ATP from other sources of energy

Chloroplasts in plant cells convert energy fromthe sunrsquos rays into ATP using light-dependent reac-tions and store that energy in sugars via light-independent reactions and the Calvin cycle

Mitochondria in both plant and animal cells con-vert food energy into ATP through a series ofchemical reactions including glycolysis the citricacid cycle and the electron transport chain

MitosisAs cells grow they reach a size where the

plasma membrane cannot transport enough nutri-ents and wastes to maintain cell growth At thispoint the cell undergoes mitosis and divides

The period prior to mitosis called interphase isone of intense metabolic activity The first stage ofmitosis is prophase when the duplicated chromo-somes condense and the mitotic spindle forms Thechromosomes line up in the center of the cell dur-ing metaphase and slowly separate during ana-phase In telophase the nucleus divides followedby cytokinesis which separates the daughter cells

0244-0249 U3 BDRev BDOL-829900 8404 147 PM Page 247

248 UNIT 3 STANDARDIZED TEST PRACTICE

Chromosome Comparison of Four Organisms

Organism Human Rye Potato Guinea pig

Number of chromosomes 46 14 48 64in body cells

Number of chromatids 92 A 96 128during metaphase

Number of chromosomes 46 14 48 64in daughter cells

Multiple Choice

Use the table below to answer questions 1ndash3

1 What number belongs in the space labeled Aunder ldquoRyerdquo in the tableA 14 C 7B 28 D 21

2 If one pair of chromatids failed to separateduring mitosis in rye cells how many chromo-somes would end up in the two daughter cellsA 28 and 28B 14 and 14C 7 and 8D 13 and 15

3 What is the relationship between the numberof chromosomes in body cells and the com-plexity of an organismA The more complex the organism the more

chromosomes it hasB The more complex the organism the fewer

chromosomes it hasC There is no relationshipD The number of chromosomes is deter-

mined by the sex of the organism

4 The isotopes of the element magnesium differin their number of ________A proteinsB electronsC neutronsD protons

5 Which of the following organelles are found inall cellsA plasma membrane and ribosomesB mitochondria and chloroplastsC microtubules and lysosomesD Golgi apparatus and endoplasmic reticulum

6 During late interphase the chromosomes dou-ble to form chromatids that are attached toeach other During which phase of mitosis dothe chromatids separateA prophaseB metaphaseC anaphaseD telophase

7 Plants must have a constant supply of ________for photosynthesis but they provide ________for cellular respirationA watermdashcarbon dioxideB carbon dioxidemdashwaterC carbon dioxidemdashoxygenD oxygenmdashwater

8 Which type of bond involves the sharing of electronsA covalentB ionicC hydrogenD electrostatic

9 The primary organelle used for storing infor-mation in a cell is the ________A cell wallB endoplasmic reticulumC mitochondriaD nucleus

When EliminatingCross It Out

List the answer choice letters on scratch paperand with your pencil cross out choices yoursquoveeliminated Yoursquoll stop yourself from choosingan answer yoursquove mentally eliminated

The assessed North Carolina objective appears next to the questionEnd-of-Course Test Practice

202

205

202

0244-0249 U3 BDRev BDOL-829900 8404 541 PM Page 248

UNIT 3 STANDARDIZED TEST PRACTICE 249

10 A biologist studies cells under a microscopethat have been drawn from an unknown solu-tion The cells appear shriveled What can thebiologist conclude about the solution A It is hypotonicB It is isotonicC It is hypertonicD It is polar

11 Which helps capture the sunrsquos energyA light-dependent reactionsB citric acid cycleC Calvin cycleD light-independent reactions

Use the word equation below to answer questions12ndash14

sucrose water glucose fructose

12 The reaction above illustrates the ________A hydrolysis of sucroseB condensation of sucroseC hydrolysis of glucoseD condensation of fructose

13 The product(s) of this reaction isare________A sucroseB waterC glucose and fructoseD sucrose and water

14 Glucose and fructose are ________A disaccharidesB polysaccharidesC monosaccharidesD starches

Use the figure below to answer questions 15ndash17

15 The illustrations above demonstrate the trans-port of an ion across the plasma membranebut they are out of sequence In what order dothey belongA D-C-B-A C C-B-D-AB A-B-D-C D A-D-B-C

16 What statement is true about diagram DA The ion movement is randomB Energy is requiredC The fatty acids in the plasma membrane

could also move apart to allow the ionthrough

D The concentration of ions is higher at thetop of diagram D than at the bottom

17 Which process is best represented by these diagramsA diffusion C endocytosisB active transport D passive transport

Energy

A B

C D

Constructed ResponseGrid In

Record your answers on your answer document

18 Open Ended How is an ionic bond different from a covalent bond

19 Open Ended Describe the role of transport proteins in plasma membranes

20 Open Ended Compare the functions of mitochondria and chloroplasts in cells Be sure to includeATP in your answer

21 Open Ended Describe the cellular process of mitosis

205

203

202

203

203

203

ncbdolglencoecomstandardized_test

0244-0249 U3 BDRev BDOL-829900 8404 542 PM Page 249

r-phosphate bone

rogen bonds betweengenous bases

A

A

A

P

P

P

P

D

D

D

D

D

D

D

DT

T

T

G

G

C

C

Substrate

Activesite

The Life of a Cell

Color-enhanced TEM Magnification 41 150

An enzyme has an area called anactive site in which a specific sub-strate undergoes a chemical reaction

Color-enhanced TEMMagnification 4800

Nucleic acids are made of subunits called nucleo-tides Each one consists of a sugar a phosphate groupand a nitrogenous base

Organelles

THE LIFE OF A CELL 245

A prokaryotic cell does notcontain membrane-boundorganelles

Organic CompoundsCarbohydrates are chemical compounds made

of carbon hydrogen and oxygen Common carbo-hydrates include sugars starches and celluloseLipids known as fats and oils contain a glycerolbackbone and three fatty acid chains Proteins arelarge molecules made of amino acids connected bypeptide bonds Enzymes are proteins that changethe rates of chemical reactions Nucleic acids suchas DNA and RNA are complex biomolecules thatstore cellular information in the form of a code

Eukaryotes and Prokaryotes All cells are surrounded by a plasma membrane

Eukaryotic cells contain membrane-bound organelleswithin the cell Cells without internal membrane-bound organelles are called prokaryotic cells

A eukaryotic cell con-tains membrane-bound organelles

(t)Dr Kari LounatmaaScience Photo LibraryPhoto Researchers (b)Moredun Animal Health LtdScience Photo LibraryPhoto Researchers

0244-0249 U3 BDRev BDOL-829900 8404 145 PM Page 245

246 BIODIGEST UNIT 3 REVIEW

Carbohydrate

Phospholipidbilayer

ProteinFatty acid tail

Phosphate head

The plasma membrane is composed ofa lipid bilayer with embedded proteins

Plasma membrane

Mitochondrion

Nucleus

Chloroplast

Cell wall

Vacuole

Golgi apparatus

Ribosomes

Roughendoplasmic

reticulum

Plant cell Animal cell

The Life of a Cell

Color-enhanced TEM Magnification unavailable Color-enhanced TEM Magnification 1250

Cell Organelles The organelles of a cell work together to carry

out the functions necessary for cell survival

Gateway to the CellAccording to the fluid mosaic model the

plasma membrane is formed by two layers ofphospholipids with the fatty acid chains facingeach other the phosphate groups face the cellrsquosinternal and external environments and proteinsare embedded in the membrane

Control of Cell FunctionsThe nucleus contains the master plans for pro-

teins which are then produced by organellescalled ribosomes The nucleus also controls cellularfunctions

Assembly Transport and Storage The cytoplasm suspends the cellrsquos organelles

including endoplasmic reticulum Golgi apparatusvacuoles and lysosomes The endoplasmic reticulumand Golgi apparatus transport and modify proteins

Energy Transformers Chloroplasts are found in plant cells They

capture the sunrsquos light energy so it can be trans-formed into useable chemical energy Mitochon-dria are found in both animal and plant cells They transform the food you eat into a useableenergy form

Support and LocomotionA network of microfilaments and microtubules

attach to the plasma membrane to give the cellstructure Cilia are short numerous projections thatmove like the oars of a boat Flagella are longerprojections that move in a whiplike fashion to propel a cell

(l)Biophoto AssociatesPhoto Researchers (r) Dr Gopel MurtiPhototake NYC

0244-0249 U3 BDRev BDOL-829900 8404 146 PM Page 246

The Life of a Cell

Cellular EnvironmentsIsotonic solution same number of dissolvedsubstances inside and outside the cellHypotonic solution more dissolved sub-stances inside the cell water enters the cellHypertonic solution fewer dissolved sub-stances inside the cell water leaves the cell

ATP production for eachmolecule of glucoseGlycolysis produces a net gain of two ATPtwo NADH and two H+

Citric acid cycle (Krebs cycle) producestwo ATP six NADH and two FADH2Electron transport chain produces 32 ATPfrom NADH and FADH2Lactic acid fermentation produces two ATPand lactic acid

THE LIFE OF A CELL 247

Interphase

Prophase

Metaphase

Anaphase

Telophase

During the stages of mitosis chromosomes are sepa-rated into two daughter cells

Carrier protein

Higher concentrationof ions

Ions Lower concentrationof ions Energy

Active transport

Diffusion and OsmosisThe selectively permeable plasma membrane

allows only certain substances to cross Diffusion is the movement of a substance from an area ofhigher concentration to an area of lower concen-tration Diffusion of water across a selectively per-meable membrane is called osmosis

Simple diffusion occurs by random movementof molecules or ions In facilitated diffusion pro-teins bind to and move molecules across a mem-brane Active transport uses energy to movemolecules against a concentration gradient

Energy in a Cell Adenosine triphosphate (ATP) is the most com-

mon energy source in a cell Two organelles helpform ATP from other sources of energy

Chloroplasts in plant cells convert energy fromthe sunrsquos rays into ATP using light-dependent reac-tions and store that energy in sugars via light-independent reactions and the Calvin cycle

Mitochondria in both plant and animal cells con-vert food energy into ATP through a series ofchemical reactions including glycolysis the citricacid cycle and the electron transport chain

MitosisAs cells grow they reach a size where the

plasma membrane cannot transport enough nutri-ents and wastes to maintain cell growth At thispoint the cell undergoes mitosis and divides

The period prior to mitosis called interphase isone of intense metabolic activity The first stage ofmitosis is prophase when the duplicated chromo-somes condense and the mitotic spindle forms Thechromosomes line up in the center of the cell dur-ing metaphase and slowly separate during ana-phase In telophase the nucleus divides followedby cytokinesis which separates the daughter cells

0244-0249 U3 BDRev BDOL-829900 8404 147 PM Page 247

248 UNIT 3 STANDARDIZED TEST PRACTICE

Chromosome Comparison of Four Organisms

Organism Human Rye Potato Guinea pig

Number of chromosomes 46 14 48 64in body cells

Number of chromatids 92 A 96 128during metaphase

Number of chromosomes 46 14 48 64in daughter cells

Multiple Choice

Use the table below to answer questions 1ndash3

1 What number belongs in the space labeled Aunder ldquoRyerdquo in the tableA 14 C 7B 28 D 21

2 If one pair of chromatids failed to separateduring mitosis in rye cells how many chromo-somes would end up in the two daughter cellsA 28 and 28B 14 and 14C 7 and 8D 13 and 15

3 What is the relationship between the numberof chromosomes in body cells and the com-plexity of an organismA The more complex the organism the more

chromosomes it hasB The more complex the organism the fewer

chromosomes it hasC There is no relationshipD The number of chromosomes is deter-

mined by the sex of the organism

4 The isotopes of the element magnesium differin their number of ________A proteinsB electronsC neutronsD protons

5 Which of the following organelles are found inall cellsA plasma membrane and ribosomesB mitochondria and chloroplastsC microtubules and lysosomesD Golgi apparatus and endoplasmic reticulum

6 During late interphase the chromosomes dou-ble to form chromatids that are attached toeach other During which phase of mitosis dothe chromatids separateA prophaseB metaphaseC anaphaseD telophase

7 Plants must have a constant supply of ________for photosynthesis but they provide ________for cellular respirationA watermdashcarbon dioxideB carbon dioxidemdashwaterC carbon dioxidemdashoxygenD oxygenmdashwater

8 Which type of bond involves the sharing of electronsA covalentB ionicC hydrogenD electrostatic

9 The primary organelle used for storing infor-mation in a cell is the ________A cell wallB endoplasmic reticulumC mitochondriaD nucleus

When EliminatingCross It Out

List the answer choice letters on scratch paperand with your pencil cross out choices yoursquoveeliminated Yoursquoll stop yourself from choosingan answer yoursquove mentally eliminated

The assessed North Carolina objective appears next to the questionEnd-of-Course Test Practice

202

205

202

0244-0249 U3 BDRev BDOL-829900 8404 541 PM Page 248

UNIT 3 STANDARDIZED TEST PRACTICE 249

10 A biologist studies cells under a microscopethat have been drawn from an unknown solu-tion The cells appear shriveled What can thebiologist conclude about the solution A It is hypotonicB It is isotonicC It is hypertonicD It is polar

11 Which helps capture the sunrsquos energyA light-dependent reactionsB citric acid cycleC Calvin cycleD light-independent reactions

Use the word equation below to answer questions12ndash14

sucrose water glucose fructose

12 The reaction above illustrates the ________A hydrolysis of sucroseB condensation of sucroseC hydrolysis of glucoseD condensation of fructose

13 The product(s) of this reaction isare________A sucroseB waterC glucose and fructoseD sucrose and water

14 Glucose and fructose are ________A disaccharidesB polysaccharidesC monosaccharidesD starches

Use the figure below to answer questions 15ndash17

15 The illustrations above demonstrate the trans-port of an ion across the plasma membranebut they are out of sequence In what order dothey belongA D-C-B-A C C-B-D-AB A-B-D-C D A-D-B-C

16 What statement is true about diagram DA The ion movement is randomB Energy is requiredC The fatty acids in the plasma membrane

could also move apart to allow the ionthrough

D The concentration of ions is higher at thetop of diagram D than at the bottom

17 Which process is best represented by these diagramsA diffusion C endocytosisB active transport D passive transport

Energy

A B

C D

Constructed ResponseGrid In

Record your answers on your answer document

18 Open Ended How is an ionic bond different from a covalent bond

19 Open Ended Describe the role of transport proteins in plasma membranes

20 Open Ended Compare the functions of mitochondria and chloroplasts in cells Be sure to includeATP in your answer

21 Open Ended Describe the cellular process of mitosis

205

203

202

203

203

203

ncbdolglencoecomstandardized_test

0244-0249 U3 BDRev BDOL-829900 8404 542 PM Page 249

246 BIODIGEST UNIT 3 REVIEW

Carbohydrate

Phospholipidbilayer

ProteinFatty acid tail

Phosphate head

The plasma membrane is composed ofa lipid bilayer with embedded proteins

Plasma membrane

Mitochondrion

Nucleus

Chloroplast

Cell wall

Vacuole

Golgi apparatus

Ribosomes

Roughendoplasmic

reticulum

Plant cell Animal cell

The Life of a Cell

Color-enhanced TEM Magnification unavailable Color-enhanced TEM Magnification 1250

Cell Organelles The organelles of a cell work together to carry

out the functions necessary for cell survival

Gateway to the CellAccording to the fluid mosaic model the

plasma membrane is formed by two layers ofphospholipids with the fatty acid chains facingeach other the phosphate groups face the cellrsquosinternal and external environments and proteinsare embedded in the membrane

Control of Cell FunctionsThe nucleus contains the master plans for pro-

teins which are then produced by organellescalled ribosomes The nucleus also controls cellularfunctions

Assembly Transport and Storage The cytoplasm suspends the cellrsquos organelles

including endoplasmic reticulum Golgi apparatusvacuoles and lysosomes The endoplasmic reticulumand Golgi apparatus transport and modify proteins

Energy Transformers Chloroplasts are found in plant cells They

capture the sunrsquos light energy so it can be trans-formed into useable chemical energy Mitochon-dria are found in both animal and plant cells They transform the food you eat into a useableenergy form

Support and LocomotionA network of microfilaments and microtubules

attach to the plasma membrane to give the cellstructure Cilia are short numerous projections thatmove like the oars of a boat Flagella are longerprojections that move in a whiplike fashion to propel a cell

(l)Biophoto AssociatesPhoto Researchers (r) Dr Gopel MurtiPhototake NYC

0244-0249 U3 BDRev BDOL-829900 8404 146 PM Page 246

The Life of a Cell

Cellular EnvironmentsIsotonic solution same number of dissolvedsubstances inside and outside the cellHypotonic solution more dissolved sub-stances inside the cell water enters the cellHypertonic solution fewer dissolved sub-stances inside the cell water leaves the cell

ATP production for eachmolecule of glucoseGlycolysis produces a net gain of two ATPtwo NADH and two H+

Citric acid cycle (Krebs cycle) producestwo ATP six NADH and two FADH2Electron transport chain produces 32 ATPfrom NADH and FADH2Lactic acid fermentation produces two ATPand lactic acid

THE LIFE OF A CELL 247

Interphase

Prophase

Metaphase

Anaphase

Telophase

During the stages of mitosis chromosomes are sepa-rated into two daughter cells

Carrier protein

Higher concentrationof ions

Ions Lower concentrationof ions Energy

Active transport

Diffusion and OsmosisThe selectively permeable plasma membrane

allows only certain substances to cross Diffusion is the movement of a substance from an area ofhigher concentration to an area of lower concen-tration Diffusion of water across a selectively per-meable membrane is called osmosis

Simple diffusion occurs by random movementof molecules or ions In facilitated diffusion pro-teins bind to and move molecules across a mem-brane Active transport uses energy to movemolecules against a concentration gradient

Energy in a Cell Adenosine triphosphate (ATP) is the most com-

mon energy source in a cell Two organelles helpform ATP from other sources of energy

Chloroplasts in plant cells convert energy fromthe sunrsquos rays into ATP using light-dependent reac-tions and store that energy in sugars via light-independent reactions and the Calvin cycle

Mitochondria in both plant and animal cells con-vert food energy into ATP through a series ofchemical reactions including glycolysis the citricacid cycle and the electron transport chain

MitosisAs cells grow they reach a size where the

plasma membrane cannot transport enough nutri-ents and wastes to maintain cell growth At thispoint the cell undergoes mitosis and divides

The period prior to mitosis called interphase isone of intense metabolic activity The first stage ofmitosis is prophase when the duplicated chromo-somes condense and the mitotic spindle forms Thechromosomes line up in the center of the cell dur-ing metaphase and slowly separate during ana-phase In telophase the nucleus divides followedby cytokinesis which separates the daughter cells

0244-0249 U3 BDRev BDOL-829900 8404 147 PM Page 247

248 UNIT 3 STANDARDIZED TEST PRACTICE

Chromosome Comparison of Four Organisms

Organism Human Rye Potato Guinea pig

Number of chromosomes 46 14 48 64in body cells

Number of chromatids 92 A 96 128during metaphase

Number of chromosomes 46 14 48 64in daughter cells

Multiple Choice

Use the table below to answer questions 1ndash3

1 What number belongs in the space labeled Aunder ldquoRyerdquo in the tableA 14 C 7B 28 D 21

2 If one pair of chromatids failed to separateduring mitosis in rye cells how many chromo-somes would end up in the two daughter cellsA 28 and 28B 14 and 14C 7 and 8D 13 and 15

3 What is the relationship between the numberof chromosomes in body cells and the com-plexity of an organismA The more complex the organism the more

chromosomes it hasB The more complex the organism the fewer

chromosomes it hasC There is no relationshipD The number of chromosomes is deter-

mined by the sex of the organism

4 The isotopes of the element magnesium differin their number of ________A proteinsB electronsC neutronsD protons

5 Which of the following organelles are found inall cellsA plasma membrane and ribosomesB mitochondria and chloroplastsC microtubules and lysosomesD Golgi apparatus and endoplasmic reticulum

6 During late interphase the chromosomes dou-ble to form chromatids that are attached toeach other During which phase of mitosis dothe chromatids separateA prophaseB metaphaseC anaphaseD telophase

7 Plants must have a constant supply of ________for photosynthesis but they provide ________for cellular respirationA watermdashcarbon dioxideB carbon dioxidemdashwaterC carbon dioxidemdashoxygenD oxygenmdashwater

8 Which type of bond involves the sharing of electronsA covalentB ionicC hydrogenD electrostatic

9 The primary organelle used for storing infor-mation in a cell is the ________A cell wallB endoplasmic reticulumC mitochondriaD nucleus

When EliminatingCross It Out

List the answer choice letters on scratch paperand with your pencil cross out choices yoursquoveeliminated Yoursquoll stop yourself from choosingan answer yoursquove mentally eliminated

The assessed North Carolina objective appears next to the questionEnd-of-Course Test Practice

202

205

202

0244-0249 U3 BDRev BDOL-829900 8404 541 PM Page 248

UNIT 3 STANDARDIZED TEST PRACTICE 249

10 A biologist studies cells under a microscopethat have been drawn from an unknown solu-tion The cells appear shriveled What can thebiologist conclude about the solution A It is hypotonicB It is isotonicC It is hypertonicD It is polar

11 Which helps capture the sunrsquos energyA light-dependent reactionsB citric acid cycleC Calvin cycleD light-independent reactions

Use the word equation below to answer questions12ndash14

sucrose water glucose fructose

12 The reaction above illustrates the ________A hydrolysis of sucroseB condensation of sucroseC hydrolysis of glucoseD condensation of fructose

13 The product(s) of this reaction isare________A sucroseB waterC glucose and fructoseD sucrose and water

14 Glucose and fructose are ________A disaccharidesB polysaccharidesC monosaccharidesD starches

Use the figure below to answer questions 15ndash17

15 The illustrations above demonstrate the trans-port of an ion across the plasma membranebut they are out of sequence In what order dothey belongA D-C-B-A C C-B-D-AB A-B-D-C D A-D-B-C

16 What statement is true about diagram DA The ion movement is randomB Energy is requiredC The fatty acids in the plasma membrane

could also move apart to allow the ionthrough

D The concentration of ions is higher at thetop of diagram D than at the bottom

17 Which process is best represented by these diagramsA diffusion C endocytosisB active transport D passive transport

Energy

A B

C D

Constructed ResponseGrid In

Record your answers on your answer document

18 Open Ended How is an ionic bond different from a covalent bond

19 Open Ended Describe the role of transport proteins in plasma membranes

20 Open Ended Compare the functions of mitochondria and chloroplasts in cells Be sure to includeATP in your answer

21 Open Ended Describe the cellular process of mitosis

205

203

202

203

203

203

ncbdolglencoecomstandardized_test

0244-0249 U3 BDRev BDOL-829900 8404 542 PM Page 249

The Life of a Cell

Cellular EnvironmentsIsotonic solution same number of dissolvedsubstances inside and outside the cellHypotonic solution more dissolved sub-stances inside the cell water enters the cellHypertonic solution fewer dissolved sub-stances inside the cell water leaves the cell

ATP production for eachmolecule of glucoseGlycolysis produces a net gain of two ATPtwo NADH and two H+

Citric acid cycle (Krebs cycle) producestwo ATP six NADH and two FADH2Electron transport chain produces 32 ATPfrom NADH and FADH2Lactic acid fermentation produces two ATPand lactic acid

THE LIFE OF A CELL 247

Interphase

Prophase

Metaphase

Anaphase

Telophase

During the stages of mitosis chromosomes are sepa-rated into two daughter cells

Carrier protein

Higher concentrationof ions

Ions Lower concentrationof ions Energy

Active transport

Diffusion and OsmosisThe selectively permeable plasma membrane

allows only certain substances to cross Diffusion is the movement of a substance from an area ofhigher concentration to an area of lower concen-tration Diffusion of water across a selectively per-meable membrane is called osmosis

Simple diffusion occurs by random movementof molecules or ions In facilitated diffusion pro-teins bind to and move molecules across a mem-brane Active transport uses energy to movemolecules against a concentration gradient

Energy in a Cell Adenosine triphosphate (ATP) is the most com-

mon energy source in a cell Two organelles helpform ATP from other sources of energy

Chloroplasts in plant cells convert energy fromthe sunrsquos rays into ATP using light-dependent reac-tions and store that energy in sugars via light-independent reactions and the Calvin cycle

Mitochondria in both plant and animal cells con-vert food energy into ATP through a series ofchemical reactions including glycolysis the citricacid cycle and the electron transport chain

MitosisAs cells grow they reach a size where the

plasma membrane cannot transport enough nutri-ents and wastes to maintain cell growth At thispoint the cell undergoes mitosis and divides

The period prior to mitosis called interphase isone of intense metabolic activity The first stage ofmitosis is prophase when the duplicated chromo-somes condense and the mitotic spindle forms Thechromosomes line up in the center of the cell dur-ing metaphase and slowly separate during ana-phase In telophase the nucleus divides followedby cytokinesis which separates the daughter cells

0244-0249 U3 BDRev BDOL-829900 8404 147 PM Page 247

248 UNIT 3 STANDARDIZED TEST PRACTICE

Chromosome Comparison of Four Organisms

Organism Human Rye Potato Guinea pig

Number of chromosomes 46 14 48 64in body cells

Number of chromatids 92 A 96 128during metaphase

Number of chromosomes 46 14 48 64in daughter cells

Multiple Choice

Use the table below to answer questions 1ndash3

1 What number belongs in the space labeled Aunder ldquoRyerdquo in the tableA 14 C 7B 28 D 21

2 If one pair of chromatids failed to separateduring mitosis in rye cells how many chromo-somes would end up in the two daughter cellsA 28 and 28B 14 and 14C 7 and 8D 13 and 15

3 What is the relationship between the numberof chromosomes in body cells and the com-plexity of an organismA The more complex the organism the more

chromosomes it hasB The more complex the organism the fewer

chromosomes it hasC There is no relationshipD The number of chromosomes is deter-

mined by the sex of the organism

4 The isotopes of the element magnesium differin their number of ________A proteinsB electronsC neutronsD protons

5 Which of the following organelles are found inall cellsA plasma membrane and ribosomesB mitochondria and chloroplastsC microtubules and lysosomesD Golgi apparatus and endoplasmic reticulum

6 During late interphase the chromosomes dou-ble to form chromatids that are attached toeach other During which phase of mitosis dothe chromatids separateA prophaseB metaphaseC anaphaseD telophase

7 Plants must have a constant supply of ________for photosynthesis but they provide ________for cellular respirationA watermdashcarbon dioxideB carbon dioxidemdashwaterC carbon dioxidemdashoxygenD oxygenmdashwater

8 Which type of bond involves the sharing of electronsA covalentB ionicC hydrogenD electrostatic

9 The primary organelle used for storing infor-mation in a cell is the ________A cell wallB endoplasmic reticulumC mitochondriaD nucleus

When EliminatingCross It Out

List the answer choice letters on scratch paperand with your pencil cross out choices yoursquoveeliminated Yoursquoll stop yourself from choosingan answer yoursquove mentally eliminated

The assessed North Carolina objective appears next to the questionEnd-of-Course Test Practice

202

205

202

0244-0249 U3 BDRev BDOL-829900 8404 541 PM Page 248

UNIT 3 STANDARDIZED TEST PRACTICE 249

10 A biologist studies cells under a microscopethat have been drawn from an unknown solu-tion The cells appear shriveled What can thebiologist conclude about the solution A It is hypotonicB It is isotonicC It is hypertonicD It is polar

11 Which helps capture the sunrsquos energyA light-dependent reactionsB citric acid cycleC Calvin cycleD light-independent reactions

Use the word equation below to answer questions12ndash14

sucrose water glucose fructose

12 The reaction above illustrates the ________A hydrolysis of sucroseB condensation of sucroseC hydrolysis of glucoseD condensation of fructose

13 The product(s) of this reaction isare________A sucroseB waterC glucose and fructoseD sucrose and water

14 Glucose and fructose are ________A disaccharidesB polysaccharidesC monosaccharidesD starches

Use the figure below to answer questions 15ndash17

15 The illustrations above demonstrate the trans-port of an ion across the plasma membranebut they are out of sequence In what order dothey belongA D-C-B-A C C-B-D-AB A-B-D-C D A-D-B-C

16 What statement is true about diagram DA The ion movement is randomB Energy is requiredC The fatty acids in the plasma membrane

could also move apart to allow the ionthrough

D The concentration of ions is higher at thetop of diagram D than at the bottom

17 Which process is best represented by these diagramsA diffusion C endocytosisB active transport D passive transport

Energy

A B

C D

Constructed ResponseGrid In

Record your answers on your answer document

18 Open Ended How is an ionic bond different from a covalent bond

19 Open Ended Describe the role of transport proteins in plasma membranes

20 Open Ended Compare the functions of mitochondria and chloroplasts in cells Be sure to includeATP in your answer

21 Open Ended Describe the cellular process of mitosis

205

203

202

203

203

203

ncbdolglencoecomstandardized_test

0244-0249 U3 BDRev BDOL-829900 8404 542 PM Page 249

248 UNIT 3 STANDARDIZED TEST PRACTICE

Chromosome Comparison of Four Organisms

Organism Human Rye Potato Guinea pig

Number of chromosomes 46 14 48 64in body cells

Number of chromatids 92 A 96 128during metaphase

Number of chromosomes 46 14 48 64in daughter cells

Multiple Choice

Use the table below to answer questions 1ndash3

1 What number belongs in the space labeled Aunder ldquoRyerdquo in the tableA 14 C 7B 28 D 21

2 If one pair of chromatids failed to separateduring mitosis in rye cells how many chromo-somes would end up in the two daughter cellsA 28 and 28B 14 and 14C 7 and 8D 13 and 15

3 What is the relationship between the numberof chromosomes in body cells and the com-plexity of an organismA The more complex the organism the more

chromosomes it hasB The more complex the organism the fewer

chromosomes it hasC There is no relationshipD The number of chromosomes is deter-

mined by the sex of the organism

4 The isotopes of the element magnesium differin their number of ________A proteinsB electronsC neutronsD protons

5 Which of the following organelles are found inall cellsA plasma membrane and ribosomesB mitochondria and chloroplastsC microtubules and lysosomesD Golgi apparatus and endoplasmic reticulum

6 During late interphase the chromosomes dou-ble to form chromatids that are attached toeach other During which phase of mitosis dothe chromatids separateA prophaseB metaphaseC anaphaseD telophase

7 Plants must have a constant supply of ________for photosynthesis but they provide ________for cellular respirationA watermdashcarbon dioxideB carbon dioxidemdashwaterC carbon dioxidemdashoxygenD oxygenmdashwater

8 Which type of bond involves the sharing of electronsA covalentB ionicC hydrogenD electrostatic

9 The primary organelle used for storing infor-mation in a cell is the ________A cell wallB endoplasmic reticulumC mitochondriaD nucleus

When EliminatingCross It Out

List the answer choice letters on scratch paperand with your pencil cross out choices yoursquoveeliminated Yoursquoll stop yourself from choosingan answer yoursquove mentally eliminated

The assessed North Carolina objective appears next to the questionEnd-of-Course Test Practice

202

205

202

0244-0249 U3 BDRev BDOL-829900 8404 541 PM Page 248

UNIT 3 STANDARDIZED TEST PRACTICE 249

10 A biologist studies cells under a microscopethat have been drawn from an unknown solu-tion The cells appear shriveled What can thebiologist conclude about the solution A It is hypotonicB It is isotonicC It is hypertonicD It is polar

11 Which helps capture the sunrsquos energyA light-dependent reactionsB citric acid cycleC Calvin cycleD light-independent reactions

Use the word equation below to answer questions12ndash14

sucrose water glucose fructose

12 The reaction above illustrates the ________A hydrolysis of sucroseB condensation of sucroseC hydrolysis of glucoseD condensation of fructose

13 The product(s) of this reaction isare________A sucroseB waterC glucose and fructoseD sucrose and water

14 Glucose and fructose are ________A disaccharidesB polysaccharidesC monosaccharidesD starches

Use the figure below to answer questions 15ndash17

15 The illustrations above demonstrate the trans-port of an ion across the plasma membranebut they are out of sequence In what order dothey belongA D-C-B-A C C-B-D-AB A-B-D-C D A-D-B-C

16 What statement is true about diagram DA The ion movement is randomB Energy is requiredC The fatty acids in the plasma membrane

could also move apart to allow the ionthrough

D The concentration of ions is higher at thetop of diagram D than at the bottom

17 Which process is best represented by these diagramsA diffusion C endocytosisB active transport D passive transport

Energy

A B

C D

Constructed ResponseGrid In

Record your answers on your answer document

18 Open Ended How is an ionic bond different from a covalent bond

19 Open Ended Describe the role of transport proteins in plasma membranes

20 Open Ended Compare the functions of mitochondria and chloroplasts in cells Be sure to includeATP in your answer

21 Open Ended Describe the cellular process of mitosis

205

203

202

203

203

203

ncbdolglencoecomstandardized_test

0244-0249 U3 BDRev BDOL-829900 8404 542 PM Page 249

UNIT 3 STANDARDIZED TEST PRACTICE 249

10 A biologist studies cells under a microscopethat have been drawn from an unknown solu-tion The cells appear shriveled What can thebiologist conclude about the solution A It is hypotonicB It is isotonicC It is hypertonicD It is polar

11 Which helps capture the sunrsquos energyA light-dependent reactionsB citric acid cycleC Calvin cycleD light-independent reactions

Use the word equation below to answer questions12ndash14

sucrose water glucose fructose

12 The reaction above illustrates the ________A hydrolysis of sucroseB condensation of sucroseC hydrolysis of glucoseD condensation of fructose

13 The product(s) of this reaction isare________A sucroseB waterC glucose and fructoseD sucrose and water

14 Glucose and fructose are ________A disaccharidesB polysaccharidesC monosaccharidesD starches

Use the figure below to answer questions 15ndash17

15 The illustrations above demonstrate the trans-port of an ion across the plasma membranebut they are out of sequence In what order dothey belongA D-C-B-A C C-B-D-AB A-B-D-C D A-D-B-C

16 What statement is true about diagram DA The ion movement is randomB Energy is requiredC The fatty acids in the plasma membrane

could also move apart to allow the ionthrough

D The concentration of ions is higher at thetop of diagram D than at the bottom

17 Which process is best represented by these diagramsA diffusion C endocytosisB active transport D passive transport

Energy

A B

C D

Constructed ResponseGrid In

Record your answers on your answer document

18 Open Ended How is an ionic bond different from a covalent bond

19 Open Ended Describe the role of transport proteins in plasma membranes

20 Open Ended Compare the functions of mitochondria and chloroplasts in cells Be sure to includeATP in your answer

21 Open Ended Describe the cellular process of mitosis

205

203

202

203

203

203

ncbdolglencoecomstandardized_test

0244-0249 U3 BDRev BDOL-829900 8404 542 PM Page 249