Bài giảng Biology - Chapter 26: The Tree of Life An Introduction to Biological Diversity

Chapter 26The Tree of LifeAn Introduction to Biological DiversityOverview: Changing Life on a Changing EarthLife is a continuumExtending from the earliest organisms to the great variety of species that exist todayGeological events that alter environmentsChange the course of biological evolutionConversely, life changes the planet that it inhabitsFigure 26.1Geologic history and biological history have been episodicMarked by what were in essence revolutions that opened many new ways of lifeConcept 26.1: Conditions on early Earth made the origin of life possibleMost biologists now think that it is at least a credible hypothesis That chemical and physical processes on early Earth produced very simple cells through a sequence of stagesAccording to one hypothetical scenario There were four main stages in this processSynthesis of Organic Compounds on Early EarthEarth formed about 4.6 billion years agoAlong with the rest of the solar systemEarth’s early atmosphereContained water vapor and many chemicals released by volcanic eruptions As material circulated through the apparatus, Miller and Urey periodically collected samples for analysis. They identified a variety of organic molecules, including amino acids such as alanine and glutamic acid that are common in the proteins of organisms. They also found many other amino acids and complex,oily hydrocarbons.RESULTSFigure 26.2 Miller and Urey set up a closed system in their laboratory to simulate conditions thought to have existed on early Earth. A warmed flask of water simulated the primeval sea. The strongly reducing “atmosphere” in the system consisted of H2, methane (CH4), ammonia (NH3), and water vapor. Sparks were discharged in the synthetic atmosphere to mimic lightning. A condenser cooled the atmosphere, raining water and any dissolved compounds into the miniature sea. EXPERIMENTElectrodeCondenserCooled watercontainingorganic moleculesH2OSample forchemical analysisColdwaterWater vaporCH4H2NH3CONCLUSION Organic molecules, a first step in the origin of life, can form in a strongly reducing atmosphere.Laboratory experiments simulating an early Earth atmosphereHave produced organic molecules from inorganic precursors, but the existence of such an atmosphere on early Earth is unlikelyInstead of forming in the atmosphereThe first organic compounds on Earth may have been synthesized near submerged volcanoes and deep-sea ventsFigure 26.3Extraterrestrial Sources of Organic CompoundsSome of the organic compounds from which the first life on Earth aroseMay have come from spaceCarbon compoundsHave been found in some of the meteorites that have landed on EarthLooking Outside Earth for Clues About the Origin of LifeThe possibility that life is not restricted to EarthIs becoming more accessible to scientific testingAbiotic Synthesis of PolymersSmall organic moleculesPolymerize when they are concentrated on hot sand, clay, or rockProtobiontsProtobiontsAre aggregates of abiotically produced molecules surrounded by a membrane or membrane-like structureLaboratory experiments demonstrate that protobiontsCould have formed spontaneously from abiotically produced organic compoundsFor example, small membrane-bounded droplets called liposomesCan form when lipids or other organic molecules are added to water20 m(a) Simple reproduction. This lipo-some is “giving birth” to smallerliposomes (LM).(b) Simple metabolism. If enzymes—in this case, phosphorylase and amylase—are included in the solution from which the droplets self-assemble, some liposomes can carry out simple metabolic reactions and export the products.Glucose-phosphateGlucose-phosphatePhosphorylaseStarchAmylaseMaltoseMaltosePhosphateFigure 26.4a, bThe “RNA World” and the Dawn of Natural SelectionThe first genetic materialWas probably RNA, not DNARNA molecules called ribozymes have been found to catalyze many different reactions, includingSelf-splicingMaking complementary copies of short stretches of their own sequence or other short pieces of RNAFigure 26.5Ribozyme(RNA molecule)TemplateNucleotidesComplementary RNA copy355Early protobionts with self-replicating, catalytic RNAWould have been more effective at using resources and would have increased in number through natural selectionConcept 26.2: The fossil record chronicles life on EarthCareful study of fossilsOpens a window into the lives of organisms that existed long ago and provides information about the evolution of life over billions of yearsHow Rocks and Fossils Are Dated Sedimentary strataReveal the relative ages of fossilsIndex fossilsAre similar fossils found in the same strata in different locationsAllow strata at one location to be correlated with strata at another locationFigure 26.6The absolute ages of fossilsCan be determined by radiometric datingFigure 26.71234Accumulating “daughter” isotopeRatio of parent isotope to daughter isotopeRemaining “parent” isotope1111Time (half-lives)24816The magnetism of rocksCan also provide dating informationMagnetic reversals of the north and south magnetic polesHave occurred repeatedly in the pastLeave their record on rocks throughout the worldThe Geologic RecordBy studying rocks and fossils at many different sitesGeologists have established a geologic record of Earth’s historyThe geologic record is divided intoThree eons: the Archaean, the Proterozoic, and the PhanerozoicMany eras and periodsMany of these time periodsMark major changes in the composition of fossil speciesThe geologic recordTable 26.1Mass ExtinctionsThe fossil record chronicles a number of occasionsWhen global environmental changes were so rapid and disruptive that a majority of species were swept awayFigure 26.8CambrianProterozoic eonOrdovicianSilurianDevonianCarboniferousPermianTriassicJurassicCretaceousPaleogeneNeogeneNumber of families ( )Number oftaxonomicfamiliesExtinction rateCretaceous mass extinctionPermian mass extinctionMillions of years agoExtinction rate ( )PaleozoicMesozoic02060408010060050040030020010002,5001,5001,00050002,000Ceno-zoicTwo major mass extinctions, the Permian and the CretaceousHave received the most attentionThe Permian extinctionClaimed about 96% of marine animal species and 8 out of 27 orders of insectsIs thought to have been caused by enormous volcanic eruptionsThe Cretaceous extinctionDoomed many marine and terrestrial organisms, most notably the dinosaursIs thought to have been caused by the impact of a large meteorFigure 26.9NORTHAMERICAChicxulubcraterYucatánPeninsulaMuch remains to be learned about the causes of mass extinctionsBut it is clear that they provided life with unparalleled opportunities for adaptive radiations into newly vacated ecological nichesThe analogy of a clockCan be used to place major events in the Earth’s history in the context of the geological recordFigure 26.10Land plantsAnimalsMulticellulareukaryotesSingle-celledeukaryotesAtmosphericoxygenProkaryotesOrigin of solarsystem andEarthHumansCeno-zoicMeso-zoicPaleozoicArchaeanEonBillions of years agoProterozoicEon1234Concept 26.3: As prokaryotes evolved, they exploited and changed young EarthThe oldest known fossils are stromatolitesRocklike structures composed of many layers of bacteria and sedimentWhich date back 3.5 billion years agoLynn Margulis (top right), of the University of Massachussetts, and Kenneth Nealson, of the University of Southern California, are shown collecting bacterial mats in a Baja California lagoon. Themats are produced by colonies of bacteria that live in environments inhospitable to most other life. A section through a mat (inset) shows layers of sediment that adhere to the sticky bacteria asthe bacteria migrate upward.Some bacterial mats form rocklike structures called stromatolites,such as these in Shark Bay, Western Australia. The Shark Baystromatolites began forming about 3,000 years ago. The insetshows a section through a fossilized stromatolite that is about3.5 billion years old.(a)(b)Figure 26.11a, bThe First ProkaryotesProkaryotes were Earth’s sole inhabitantsFrom 3.5 to about 2 billion years agoElectron Transport SystemsElectron transport systems of a variety of typesWere essential to early lifeHave: some aspects that possibly precede life itselfPhotosynthesis and the Oxygen RevolutionThe earliest types of photosynthesisDid not produce oxygenOxygenic photosynthesisProbably evolved about 3.5 billion years ago in cyanobacteriaFigure 26.12When oxygen began to accumulate in the atmosphere about 2.7 billion years agoIt posed a challenge for lifeIt provided an opportunity to gain abundant energy from lightIt provided organisms an opportunity to exploit new ecosystemsConcept 26.4: Eukaryotic cells arose from symbioses and genetic exchanges between prokaryotesAmong the most fundamental questions in biologyIs how complex eukaryotic cells evolved from much simpler prokaryotic cellsThe First EukaryotesThe oldest fossils of eukaryotic cellsDate back 2.1 billion yearsEndosymbiotic Origin of Mitochondria and PlastidsThe theory of endosymbiosisProposes that mitochondria and plastids were formerly small prokaryotes living within larger host cellsThe prokaryotic ancestors of mitochondria and plastidsProbably gained entry to the host cell as undigested prey or internal parasitesFigure 26.13CytoplasmDNAPlasmamembraneAncestralprokaryoteInfolding ofplasma membraneEndoplasmicreticulumNuclear envelopeNucleusEngulfingof aerobicheterotrophicprokaryoteCell with nucleusand endomembranesystemMitochondrionAncestralheterotrophiceukaryotePlastidMitochondrionEngulfing ofphotosyntheticprokaryote insome cellsAncestral PhotosyntheticeukaryoteIn the process of becoming more interdependentThe host and endosymbionts would have become a single organismThe evidence supporting an endosymbiotic origin of mitochondria and plastids includesSimilarities in inner membrane structures and functionsBoth have their own circular DNAEukaryotic Cells as Genetic ChimerasAdditional endosymbiotic events and horizontal gene transfersMay have contributed to the large genomes and complex cellular structures of eukaryotic cellsSome investigators have speculated that eukaryotic flagella and ciliaEvolved from symbiotic bacteria, based on symbiotic relationships between some bacteria and protozoansFigure 26.1450 mConcept 26.5: Multicellularity evolved several times in eukaryotesAfter the first eukaryotes evolvedA great range of unicellular forms evolvedMulticellular forms evolved alsoThe Earliest Multicellular EukaryotesMolecular clocksDate the common ancestor of multicellular eukaryotes to 1.5 billion yearsThe oldest known fossils of eukaryotesAre of relatively small algae that lived about 1.2 billion years agoLarger organisms do not appear in the fossil recordUntil several hundred million years laterChinese paleontologists recently described 570-million-year-old fossilsThat are probably animal embryosFigure 26.15a, b150 m200 m(a) Two-cell stage(b) Later stageThe Colonial ConnectionThe first multicellular organisms were coloniesCollections of autonomously replicating cellsFigure 26.1610 mSome cells in the coloniesBecame specialized for different functionsThe first cellular specializationsHad already appeared in the prokaryotic worldThe “Cambrian Explosion”Most of the major phyla of animalsAppear suddenly in the fossil record that was laid down during the first 20 million years of the Cambrian periodPhyla of two animal phyla, Cnidaria and PoriferaAre somewhat older, dating from the late ProterozoicFigure 26.17EarlyPaleozoicera(Cambrianperiod)Millions of years ago500542LateProterozoiceonSpongesCnidariansEchinodermsChordatesBrachiopodsAnnelidsMolluscsArthropodsMolecular evidenceSuggests that many animal phyla originated and began to diverge much earlier, between 1 billion and 700 million years agoColonization of Land by Plants, Fungi, and AnimalsPlants, fungi, and animalsColonized land about 500 million years agoSymbiotic relationships between plants and fungiAre common today and date from this timeContinental DriftEarth’s continents are not fixedThey drift across our planet’s surface on great plates of crust that float on the hot underlying mantleOften, these plates slide along the boundary of other platesPulling apart or pushing against each otherFigure 26.18NorthAmericanPlateCaribbeanPlateJuan de FucaPlateCocos PlatePacificPlateNazcaPlateSouthAmericanPlateAfricanPlateScotia PlateAntarcticPlateArabianPlateEurasian PlatePhilippinePlateIndianPlateAustralianPlateMany important geological processesOccur at plate boundaries or at weak points in the plates themselvesVolcanoes andvolcanic islandsTrenchOceanic ridgeOceanic crustSeafloor spreadingSubduction zoneFigure 26.19The formation of the supercontinent Pangaea during the late Paleozoic eraAnd its breakup during the Mesozoic era explain many biogeographic puzzlesFigure 26.20India collided with Eurasia just 10 millionyears ago, forming theHimalayas, the tallestand youngest of Earth’smajor mountainranges. The continentscontinue to drift.By the end of theMesozoic, Laurasiaand Gondwanaseparated into thepresent-day continents.By the mid-Mesozoic,Pangaea split intonorthern (Laurasia)and southern(Gondwana)landmasses.CenozoicNorth AmericaEurasiaAfricaSouthAmericaIndiaMadagascarAntarcticaAustraliaLaurasiaMesozoicGondwanaAt the end of thePaleozoic, all ofEarth’s landmasseswere joined in thesupercontinentPangaea.PangaeaPaleozoic25113565.50Millions of years agoConcept 26.6: New information has revised our understanding of the tree of lifeMolecular DataHave provided new insights in recent decades regarding the deepest branches of the tree of lifePrevious Taxonomic SystemsEarly classification systems had two kingdomsPlants and animalsRobert Whittaker proposed a system with five kingdomsMonera, Protista, Plantae, Fungi, and AnimaliaFigure 26.21PlantaeFungiAnimaliaProtistaMoneraEukaryotesProkaryotesReconstructing the Tree of Life: A Work in ProgressA three domain systemHas replaced the five kingdom systemIncludes the domains Archaea, Bacteria, and EukaryaEach domainHas been split by taxonomists into many kingdomsOne current view of biological diversityFigure 26.22ProteobacteriaChlamydiasSpirochetesCyanobacteriaGram-positive bacteriaKorarchaeotesEuryarchaeotes, crenarchaeotes, nanoarchaeotesDiplomonads, parabasalidsEuglenozoansAlveolates (dinoflagellates, apicomplexans, ciliates)Stramenopiles (water molds, diatoms, golden algae, brown algae)Cercozoans, radiolariansRed algaeChlorophytesCharophyceansDomain ArchaeaDomain EukaryaUniversal ancestorDomain Bacteria Chapter 27 Chapter 28Bryophytes (mosses, liverworts, hornworts)PlantsFungiAnimalsSeedless vascular plants (ferns)GymnospermsAngiospermsAmoebozoans (amoebas, slime molds)ChytridsZygote fungiArbuscular mycorrhizal fungiSac fungiClub fungiChoanoflagellatesSpongesCnidarians (jellies, coral)Bilaterally symmetrical animals (annelids,arthropods, molluscs, echinoderms, vertebrates)Chapter 29Chapter 30Chapter 28Chapter 31Chapter 32Chapters 33, 34Figure 26.21