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APBiology-Part1:TheCell
TableofContents
Preface
1.AboutOpenStax
2.AboutOpenStax’sResources
Customization
Errata
Format
3.AboutBiology
4.CoverageandScope
PedagogicalFoundationandFeatures
ArtandAnimationsThatEngage
5.AdditionalResources
6.AbouttheAuthors
SeniorContributingAuthors
ContributingAuthorsandReviewers
I.Biochemistry
Chapter1.1.1PropertiesofWaterandCarbon

1.1.Atoms,Isotopes,Ions,andMolecules:TheBuildingBlocks
TheStructureoftheAtom
AtomicNumberandMass
Isotopes
ThePeriodicTable
ElectronShellsandtheBohrModel
ElectronOrbitals
ChemicalReactionsandMolecules
IonsandIonicBonds
CovalentBondsandOtherBondsandInteractions
PolarCovalentBonds
NonpolarCovalentBonds


HydrogenBondsandVanDerWaalsInteractions
1.2.Water
Water’sPolarity
Water’sStates:Gas,Liquid,andSolid
Water’sHighHeatCapacity
Water’sHeatofVaporization
Water’sSolventProperties
Water’sCohesiveandAdhesiveProperties
pH,Buffers,Acids,andBases
1.3.Carbon
Hydrocarbons
HydrocarbonChains
HydrocarbonRings
Isomers
Enantiomers
FunctionalGroups

Chapter2.1.2StructureandFunctionofLargeBiomolecules
2.1.SynthesisofBiologicalMacromolecules
DehydrationSynthesis
Hydrolysis
2.2.Carbohydrates
MolecularStructures
Monosaccharides
Disaccharides
Polysaccharides
BenefitsofCarbohydrates
2.3.Lipids
FatsandOils
TransFats
OmegaFattyAcids
Waxes
Phospholipids
Steroids
2.4.Proteins
TypesandFunctionsofProteins
AminoAcids
ProteinStructure


PrimaryStructure
SecondaryStructure
TertiaryStructure
QuaternaryStructure
DenaturationandProteinFolding
2.5.NucleicAcids
DNAandRNA

DNADouble-HelixStructure
RNA
Chapter3.1.3TheCell
3.1.StudyingCells
Microscopy
LightMicroscopes
ElectronMicroscopes
CellTheory
3.2.ProkaryoticCells
ComponentsofProkaryoticCells
CellSize
3.3.EukaryoticCells
ThePlasmaMembrane
TheCytoplasm
TheNucleus
TheNuclearEnvelope
ChromatinandChromosomes
TheNucleolus
Ribosomes
Mitochondria
Peroxisomes
VesiclesandVacuoles
AnimalCellsversusPlantCells
TheCentrosome
Lysosomes
TheCellWall
Chloroplasts
TheCentralVacuole
3.4.TheEndomembraneSystemandProteins
TheEndoplasmicReticulum



RoughER
SmoothER
TheGolgiApparatus
Lysosomes
3.5.TheCytoskeleton
Microfilaments
IntermediateFilaments
Microtubules
FlagellaandCilia
3.6.ConnectionsbetweenCellsandCellularActivities
ExtracellularMatrixofAnimalCells
IntercellularJunctions
Plasmodesmata
TightJunctions
Desmosomes
GapJunctions
Chapter4.1.4MembraneStructureandFunction
4.1.ComponentsandStructure
FluidMosaicModel
Phospholipids
Proteins
Carbohydrates
MembraneFluidity
4.2.PassiveTransport
SelectivePermeability
Diffusion
FactorsThatAffectDiffusion
Facilitatedtransport

Channels
CarrierProteins
Osmosis
Mechanism
Tonicity
HypotonicSolutions
HypertonicSolutions
IsotonicSolutions
TonicityinLivingSystems


4.3.ActiveTransport
ElectrochemicalGradient
MovingAgainstaGradient
CarrierProteinsforActiveTransport
PrimaryActiveTransport
SecondaryActiveTransport(Co-transport)
4.4.BulkTransport
Endocytosis
Phagocytosis
Pinocytosis
Receptor-mediatedEndocytosis
Exocytosis
II.CellularEnergy
Chapter5.2.1Metabolism
5.1.EnergyandMetabolism
MetabolismofCarbohydrates
MetabolicPathways
AnabolicandCatabolicPathways
5.2.Potential,Kinetic,Free,andActivationEnergy

TypesofEnergy
FreeEnergy
EndergonicReactionsandExergonicReactions
ActivationEnergy
5.3.TheLawsofThermodynamics
TheFirstLawofThermodynamics
TheSecondLawofThermodynamics
5.4.ATP:AdenosineTriphosphate
5.5.Enzymes
EnzymeActiveSiteandSubstrateSpecificity
InducedFitandEnzymeFunction
ControlofMetabolismThroughEnzymeRegulation
RegulationofEnzymesbyMolecules
EnzymeCompartmentalization
FeedbackInhibitioninMetabolicPathways
Chapter6.2.2CellularRespiration
6.1.EnergyinLivingSystems
ElectronsandEnergy


ElectronCarriers
ATPinLivingSystems
ATPStructureandFunction
EnergyfromATP
Phosphorylation
SubstratePhosphorylation
OxidativePhosphorylation
6.2.Glycolysis
FirstHalfofGlycolysis(Energy-RequiringSteps)
SecondHalfofGlycolysis(Energy-ReleasingSteps)

OutcomesofGlycolysis
6.3.OxidationofPyruvateandtheCitricAcidCycle
BreakdownofPyruvate
AcetylCoAtoCO2
CitricAcidCycle
StepsintheCitricAcidCycle
ProductsoftheCitricAcidCycle
6.4.OxidativePhosphorylation
ElectronTransportChain
ComplexI
QandComplexII
ComplexIII
ComplexIV
Chemiosmosis
ATPYield
6.5.MetabolismwithoutOxygen
AnaerobicCellularRespiration
LacticAcidFermentation
AlcoholFermentation
OtherTypesofFermentation
6.6.ConnectionsofCarbohydrate,Protein,andLipidMetabolic
Pathways
ConnectionsofOtherSugarstoGlucoseMetabolism
ConnectionsofProteinstoGlucoseMetabolism
ConnectionsofLipidandGlucoseMetabolisms
6.7.RegulationofCellularRespiration
RegulatoryMechanisms


ControlofCatabolicPathways

Glycolysis
CitricAcidCycle
ElectronTransportChain
Chapter7.2.3Photosynthesis
7.1.OverviewofPhotosynthesis
MainStructuresandSummaryofPhotosynthesis
TheTwoPartsofPhotosynthesis
7.2.TheLight-DependentReactionsofPhotosynthesis
WhatIsLightEnergy?
AbsorptionofLight
UnderstandingPigments
HowLight-DependentReactionsWork
GeneratinganEnergyCarrier:ATP
7.3.UsingLightEnergytoMakeOrganicMolecules
TheCalvinCycle
Stage1:Fixation
Stage2:Reduction
Stage3:Regeneration
TheEnergyCycle
III.CellCommunication
Chapter8.3.1CellCommunication
8.1.SignalingMoleculesandCellularReceptors
FormsofSignaling
ParacrineSignaling
EndocrineSignaling
AutocrineSignaling
DirectSignalingAcrossGapJunctions
TypesofReceptors
Internalreceptors
Cell-SurfaceReceptors

SignalingMolecules
SmallHydrophobicLigands
Water-SolubleLigands
OtherLigands
8.2.PropagationoftheSignal
BindingInitiatesaSignalingPathway


MethodsofIntracellularSignaling
Phosphorylation
SecondMessengers
8.3.ResponsetotheSignal
GeneExpression
IncreaseinCellularMetabolism
CellGrowth
CellDeath
TerminationoftheSignalCascade
8.4.SignalinginSingle-CelledOrganisms
SignalinginYeast
SignalinginBacteria
Chapter9.3.2TheCellCycle
9.1.CellDivision
GenomicDNA
EukaryoticChromosomalStructureandCompaction
9.2.TheCellCycle
Interphase
G1Phase(FirstGap)
SPhase(SynthesisofDNA)
G2Phase(SecondGap)
TheMitoticPhase

Karyokinesis(Mitosis)
Cytokinesis
G0Phase
9.3.ControloftheCellCycle
RegulationoftheCellCyclebyExternalEvents
RegulationatInternalCheckpoints
TheG1Checkpoint
TheG2Checkpoint
TheMCheckpoint
RegulatorMoleculesoftheCellCycle
PositiveRegulationoftheCellCycle
NegativeRegulationoftheCellCycle
9.4.CancerandtheCellCycle
Proto-oncogenes


TumorSuppressorGenes
9.5.ProkaryoticCellDivision
BinaryFission
AppendixA.ThePeriodicTableofElements
Index


Preface
CreativeCommonsAttributionLicense4.0
/>2017/06/1319:25:45+0000
Biologyisdesignedformulti-semesterbiologycoursesforsciencemajors.Itis
groundedonanevolutionarybasisandincludesexcitingfeaturesthathighlight
careersinthebiologicalsciencesandeverydayapplicationsoftheconceptsat
hand.Tomeettheneedsoftoday’sinstructorsandstudents,somecontenthas

beenstrategicallycondensedwhilemaintainingtheoverallscopeandcoverage
oftraditionaltextsforthiscourse.Instructorscancustomizethebook,adaptingit
totheapproachthatworksbestintheirclassroom.Biologyalsoincludesan
innovativeartprogramthatincorporatescriticalthinkingandclickerquestionsto
helpstudentsunderstand—andapply—keyconcepts.
WelcometoBiology,anOpenStaxresource.Thistextbookwaswrittento
increasestudentaccesstohigh-qualitylearningmaterials,maintaininghighest
standardsofacademicrigoratlittletonocost.

1.AboutOpenStax
OpenStaxisanonprofitbasedatRiceUniversity,andit’sourmissionto
improvestudentaccesstoeducation.Ourfirstopenlylicensedcollegetextbook
waspublishedin2012,andourlibraryhassincescaledtoover20booksfor
collegeandAPcoursesusedbyhundredsofthousandsofstudents.Ouradaptive
learningtechnology,designedtoimprovelearningoutcomesthrough


personalizededucationalpaths,isbeingpilotedincollegecoursesthroughoutthe
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alliancewithothereducationalresourceorganizations,OpenStaxisbreaking
downthemostcommonbarrierstolearningandempoweringstudentsand
instructorstosucceed.

2.AboutOpenStax’sResources
Customization
Errata
Format

Customization
BiologyislicensedunderaCreativeCommonsAttribution4.0International(CC

BY)license,whichmeansthatyoucandistribute,remix,andbuilduponthe
content,aslongasyouprovideattributiontoOpenStaxanditscontent
contributors.
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onopenstax.orgformoreinformation.

Errata


AllOpenStaxtextbooksundergoarigorousreviewprocess.However,likeany
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Ifyouhaveacorrectiontosuggest,submititthroughthelinkonyourbookpage
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Format
YoucanaccessthistextbookforfreeinwebvieworPDFthroughopenstax.org,
andinlow-costprintandiBookseditions.

3.AboutBiology
Biologyisdesignedtocoverthescopeandsequencerequirementsofatypical
two-semesterbiologycourseforsciencemajors.Thetextprovides

comprehensivecoverageoffoundationalresearchandcorebiologyconcepts
throughanevolutionarylens.Biologyincludesrichfeaturesthatengagestudents
inscientificinquiry,highlightcareersinthebiologicalsciences,andoffer
everydayapplications.Thebookalsoincludesclickerquestionstohelpstudents
understand—andapply—keyconcepts.

4.CoverageandScope
PedagogicalFoundationandFeatures
ArtandAnimationsThatEngage


IndevelopingBiology,welistenedtohundredsofGeneralBiologyinstructors
whoreadilyprovidedfeedbackabouttheircourses,students,challenges,and
hopesforinnovation.Theexpenseoftextbooksandrelateditemsdidprovetobe
abarriertolearning.Butmoreimportantly,theseteacherssuggested
improvementsforthetextbook,whichwouldultimatelyleadtomoremeaningful
andmemorablelearningexperiencesforstudents.
Theresultisabookthataddressesacoreorganizationalrealityofthecourseand
itsmaterials—thesheerbreadthofthetopicalcoverage.Weprovideathorough
treatmentofbiology’sfoundationalconceptswhilecondensingselectedtopicsin
responsetothemarket’srequestforatextbookwithascopethatismanageable
forinstructorsandstudentsalike.Wealsostrivetomakebiology,asadiscipline,
interestingandaccessibletostudents.Inadditiontoacomprehensivecoverage
ofcoreconceptsandfoundationalresearch,wehaveincorporatedfeaturesthat
drawlearnersintothedisciplineinmeaningfulways.
Thepedagogicalchoices,chapterarrangements,andlearningobjective
fulfillmentweredevelopedandvettedwiththefeedbackofanotheronehundred
reviewers,whothoroughlyreadthematerialandoffereddetailedcritical
commentary.
Unit1:TheChemistryofLife.Ouropeningunitintroducesstudentstothe

sciences,includingthescientificmethodandthefundamentalconceptsof
chemistryandphysicsthatprovideaframeworkwithinwhichlearners
comprehendbiologicalprocesses.
Unit2:TheCell.Studentswillgainsolidunderstandingofthestructures,
functions,andprocessesofthemostbasicunitoflife:thecell.
Unit3:Genetics.Ourcomprehensivegeneticsunittakeslearnersfromthe
earliestexperimentsthatrevealedthebasisofgeneticsthroughtheintricacies
ofDNAtocurrentapplicationsintheemergingstudiesofbiotechnologyand
genomics.
Unit4:EvolutionaryProcesses.Thecoreconceptsofevolutionarediscussed
inthisunitwithexamplesillustratingevolutionaryprocesses.Additionally,
theevolutionarybasisofbiologyreappearsthroughoutthetextbookingeneral
discussionandisreinforcedthroughspecialcall-outfeatureshighlighting


specificevolution-basedtopics.
Unit5:BiologicalDiversity.Thediversityoflifeisexploredwithdetailed
studyofvariousorganismsanddiscussionofemergingphylogenetic
relationships.Thisunitmovesfromvirusestolivingorganismslikebacteria,
discussestheorganismsformerlygroupedasprotists,anddevotesmultiple
chapterstoplantandanimallife.
Unit6:PlantStructureandFunction.Ourplantunitthoroughlycoversthe
fundamentalknowledgeofplantlifeessentialtoanintroductorybiology
course.
Unit7:AnimalStructureandFunction.Anintroductiontotheformand
functionoftheanimalbodyisfollowedbychaptersonspecificbodysystems
andprocesses.Thisunittouchesonthebiologyofallorganismswhile
maintaininganengagingfocusonhumananatomyandphysiologythathelps
studentsconnecttothetopics.
Unit8:Ecology.Ecologicalconceptsarebroadlycoveredinthisunit,with

featureshighlightinglocalized,real-worldissuesofconservationand
biodiversity.

PedagogicalFoundationandFeatures
Biologyisgroundedinasolidscientificbase,withfeaturesthatengagethe
studentsinscientificinquiry,including:
EvolutionConnectionfeaturesupholdtheimportanceofevolutiontoall
biologicalstudythroughdiscussionslike“TheEvolutionofMetabolic
Pathways”and“AlgaeandEvolutionaryPathstoPhotosynthesis.”
ScientificMethodConnectioncall-outswalkstudentsthroughactualor
thoughtexperimentsthatelucidatethestepsofthescientificprocessas
appliedtothetopic.Featuresinclude“DeterminingtheTimeSpentinCell
CycleStages”and“TestingtheHypothesisofIndependentAssortment.”
CareerConnectionfeaturespresentinformationonavarietyofcareersinthe
biologicalsciences,introducingstudentstotheeducationalrequirementsand


day-to-dayworklifeofavarietyofprofessions,suchasmicrobiologist,
ecologist,neurologist,andforensicscientist.
EverydayConnectionfeaturestiebiologicalconceptstoemergingissuesand
discussscienceintermsofeverydaylife.Topicsinclude“ChesapeakeBay”
and“CanSnailVenomBeUsedasaPharmacologicalPainKiller?”

ArtandAnimationsThatEngage
Ourartprogramtakesastraightforwardapproachdesignedtohelpstudentslearn
theconceptsofbiologythroughsimple,effectiveillustrations,photos,and
micrographs.Biologyalsoincorporateslinkstorelevantanimationsand
interactiveexercisesthathelpbringbiologytolifeforstudents.
ArtConnectionfeaturescalloutcorefiguresineachchapterforstudent
study.Questionsaboutkeyfigures,includingclickerquestionsthatcanbe

usedintheclassroom,engagestudents’criticalthinkingtoensuregenuine
understanding.
LinktoLearningfeaturesdirectstudentstoonlineinteractiveexercisesand
animationstoaddafullercontexttocorecontent.

5.AdditionalResources
StudentandInstructorResources
We'vecompiledadditionalresourcesforbothstudentsandinstructors,including
GettingStartedGuides,aninstructorsolutionmanual,supplementaltestitems,
andPowerPointslides.Instructorresourcesrequireaverifiedinstructoraccount,
whichcanberequestedonyouropenstax.orglog-in.Takeadvantageofthese
resourcestosupplementyourOpenStaxbook.
PartnerResources


OpenStaxPartnersareouralliesinthemissiontomakehigh-qualitylearning
materialsaffordableandaccessibletostudentsandinstructorseverywhere.Their
toolsintegrateseamlesslywithourOpenStaxtitlesatalowcost.Toaccessthe
partnerresourcesforyourtext,visityourbookpageonopenstax.org.

6.AbouttheAuthors
SeniorContributingAuthors
ContributingAuthorsandReviewers

SeniorContributingAuthors
YaelAvissar(CellBiology),RhodeIslandCollege
JungChoi(Genetics),GeorgiaInstituteofTechnology
JeanDeSaix(Evolution),UniversityofNorthCarolinaatChapelHill
VladimirJurukovski(AnimalPhysiology),SuffolkCountyCommunityCollege
RobertWise(PlantBiology),UniversityofWisconsin,Oshkosh

ConnieRye(GeneralContentLead),EastMississippiCommunityCollege

ContributingAuthorsandReviewers
JulieAdams,AuroraUniversity
SummerAllen,BrownUniversity
JamesBader,CaseWesternReserveUniversity
DavidBailey,St.NorbertCollege
MarkBelk,BrighamYoungUniversity
NancyBoury,IowaStateUniversity
LisaBonneau,MetropolitanCommunityCollege–BlueRiver
GracielaBrelles-Marino,CaliforniaStateUniversityPomona
MarkBrowning,PurdueUniversity
SueChaplin,UniversityofSt.Thomas
GeorgeCline,JacksonvilleStateUniversity


DebCook,GeorgiaGwinnettCollege
DianeDay,ClaytonStateUniversity
FrankDirrigl,TheUniversityofTexasPanAmerican
WaneeneDorsey,GramblingStateUniversity
NickDowney,UniversityofWisconsinLaCrosse
RickDuhrkopf,BaylorUniversity
KristyDuran,AdamsStateUniversity
StanEisen,ChristianBrothersUniversity
BrentEwers,UniversityofWyoming
MyriamFeldman,LakeWashingtonInstituteofTechnology
MichaelFine,VirginiaCommonwealthUniversity
LindaFlora,DelawareCountyCommunityCollege
ThomasFreeland,WalshUniversity
DavidGrisé,TexasA&MUniversity–CorpusChristi

AndreaHazard,SUNYCortland
MichaelHedrick,UniversityofNorthTexas
LindaHensel,MercerUniversity
MarkKopeny,UniversityofVirginia
NormanJohnson,UniversityofMassachusettsAmherst
GraceLasker,LakeWashingtonInstituteofTechnology;WaldenUniversity
SandyLatourelle,SUNYPlattsburgh
TheoLight,ShippensburgUniversity
ClarkLindgren,GrinnellCollege
JamesMalcolm,UniversityofRedlands
MarkMeade,JacksonvilleStateUniversity
RichardMerritt,HoustonCommunityCollege
JamesMickle,NorthCarolinaStateUniversity
JasleenMishra,HoustonCommunityCollege
DudleyMoon,AlbanyCollegeofPharmacyandHealthSciences
ShobhanaNatarajan,BrookhavenCollege
JonasOkeagu,FayettevilleStateUniversity
DianaOliveras,UniversityofColoradoBoulder
JohnPeters,CollegeofCharleston
JoelPiperberg,MillersvilleUniversity
JohannaPorter-Kelley,Winston-SalemStateUniversity
RobynPuffenbarger,BridgewaterCollege
DennisRevie,CaliforniaLutheranUniversity


AnnRushing,BaylorUniversity
SanghaSaha,CityCollegeofChicago
EdwardSaiff,RamapoCollegeofNewJersey
BrianShmaefsky,LoneStarCollegeSystem
RobertSizemore,AlcornStateUniversity

MarcSmith,SinclairCommunityCollege
FrederickSpiegel,UniversityofArkansas
FrederickSproull,LaRocheCollege
BobSullivan,MaristCollege
MarkSutherland,HendrixCollege
ToureThompson,AlabamaA&MUniversity
ScottThomson,UniversityofWisconsin–Parkside
AllisonvandeMeene,UniversityofMelbourne
MaryWhite,SoutheasternLouisianaUniversity
StevenWilt,BellarmineUniversity
JamesWise,HamptonUniversity
RennaWolfe
VirginiaYoung,MercerUniversity
LeslieZeman,UniversityofWashington
DanielZurek,PittsburgStateUniversity
ShobhanaNatarajan,AlconLaboratories,Inc.


PartI.Biochemistry


Chapter1.1.1PropertiesofWaterand
Carbon

Figure1.1.
Atomsarethebuildingblocksofmoleculesfoundintheuniverse—air,soil,water,rocks...andalsothe
cellsofalllivingorganisms.Inthismodelofanorganicmolecule,theatomsofcarbon(black),hydrogen
(white),nitrogen(blue),oxygen(red),andsulfur(yellow)areshowninproportionalatomicsize.Thesilver
rodsindicatechemicalbonds.(credit:modificationofworkbyChristianGuthier)


Introduction*
Elementsinvariouscombinationscompriseallmatter,includinglivingthings.
Someofthemostabundantelementsinlivingorganismsincludecarbon,
hydrogen,nitrogen,oxygen,sulfur,andphosphorus.Theseformthenucleic
acids,proteins,carbohydrates,andlipidsthatarethefundamentalcomponentsof
livingmatter.Biologistsmustunderstandtheseimportantbuildingblocksand
theuniquestructuresoftheatomsthatmakeupmolecules,allowingforthe
formationofcells,tissues,organsystems,andentireorganisms.


Allbiologicalprocessesfollowthelawsofphysicsandchemistry,soinorderto
understandhowbiologicalsystemswork,itisimportanttounderstandthe
underlyingphysicsandchemistry.Forexample,theflowofbloodwithinthe
circulatorysystemfollowsthelawsofphysicsthatregulatethemodesoffluid
flow.Thebreakdownofthelarge,complexmoleculesoffoodintosmaller
molecules—andtheconversionofthesetoreleaseenergytobestoredin
adenosinetriphosphate(ATP)—isaseriesofchemicalreactionsthatfollow
chemicallaws.Thepropertiesofwaterandtheformationofhydrogenbondsare
keytounderstandinglivingprocesses.Recognizingthepropertiesofacidsand
basesisimportant,forexample,toourunderstandingofthedigestiveprocess.
Therefore,thefundamentalsofphysicsandchemistryareimportantforgaining
insightintobiologicalprocesses.

1.1.Atoms,Isotopes,Ions,andMolecules:
TheBuildingBlocks*
Bytheendofthissection,youwillbeableto:
Definematterandelements
Describetheinterrelationshipbetweenprotons,neutrons,andelectrons
Comparethewaysinwhichelectronscanbedonatedorsharedbetween
atoms

Explainthewaysinwhichnaturallyoccurringelementscombinetocreate
molecules,cells,tissues,organsystems,andorganisms
TheStructureoftheAtom
AtomicNumberandMass
Isotopes
ThePeriodicTable
ElectronShellsandtheBohrModel


ElectronOrbitals
ChemicalReactionsandMolecules
IonsandIonicBonds
CovalentBondsandOtherBondsandInteractions
PolarCovalentBonds
NonpolarCovalentBonds
HydrogenBondsandVanDerWaalsInteractions
Atitsmostfundamentallevel,lifeismadeupofmatter.Matterisanysubstance
thatoccupiesspaceandhasmass.Elementsareuniqueformsofmatterwith
specificchemicalandphysicalpropertiesthatcannotbebrokendowninto
smallersubstancesbyordinarychemicalreactions.Thereare118elements,but
only92occurnaturally.Theremainingelementsaresynthesizedinlaboratories
andareunstable.
Eachelementisdesignatedbyitschemicalsymbol,whichisasinglecapital
letteror,whenthefirstletterisalready“taken”byanotherelement,a
combinationoftwoletters.SomeelementsfollowtheEnglishtermforthe
element,suchasCforcarbonandCaforcalcium.Otherelements’chemical
symbolsderivefromtheirLatinnames;forexample,thesymbolforsodiumis
Na,referringtonatrium,theLatinwordforsodium.
Thefourelementscommontoalllivingorganismsareoxygen(O),carbon(C),
hydrogen(H),andnitrogen(N).Inthenon-livingworld,elementsarefoundin

differentproportions,andsomeelementscommontolivingorganismsare
relativelyrareontheearthasawhole,asshowninTable1.1.Forexample,the
atmosphereisrichinnitrogenandoxygenbutcontainslittlecarbonand
hydrogen,whiletheearth’scrust,althoughitcontainsoxygenandasmall
amountofhydrogen,haslittlenitrogenandcarbon.Inspiteoftheirdifferences
inabundance,allelementsandthechemicalreactionsbetweenthemobeythe
samechemicalandphysicallawsregardlessofwhethertheyareapartofthe
livingornon-livingworld.
Table1.1.
ApproximatePercentageofElementsinLivingOrganisms(Humans)
ComparedtotheNon-livingWorld


Element

Life(Humans)

Atmosphere

Earth’sCrust

Oxygen(O)

65%

21%

46%

Carbon(C)


18%

trace

trace

Hydrogen(H)

10%

trace

0.1%

Nitrogen(N)

3%

78%

trace

TheStructureoftheAtom
Tounderstandhowelementscometogether,wemustfirstdiscussthesmallest
componentorbuildingblockofanelement,theatom.Anatomisthesmallest
unitofmatterthatretainsallofthechemicalpropertiesofanelement.For
example,onegoldatomhasallofthepropertiesofgoldinthatitisasolidmetal
atroomtemperature.Agoldcoinissimplyaverylargenumberofgoldatoms
moldedintotheshapeofacoinandcontainingsmallamountsofotherelements

knownasimpurities.Goldatomscannotbebrokendownintoanythingsmaller
whilestillretainingthepropertiesofgold.
Anatomiscomposedoftworegions:thenucleus,whichisinthecenterofthe
atomandcontainsprotonsandneutrons,andtheoutermostregionoftheatom
whichholdsitselectronsinorbitaroundthenucleus,asillustratedinFigure1.2.
Atomscontainprotons,electrons,andneutrons,amongothersubatomic
particles.Theonlyexceptionishydrogen(H),whichismadeofoneprotonand
oneelectronwithnoneutrons.