Biology - An Illustrated Guide to Science (794127), страница 16
Текст из файла (страница 16)
Eachisland has its own microclimate withdifferent flora and fauna.warbler finchlarge insectsinsectivorous tree finchbuds and fruitvegetarian tree finchinsect larvaewoodpecker(tool-using) finch● The biologist Charles Darwin visitedthe Galapagos Islands in the nineteenthcentury. He noticed that each islandhad its own local type of finches. Theywere adapted to eat the food availableon their particular island. All of thefinches were slightly different fromeach other and from the primitivefinch found on the mainland of SouthAmerica.● Darwin suggested that certainindividuals on each island had asurvival advantage if they were betterat eating the locally available food.Over many generations these localfinches increased in number, andbecause they were isolated from thefinches on the other islands,eventually became a separate species.© Diagram Visual Information Ltd.Darwin’s finches92CONTINUITYKey wordscontinental driftEvidence for evolution:continental driftContinental driftSingle landmass Pangaea(250 million years ago)PangaeaContinental driftThe landmasses on Earth’s surface areconstantly moving.
They are carried byimmense forces generated byconvection currents in the liquid rockin the mantle of the planet.● Scientists can observe thesemovements using satellite images thatshow, for example, that the NorthAmerican and Eurasian landmasses aremoving apart by approximately onecentimeter every year. This movementis called con tin en tal drift.● By plotting these movementsbackward, we can reconstruct thelandmasses as they were millions ofyears ago. At one point 250 millionyears ago, all the continents werecombined in a single landmass calledPangaea (Greek for “all land”).
Overmillions of years, this broke up intoour present-day continents.●Breakup of Pangaea into Laurasia andGondwana (180 million years ago)LaurasiaGondwanaSeparation of the continents(60 million years ago)EuropeAsiaNorth AmericaAfricaFossil relativesThe Mesosaurus is a type of lizard thatis now extinct.
Its fossils are foundonly in South America and South WestAfrica.● This surprising fact is easily explainedby continental drift. When Mesosauruswas alive, South West Africa and SouthAmerica must have been joined.● This is evidence for a single specieson a single landmass rather thantwo identical species having toevolve separately—a far lesslikely scenario.●IndiaSouth AmericaAustraliaAntarcticaPresent dayNorth AmericaEuropeAsiaIndiaAfrica© Diagram Visual Information Ltd.AustraliaSouthAmericaAntarcticaFossil reptile Mesosaurusfound only in South Americaand South West Africa93Classification of livingorganismsDIVERSITYKey wordsbacteriumchlorophyllphotosynthesisvirusTree diagram of living organismsall living organismsProkaryotes●ProkaryotesEukaryotesProkaryotes are the simplest livingorganisms and include all living thingswithout a proper membrane-boundnucleus.
All prokaryotes aremicroscopic, and they includebacteria and viru ses.EukaryotesEukaryotes are organisms withmembrane-bound structures presentin their cells. The most obvious ofthese structures is the nucleus.● Eukaryotes can be single ormulticellular and are more complexthan prokaryotes.●unicellularorganismsmulticellularorganismsTypes of eukaryoteMonera(bacteria)Eukaryotes can be split into four maingroups: unicellular organisms, fungi,plants, and animals.● Eukaryotic unicellular organismsinclude the Protista and a range ofmicroscopic algae.● The fungi are plantlike organisms thatdo not possess chlorophyll anddepend on organic matter from otherorganisms for food.
Many fungi areimportant in decomposition and decayin the environment.● Plants are organisms that carry outphotosyn thesis. They typically havecellulose-rich cell walls.● Animals depend on plants or otheranimals for food. They do not possesscell walls or chlorophyll. Almost allanimals are multicellular.Protista (Amoeba proteus, Spirogyra)plantae(tree)animalia(rabbit)fungi© Diagram Visual Information Ltd.●94DIVERSITYKey wordsbacteriumcytoplasmmesosomeorganellephotosynthesisplasmamembraneplasmidribosomeClassificationBacteria are prokaryotes and so areunicellular organisms that do notpossess membrane-bound organ elles.All are microscopic.
Some carry outphotosyn thesis while others require anexternal source of organic matter andare involved in decomposition anddecay.● Bacteria are sorted into groupsdepending on their cell shape andhow these cells stick together.Kingdom Monera:BacteriaGeneralized rod-shaped bacterium (1.5 µm)genetic material (DNA)pili (sometimes present)ribosomesplasmidcytoplasmmesosome●cell wallflagellum(sometimespresent)Cellular structureBacteria contain a single largemolecule of DNA that floats freelywithin the cytoplasm of the cell.
Othersmaller circles of DNA called plasm idsalso exist and can pass betweenbacteria to carry genes between types.● The outer surface of the cell issometimes covered by a slime layer.Inside this is a cell wall.● Sometimes present is a flagellum—a long, whiplike structure that canthrash about to propel the cellforward. Smaller hairs called pilibehave in a similar way.● The plasm a m em bran e is foundinside the cell wall.
It has a number ofprocesses called m esosom es thatprotrude into the center of the cell.They are associated with the synthesisof DNA and the secretion of proteins.● Other structures include ribosom es(site of protein synthesis), and foodreserves—oil globules (fat stores) andstarch grains (food stores).© Diagram Visual Information Ltd.●plasma membraneslime layer(sometimes present)Some common bacteriaCocciStaphylococciStreptococciDiplococciBacilliSpirillumVibrio95Kingdom Protista:AmoebaDIVERSITYKey wordscontractilevacuoleexocytosisnucleusorganelleTypical amebaExternal viewInternal structurepseudopodiumClassification● Protists are eukaryotes and sopossess membrane-boundorgan elles—specialized regions inthe cell that carry out particularfunctions.● Protists have a fully developedn u cleu s, but despite this, all areunicellular, microscopic organisms.● The genus Am oeba is an example of anon-photosynthetic protist that eatssmaller microorganisms.contractilevacuoleExternal view (profile)Cellular structureAmebas are microscopic, in the sizerange 0.0004–0.004 inches (10–100microns), and are usually invisible tothe naked eye.
A few of the largestspecies are just visible.● An ameba has a single nucleus and asimple con tractile vacu ole, whichpumps fluid from within the cell to theoutside by alternately filling and thencontracting. It functions in maintainingosmotic equilibrium, regulating thebody’s salt and water balance● An ameba is bounded by a plasmamembrane, and its shape can changeas cytoplasm contained within the cellflows forward. The cell bulges outwardin some places to create apseu dopodiu m .● Amebas feed by throwing pseudopodiaaround a prey organism and engulfingit in a vacuole.
Enzymes are thensecreted into this vacuole to digest thefood and allow it to be absorbed intothe ameba. Indigestible remains areejected from the cell by exocytosis.● The endoplasm, the cytoplasm nearthe ameba’s nucleus, is highlygranular, but the area immediatelybelow the cell membrane is clear: thisis called the ectoplasm.ectoplasmnucleusgranular endoplasmfood vacuole containingingested foodpseudopodium© Diagram Visual Information Ltd.●96DIVERSITYKey wordsbuccal cavityciliumnucleusorganelleosmoregulationvacuoleKingdom Protista:ParameciumParameciumExternal viewClassificationInternal structureProtists are eukaryotes and so possessmembrane-bound organ elles,including a fully-developed n u cleu s.All protists are unicellular microscopicorganisms.● A Param eciu m is a water-dwelling,non-photosynthetic microorganismthat ingests small algae and bacteriafor food.●posterior endposteriorcontractilevacuolefood vacuoleCellular structureA Param eciu m is covered with smallhair-like structures called cilia.
Thesebeat in coordinated patterns to drivethe Param eciu m through the water.Trichocysts are the structuresembedded in the cell that produce thecilia.● The oral groove, a deep groove in thesurface of the Param eciu m , leadsfrom the oral vestibule to the bu ccalcavity (the oral region) and cytosome(mouth), where food can be engulfedto form a food vacu ole. Enzymes arereleased into this vacuole to digest thefood and allow it to be absorbed intothe cell. Cilia beat to create currentsthat push food into this area.
Afterdigestion, the vacuoles fuse withthe cytoproct, which empties thecell’s waste material to theoutside.● The nucleus in Param eciu mis complex, with twocomponents: themacronucleus, whichcontrols most of thefunctions of the cell, andthe smaller micronucleus,which is concerned withreproduction.● Osm oregu lation , theregulation of the body’ssalt and water balance,depends on contractilevacuoles that collect excesswater in the cell and then burstto expel it.cilia© Diagram Visual Information Ltd.●cytoprocttrichocystscytostome(mouth)buccal cavityoral vestibulelarge nucleus(macronucleus)small nucleus (micronucleus)anterior contractile vacuoleoral grooveanterior end97Kingdom Protista:SpirogyraDIVERSITYKey wordscellulosechloroplastcytoplasmphotosynthesispyrenoidSpirogyraFilamentTransverse sectionvacuolecell wallClassification●vacuolecytoplasmic liningnucleuscytoplasmic strandtonoplastchloroplastSingle cellcell wallchloroplastcytoplasmic liningpyrenoidvacuolecytoplasmic strandnucleustonoplastCellular structureThe most noticeable component inthe Spirogyra cell is the large spiralledchloroplast that runs around theperiphery of the cell immediatelyinside the cell wall.
![](https://s.studizba.com/z.php?f=/templates/si/i/noavatar.png&w=100&h=100&t=1"){kind=avatar}
