Diversity of Life on EarthChapter 18: Principles of Science
This lecture will help you understand:Classifying LifeThe Three Domains of LifeBacteriaArchaeaProtistsPlantsMoving Water Up a TreeFungiAnimalsHow Birds FlyViruses and PrionsScience and Society: Swine Flu
Classifying LifeThousands of years ago, Aristotle organized life into a "chain of being." Other scientists used this strategy to arrange living things from "simple" to "complex." Humans were at the top of the chain.
Classifying LifeIn the 18th century, Carolus Linnaeus developed a system for classification that emphasized the shared similarities of organisms.The Linnaean system classified organisms using a series of hierarchical levels.
Classifying LifeBiologists now classify life based on its evolutionary history. This systemis less arbitrary than one based on "similarities."allows biologists to more effectively study the evolution of specific traits in organisms.
Classifying LifeThe evolutionary history and relationships of living things can be diagrammed in an evolutionary tree.
Classifying LifeBiological groups constructed based on evolutionary history are clades. A clade is a group of species that includes an ancestor and all of its descendants.Many well-known Linnaean groups are clades. However, others are not. For example, the "reptiles" must include birds if it is to be a clade.
The Three Domains of LifeLife is classified into three domains:
The Three Domains of LifeDomain Eukarya includes four kingdoms:PlantsFungiAnimalsProtists (everything that doesn't fit into the other three kingdoms)
The Three Domains of Life
BacteriaBacteria are diverse.Some bacteria are autotrophs that photosynthesize. Some are chemoautotrophs. Some are heterotrophs.Most bacteria are single-celled, but others gather in multicellular clusters.Bacteria reproduce asexually by dividing, but most occasionally exchange genetic material.Bacteria vary in shape, and some have flagella for locomotion.
BacteriaImportance of bacteria to humans:They break down organic matter, making carbon available for photosynthesis.They help make nitrogen available to living things.Some produce vitamins in our bodies.Some bacteria in our bodies prevent harmful species from infecting us.Some are essential for making cheese and yogurt.Some cause disease.Genetically engineered bacteria produce insulin and other important products.
ArchaeaArchaea are not bacteria. They are a distinct domain of prokaryotic organisms. Some archaea are "extremophiles" that thrive in harsh environments. Some are chemoautotrophs that make food using chemical energy from molecules such as hydrogen sulfide.Certain archaea provide clues about what the earliest living organisms may have been like.
ProtistsProtists are eukaryotes that are not plants, fungi, or animals.They may be autotrophs or heterotrophs.They may be single-celled or multicellular.They may use asexual or sexual reproduction.
ProtistsAutotrophic protists:Diatoms Some dinoflagellatesSeaweed such as kelp, red algae, and green algae
ProtistsHeterotrophic protists:Some dinoflagellatesAmoebasCiliatesFlagellates
PlantsPlants are terrestrial, multicellular, autotrophic eukaryotes that obtain energy through photosynthesis.Plant adaptations to a terrestrial existence:RootsShoots: stems and leavesVascular system (found in most plants): xylem and phloem
Moving Water Up a TreeHow does a plant transport water up to its highest branches and leaves?Transpiration-cohesion-tension mechanism
FungiFungi are heterotrophs that release digestive enzymes over organic matter and then absorb the nutrients.Many fungi are decomposers that obtain the bulk of their nutrients from dead organic matter. They play a crucial role in terrestrial ecosystems.Fungi may be single-celled or multicellular.Fungi are more closely related to animals than to plants.
FungiFungi may reproduce sexually or asexually. Many reproduce using spores.
FungiImportance of fungi to humans:Fungi play a role in decomposition.Mycorrhizae, the close association of plant roots with fungi, are essential to many important plant species.Yeast is used in baking and brewing.Fungi are used to make blue cheeses.Fungi are a source of important medicines such as penicillin.Fungal diseases include: yeast infections, ringworm, and athlete's foot.
AnimalsAnimals are multicellular, heterotrophic eukaryotes that obtain nutrients by eating other organisms.Most reproduce sexually and are diploid during most of their life cycle. The gametessperm and eggare the only haploid stage of the life cycle.Some go through a juvenile period as a larva.Most have muscles, sense organs, and nervous systems.
AnimalsRelationships among the major groups of animals
AnimalsSponges Sponges are sedentary marine animals.Special cells in the sponge beat flagella that move water through the sponge, allowing cells to capture bacteria, digest them, and then distribute nutrients to other cells.
AnimalsCnidariansinclude jellyfish, sea anemones, and corals.have two distinct tissue layers separated by a jellylike middle layer.use tentacles armed with barbed stinging cells to catch prey.alternate between a sedentary polyp stage and a mobile bell-shaped medusa stage.may exist primarily in one form (corals are polyps, jellyfish are medusae).
AnimalsFlatworms Flatworms have distinct head and tail ends and back and belly sides. A single opening serves as mouth and anus.The flat shape allows the animal to obtain oxygen across the skin via diffusion.Example: tapeworms
AnimalsRoundwormshave small, slender bodies with tapered ends and a round cross-section.have both a mouth and an anus.shed a tough outer cuticle periodically during growth.have a longitudinal muscles that cause them to move like flailing whips.are responsible for hookworm, pinworm, elephantiasis, and trichinosis.
AnimalsArthropods Include crustaceans, chelicerates, and uniramiansFeatures:ExoskeletonSegmented bodies and jointed legsA brain and well-developed sense organs
AnimalsMollusksMollusks include bivalves, cephalopods, and gastropods.Most have a protective shell.They use a muscular "foot" for locomotion.A visceral mass holds the digestive and reproductive organs.A mantle secretes the shell.
AnimalsAnnelids Annelids are segmented worms such as earthworms and leeches.The muscles of earthworms are oriented both circularly and longitudinally, providing flexibility in motion.
AnimalsEchinodermsInclude starfish, sea urchins, and sea cucumbersFeatures:Endoskeleton Tube feet
AnimalsChordates Chordates include tunicates, lancelets, and vertebrates.All chordates have, at some point in their life history:A brain and spinal cordA notochord that supports the backGill slitsA tail that extends beyond the anusSome of the chordate features are not apparent in adults. For example, humans have no tails, but human embryos do go through a tailed stage.
AnimalsTunicatesSedentary filter feeders
LanceletsSmall, blade-shaped swimmersFilter feeders
AnimalsVertebrates Animals with backbonesInclude:Jawless fishesCartilaginous fishesRay-finned fishesLungfishes and coelacanthsAmphibiansReptilesMammals
AnimalsLamprey, a jawless fish
AnimalsAmphibiansAmphibians include salamanders, frogs, and caecilians.Amphibians may have aquatic larvae and terrestrial adults.They must live in moist environments to prevent their skin and eggs from drying out.Many species have gone extinct in the last few decades.
AnimalsAmniotes Include reptiles and mammalsFeatures:Skin made of dead cells, protecting from water lossShelled eggsWell adapted to diverse terrestrial habitats
AnimalsReptiles Include turtles, lizards and snakes, crocodilians, and birds
AnimalsMammalsInclude monotremes, marsupials, and placentalsFeatures:Have hairFeed their young milkSome are terrestrial, some are aquatic, and some are able to fly.
AnimalsEctotherms use behavior to regulate their body temperature.All reptiles except birds are ectotherms.Endotherms maintain a constant body temperature by breaking down relatively large amounts of food.Birds and mammals are endotherms.
Viruses and PrionsVirusesare small pieces of genetic material wrapped in a protein coat.have some, but not all, of the characteristics of life:Not made of cellsReproduce only within a host cellHave genesEvolvemay have genes made of DNA or RNA.have genes that mutate quickly.are responsible for many human diseases, as well as those of other species.
Viruses and PrionsPrions are incorrectly folded proteins."reproduce" by converting normal proteins into misfolded prions.cause mad cow disease and Creutzfeldt-Jacob disease in humans.
Science and Society: Swine FluA swine flu epidemic started in March 2009.It caused an unusual number of severe illnesses and deaths, including in young, healthy people.The H1N1 virus responsible for swine flu combines genes from swine, human, and bird flu viruses.A vaccine was developed relatively quickly, but manufacturing enough vaccine quickly proved difficult.This virus can now be spread from person to person.