Biology Jean Brainard, Ph.D. (JBrainard) Jean Brainard, Ph.D. (JBrainard) Jean Brainard, Ph.D. (JeanB) Jean Brainard, Ph.D. (JeanB) SayThankstotheAuthors Clickhttp://www.ck12.org/saythanks (Nosigninrequired) www.ck12.org iii AUTHORS JeanBrainard,Ph.D.(JBrainard) To access a customizable version of this book, as well as other JeanBrainard,Ph.D.(JBrainard) interactivecontent,visitwww.ck12.org JeanBrainard,Ph.D.(JeanB) JeanBrainard,Ph.D.(JeanB) CONTRIBUTORS BarbaraAkre,(BAkre) CK-12 Foundation is a non-profit organization with a mission to Jennifer Blanchette, Ph.D. reduce the cost of textbook materials for the K-12 market both (JBlanchette)contributor in the U.S. and worldwide. 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Printed: July18,2012 iv www.ck12.org Contents 1 WhatisBiology? 1 1.1 ScienceandtheNaturalWorld . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 1.2 Biology: TheStudyofLife . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 1.3 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 2 TheChemistryofLife 24 2.1 MatterandOrganicCompounds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 2.2 BiochemicalReactions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37 2.3 Water,Acids,andBases . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44 2.4 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51 3 CellularStructureandFunction 52 3.1 IntroductiontoCells . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53 3.2 CellStructures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63 3.3 CellTransportandHomeostasis. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74 3.4 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82 4 PhotosynthesisandCellularRespiration 83 4.1 EnergyforLife . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84 4.2 Photosynthesis: SugarasFood . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90 4.3 PoweringtheCell: CellularRespiration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99 4.4 AnaerobicRespiration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 108 4.5 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113 5 TheCellCycle,Mitosis,andMeiosis 114 5.1 CellDivisionandtheCellCycle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 115 5.2 ChromosomesandMitosis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 122 5.3 ReproductionandMeiosis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 128 5.4 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 138 6 GregorMendelandGenetics 139 6.1 Mendel’sInvestigations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 140 6.2 MendelianInheritance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 149 6.3 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 158 7 MolecularGenetics: FromDNAtoProteins 159 7.1 DNAandRNA . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 160 7.2 ProteinSynthesis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 167 7.3 Mutation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 174 7.4 RegulationofGeneExpression . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 181 8 HumanGeneticsandBiotechnology 187 8.1 HumanChromosomesandGenes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 188 Contents www.ck12.org v 8.2 HumanInheritance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 195 8.3 Biotechnology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 206 8.4 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 213 9 Life: FromtheFirstOrganismOnward 214 9.1 EarthFormsandLifeBegins . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 215 9.2 TheEvolutionofMulticellularLife . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 227 9.3 Classification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 237 9.4 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 242 10 TheTheoryofEvolution 243 10.1 DarwinandtheTheoryofEvolution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 244 10.2 EvidenceforEvolution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 254 10.3 MicroevolutionandtheGeneticsofPopulations . . . . . . . . . . . . . . . . . . . . . . . . . . 263 10.4 MacroevolutionandtheOriginofSpecies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 271 10.5 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 276 11 ThePrinciplesofEcology 277 11.1 TheScienceofEcology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 278 11.2 RecyclingMatter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 289 11.3 Biomes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 296 11.4 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 309 12 CommunitiesandPopulations 310 12.1 CommunityInteractions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 311 12.2 CharacteristicsofPopulations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 320 12.3 HumanPopulationGrowth . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 328 12.4 TheBiodiversityCrisis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 335 12.5 NaturalResourcesandClimateChange . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 344 12.6 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 356 13 Microorganisms: ProkaryotesandViruses 357 13.1 Prokaryotes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 358 13.2 Viruses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 370 13.3 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 377 14 Eukaryotes: ProtistsandFungi 378 14.1 IntroductiontoProtists . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 379 14.2 TypesofProtists . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 385 14.3 IntroductiontoFungi . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 392 14.4 EcologyofFungi . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 400 14.5 Protists,Fungi,andHumanDisease. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 406 14.6 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 412 15 PlantEvolutionandClassification 413 15.1 IntroductiontothePlantKingdom . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 414 15.2 FourTypesofModernPlants . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 428 15.3 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 443 16 PlantBiology 444 16.1 PlantTissuesandGrowth . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 445 16.2 PlantOrgans: Roots,Stems,andLeaves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 450 16.3 VariationinPlantLifeCycles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 461 Contents vi www.ck12.org 16.4 PlantAdaptationsandResponses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 468 16.5 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 474 17 IntroductiontoAnimals 475 17.1 OverviewofAnimals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 476 17.2 OverviewofInvertebrates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 488 17.3 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 498 18 FromSpongestoInvertebrateChordates 499 18.1 Sponges,Cnidarians,Flatworms,andRoundworms . . . . . . . . . . . . . . . . . . . . . . . . 500 18.2 MollusksandAnnelids . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 512 18.3 ArthropodsandInsects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 520 18.4 EchinodermsandInvertebrateChordates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 532 18.5 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 540 19 FromFishtoBirds 542 19.1 OverviewofVertebrates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 543 19.2 Fish . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 551 19.3 Amphibians . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 560 19.4 Reptiles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 569 19.5 Birds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 577 19.6 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 589 20 MammalsandAnimalBehavior 590 20.1 MammalianTraits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 591 20.2 ReproductioninMammals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 601 20.3 EvolutionandClassificationofMammals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 608 20.4 OverviewofAnimalBehavior . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 620 20.5 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 631 21 IntroductiontotheHumanBody: Bones,Muscles,andSkin 632 21.1 OrganizationoftheHumanBody . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 633 21.2 TheSkeletalSystem . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 639 21.3 TheMuscularSystem . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 648 21.4 TheIntegumentarySystem . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 656 21.5 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 662 22 TheNervousandEndocrineSystems 663 22.1 TheNervousSystem . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 664 22.2 TheEndocrineSystem . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 684 22.3 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 693 23 TheCirculatory,Respiratory,Digestive,andExcretorySystems 694 23.1 TheCirculatorySystem . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 695 23.2 TheRespiratorySystem . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 705 23.3 TheDigestiveSystem . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 713 23.4 TheExcretorySystem . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 729 23.5 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 736 24 TheImmuneSystemandDisease 737 24.1 NonspecificDefenses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 738 24.2 TheImmuneResponse . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 744 24.3 ImmuneSystemDiseases . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 754 Contents www.ck12.org vii 24.4 EnvironmentalProblemsandHumanHealth . . . . . . . . . . . . . . . . . . . . . . . . . . . . 761 24.5 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 768 25 ReproductionandHumanDevelopment 769 25.1 MaleReproductiveSystem . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 770 25.2 FemaleReproductiveSystem . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 777 25.3 FromFertilizationtoOldAge . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 786 25.4 SexuallyTransmittedInfections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 797 25.5 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 803 26 BiologyGlossary 804 26.1 A . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 805 26.2 B . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 809 26.3 C . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 811 26.4 D . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 815 26.5 E . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 817 26.6 F . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 820 26.7 G . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 822 26.8 H . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 825 26.9 I . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 827 26.10 J . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 829 26.11 K . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 830 26.12 L . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 831 26.13 M . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 833 26.14 N . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 836 26.15 O . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 838 26.16 P . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 839 26.17 Q . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 844 26.18 R . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 845 26.19 S . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 847 26.20 T . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 851 26.21 U . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 853 26.22 V . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 854 26.23 W . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 855 26.24 X . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 856 26.25 Y . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 857 26.26 Z . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 858 Contents www.ck12.org 1 C 1 HAPTER What is Biology? Chapter Outline 1.1 SCIENCE AND THE NATURAL WORLD 1.2 BIOLOGY: THE STUDY OF LIFE 1.3 REFERENCES Isthispictureacolorfulworkofabstractart,orisitsomethingelse? Imagineshrinkingdowntoatinysize,sosmall youcouldenterabloodvessel. Thepictureshowswhatyoumightseerushingtowardyou. Doyouknowwhatthe redobjectsare? Ifyouguessedredbloodcells,youareright. Whatabouttheknobbygreenobjects? Watchoutfor these! Theyarevirusesthathaveinvadedtheblood. Whenyoureadthisbook,youwilltakeanexcitingjourneyinto therealmof bloodcells, viruses, andjustabout everythingelsethatisrelatedto life. Youwill learnhowyourown bodyworks,whatmakeslivingthingsunique,andwhatyouandviruseshaveincommon. Thisfirstchapterexplains howscientistslearnaboutthenaturalworldandintroducesyoutobiology,thescienceoflife. Chapter1. WhatisBiology? 2 www.ck12.org 1.1 Science and the Natural World Lesson Objectives • Identifythegoalofscience. • Describehowscientistsstudythenaturalworld. • Explainhowandwhyscientistsdoexperiments. • Describetypesofscientificinvestigations. • Explainwhatascientifictheoryis. Vocabulary dependentvariable variableinascientificexperimentthatisaffectedbyanothervariable,calledtheindependent variable evidence anytypeofdatathatmaybeusedtotestahypothesis experiment specialtypeofscientificinvestigationthatisperformedundercontrolledconditions hypothesis possibleanswertoascientificquestion;mustbefalsifiable independentvariable variable in a scientific experiment that is manipulated by the researcher to investigate its affectonanothervariable,calledthedependentvariable model representationofpartoftherealworld observation anythingthatisdetectedwiththesenses prediction statementthattellswhatwillhappenundercertainconditions science distinctivewayofgainingknowledgeaboutthenaturalworldthattriestoanswerquestionswithevidence andlogic scientificinvestigation planforaskingquestionsandtestingpossibleanswers scientificlaw statementdescribingwhatalwayshappensundercertainconditionsinnature scientificmethod theprocessofascientificinvestigation scientifictheory broad explanation that is widely accepted as true because it is supported by a great deal of evidence 1.1. ScienceandtheNaturalWorld www.ck12.org 3 Introduction Did you ever wonder why giraffes have such long necks or how birds learn to sing their special songs? If you ever asked questions such as these about the natural world, then you were thinking like a scientist. The word science comes from a Latin word that means “knowledge.” Science is a distinctive way of gaining knowledge about the naturalworldthatstartswithaquestionandthentriestoanswerthequestionwithevidenceandlogic. Scienceisan excitingexplorationofallthewhysandhowsthatanycuriouspersonmighthaveabouttheworld. Youcanbepart of that exploration. Besides your curiosity, all you need is a basic understanding of how scientists think and how scienceisdone,startingwiththegoalofscience. The Goal of Science The goal of science is to understand the natural world. To achieve this goal, scientists make certain assumptions. Theyassumethat: • Naturecanbeunderstoodthroughsystematicstudy. • Scientificideasareopentorevision. • Soundscientificideaswithstandthetestoftime. • Sciencecannotprovideanswerstoallquestions. NatureCanBeUnderstood Scientiststhinkofnatureasasinglesystemcontrolledbynaturallaws. Bydiscoveringnaturallaws,scientistsstrive to increase their understanding of the natural world. Laws of nature are expressed as scientific laws. A scientific lawisastatementthatdescribeswhatalwayshappensundercertainconditionsinnature. Anexampleofascientificlawisthelawofgravity,whichwasdiscoveredbySirIsaacNewton(seeFigure1.1). The lawofgravitystatesthatobjectsalwaysfalltowardsEarthbecauseofthepullofgravity. Basedonthislaw,Newton couldexplainmanynaturalevents. Hecouldexplainnotonlywhyobjectssuchasapplesalwaysfalltotheground, buthecouldalsoexplainwhythemoonorbitsEarth. IsaacNewtondiscoveredlawsofmotionaswellasthelawof gravity. Hislawsofmotionallowedhimtoexplainwhyobjectsmoveastheydo. ScientificIdeasCanChange Science is more of a process than a set body of knowledge. Scientists are always testing and revising their ideas, and as new observations are made, existing ideas may be challenged. Ideas may be replaced with new ideas that better fit the facts, but more often existing ideas are simply revised. For example, when Albert Einstein developed his theory of relativity, he didn’t throw out Newton’s laws of motion. Instead, he showed that Newton’s laws are a part of a bigger picture. In this way, scientists gradually build an increasingly accurate and detailed understanding ofthenaturalworld. ScientificKnowledgeCanWithstandtheTestofTime Many scientific ideas have withstood the test of time. For example, about 200 years ago, the scientist John Dalton proposed atomic theory—the theory that all matter is made of tiny particles called atoms. This theory is still valid today. Therearemanyotherexamplesofbasicscienceideasthathavebeentestedrepeatedlyandfoundtobetrue. Youwilllearnaboutmanyofthemasyoustudybiology. Chapter1. WhatisBiology?